Major Project Part I

1. Introduction

Over recent years the nonwovens market has been one of the fastest growing and most exciting sectors of the textiles market. Boosted by the development of new products for numerous applications and the expansion of many established Western products into developing markets, global consumption of nonwovens has grown on average by almost 6% per annum in weight terms between 1995 and 2000(1). The world production of nonwovens rose from 2.16 million tonnes in 1994 to 4.43 million tonnes in 2004 with an anticipated value jump from $9 billion to $15.9 billion, respectively, during this period. The rising market potential would push nonwovens production to 6.31 million tonnes in 2009 when the total value of production is anticipated to be $25 billion, Europe and North America, which had the lion's share of 1.35 million tonnes and 1.16 million tonnes, respectively, in 2004 world production figure of 4.43 million tonnes, may give way to the Asia-Pacific region, which is projected to increase its non-woven products output from 1.02 million tonnes in 2004 to 1.67 million tonnes by 2009. At present, the total volume of nonwovens produced from India is estimated at 35,000 tonnes, as compared to China's non-woven product output of 7.55 lakh tonnes (China is a dominating force in nonwovens among the Asia-Pacific region and the third largest non-woven producing region after America and Europe because of life-style changes, the rising middle-class, and its economy) (23), The non-woven materials produced under these processes are widely used for technical applications such as surgical gowns, diaper cover stocks, automotive linings, military applications such as decontamination wipes and geo-textiles such as insulating tank/lake bunds. Although a large number of fibers are available, commercially important nonwoven fabrics have been limited to relatively few types, the dominant fibers include polyolefin, polyester, and rayon. These three fiber types made up a substantial part of the overall nonwovens markets for fibers. The increasing importance of olefin-based fibers is well illustrated by data from major nonwovens-producing regions that show increasing shipments of PP and PE at the expense of some natural fibers, rayon and polyester. Much of this shift in fiber consumption can be attributed to the growing use of olefin-based nonwovens in absorbent products around the world. 1

Rayon was a major fiber used in the nonwovens industry until 1985. Over the past decade, production of rayon has decreased considerably in the US and Western Europe because of the increasing cost of the fiber. Since cost of PP and PET dropped compared to that of rayon, and yet they provide superior strength there was big drop in 1989, after which the shipment of rayon staple kept declining slowly. Nonwovens made of rayon are mainly found in medical/surgical/sanitary products and wipes. The cleanliness and absorptive properties made rayon popular in these fields. Similarly, cotton is the preferred fiber in tampon and incontinence products. Its consumption is stable at 40-45 million pounds. Nylon, which is more expensive than most other fibers, is used in a lesser extent. The other specialty fiber has only a limited market share, probably not more than 15 percent of the whole Nonwovens market. Generally Nonwovens are highly anisotropy unlike weaving, knitting. However the properties of the nonwoven is predicted in connection with way in which fibres are oriented in an nonwoven structure. So the properties like tensile strength, bending rigidity, liquid distribution, etc of nonwoven is highly depends are the fibre arrangement in an nonwoven. Nonwovens are applied in various purposes, out of which it is used most predominantly in baby diapher, feminine product, geotextiles, medical equipments such as gowns, sterilization covers etc. Where in which Liquid transmission behavior play an vital role in all above application mentioned. In plane liquid distribution is movement of liquid with in the plane of fabrics as opposed to the movement of liquid perpendicular to the plane of the fabric which is referred to a transplaner distribution. Inplane wicking is used to assist the liquid over a given area, so that either total evaporation of liquid can occur more readily such in case of perspiration on clothing. So it is well understood that Inplane liquid distribution on the nonwoven is the important factor which determines the usage of nonwoven positively in above mentioned key applicational area. Inplane liquid distribution of nonwoven depends on various fibre and process parameters. Among these, Pore volume present in the nonwoven significantly affects the liquid distribution. This report focus on the study of liquid distribution over nonwoven structure by identifying their pore volume, which in turn responsible for rate of liquid transmission and change in pore volume pressure.

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Also this report consists of t study performed by experimenting the existing modified inplane wicking tester, in order to redesign its structure to achieve higher accuracy in achieving the results.

2. Objectives

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1. Design modification of existing Modified Inplane wicking Tester: minor and major modifications are required to be carried out in an existing instrument inorder to increase the precision of an instrument by controlling vibration, facilitating sample mounting system, etc. 2. Estimation of pore volume of nonwoven material by sophisticated method, and finding relation ship between the pore volume Vs varying GSM of nonwoven with same fibres and method of manufacturing. 3. To study the absorbency related parameters of nonwovens viz., absorbent capacity, spreading time, maximum absorption and rate of absorption through modified GATS in-plane wicking method after modifying the design of an instrument.

3. Literature Survey

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3.1. Nonwoven TNonwoven fabricTs are broadly defined as sheet or web structures bonded together by entangling fiber or filaments (and by perforating films) mechanically, thermally or chemicallyP(1)P. They are flat, porous sheets that are made directly from separate fibers or from molten plastic or plastic film. They are not made by weaving or knitting and do not require converting the fibers to yarn. Nonwoven fabrics are engineered fabrics that may be a limited life, single-use fabric or a very durable fabric. Nonwoven fabrics provide specific functions such as absorbency, liquid repellency, resilience, stretch, softness, strength, flame retardancy, washability, cushioning, filtering, bacterial barrier and sterility. These properties are often combined to create fabrics suited for specific jobs, while achieving a good balance between product use-life and cost. They can mimic the appearance, texture and strength of a woven fabric and can be as bulky as the thickest padding. In combination with other materials, they provide a spectrum of products with diverse properties, and are used alone or as components of apparel, home furnishings, health care, engineering, industrial and consumer goods. Listed below are some of the more familiar products made with nonwovens, TDisposable diapers T TSanitary napkins & tampons T TSterile wraps, caps, gowns, masks and drapings used in the medical field T THousehold and personal wipes T TLaundry aids (fabric dryer-sheets) T TApparel interlining T TCarpeting and upholstery fabrics, padding and backing T TWall coverings T TAgricultural coverings and seed strips T TAutomotive headliners and upholstery T TFilters T TEnvelopes T TTags T

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TLabels T TInsulation T THouse wraps T TRoofing products T TCivil engineering fabrics/geotextiles T As you can see, there are many uses for nonwoven fabrics. Technology and ingenuity are creating the capability of these fabrics to provide high quality and functional products. 3.2. Method of Nonwoven manufacturing Nonwovens are textile assemblies made up of fibers that are neither interlaced nor interlocked, but instead they are held together through mechanical, thermal or chemical bonding P(2)P. It is this unique way of producing the materials that results in the materials being highly anisotropic. The different methods of producing nonwovens result in different structural, mechanical and absorbency properties like orientation of fibres, porosity of fabric, and tensile strength of fabric, absorbency in machine and cross direction. Basically two main step involved in nonwoven manufacturing, they are, 1. Web formation : This is the primary stage in which the mass of individual fibres are placed either cross, or parallel or random lay inorder to form an sheet of web. 2.Web bonding: After the formation of the web, all the fibres loosely held are made intact through bonding technique. They are briefly discussed below, 1. Web forming methods

2. Web bonding methods

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a. Dry laid process.

a. Mechanical bonding.

b. wet-laid process.

b. Chemical bonding.

c. Extrusion process.

c. Thermal and pressure.

The anisotropic properties of nonwovens can be utilized for deciding and controlling the directional spreading of liquid distribution in nonwoven products and achieve the maximum out of it. The process variables like needling density or needling depth or web thickness or delivery rate or after calendaring, the bonding area or type of adhesive or amount of heat and pressure, parallel-laid or cross laid webs, continuous filament or staple filament etc will finally decide the anisotropic properties of end product. 3.3. Anisotropy Anisotropy is Hallmark character of Nonwoven and they are highly anisotropic materials unlike woven and knitted fabrics where the properties of the material depend on the way in which the yarns are interlaced or Interlooped, nonwoven’s properties depend greatly on the way in which the fibers lay within the material. The method in which the fibers are laid down and any further processing determine the anisotropy of a nonwoven. The anisotropy of a nonwoven is an important structural characteristic of the material because it allows the user to isolate directional properties of the nonwoven and, because of this, the structure can be engineered such that the material serves a specific purpose. Properties of nonwovens have been studied extensively to determine if they are in fact directionally dependent properties. Hearle and StevensonP (3)P, among other things, studied the effect of anisotropy on the tensile properties of the material. Three test groups were examined whose difference was the directional percentage of fibers. The first group was random laid, the second cross laid, and the third parallel laid. The anisotropy of these materials were measured using a Visual technique that consisted of projecting the image of the material onto a screen and manually determining the anisotropy. Tensile tests were also carried out by using a standard test on an instron machine. The angles tested varied between zero degrees (Machine direction) and ninety degrees (cross direction) in 15-degree intervals. They found that the random group had the highest strength to break in the machine direction and that it this value decreased slightly

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as it got closer to the cross direction. Although it might be expected that the breaking strength would be the same in every direction given that it is a random laid material and thus essentially isotropic, the processing tends to slightly align the fibers in the machine direction resulting in a slightly higher value in this direction. The cross laid material was found to have the largest breaking strength in the cross direction as expected and then a decreasing value until it reached the machine direction. The parallel laid material on the other hand had the largest breaking strength in the machine direction and decreased until it reached the cross direction. The trends that both the cross and parallel laid materials displayed were expected because it is intuitive that the greater number of fibers in a given direction would result in higher strength. However, the difference in strength in the machine direction and cross direction of the parallel laid materials was much larger than it was for the cross laid materials. Once again this is probably due to the processing parameters. Hearle and Stevenson showed that the fiber orientation directly influences tensile properties of nonwovens. It is not surprising that tensile tests are used to determine a material’s anisotropy. The effect of anisotropy on other properties has been examined as well. Pourdeyhimi and KimP(4)P investigated the effect of bonding temperature and also anisotropy on the bending rigidity of nonwoven materials. The material utilized for the test was dry staple unidirectional carded webs. The bonding temperature varied between 140º and 180ºC. It was found that as the temperature of the bond increased the bending rigidity also increased. What was also found is that although the bending rigidity increased due to bonding temperature it still directly correlated with the material’s anisotropy. The effect of anisotropy of a nonwoven has been shown to be a determining factor on many of its properties. To accurately determine the effect of anisotropy on liquid distribution a suitable test method must be determined. 3.4. Wetting Wetting and wetability has clear dissimilarity between each other but some times they are used interchangeably(5)P .The wetting of a solid surface is understood to be the condition resulting from its contact with a specified liquid under specific conditions. Wettability is the potential of a surface to interact with liquids with specified characteristics. According to Harnett and Mehta “wettability” is the initial behavior of a fabric, yarn, or fibre when

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brought into contact with liquid. It also describes the interaction between liquid and the substrate prior to wicking process. For a liquid to move in a fibrous medium, it must wet the fibre surfaces before being transported through the inter fibre pores by means of capillary action. While the interactions of molecules in the bulk of a liquid are balanced by an equal attractive force in all directions, the molecules on the surface of a liquid experience an imbalance of forces. Hence, there is presence of free energy at the surface of the liquid. The excess energy is called surface free energy which tends to keep the surface area of the liquid to a minimum and restricts the advancement the liquid over the solid surface. For a liquid to wet a solid completely or for the solid to be submerged in a liquid, the solid surfaces must have sufficient surface energy to overcome the free surface energy of the liquid. The surface free energy can be quantified as a measurement of energy per area. It is usually termed as surface tension quantified as force per length with units mN/m or dynes /cm.

Fig. 1 Equilibrium state of a liquid drop on a solid surface The forces involved in the equilibrium that exists when a liquid is in contact with a solid and a vapor at the same time are given by the following (Young-Dupré) equation γ BSV B- γ BSL B= γ BLV B cos θ where γ represents the interfacial tension that exists between the various combinations of solid, liquid, and vapor; the subscripts S, L, and V standing for solid, liquid, and vapor, and θ is the equilibrium contact angle (Fig. 1). The term γ BLVB is denoted as surface tension of the liquid for liquid/vapor interface. The term γ BLVB cos θ, has been called “adhesion tension” or “specific wettability”. Above Equation is valid only for a drop resting at equilibrium on a

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smooth, homogeneous, impermeable, and non deformable surface. The equation has been widely used to explain wetting and wicking phenomena. The contact angle θ is the angle between the tangent to the liquid vapor (air) interface and the solid-liquid interface.

3.5. Contact Angle Contact angle is represented by θ which gives clear view about the principle of wetability of the solid material against contact liquid. Contact angle is a measure of the wetting of a liquid on a solid surface. It is expressed in degrees, with 0 degrees being complete wetting and 180 degrees being absolute non-wetting. It is a useful measurement for researchers interested in wetting, adhesion and other phenomena where liquids contact solids. It can also be used to characterize the solid surface itself when contact angles for various wetting liquids are comparedP(6)P This application note provides a brief introduction to the use and measurement of contact angles. The techniques used for measurement are discussed and compared. Contact angle θ, is a quantitative measure of the wetting of a solid by a liquid. It is defined geometrically as the angle formed by a liquid at the three phase boundary where a liquid, gas and solid intersect as shown below:

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Fig 2. Represents the significance of varying contact angle Vs Wettability It can be seen from this figure that low values of θ indicate that the liquid spreads, or wets well, while high values indicate poor wetting. If the angle θ is less than 90 the liquid is said to wet the solid. If it is greater than 90 it is said to be non-wetting. A zero contact angle represents complete wetting. The measurement of a single static contact angle to characterize the interaction is no longer thought to be adequate. For any given solid/ liquid interaction there exists a range of contact angles which may be found. The value of static contact angles are found to depend on the recent history of the interaction. When the drop has recently expanded the angle is said to represent the ‘advanced’ contact angle. When the drop has recently contracted the angle is

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said to represent the ‘receded’ contact angle. These angles fall within a range with advanced angles approaching a maximum value and receded angles approaching a minimum value. If the three phase (liquid/solid/vapor) boundary is in actual motion the angles produced are called Dynamic Contact Angles and are referred to as ‘advancing’ and ‘receding’ angles. The difference between ‘advanced’ and ‘advancing’, ‘receded’ and ‘receding’ is that in the static case motion is incipient in the dynamic case motion is actual. Dynamic contact angles may be assayed at various rates of speed. Dynamic contact angles measured at low velocities should be equal to properly measured static angles. 3.5.1. Hysteresis The difference between the maximum(advanced/advancing) and minimum(receded/receding) contact angle values is called the contact angle hysteresis. A great deal of research has gone into analysis of the significance of hysteresis. It has been used to help characterize surface heterogeneity, roughness and mobility. Briefly, for surfaces which are not homogeneous there will exist domains on the surface which present barriers to the motion of the contact line. For the case of chemical heterogeneity these domains represent areas with different contact angles than the surrounding surface. For example when wetting with water, hydrophobic domains will pin the motion of the contact line as the liquid advances thus increasing the contact angles. When the water recedes the hydrophilic domains will hold back the draining motion of the contact line thus decreasing the contact angle. From this analysis it can be seen that, when testing with water, advancing angles will be sensitive to the hydrophobic domains and receding angles will characterize the hydrophilic domains on the surface. For situations in which surface roughness generates hysteresis, the actual microscopic variations of slope in the surface create the barriers, which pin the motion of the contact line and alter the macroscopic contact angles. There has been a great deal of research investigating the significance of hysteresis and you are recommended to the papers cited at the end of this note for further details.

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Contact angle can also be considered in terms of the thermodynamics of the materials involved. This analysis involves the interfacial free energies between the three phases and is given by, γ Blv Bcos θ = γ Bsv B- γ Bsl where γ Blv B, γ Bsv Band γ Bsl Brefer to the interfacial energies of the liquid/vapor, solid/vapor and solid/liquid interfaces. 3.5.2. Contact angle measurement Two different approaches are commonly used to measure contact angles of non-porous solids, goniometry and tensiometry. Goniometry involves the observation of a sessile drop of test liquid on a solid substrate. Tensiometry involves measuring the forces of interaction as a solid is contacted with a test liquid. Both techniques are described below with comments on the choice of either technique for particular research applications. In the case of porous solids, powders and fabrics another approach is commonly used. This technique involves using a tensiometer, and the Washburn method. It is the method of choice when your sample contains a porous architecture which absorbs the wetting liquid. It is described briefly below.

3.6.Methods of Measurement 3.6.1. Goniometry A drop of the wetting liquid is placed on the solid sample. The image of the drop shape is investigated with the contact angle being the tangent between the drop edge and the solid surface. Analysis of the shape of a drop of test liquid placed on a solid is the basis for goniometry. The basic elements of a goniometer include a light source, sample stage, lens and image

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capture. Contact angle can be assessed directly by measuring the angle formed between the solid and the tangent to the drop surface. The production of drops with advanced and receded edges involves one of two strategies. Drops can be made to have advanced edges by addition of liquid. Receded edges may be produced by allowing sufficient evaporation or by withdrawing liquid from the drop. Alternately, both advanced and receded edges are produced when the stage on which the solid is held is tilted to the point of incipient motion. Using an instrument with high speed image capture capabilities shapes of drops in motion may be analyzed. KSV Instruments supplies two instruments for goniometry, theT CAM100T and TCAM 200.T The CAM100 uses a 50mm USB camera for image capture. The CAM200 instruments use a high speed CCD camera for image capture. The images are analyzed with computer software. 3.6.2. Advantages Goniometry can be used in many situations where tensiometry cannot. You can use a great variety of solid substrates provided they have a relatively flat portion for testing and can fit on the stage of the instrument. Substrates with regular curvature, such as contact lenses are also easily analyzed. Testing can be done using very small quantities of liquid. It is also easy to test high temperature liquids such as polymer melts. 3.6.3. Limitations The assignment of the tangent line which will define the contact angle is a factor which can limit the reproducibility of contact angle measurements. Conventional goniometry relies on the consistency of the operator in the assignment of the tangent line. This can lead to significant error, especially subjective error between multiple users. KSV Instruments’ TCAM 200T and TCAM100T remove this problem by using computer analysis of the drop shape to generate consistent contact angle data.

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The conditions which produce advanced and receded angles are sometimes difficult to reproduce. Although drops in motion can produce data on dynamic contact angles the velocity of motion cannot be controlled. It is also less suited, when compared to tensiometry, to analysis of the effects of wetting on changes in contact angle. In addition the amount of surface sampled for each measurement is limited and multiple measurements should be used to characterize a surface. Fibers are not easily studied by goniometry. 3.6.4. Optical contact angle and surface tension meter

Fig 3.Optical contact angle and surface tension meter with optional automatic dispenser CAM 200 is a video camera based fully computer controlled contact angle meter for the measurement of static or advancing/receding contact angles. Also surface tension measurements can be performed using the pendant drop technique. The instrument has a 32-bit Microsoft Windows95 based software, which allows analysis of contact angles, critical surface tension (Zisman plot) and surface free energy of solids (Fowkes, etc.). Determination of contact angle and surface tension is based on true Young and Laplace equation. Instead of using separate files for each measurement the software contains an internal database system where all the recorded data is stored. This allows a convenient method to

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keep all the data organized for future analysis. To save space recordings are saved using proprietary image compression which retains all important information. There are separate databases for liquids and solids where all information about the test materials is be stored. 3.6.5 Tensiometer 3.6.5.1. Basic Terminology to study Tensiometer 3.6.5.1.1. Surface Tension Surface tension is a measure of the cohesive energy of a liquid. It is the excess free energy at the interface of contact between two fluids. When one fluid is a gas the tension is termed surface tension, when both fluids are liquids it is termed interfacial tension. It is expressed in units of milliNewtons/meter (mN/m) or dynes/centimeter. It is useful in analyzing fluids are foaming, spreading, emulsification, washability and other fluid characteristics. Surface tension is a measurement of the cohesive energy present at an interface. The molecules of a liquid attract each other. The interactions of a molecule in the bulk of a liquid are balanced by an equal attractive force in all directions. Molecules on the surface of a liquid experience an imbalance of forces as indicated below.

Fig.4. represents the Surface free energy of liquid. The net effect of this situation is the presence of free energy at the surface. The excess energy is called surface free energy and can be quantified as a measurement of energy/area. It is also possible to describe this situation as having a line tension or surface tension which is

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quantified as a force/length measurement. The common units for surface tension are dynes/cm or mN/m. These units are equivalent. This excess energy exists at the interface of two fluids. If one of the fluids is the vapor phase of a liquid being tested the measurement is referred to as surface tension. If the surface investigated is the interface of two liquids the measurement is referred to as interfacial tension. In either case the more dense fluid is referred to herein as the ‘heavy phase’ and the less dense fluid is referred to as the ‘light phase’. Solids also may be described to have a surface free energy at their interfaces but direct measurement of its value is not possible through techniques used for liquids. Polar liquids, such as water, have strong intermolecular interactions and thus high surface tensions. Any factor which decreases the strength of this interaction will lower surface tension. Thus an increase in the temperature of this system will lower surface tension. Any contamination, especially by surfactants, will lower surface tension. Therefore researchers should be very cautious about the issue of contamination.

3.6.5.1.2. Measurement of Surface Tension by Tensiometry Technique The measurement of surface and interfacial tension as performed by a tensiometer is based on force measurements of the interaction of a probe with the surface of interface of two fluids. With any of the techniques described herein you may perform interfacial tension measurements just like surface tension measurements by insuring that the bulk of the probe is submersed in the light phase prior to beginning the experiment. In these experiments a probe is hung on a balance and brought into contact with the liquid interface tested. The forces experienced by the balance as the probe interacts with the surface of the liquid can be used to calculate surface tension. The forces present in this situation depend on the following factors; size and shape of the probe, contact angle of the liquid/solid interaction and surface tension of the liquid. The size and shape of the probe are easily controlled. The contact angle is controlled to be zero (complete wetting). This is achieved by 17

using probes with high energy surfaces. KSV probes are made of a platinum/iridium alloy which insures complete wetting and easy and reliable cleaning. The mathematical interpretation of the force measurements depends on the shape of the probe used. Two types of probes are commonly used, the DuNouy Ring and the Wilhelmy Plate. Both are available from KSV Instruments. Choice of probes DuNouy ring: This method utilizes the interaction of a platinum ring with the surface being tested. The ring is submerged below the interface and subsequently raised upwards. As the ring moves upwards it raises a meniscus of the liquid. Eventually this meniscus tears from the ring and returns to it’s original position. Prior to this event, the volume, and thus the force exerted , of the meniscus passes through a maximum value and begins to diminish prior to the actually tearing event. The process is shown in the diagram below:

Fig 5. Representation of the variation of Force during ascending and descending of probe 1) The ring is above the surface and the force is zeroed.

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2) The ring hits the surface and there is a slight positive force because of the adhesive force between the ring and the surface. 3) The ring must be pushed through the surface (due to the surface tension) which causes a small negative force. 4) The ring breaks through the surface and a small positive force is measured due to the supporting wires of the ring. 5) When lifted through the surface the measured force starts to increase. 6) The force keeps increasing until 7) The maximum force is reached 8) After the maximum there is a small decrease of in the force until the lamella breaks. The calculation of surface or interfacial tension by this technique is based on the measurement of this maximum force. The depth of immersion of the ring and the level to which it is raised when it experiences the maximum pull are irrelevant to this technique. The original calculations based on the ring technique were based on theories which apply to rings of infinite diameter and do not consider an additional volume of liquid which is raised due to the proximity of one side of the ring to the other. This additional liquid lifted is diagrammed below as the shaded portion:

Fig 6.Representation additional liquid lifted during upward movement of probe.

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Mathematical corrections which compensate for this extra liquid have been produced. KSV software utilizes the corrections suggested by Huh and Mason in reference cited below.

3.6.5.2. Dynamic Contact Angle measurement Measurement of dynamic contact angles provides information on the properties of surfaces such as porosity and homogeneity, surface topography and reactivity. The method is based on the Wilhelmy plate principle where the solid sample is held by the electro balance and then dipped or pulled from the substance. Therefore the weight of the sample alternates depending on direction of the movement. The force changes obtained are directly proportional to the contact angle. The contact angle is the angle formed by the tangent to the point of contact at the solid/liquid interfaces. As the solid sample penetrates the surface and dips into the liquid a advancing contact angle is determined and the pull of the sample from the substance provides receding contact angle information. The progress of the experiment is expressed in form of graphical buoyancy slope where the x axis represent the immersion depth and the y-axis the force. The contact angles is calculated from the force versus depth information. A sample of the solid is hung on a force balance and brought into contact with the wetting liquid. The change in forces when the solid contacts the liquid are used to calculate contact angles. The tensiometric method for measuring contact angles measures the forces that are present when a sample of solid is brought into contact with a test liquid. If the forces of interaction, geometry of the solid and surface tension of the liquid are known the contact angle may be calculated. The user first makes a measurement of the surface tension of the liquid using either a Wilhelmy plate or DuNouy ring. The sample of the solid to be tested is then hung on the balance and tared. The liquid is then raised to contact the solid. When the solid contacts the liquid the change in forces is detected and the instrument registers this elevation as zero depth of immersion. As the solid is pushed into the liquid the forces on the balance are recorded. The forces on the balance are

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FBtotalB = wetting force + weight of probe - buoyancy Sigma70 instrument tared the weight of the probe and can remove the effects of the buoyancy force by extrapolating the graph back to zero depth of immersion. The remaining component force is the wetting force which is defined as, Wetting force = γ BLVB P cosθ Where γ BLVB is the liquid surface tension, P is the perimeter of the probe and θ is the contact angle. Thus at any depth data is received which can be used to calculate contact angle. This contact angle, which is obtained from data generated as the probe advances into the liquid, is the advancing contact angle. The sample is immersed to a set depth and the process is reversed. As the probe retreats from the liquid data collected is used to calculate the receding contact angle.

3.6.5.3. Automatic surface tension/contact angle meter

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Fig 7. Automatic surface tension/contact angle meter Above figure illustrates the fully computer controlled and automatic Tensiometer for the measurement of surface/interfacial tensions and contact angles of liquids. Sigma 70 uses Wilhelmy plate or Du Nouy ring method for force measurement and its super sensitive fiber range balance operates at 0.25 mN to 25 mN range. Standard programs include automatic determination of TCMCT, push and pull Tsurface and interfacial tension Tmeasurements, Tpodwer wettabilityT and measurement of Tdynamic advancing and receding contact anglesT. Measuring parameters are displayed on-line in clear digits on the interface unit and graphical result presentation can be monitored at the computer screen. All experimental data is stored on the hard disk and the flexible multitasking Windows software allows customized application development. 3.6.5.3.1. Features Full computer control and automatic operation of all measuring modes Expansive Windows software programs Uses Wilhelmy plate or Du Nouy ring method Super sensitive fiber-range balance - up to 0.05 µN Software controlled sample thermostation and stirring Direct reading of sample temperature Fully automatic dispenser for TCMC Tmeasurements On-line digital displays of measuring parameters Automatic calculation of ring correction values Automatic calibration, zeroing, tarring and reset to start point Result and graphics presented on screen Data export to Lotus 1-2-3 or equivalent, hard disk data storage Computer requirements IBM PC/AT compatible computer required 3.6.5.3.2. Performance Surface and interfacial tension measurements, push and pull modes

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Dynamic advancing and receding contact angle measurements (TDCAT) Wettability characteristics of Tsingle fibersT Automatic critical micelle concentrations (TCMCT) determination Adsorption behavior measurement Surface recovery and dehydration rate measurement Measurement of surface free energy Density of liquids Critical surface tension (Zisman plot) Determination of wetted length of solids and fibers 3.6.5.3.3. Options On-line measurement of sample pH Special sample vessel for temperatures up to 300º C Evaporation preventer, thermostated double wall lid made of glass 3.6.5.3.4. Advantages The use of tensiometry for measurement of contact angle has several advantages over conventional goniometry. At any point on the immersion graph, all points along the perimeter of the solid at that depth contribute to the force measurement recorded. Thus the force used to calculate Ө at any given depth of immersion is already an averaged value. You may calculate an averaged value for the entire length of the sample or average any part of the immersion graph data to assay changes in contact angle along the length of the sample. This technique allows the user to analyze contact angles produced from wetting over an entire range of velocities from static to rapid wetting. Because the contact angles are determined from the forces measured by the instrument there is no possibility of subjective error. The graphs produced by this technique are very useful in studying hysteresis. Variations of contact angles, both advancing and receding, for the entire length of the sample tested are visualized on the same graph. In addition variations generated over multiple wetting /

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dewetting cycles can yield information on changes caused by wetting(such as absorption or surface reorientation). 3.6.5.3.5. Limitations There are two major limitations for the application of this technique. Firstly the user must have enough of the liquid being tested available so that he can immerse a portion of his solid in it. Secondly the solid in question must be available in samples which meet the following constraints. The sample must be formed or cut in a regular geometry such that it has a constant perimeter over a portion of it’s length. Rods, plates or fibers of known perimeter are ideal. The sample must have the same surface on all sides which contact the liquid. The sample must also be small enough so that it can be hung on the microbalance. It is also more difficult to use this technique in systems which are measured at high temperatures. Temperatures at or below 100˚ C are easily handled but for measurements above this range goniometry is recommended.

3.6.6. Washburn Method This method is chosen when the solid sample to be tested contains a porous architecture which leads to absorption of the wetting liquid. The solid is brought into contact with the testing liquid and the mass of liquid absorbed into the solid is measured as a function of time. The amount absorbed is a function of the viscosity, density and surface tension of the liquid, the material constant of the solid , and the contact angle of the interaction. If the viscosity, density and surface tension of the liquid are known the material constant and contact angle can be solved for. 3.7. Powder wettability

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If you wish to characterize the wetting behavior of a particular liquid/solid pair you only need to measure the contact angle. It is possible to characterize the wettability of your solid in a more general way. Various methods are used but the same basic principle applies for each. The solid is tested against a series of liquids and contact angles are measured. Calculations based on these measurements produce a parameter (critical surface tension, surface free energy, etc) which quantifies a characteristic of the solid which mediates wetting. The wetting of powders and porous solids also involves contact angle phenomena but is complicated by the presence of a porous architecture. Although various methods are employed to characterize this architecture, contact angles are still the primary parameters used to characterize wetting. Rough estimates of wettability can be made by placing powders on any given liquid and observing if the solid wets into the liquid (the time required for wetting may also be noted). Solids with contact angles above 90° will not wet into the liquid. A series of liquids of varying surface tensions can be tested against your solid. Liquids with lower surface tensions yield lower contact angles. For some liquids the contact angle with a given solid will be greater than 90° and the solid will not wet while with a liquid of lower surface tension the contact angle will be less than 90° and wetting will occur. Using this crude approach some relevant information on wetting of solids may be found. To produce a quantitative measure of wetting, a contact angle, two approaches are generally used: goniometry and tensiometry. This is comprehensively discussed in the contact angle measurement topic. 3.8. Wicking Due to the pressure difference between capillary and capillary forces, wicking occurs in nonwoven, which enhance the bulk of liquid uptake into the nonwoven system. As we discussed above in wetting, wicking also involves the interaction of different phases like solid to liquid, liquid to vapour, solid to Vapour. The capillaries are the major factor in liquid movement through the material. Capillaries are not always the only force that drives liquid into the material. Along with wicking, the process of absorption can occur. Although these

25

two terms are sometimes used interchangeably, they are actually two separate processes. Whereas wicking is liquid uptake by the capillaries (interstices) formed by the yarns and fibers, absorption is the uptake of liquid into the fibers themselves. For instance, materials such as polyester coated with a hydrophilic finish ,only move liquid through the material by wicking, but materials such as cotton are naturally absorbent and therefore, both wicking and absorption occur. Fiber swelling due to absorption can actually hinder the capillary flow because it changes the capillary geometry. In addition to absorption and wicking a third process of liquid movement can occur. This process is referred to as adsorption, which is the movement of a thin layer of liquid on the outside of the material. The pressure difference in the capillary can be described by the Young-LaPlace equation,

26

r =pore radius ∆P = ( 2γCOS θ) / r

θ =contact angle γ =liquid surface tension P =capillary pressure The specific case of spherical meniscus inside a cylindrical capillary, according to this equation, the smaller the pore size the greater the pressure within the capillary. Therefore, when external pressure is applied to a dry fabric and is slowly decreased until liquid begins to penetrate, the smaller pores will fill first and conversely when the external pressure, applied to a wet material, is increased, the smaller pores drain last. When there is no longer a pressure difference across the meniscus of the liquid in the capillary, equilibrium has been achieved and wicking ceases. This can be caused by the meniscus reaching the edge of the capillary or by a drastic change in the radius of the capillary. It has been demonstrated that the contact angle plays an important role in the driving mechanism for bulk liquid uptake into a material. It can affect both the amount absorbed and the rate of absorption. Wicking can only occur when a liquid wets fibres assembled with capillary spaces between them. The resulting capillary forces drive the liquid into the capillary spaces. Wicking can be visualized as a spontaneous displacement of a solid-air interface with a solid-liquid interface in a capillary system For the process to be spontaneous free energy has to be gained and the work of penetration has to be positiveP(7)P. This is the case when the interfacial energy of the fibre surface in contact with vapor (air) γ BSVB exceeds the interfacial energy between the liquid and the fibre surface γ BSLB WB = γ rB - γ rB PB

SV B

SL

The work of penetration WBP Bis a measure of energy required for capillary penetration. When a liquid in a capillary wets the walls of the capillary, a meniscus is formed. The

27

surface tension of the liquid causing a pressure differences ∆P across the curved liquid-air (vapor) interface is related to the curvature of this interface according to Young-Laplace equation. ∆P= γ

LV (B

1/RB1B+1/RB2B)

For a capillary with a circular cross section, the radii of the curved interface RB1B and RB2B are equal:

∆P= 2 rB LV B/ R If the capillary is circular with radius r, the meniscus will be approximately hemispherical with a constant radius of curvature, R = r/cosθ The capillary pressure is

∆P= 2 rB LV Bcos θ / r When the capillary wall is completely wettable by the liquid, then cos θ = 1. For a positive capillary pressure, the values of θ have to be between 0° and 90°. Capillary pressure is inversely related to the capillary radius. The term “wicking” involves two kinetically different processes P(8)Pa spontaneous flow of a liquid within the capillary spaces accompanied by a simultaneous diffusion of the liquid into the interior of fibers or a film on fibres. If the penetration of liquid is limited to the capillary spaces and the fibres do not imbibe the liquid, the wicking process is termed “capillary penetration” or “capillary sorption”. For a theoretical treatment of capillary flow in fabrics, the fibrous assemblies are usually considered to consist of a number of parallel capillaries. The advancement of the liquid front in a capillary can be visualized as occurring in small jumps. The advancing wetting line in a single capillary stretches the meniscus of the liquid until the elasticity of the meniscus and the inertia of flow are exceeded. The meniscus contracts, pulling more liquid into the capillary to restore the equilibrium state of the meniscus. The movement of the liquid in a non-homogeneous capillary system such as a fibrous assembly is discontinuous for another reason as well. The wetting front advances into the capillary system in small jumps, because the irregular capillary spaces have various dimensions the wicking rate is not solely governed by interfacial tensions and the wettability

28

of the fibres, but by other factors as well. The wicking rate depends on the capillary dimensions of the substrate and the viscosity of the liquid alsoP(9)P. Most textile processes are time limited, and the rate of wicking is therefore important. However, the wicking rate is not solely governed by interfacial tensions and the wettability of the fibres, but by other factors as well. The wicking rate depends on the capillary dimensions of the substrate and the viscosity of the liquid. The mass rate (M) at which a liquid moves through a porous channel is related to the pressure difference (p or ∆P) across the channel in the absence of gravitational force and neglecting inertial forces (as acceleration is small) by Poiseuille’s lawP(10)P.

29

M = π p ρρBLB rP4 P/ 8 η h If the pressure differences ∆P is due to capillary forces, then M = π ρBLB rP3 P γ BLV Bcos θ / 4 η h The volume rate of flow (V) is V = π rP3 P γ BLV Bcos θ / 4 η h Linear rate of flow (u) is u = dh/dt = r γ BLV Bcos θ / 4 η h Where h is height of liquid rise in the capillary channel. Lucas-Washburn equation for the rate of fluid flow against gravitational forces, through porous solid as a bundle of round capillary tubes, each is very small with radius r, given by: dh/dt =

γ LV r cos θ - rP2P ρBLB g /8 η 4ηh

where, g is the acceleration due to gravity. The second term is negligible either the flow is horizontal or r is very small (rP2P = 0). When the capillary forces are balanced by the gravitational forces liquid rise stops and equilibrium is reached as given

γ BLV Bcos θ 2πr = πrP2P ρBLB gh Hence, equilibrium wicking height hBeqB = 2 γ BLV Bcos θ / r ρBLB g According to Lucas-Washburn equation neglecting gravitational forces, the wicking height, h is directly proportional to square root of time t: h= (r γ BLV Bcos θ / 2τP2P η)P1/2 PtP1/2P = ktP1/2

30

P

where, hτ is the actual distance traveled, τ is the tortuosity factor 3.9. Factors affecting Wetting and Wicking Following are the most critical factor which influence the characterization of wetting and wicking phenomina Material Characteristics 1. Fibre characteristics Wetting and wicking depends on the moisture absorption nature of the individual fibre (hydrophobic, hydrophilic and blends of the two), uniformity of mixing, cross section of fibre, fibre deniers, inherent porosity or the hollowness of fibre, continuous filament or staple, crimp etc. 2. Fabric characteristics The way in which the fibres are arranged in nonwoven (cross-laid, parallel-laid or random-laid), thickness of material, porosity of fabric, the discontinuity of fibre in web, the type of bonding applied, surface finish applied etc. 3. Fluid characteristics viscosity of fluid, surface tension of fluid, the composition of fluid (whether saline or distill), the amount of polar and non-polar groups etc. The capacity to retain large volumes of fluids under pressure and rapidity of imbibition are important factors in nonwovens used in absorbent applications. Absorbency being the result of absorbate/absorbent interaction, optimum ultimate performance of a nonwoven absorbent depends mainly upon interplay above three groups of variables. Some main factors influencing the direction of liquid spreading and the amount of absorbency are the orientation of web, porosity of material etc. 3.10. Pore and porosity Pore and its importance in wicking are considered as a high prior to this project and comprehensive the theory related to pores are discussed below. Connectivity of the pores in the fabric influence how fast and how much liquid is transported through the material. The pores within the structure are responsible for liquid flow through a material. Also the size of the pore and their volume determines the rate of absorption of liquid. They are generally discontinuous as because of the discontinuity of the fibres in nonwovens. Three kinds of pores may be present in a material as shown in fig 8..first; the closed pores are not accessible. Second, the blind pores terminate inside the material and do not permit fluid

31

flow. Third, the through pores are open to the outside and permit fluid flow. Through pores are of primary interest for many of the applications of nonwovens. The important through pore characteristics of nonwovens include the most constricted pore diameters, the largest pore diameter, the mean pore diameter, pore volume, pore distribution, surface area, gas permeability and liquid Permeability

Fig. 8. Different kinds of pores.

The porosity ( φ) of a material is defined as the fraction of void space within the material [2]. φ =1 −( ρb / ρs ) ρb = fabric density ρs = fibre density

The fabric density can be found by: ρb = fabric

weight / thickness

and the maximum absorption capacity can be found with: Cm = ( ρl φ) / ρs (1 −φ)

Cm = (ρl φ) / ρs (1- φ)

Where,

32

ρl= liquid density . Wicking can only occur when a liquid wets fibres assembled with capillary spaces between them. The resulting capillary forces drive the liquid into the capillary spaces. Wicking can be visualized as a spontaneous displacement of a solid-air interface with a solid-liquid interface in a capillary system. A porous medium can be defined as a solid matrix consisting of interconnected empty spaces. This matrix has a dimension known as the porosity of the material. The porosity is the percent of the material that is empty space and is usually represented by ϕ . Of interest is not only the total porous area of the material, but actually the pore size distribution. The technique of measuring this size distribution is discussed below. Liquid flow analysis has been used in many ways to describe structural characteristics of textile materials. Rebenfeld and Miller describeP(11)P ways in which to measure both the pore dimensions and the directional permeabilities of the material. They argue that the average porosity of a material can be a deceptive value. That two materials with the same overall porosity could behave quite differently because of differences in the directional porosities and also because the pore size can vary greatly within a single structure. Therefore, quantifying the pore size distribution can help in understanding the behavior of the material. A more appropriate method is the liquid porosimetry in which pore dimension distributions are determined using liquids. The most widely used technique is that of the mercury intrusion method. This method is not valid for many textile structures because of the compression loading which can cause damage to the structure. Furthermore, it can only measure pores accurately up to 5μm; textile structures can have pores that are as large as 1000μm. The method described by Rebenfeld and Miller a pre-saturated material is placed on a membrane in a chamber. The chamber is then filled with pressurized gas in incremental amounts over time and the pores begin to drain starting with the largest ones first. A computer controls this process. A balance monitors the liquid that is drained from the material. The process in measuring the in-plane flow of the liquid, also described by Rebenfeld and Miller, is much like that of the liquid porosimetry in that pressurized air is used to force liquid into the material. A highly viscous fluid is chosen so that the flow is a function of material structure

33

only and not that of the intrinsic wetting properties of the material. The flow is monitored by a video camera and then analyzed using an image analysis system. 3.10.1. Pore Size Distribution The total pore space consists of ores of different sizes. It is not possible to specify pore size geometrically. Since the pores are irregularly shaped and are not well defined entities. The concept of pore size distribution is therefore equally nebulous(24)P. Scheidegger offered a possible way out of the dilemma by defining the pre diameter at any point within the pore space as the diameter of the largest sphere which contains this point and remains wholly within the pre space. This definition suggests that even in the more simple porous structures. Short of a capillary tube, there exists a more or less continuous function describing the pre size distribution. 3.10.2. DARCY Law’s The Darcy flow can then be determined using the analysis of the images. Darcy described steady-state unidirectional flow through an isotropic porous medium in 1856 and can only be applied to systems for which slow laminar flow is found. This equation describes the relationship between flow rate and the pressure differenceP(12)P.

It should be noted that K is independent of the properties of the fluid and instead is controlled by the structural characteristics of the material. The quantification of K for simple structural parameters has been the focal point of many studies. The Carman- Kozeny approach is a hydraulic radius theory that defines K for a bed of particles or fibers to be P(13)

34

Although the Carmen-Kozeny constant is a popular approach for measuring permeability, others have tried to quantify it in terms of the geometry of the material. Ariadurai and Potluri P(14)Phave examined the flow of liquid through woven geotextiles and tried to model the flow with the intentions of increasing liquid movement through the materials. Ariadurai and Potluri based their model for fluid flow through a woven geotextile on the actual structure of the woven material and its yarn. The geotextiles studied in this work can be assumed to be infinitely wide and therefore it was only necessary to study the unidirectional flow through the warp direction. This model is based on the Poiseuille’s equation for volumetric flow rate flow through noncircular channels and is written as:

And where the specific permeability can be written as:

The foundation for the hydraulic radius for the woven structure is based on the basic geometry of the material. The hydraulic radii (the cross sectional area of the liquid moving through a capillary divided by the wetted perimeter) for the yarns are determined by assuming that the yarn has a racetrack sectional geometry. Thus, the volumetric flow rate and specific permeability can be determined by using these equations if the shape constants can be determined. Finally, the hydraulic transmissivity (in-plane permeability) can be found. Ariadurai and Potluri’s tests, carried out to analyze the equations, were conducted with compliance to British and ASTM standards for determining transmissivity values. The results were found to correlate well with the proposed model. Rebenfeld et alP(15,16,17,18)P describes in many papers a way to quantify in-plane liquid distribution within a porous network and how 35

this applies to the directional permeabilities. The process by which the experiments are carried out is the process described earlier on page 24 for measuring in-plane flow. This process forces a liquid into the material and the flow front is recorded using a video camera. An isotropic material will be expected to have a circular fluid front while an anisotropic material will have a fluid front that deviates from a circular front. Due to the nature of the fluid front the image can then be analyzed to determine the dominant directional permeabilities of the material. The process for analyzing these fronts is based on Darcy’ law, where the equation is written in the form:

For the analysis of a flow in a medium, the continuity equation and Darcy’s Law are combined to give,

,

and

In the above equation 1 and 2 are the principal flow directions. For an isotropic flow Front (k2 / k1 = 1), and analyzing the front at R = Rf the corresponding Darcy’s equation is equal to:

where porosity, ε , is equal to:

36

The permeability of the material can then be calculated by obtaining the slope of the least square line, m , Once this is obtained the permeability for the isotropic flow front k is found using the following:

An exact solution from the above equations cannot be determined for anisotropic flows. Instead, Rebenfeld et al. used finite elemental analysis and analytical expansion to determine the solution for k1 and k2 from experimental data. It was determined from these studies that the directional in-plane flow of liquid is not determined by the fluid viscosity, driving pressure, or surface wettability, but in fact was influenced by the structure of the materialP(19)P. While in this study Rebenfeld et al. examined the in-plane permeabilities in the main flow directions, in another study Rebenfeld et alP(20)P examined the local flow rates to determine the local permeabilities, which are a function of the local heterogeneities. For example, even though a fluid front may have an overall circular shape, the local curvature will not be perfectly smooth due to local imperfections in the fabric. Processing and handling of the material can cause these local imperfections. Rebenfeld et al. determined a process by which the local permeabilities of the material at given angles could be estimated by examining an image recorded during testing. Again the experimental set-up and test procedure are the same as these reported in previous experiments. Also, like past studies this one is based on Darcy’s law. The liquid fluid front boundary is extracted at given intervals. This boundary is then subdivided into tendegree intervals and placed on a grid so that sections of the “pie “ could be analyzed. For each slice, the average permeability is calculated between every two-boundary intervals using the following form of Darcy’s Law,

When a liquid front is moving through the plane of a material due to an applied pressure, there is a pressure drop across the face of the material. This model, however, is a 37

simplification of the movement of the liquid because it assumes that there is no pressure drop in the angular direction. A computer simulation of the fluid front using this model showed that the results using this assumption and the results obtained from the actual fluid front correlated well. Once the permeability of the slice is known, the average permeability of each grid square can be obtained by

With this method, not only are the principal flow directions analyzed, but the local flow directions are also analyzed. The local flow properties reflect the fabric’s local heterogeneities, which are inherent in any nonwoven fabric. The results could be misleading if only the maximum and minimum flow directions or the overall flow permeability were analyzed. These results may give the impression that the shape of the liquid front is a homogeneous ellipse, when in fact it is not. A smooth homogeneous ellipse almost never occurs due to process and handling. NederveenP(21)P

studied the relationship between different theoretical models for liquid

flowP in a porous material with that of the actual experimental results. The models are based on the Lucas-Washburn equation and Darcy’s permeability. The Darcy expression for permeability is:

This equation assumes that the capillaries are straight and parallel to one another. However, because not all of the channels are parallel to one another and their path is tortuous, the 2 in the denominator of the above equation is replaced with the Kozeny constant, k . This constant takes into consideration both of these effects within a porous medium. For porosities less than 0.6, the Kozeny constant was found to be between 4 and 6. If the porosities are greater than 0.7, the Davies expression, discussed below, can be used to determine the Kozeny constant and the expression for this constant is as follows,

38

If an ideal structure, defined as a material with constant fiber radius where all fibers are parallel to the direction of flow, is considered, the Darcy permeability combined with the Davies expression, could be re-written as,

Iberall proposed a model based on the forces applied to the structure during steady flow. If the velocity is very small, the equation is written as,

For liquid rise in a capillary tube, the Lucas-Washburn equation is frequently used to describe the flow. For this purpose this equation has the form,

The models tested by Nederveen for liquid rise in a porous medium are referred to as model one and model two. Model one assumes that the number of capillaries within the medium is twice that of the number fibers. The equation for this model is once again the general solution found for the Lucas-Washburn equation except that there is a change in T and H

39

Model two does not assume a particular amount of capillaries. Instead, it is based on the circumference of the fibers. The same ideal structure assumed for Iberall’s equation is assumed for model two. The upward tension for this model is written as,

Therefore, the value for T is the same as for model one, but the value for H changes to,

To test the validity of these models two separate tests were conducted testing the permeability in one and the liquid rise in the other. Both tests used fibrous mats made from a polyester fiber treated with a hydrophilic finish. These fibers did not swell. The material for the permeability test was clamped between two horizontal plates one end of the material was exposed to a liquid reservoir while at the other end there was a balance. The liquid moved through the structure and was collected on the balance at the other end. The readings were taken every minute for an hour. The material for the liquid rise was also clamped between two plates, but the material was positioned vertically. The plates were tightened more on one side so that the material’s density varies over the width of the material. This enabled the measurement of different densities during one trial. The bottom of the material was placed in the liquid and the level of the liquid was marked on the plate at specific times. The results from the permeability tests compared the results from the experiment to the permeabilities of the Iberall equation and the Davies equation. Neither of the equations predicted the experimental values closely although the Davies equation was closer match. The maximum height for the vertical rise experiments were recorded and compared to the two models. Model one predicted values much higher than the maximum and model two seemed to be very close to the actual value. Thus, it was concluded that using model two as a modification of the Lucas-Washburn equation results in an accurate prediction of the vertical rise of liquid through a porous medium with negligible swelling. Tests were also performed on cotton and on viscose fibers. These fibers tend to swell when

40

exposed to liquid. The results from these tests did not correlate well with the theoretical values. 3.11. Test methods for liquid wicking Various methods are available to test the wicking of Textile material in the form of fibre, Yarn, and fabric etc. The prominently used methods for testing nonwovens are discussed below, Different types of wicking tests Wicking From a Limited (Finite) ReservoirP(22)P 1. Standard Spot tests 2. Radial wicking or ring test Wicking From an Infinite Reservoir 1. Immersion 2. Longitudinal Wicking 3. Transplanar or Transverse or Demand Wicking

3.12. Limitation of existing method of wicking testing 1. Problems with both the vertical and downward wicking test are edge effects. The edge effect is due to the equilibrium that occurs when the liquid reaches the edge of the material.The liquid front ceases at these edges and therefore, can cause a change in rate of the overall velocity within the material. Therefore, the actual velocity in each direction may not be known. Also a problem is the inability to accurately compare the wicking rate of one direction to that of another. Because equilibrium occurs at the edges the differences in the rates per angular direction may potentially be affected and therefore the true difference in rates for each direction may not be known.The vertical wicking test is shown in Fig 3.10.

41

Fig 9. Vertical wicking test

2. Limitation with the basket or sink test, first, the rolled up material forms extra Capillaries between its layers. These capillaries have the potential of holding liquid thus the reading for the weight may be a greater than the actual amount of liquid that the material could absorb for a given period of time. Second, the absorption rate cannot be modeled by using this test procedure. 3. Limitations of the GATS (gravimetric absorbency test system).A schematic diagram of GATS is shown in Fig 3.11. First, an extra capillary may form between the plate and the material, especially when using the point test plate. This may result in faster absorption times than would normally be associated with the intrinsic wicking ability of the material.

42

Fig 10. Gravimetric Absorbency Test System Second, the platform is at a constant height. Therefore, as liquid is absorbed into the material the pressure head changes due to the liquid in the reservoir receding. This causes errors in the data. Third, there are some problems with the machine itself. The user has to place the sample on the platform at the same time that the test is begun. Of course, this results in errors due to human involvement. Finally, the directionality of the wicking cannot be isolated. This means that although the total absorption of the material can be measured, the rate of wicking in a given direction is not known. 4.Limitations of NCRC developed utilizes the GATS equipment, but uses a plate that is rectangular in shape and measures the liquid spread of a strip of material cut in a given direction (such as the cross or machine direction). One of the problems that arise with this test is overflow of the liquid into the trough of the plate. This in turn, results in inconclusive results because the data that is being recorded is not only a function of the liquid being absorbed by the material, but also a function of the liquid that is filling the trough. Also, like the vertical wicking test there are edge effects. 3.13. Application of Wicking and Wetting The behavior of a given textile during its contact with water (or with the liquid generally) is one of the important properties of textiles. This work focuses on spontaneous liquid wicking, which especially influences the consumer properties of textiles. If the liquid rises (by absorption) in fabric, it can be used as a liquid perspiration outlet from the skin, for the production of hand towels and dishcloths, textiles for cleaning works, and many other such applications. Wicking makes it possible to use textiles for a series of other special applications: wicks for candles and lamps with oil, or some modern flameproof finishing’s for housing textiles.

Nonwovens are used in products such as baby diapers, feminine

products, geotextiles, Medical equipment such as gowns and sterilization covers, and may someday be a Common method for the production of clothing. In most of these areas one of the key Property of the material is its liquid transport ability and more specifically the inplane liquid distribution. In-plane liquid distribution is the movement of liquid within the

43

plane of the fabric as opposed to the movement of the liquid perpendicular to the plane of the fabric, which is referred to as transplanar distribution, which is also important, but the inplane liquid distribution is used to distribute liquid over a given area so that either total evaporation of the liquid can occur more readily, such in the case of perspiration on clothing, or so that the product can be used to its maximum capacity, such in the case of the second layer of a baby diaper. The liquid spread rate and distribution are very important in products like femine diapers top sheet layer, whose main function is to spread the liquid rapidly over the entire width of the napkin and the spread fluid is then absorbed by the core absorbing material and retained within the material in order to keep the skin dry and comfortable.

44

4. Methods and Materials

4.1. Selection of Material Nonwoven samples received from different manufacturer are enlisted below, Sample

Material

Method

of GSM

Code PE 100 VI 100 PV 120

Polyester Viscose PET/Viscose

manufacturing Needle punched Needle Punched Needle Punched

Company

100 100 120

Supreme Nonwovens Supreme Nonwovens Supreme Nonwovens

PP HPB40

(50/50) Polypropylene Thermal Bonded

40

Supreme Nonwovens

PP HPL40

(hydrophobic) Polypropylene Thermal Bonded

40

Supreme Nonwovens

PP HPL 18

(hydrophilic) Polypropylene Thermal Bonded

18

Supreme Nonwovens

PP HPL50

(hydrophilic) Polypropylene Spunbonded

50

Fibre Web India

Spunbonded Spunbonded

75 100

Fibre Web India Fibre Web India

(Hydrophilic) PP HPL75 PP HPL100 PV 50

PET/Viscose

Spun lace

50

Ginni Filaments

PE 30

(30/70) PET

Spunbonded

30

Komitex

4.2 Modified Inplane wicking Tester

45

To overcome the limitations of the available ‘In-Plane Wicking Test Method’, a new test rig has been designed, fabricated and interfaced with computer to record the readings automatically. 4.2.1. Design and Fabrication The schematic diagram of the instrument is shown in Fig 4.1 . Top plate

Glass tube beaker

Bottom plate

Sensor -2

Electronic Balance

Sample

Sensor-1

Control Unit

Computer

Modifief In-Plane Wicking Test Rig

Fig 4.1 Overall View of In-Plane Wicking Tester 4.2.2. Working Principles of the Inplane Wicking Tester The In-Plane wicking tester is mounted with a DC motor to raise and lower the stand holding the fabric assembly plates to initiate the experiment. When the DC motor is switched on, it will lower the upper part of the stand with help of traversing mechanism provided in the stand through set of reduction gears. The lowering of the upper part of stand will initiate the flow of liquid from the beaker to the sample through the Syphon tube. The liquid before touching the sample will initiate the sensor no.1 then the sensor no.1 will further forward the signal to the relay no.1.

46

The relay no.1 will stop the running of the motor and at the same time initiate the camera to acquire images of the liquid spread on the fabric and record the volume of the beaker on the balance through the control unit. The liquid thus touching the sample will be absorbed by the sample through wicking process and the absorbed liquid will spread over the sample. The liquid spread distribution of the sample over time will be recorded from the digital camera installed over the fabric assembly. As the liquid touches the edge of the top and bottom plate it initiates the sensor no.2.The sample material acts as non-conducting material between the two plates until liquid does not touch the two plates. The sensor no.2 excites the relay no.2, which further stops the camera to take images and stops recording the volume of beaker from the balance. The recording of the images from the camera and the volume of the beaker from the balance is stored in personal computer through separate software available. The stored images are further utilized for image processing of the liquid spread analysis using MATLAB software. The control unit of the instrument controls the flow of the signal from one component to another with appropriate timings. The control unit is provided with start and reset buttons. By pressing the reset button on the control unit will position the stand to its original starting position for next set of experiment.

Fig 4.2 Flow of signal in the in-plane wicking tester

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4.2.3. Driscription 1. ELECTRONIC

BALANCE:

The balance is used to measure the weight of liquid throughout the

test as to calculate the amount of absorption, rate of absorption etc. The accuracy of the balance required is 0.001 gm. 2. BEAKER: The beaker will be the source for the liquid to the fabric through syphon and glass rod tube. The volume of the beaker will be decided based on the fact that as the water is wicked into the fabric the pressure difference due to change in the distance between the fabric mount and beaker should be constant and its should not effect the hydrostatic pressure (the width of the beaker will be maintained large enough that a few ml of water to fabric from beaker should not create pressure difference). 3. SYPHON TUBE: The tube will be used to carry the liquid from the beaker to the fabric mount bottom plate. The inner orifice of the tube will be 3.0 mm which will supply liquid at a very slow and steady rate to the sample. 4. BOTTOM PLATE OF FABRIC MOUNT: The bottom plate will be holding the fabric sample on its top groove. The sample will be touching only at the centre (from where liquid will enter) and at the edges of the bottom plate (as the bottom plate is hollow there is no extra capillaries due to any surface contact with the bottom or top plates). 5. TOP

PLATE OF FABRIC MOUNT:

The top plate will just hold the sample in the bottom plate

groove in tact manner to avoid filling of trough and this small amount of tension will not affect the results. 6. STAND: The fabric holder will be resting on this stand. This will be used for lowering the fabric holder assembly during the start of the experiment to facilitate the smooth initiation of wicking of liquid into the fabric with the help of traversing mechanism provided in the middle of the stand with help of a set of gear wheels and D.C.motor.

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7. DIGITAL

CAMERA:

The camera will acquire digital images of the spreading of the liquid at

specified interval of time for digital image processing. Owing to higher initial cost, purchasing of the camera has been postponed. 8. PC: One personal computer will be required for the measurement of the volume of the liquid receding in the beaker and to store the images acquired from digital camera. System configuration: Intel Pentium-II, 40 GB, 32 Ram installed with software to record the volume of water to an accuracy of one second. 9. CONTROL UNIT: The control unit consists of back and front panel, which controls the flow of signal for the whole system. The front panel consists of the following buttons like power switch, instrument status indication lamps, emergency switch, sensor 1 with enable& disable toggle switch, sensor 2 with enable & disable toggle switch, start or stop push button, knob to control the intensity of lighting according image acquisition level, speed control knob to increase or decrease the speed of upper compartment, auto or manual button to initiate the process automatically, sensor 1 sensitivity control knob. The back panel of control unit consists of the following components. Input power supply(220 volt) from a stabilizer, an exhaust fan to maintain the temperature of the Integrated circuit chip at ambient working condition, interface sockets for interfacing electronic balance and the digital camera to the computer and instrument. A 12 amps fuse for power safety. The instrument works automatically from the start to end. The general layout of the instrument working in automatic mode is shown in the Fig 4.2. The dimension and specifications of each component of the instrument along with the electronic circuit diagram of the motor, sensors, control unit, digital camera, personal computer, electronic balance and lighting system are separately attached to the end of the report (Appendix-II). 49

4.2.4. Features of the Instrument i.

The total load of the upper compartment is less than 5 kgs, according to torqueforce calculation the required motor hp is .05 HP but for a safety a 0.5 HP motor is used.

ii.

To avoid the vibration during the downward or upward movement of the compartment smooth frictionless poles are used at the four corner of the top assembly.

iii.

Highly sensitive contact sensors are used to sense the presence of liquid at the entrance of the tube and at the edges of the plates to avoid any time delay(less than 0.1 second) in sensing the change in resistance and to feed the signal to the control unit.

iv.

An electronic balance is interfaced with the computer system to record the volume of water to an accuracy of 0.001 gm.

v.

The maximum absorption of the samples can be evaluated by activating the disable button of sensor no.2.

vi.

The timing of the sensor no.1 is adjustable so as to stop the downward movement of the upper compartment when the liquid just touches the bottom layer of the sample.

vii.

The fabric assembly is completely leveled in plane with the help of in-built spirit level mounted on the instrument to avoid any disturbance during liquid spread on the sample.

viii.

The light intensity of the lighting system can be adjusted according to the required image quality and image contrast level.

ix.

The Teflon pins provided on the bottom fabric assembly unit ensures even tension for all the mounted samples.

x.

The glass tube holder which is used to hold the glass tube firmly ensures a nonturbulent motion to the liquid flow while the upper compartment descends and to avoid any external pressure on the liquid flow through the tube to the sample.

xi.

The control unit is installed with a zener diode which ensures a stable supply of input power to avoid any speed variation, which further ensures vibration less movement of compartment.

50

4.3. Tensile testing using Instron Tester In order to compare the anisotropic nature of web in describing wet ability parameters one can correlate the anisotropic nature of samples in tensile strength. The tensile test was carried out using INSTRON instrument based on constant rate of elongation. The sample size of 75 × 50 mm strip was used to study the tensile strength in machine direction and cross direction at a constant rate of elongation (130 mm/min). 4.4. Lica Microscope Photographic analysis of nonwoven is done in Lica microscope. The picture is captured with high resoluation camera and snaps are taken from same. This Microscope can magnify upto 100 X. 4.5. Kruss Tensiometry –Vertical Wicking Tester An attempt was taken to study the pore volume of nonwoven. This is comprehensively discussed below. 4.5.1 Sample Size For Machine Direction Sample preparation, we have taken 1.8 cms length along the machine direction and 1.4 cms width along the cross direction is preferred and the vice versa is considered for cross direction 4.5.2. Instruments parameter To test the Pore volume of the fabric, we have utilized Kruss Vertical wicking tester which works under ‘Tensiometry’ Principle. This has got provision to keep liquid inside the instrument for wicking, has precise and high accurate balance, also it has various type of jaws to mount the nonwoven sample on the balance. It has glass door, which locks when experiment is on. Software is interfaced to give reading of mass with respect to time change. 4.5.3. Experiment Method Sample of above prescribed size is made and weighed accurately and noted the reading. Then the sample is hanged vertically. The upper part of the jaw holding the sample is connected to the balance through very high magnetic force. The bottom portion of fabric is freely hanged and beaker filled with n-heptane is kept below the sample and made to travel above in the speed of 6 mm / min. As the liquid –Solid interface occurs, a force is experienced and further movement of the beaker is terminated. Now

51

wicking takes places against gravity in nonwoven. As n- Hexane is low surface tension liquid, it occupies entire pore in the sample. As time proceeds, the corresponding mass of liquid absorbed is recorded and plotted as a graph given below by the instrument. After that, the pore volume of the nonwoven is determined from the calculation given below, 4.5.4. Calculation Initial Dry weight of Specimen= W1 (g) Weight of Liquid absorbed = W2 (g) Volume of the Fibres in Fabric = W1 / Density of fibres = V1 (Cm3) Volume of Liquid (n-Hexane) in Fabric = W2 / Density of Hexane (.661g.cm-3) = V2 (Cm3) Total Volume V3(Cm3) = V1 + V2 Therefore Volume Fraction is determined by 1. Volume Fraction of Fibres in nonwoven (Vf) = V1 / V3 % of Volume Fraction of Fibres in Nonwoven = Vf x 100 Wherever the pores are presents, Hexane is entrapped into those portion due to less surface tension( 18.4 mN/ cm)) when compared to Water(72.8 mN/cm). Therefore we can conclude that volume of Hexane calculated should equal to volume of pore in the fabric. 2. Volume Fraction of Pores in nonwoven (Vp) = V2 / V3 % of Volume Fraction of Fibres in Nonwoven = Vp x 100

52

5. Result and Discussion

5.1 Microscopic study of Nonwoven fabric A. Analysis of Poly propylene Sample (75 GSM) I. Fused Portion: This is portion where Thermal bond is made, where the fibres are fused at this point. The collapsed portion shows the fused point. The fibres are densely arranged at the boundary of the fused point.

Figure 5.1 and 5.2 fused portion and its Boundary area II Open pore Structure: This portion is found when the fibres are moved away from the fused and densely fibre arranged portion. Here the fibres are very loosely held with larger pore size. At fused point, cluster of fibres are formed and away from it open pores are found as shown in figure 5.4.

Figure 5.3 and 5.4 from fused portion to open pore III. Parallel fibres along machine direction:

At the place in between Four bonded

portions, it is found in many places that there is an alignment of parallel fibres along the machine direction, which forms straight capillary along machine direction and cause slightly higher volume of liquid absorbed than cross direction of same fabric which is discussed in Pore volume determination.

53

Figure 5.5 Parallel pores IV. Big pores: The big pore size is formed at random places as shown in the figure 5.6 which forms a closed pore and accumulate the water content inside the pore

Figure 5.6 Big pores V. Cross arrangements of fibres: In between the two hole portion along machine direction, there are many crisscross of fibres are found. This is as shown in figure 5.7.

Figure 5.7. Portion in between two fused point (along machine direction) B. 40 GSM PP Hydrophobic I. With available fabrics, any thing above 20 gsm, the fibres are arranged in different layer, the following fig 5.8 and 5.9 are taken from same place by focusing first and second layers of

54

fabric respectively. Further we can focus for next layer, but the picture is not clear through microscope. SEM may be the best way to identify these analyses.

Fig 5.8. First layer of fibres in nonwoven

Fig. 5.9 Second layer of fibres present in Nonwoven

C. Spun lace Structure In spun lace, it is observed that the bunch of fibres are forming cluster along machine direction at an equal interval in the fabric. From this we can conclude that the gap between the cluster of fibres are the arrangement of water jet nozzle for hydro entangling during the manufacturing process. Figure 5.11 shows the most of the fibres are arranged more parallel to each other along the machine direction.

Fig. 5.10 Witnessing the Water jet punched portion

55

Fig.11. Machine direction alignment of fibres

D .PP Hydrophilic 18 GSM: Fused and its adjacent portions are shown for finer gsm available with us in below picture

Fig. 5.11 Fused portion

Fig 5.12. Portion between four pores of PP HPL 18

5.2 Determination of pore volume of Nonwoven – PP HPL 100. Inorder find the pore volume of 100 GSM spun bonded poly propylene, a 30 samples are prepared out of which 15 are made as a machine direction sample and rest are the representative for cross direction. They are made in the dimension 1.4 cms(width) X 1.8 cms (length). For machine direction sample higher dimension is along the machine direction (length) and for cross direction, the higher dimension of the sample is along the cross direction. After cutting sharp and accurate, they are precisely weighed in a balance to noted dry weight and above procedure is to maintain for further experiment to carried off. Their results are flourished below,

56

I. Machine direction Mass of nTest

Mass of

Hexane

Total

Specific ML

Sp. MT

absorbed

Mass(g)

(g) =

(g) =

No. Fabric(g)- MF (g)- ML MT (MF / ML) (Sp. ML +1) M1 0.0257 0.05837 0.08407 2.2712 3.2712 M2 0.0256 0.05014 0.07574 1.9586 2.9586 M3 0.0258 0.05664 0.08244 2.1953 3.1953 M4 0.0221 0.04644 0.06854 2.1014 3.1014 M5 0.0249 0.04804 0.07294 1.9293 2.9293 M6 0.0243 0.04814 0.07244 1.9811 2.9811 M7 0.0255 0.04665 0.07215 1.8294 2.8294 M8 0.0229 0.04538 0.06828 1.9817 2.9817 M9 0.023 0.0423 0.0653 1.8391 2.8391 M10 0.0248 0.04806 0.07286 1.9379 2.9379 M11 0.0243 0.04865 0.07295 2.0021 3.0021 M12 0.024 0.05292 0.07692 2.2050 3.2050 M13 0.0238 0.0432 0.07 1.9412 2.9412 M14 0.0249 0.04492 0.06982 1.8040 2.8040 M15 0.0236 0.05069 0.07429 2.1479 3.1479 Mean 0.0243 0.04891 0.073249 2.0083 3.0083 Table 1. Indication of Fabric mass, mass of n Hexane absorbed by PP HPL 100 fabric along Machine direction and Table 2 below, corresponding Volume Fraction of pore and fibres.

Volum

Fibres in

n-Hexane

Total

Nonwoven 1.0989

3.0383

4.1373

e (cm3) Volume fraction of fibre 0.2656

Volume fraction of pore 0.7344

Mass vs Time

0.06

Mass [g]

0.04

0.02

0.00

57 0

100

200

300

400

Time [s]

500

600

700

Graph 1 indicates Mass Vs Time for PP HPL 100 in Machine direction for 15 Tests.

Mass² vs Time

0.0030

Mass² [g²]

0.0020

0.0010

0.0000 0

100

200

300

400

500

600

700

Time [s]

Graph 2 Indicates Mass2 Vs Time for PP HPL 100 along Machine direction for 15 Tests

II. Cross Direction: Test

Mass of

No. Fabric(g)- MF C1 0.0226 C2 0.0207 C3 0.0222 C4 0.0235

Mass of n-Hexane

Total

Specific ML

Sp. MT

absorbed

Mass(g)

(g) =

(g) =

(g)- ML 0.04111 0.0426 0.04156 0.0423

MT 0.06371 0.0633 0.06376 0.0658

58

(MF / ML) (Sp. ML +1) 1.819 2.8191 2.058 3.058 1.8721 2.8721 1.8 2.8

C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 Mean

0.0233 0.021 0.0236 0.022 0.023 0.0226 0.0229 0.0234 0.0231 0.0234 0.0234 0.0227

0.04247 0.04536 0.05177 0.04256 0.0497 0.0405 0.04195 0.03855 0.03904 0.0465 0.0498 0.0438

0.06577 0.06636 0.07537 0.06456 0.0727 0.0631 0.06485 0.06295 0.06214 0.0699 0.0732 0.0665

1.8228 2.16 2.1937 1.936 2.1609 1.7924 1.8319 1.6902 1.690 1.9872 2.1282 1.9294

2.8228 3.16 3.1936 2.9346 3.1609 2.7920 2.8319 2.6902 2.6901 2.9872 3.1282 2.9296

Table 3.above, shows the fabric mass, mass of n Hexane absorbed by PP HPL 100 fabric along Cross direction and Table 4 below, shows the corresponding Volume Fraction of fibre and pore. Fibres

n Hexane

Total

1.0989

2.9189

4.0178

Volume in Nonwoven (Cm3)

Volume fraction of fibre 0.2735

Volume fraction of pore 0.7265

Cross Direction:

Mass vs Time

0.06

Mass [g]

C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 C16

0.04

0.02

0.00 0

100

200

300

Time [s]

59

400

500

600

700

Graph 3 indicates Mass Vs Time for PP HPL 100 fabric in Cross direction for 15 Tests.

Mass² vs Time

0.0030

Mass² [g²]

C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 C16

0.0020

0.0010

0.0000 0

100

200

300

400

500

600

700

Time [s]

Graph 4 Indicates Mass2 Vs Time for PP HPL 100 along Cross direction for 15 Tests

5.3. Determination of pore volume of Nonwoven – PP HPL 75 I. Machine Direction: Mass of nTest

Mass of

No. Fabric(g)- MF M1 0.016 M2 0.0156

Hexane

Total

Specific ML

Sp. MT

absorbed

Mass(g)

(g) =

(g) =

(g)- ML 0.03455 0.03465

MT 0.04755 0.04725 60

(MF / ML) (Sp. ML +1) 1.972 2.972 2.029 3.029

M3 M4 M5 M6 M7 M8 M9 M10 Mean

0.0164 0.0158 0.0159 0.016 0.0158 0.016 0.0159 0.0158 0.01592

0.03041 0.0301 0.02869 0.03177 0.02806 0.03243 0.02888 0.02856 0.03021

0.04681 0.0459 0.04459 0.04777 0.04386 0.04843 0.04478 0.04436 0.04613

1.854 1.905 1.804 1.986 1.776 2.027 1.816 1.808 1.898

2.854 2.905 2.804 2.986 2.776 3.027 2.816 2.808 2.898

Table 5. Shows the initial fabric mass, mass of n Hexane absorbed by PP HPL 75along Machine direction and Table 6, below shows the corresponding pore and fibre volume fraction Fibres Volume in Nonwoven (Cm3)

n- Hexan 2.871

Total

1.099

3.970

Volume fraction of fibre 0.2768

Volume fraction of pore 0.7232

Mass² vs Time

0.0015

Mass² [g²]

0.0010 M1 M3 M4 M5 M6 M7 M8 M9 M10 M 1

0.0005

0.0000 0

100

200

300

400

500

600

700

Time [s]

Graph 5 Indicates Mass Vs Time for Mass PP HPL 100 vs along TimeMachine direction for 15 Tests 2

0.04 0.03

Mass [g]

0.02

M1 M3 M4 M5 M6 M7 M8 M9 M10 M 1

0.01 0.00

61 0

100

200

300

400

Time [s]

500

600

700

Graph 6 indicates the Mass Vs Time for PP HPL 75 in Machine direction for 10 Tests.

II. Cross Direction: Mass of nTest

Mass of

No. Fabric(g)- MF C1 0.0165 C2 0.0163 C3 0.0159 C4 0.0162 C5 0.0157 C6 0.0163 C7 0.01658 C8 0.01628 C9 0.01689 C10 0.016 Mean 0.016265

Hexane

Total

Specific ML

Sp. MT

absorbed

Mass(g)

(g) =

(g) =

(g)- ML 0.03856 0.03046 0.0312 0.03869 0.03112 0.02888 0.03154 0.0271 0.03256 0.02756 0.038367

MT 0.04806 0.04676 0.0471 0.04789 0.04682 0.04518 0.04812 0.04338 0.04945 0.04356 0.046632

62

(MF / ML) (Sp. ML +1) 1.913 2.913 1.869 2.869 1.962 2.962 1.956 2.956 1.982 2.982 1.772 2.772 1.902 2.902 1.665 2.665 1.928 2.928 1.723 2.723 1.867 2.867

Table 7. shows the initial fabric mass, mass of n Hexane absorbed by PP HPL 75 along Cross direction and the table 8, below shows corresponding pore and fibre volume fraction. Fibres

Liquid

Total

1.099

1.867

2.867

Volume in Nonwoven

(Cm3) Volume fraction of fibre 0.280

Volume fraction of pore 0.720

Mass vs Time

0.04 0.03

Mass [g]

0.02 C1 C2 C3 C4 C5 C6 C7 C8 C9

0.01 0.00 0

100

200

300

400

500

600

700

Time [s]

Graph 7 Indicates the Mass Vs Time for PP HPL 75 in Cross direction for 10 Tests.

Mass² vs Time

0.0020 0.0015

Mass² [g²]

0.0010 C1 C2 C3 C4 C5 C6 C7 C8 C9

0.0005 0.0000 0

100

200

300

400

Time [s]

63

500

600

700

Graph 8 Indicates Mass2 Vs Time for PP HPL 75 along Cross direction for 10 Tests Discussion Of course theoretically both cross direction and machine direction should give same readings but here cross direction shows slightly low pore fraction than the Machine direction. This correlates us that fibres arrangement in between the four fused point are almost parallel which slightly hinders the movement of liquid flow through capillary in cross direction, due to which this differences are performed. When comparing 75 and 100 gsm fabric, The Z directional pore arrangement should be higher in 100 gsm because increase in the thickness of the fabric. Due to the distribution of more pore, the volume of n- Hexane absorbed also becomes as higher when compared with 75 GSM. This has been proven from this test result. 5.4 Tensile Test A rectangular strip of 75 mm X 50 mm was used on the Instron instrument at 130 mm / min rate of traverse. The sample was tested in both machine and cross direction. the test results are based on 20 samples in each direction. the average tensile strength results are shown in the Table below Sample Code

Tensile Strength (kgf)

Tensile Strength (kgf)

Machine Direction (FM) Cross Direction(FC) PP HPL100 13.636 7.8228 PP HPL 75 8.8299 5.5915 PP HPL 50 8.6293 4.6891 Table 9. Indicates the Values of Tensile strength in cross and machine direction for PP samples From the above data, it is very well under stood that fibres are oriented along the machine direction, since the tensile test result shows maximum strength occurs in machine direction for the polypropylene. Now we can consider the microscopic structure to co-relate that the fibres between the fused points are oriented parallel which cause increase in the tensile property over machine direction for all the three fabrics mentioned in the above table.

64

5.5. Testing the Wettability characteristics of Polyester, Viscose and PV blend Needle punched fabric in vertical wicking It is proposed to study the Wetting behavior of PET, Viscose and PET /Viscose (50%/50%) blended fabrics of sample size as 4 cms in length and the contact width with liquid is in different dimension, say as 2, 2.5, 3. and 3.5 cms. Here water is used as a medium for wicking. The following are the some of the observation obtained from the test. 5.5.1. Behavior of Polyester / Viscose Fibres

Mass2 vs Time

0.6000

Mass² [g²]

0.4000

0.2000

2.5 cms 3 cms 3.5 cms

0.0000 0

200

400

600

800

1,000

1,200

Time [s] Graph 9 Indicates Mass2 Vs Time for PP HPL 100 along Machine direction of 3 different contact area

65

Mass vs Time

0.8

3.5 cms

Mass [g]

0.6

3 cms

0.4

2.5 cms

0.2 0.0 0

200

400

600

800

1,000

1,200

Time [s] Graph 10 indicates Mass Vs Time for P/V 120 fabric in Machine direction for 3 different area of contact Test. 5.5.2. Behaviour of PET

Mass² vs Time 0.2500

Mass² [g²]

0.2000 0.1500 0.1000 2 cms 3 cms

0.0500

3.5 cms 0.0000 0

200

400

600

800

1,000

1,200

Time [s] Graph 11 indicates Mass² Vs Time for PE 100 fabric in Machine direction for 3 different area of contact Test.

5.5.3. Behaviour of Viscose

66

Mass² vs

Time

0.6000

Mass² [g²]

0.4000

0.2000

2.5 cms 3 cms 3.5 cms

0.0000 0

200

400

600

800

1,000

1,200

Time [s] Graph 12 indicates Mass² Vs Time for VI 100 fabric in Machine direction for 3 different area of contact Test.

3.5 cms

Mass vs Time

0.8

Mass [g]

0.6

3 cms

2.5 cms

0.4 0.2 0.0 0

200

400

600

800

1,000

1,200

Time [s] Graph 13 indicates Mass Vs Time for VI 100 fabric in Machine direction for 3 different area of contact Test. Discussion First it is decide to test wetting / wicking behavior of Polyester viscose 120 GSM of needle punched fabric with varying contact length as prescribed above, obviously increase in contact area will have more pore and wicking is higher and higher proportionately. In order to cross

67

check which component is responsible for these wicking / wetting, 100% PET and Viscose from same method of manufacturing is taken and analyzed the wicking properties. Polyester shows the initial poor wetting behavior because of its hydrophobic in nature. So 100 % PET shows very low water absorbing capacity when compared to blended Polyester viscose fabric. Whereas, viscose as its initial wetting behavior is very good, it has absorbed water highest among PET and P/V blends

between initial first 20 to 25 seconds of

experiment.

5.6. Modelling of wicking in Nonwoven fabrics 5.6.1. Theory of Lucas washburn equation Plenty of research available to determining the Surface science, Interfacial tension, and surface tension of the liquid.

Lucas washburn equation is one among and give

comprehensive information on the rate of fluid flow through a porous capillary tubes. According to the Lucas – wash-burn equation, in vertical wicking neglecting gravitational forces the wicking length, h is directly proportional to the square root of time, t L = k t 1/2

1

Considering the fibres in textile assemblies form capillaries of effective radius ref then the water transport rate is given by the formula, 2 L2 = (γlv cos θ ref t /2 η) L2= ks t L

= length of liquid raise

γlv

= surface tension between liquid and vapor

t

= time required to raise liquid from bottom to the length L

θ

= contact angle

68

ref

= effective capillary radius

η

= viscosity of the liquid

5.6.2. Features of Nonwoven According to EDANA definition, Nonwoven are a manufactured sheet, web or bat of directionally or randomly oriented fibers, bonded by friction, and/or cohesion and/or adhesion, excluding paper or products which are woven, knitted, tufted stitch bonded incorporating binding yarns or filaments, or felted by wet milling, whether or not additionally needled. The fibers may be of natural or man-made origin. They may be staple or continuous or be formed in situ. As it is very well known that the fibres distribution is not uniform in nonwoven fabrics. However in spun bonded and melt blown, we can some how reduce the degree of anisotropy of nonwoven. Wicking of the liquid into the nonwoven is totally depends on the capillary size, and the orientation of the capillaries in the nonwoven. Capillaries are formed by the fashion of arrangement of the fibres in nonwoven. . 5.6.3. Limitation of Wash-burn Equation 1. Wash burn equation deals with the pores lies in straight path in an solid. Whereas in Nonwovens the pores are distributed randomly across and along the fabric. 2. Wash burn equation is subjected for a single capillary system, where as the fibrous and porous material like nonwoven has got many no. of capillary in its structure. Capillary constant: We have considered the above statement and worked for ‘n’ no. of capillaries in a nonwoven. Many researches are carried out to formulate the capillary constant. However, here the capillary constant defined as the product of mean capillary radius and the average capillary orientation of nonwoven sample. Capillary constant = Mean capillary radius x Capillary orientation 5.6.4. Model to determine, a. Mass of liquid transport through Nonwoven b. Mean radius of capillary

69

3

Consider figure 5.1, assuming that the fibre 1 and 2 are arranged in an angle α along machine direction. The capillary radius formed by the gap between the two fibres. If all fibres are arranged to the Machine direction (MD), the length of liquid raise is considered higher than it is arranged in a certain degree as shown in diagram 1 of same mass of water absorbed. When fibres arranged in Cross direction (CD), the length of liquid raise (L) will be very less compared to any other angle of arrangement from cross to machine direction.

M.D

CD

Fibre 1

Fibre 2

L!

L

α Capillary radius

90 - α Figure 5.1 Schematic representation of alignment of fibres and pore in nonwoven Assuming that there are ‘n’ number of fibers in an nonwoven material oriented in different angles,

70

Let us consider that P1, P2, P3 … are the proportionate of fibres arranged in angle α1, α 2, α 3……so that mean orientation of fibre P is given by, 2 2 2 1/2 2 P = Σ [(P1Cos α 1) + (P2 Cos α 2 ) + (P3 Cos α 3) +…………..] + Σ [(P1Sin α 1) + (P2 Sin

α 2 )2 + (P3 Sin α 3)2 +…………..]1/2 4

P = Σ[(PiCos αi)2 + (Pi sin αi)2]1/2

The mean orientation angle of above stated proportion of fibres is given by,

α = Σ [(P1Sin α 1) + (P2 Sin α 2 ) + (P3 Sin α 3) +…………..] / Σ [(P1Cos α 1) + (P2 Cos α 2 ) + (P3 Cos α 3) +…………..]

α = Σ [Pi sin αi] / Σ [Pi cos αi]

5

As per Lucas wash burn equation, we assumed the height of capillary raise ‘h’ and the formula for the flow of liquid through the capillary is given as follow, h2/ t = (γlv cos θ ref /2 η) Where as the effective capillary radius is given as, 6 ref = C F F = mean capillary radius, C = mean angle of orientation So wash burn equation is rewritten as, 7

h2/ t = (γlv cos θ C.F /2 η) t = (h2 2 η / γlv cos θ C.F)

For vertical wicking h = L(length of liquid raise) t = (L2 2 η / γlv cos θ C.F)

8

To determine mass of liquid absorbed: Let us say that mass of liquid absorbed by the material (M) is equal to, M (gms)= Volume of the pore X Density of the liquid Assuming the volume of pore is cylindrical M = ╥ r2. L . ρ

9

71

Where, r = radius of capillary L = length of capillary ρL= density of liquid Therefore, the mass of liquid absorbed is proportional to r, l, ρL Since the length of the capillary in nonwovens are not lying exactly Fibres straight, and all fibres are not oriented in machine or cross direction perfectly. However, the fibres arranged in certain degree,

so

as

capillaries

also

arranged

according

to

their

appropriate

angle.

Fig r

L’ L

α 90-

α

ure 5.2 represents the alignment of the pore at α degree Sin 90- α = L / L’ Therefore L’ = L / Cos α M = ╥ r2. (L / Cos α). ρ

10

L = M Cos α / (╥ r2. ρ)

11

12 72

L2 = M2 Cos2 α / (╥2 r4. ρ2) Substituting equation12 in 8 t = (M2 Cos2 α. 2 η) / (╥2 r5 .ρ2. γlv cos θ )

13

M2= t (╥2 r5. ρ2.γlv cos θ)/ Cos2 α. 2 η)

14

Cosidering the pore is passing through the orgin(See fig 2), and follows straight line equation,

15

Y=kX

∴Y = M2,

X=t

16 17

and k = (╥2 r5. ρ2. γlv cos θ) / Cos2 α. 2 η) k = r5 C / Cos2 α.

18

If orientation angle of capillary is known, pore radius can determined from this equation Where C = (╥2 ρ2. γlv cos θ ) / 2 η , so C is the known value, (M2 / t), increases with the low viscosity liquid. E Effect of wetting force When nonwoven material encounters the known density and surface tension liquid, it experiences the initial force known as Force of Wetting (Fw). Force of wetting is minimal amount at the initial stage and this has to be subtracted from the equation 8. Wetting force is illustrated below.

73

Nonwoven

Liquid θ

γlv The sensitive balance in the Kruss Tensiometry can accurately weigh this force. In addition, it can measure by weighing the solid before and after immersion.

Usually done by

suspending it from a hang down weighting device. The source of this attractive force is the surface tension of the liquid, and wilhelmy derived the relationship as, Fw = γlv Cos θ. P Where Fw = measured wetting force in mN. P = perimeter of the solid in meter.

5.7. Development Status of Modified In- plane wicking tester Modification Required

Detail of completion 1. Modifying the Sample Mounting Unit Completed inorder to facilitate easy mounting of sample without Wrinkles 2. Development of New type of Sample Completed mounting Ring and its components 3. Modification of Lifting Cabinet by Completed

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Remarks

Aluminum to reduce weight 4. Water Leakage seal to be placed over Pending the sample mounting unit. 5. Provision for installing Halogen Lamp. Pending 6. Provision for Mounting Digital / video Pending inspection Camera

Will be completed before 10 January. Searching of the suitable camera for capturing images of 15cms diameter fabric

7. Replacing existing lead screw by non Completed corrosive stainless steel / fine pitch (1mm) 8. Replacing existing supporting rod by Completed stainless steel with proper placement in the traversing unit. 9. Introducing Needle Bearings (4 Nos.) Completed for corresponding supporting rod. 10. Introducing the Fine and Narrow Completed leveling screw for sample mounting unit. 11. Introduction of typical Suction device Pending to remove air bubbles inside the liquid transport tube.

Will be carried after the mounting of Sensors in the appropriate position in the sample mounting unit. Process is Will be completed 12. Rectification / Replacement of existing before 10 January sensors, since they are not sensing going on. properly when exp. is conducted. 13. Working and activating the time delay Completed. circuit, which is inoperative now.

6. Work Progress

work Literature Survey Sample purchase Modification of the instrument(mechanical) Modification of the instrument(Electronic)

Remarks Completed Completed 60 % completed Pending and will completed

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before Jan 10th January. Experimentation on Pore volume analysis of Completed for PP and to work Nonwoven

for other sample

7. Work Schedule  Modification Inplane wicking tester is to be completed which is in progress at present  Pore volume analysis Study of existing Needle punched P/V, PET, and Viscose is to be carried out and results should be compared to correlate.  All sample available now and further receiving samples are to be studied the wettability and wicking study like rate of absorption, maximum absorption, liquid spread analysis, and the results are compared mutually.  SEM Analysis of all sample available to be done in future.  Study of selection of Camera part is to be done.  Deriving Mathematical equation for evaluating the Orientation of the fibres and pores and to correlate wetting parameters.

8.

Reference

1. www.inda.org 2. B. S. Gupta, Study of Absorbency in Nonwovens: The Role of Structural Factors and Fluid characteristics in International Conference on Nonwovens, NISTI, New Delhi, India, 1992, December 5, p. 166. 3. Hearle, J.W.S and Stevenson, P.J., “Nonwoven Fabric Studies Part III: The Anisotropy of Nonwoven Fabrics”, Textile Research Journal, 11, 877-888, 1963.

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4.

Pourdeyhimi, B. and Kim, H, “Angular Nonwoven Properties”, Textile Asia, 3, 3336, 2000.

5. Wetting and Wicking in Fibrous Materials, Textile Progress,

A.Patnaik,

R.S.Rengasamy, V.K.Kothari, A.Ghosh, 2006 Vol. 38, No1, P 1- 3 6. www.ksvinc.com 7. E. Kissa, Wetting and Wicking, Text. Res. J., 1996, 66, No. 10, 660-668. 8. Pourdeyhimi, B. and Kim, H, “Angular Nonwoven Properties”, Textile Asia, 3, 3336, 2000. 9.

Hearle, J.W.S and Stevenson, P.J., “Nonwoven Fabric Studies Part III: The Anisotropy of Nonwoven Fabrics”, Textile Research Journal, 11, 877-888, 1963.

10. Pourdeyhimi, B. and Kim, H, “Angular Nonwoven Properties”, Textile Asia, 3, 3336, 2000. 11. Rebenfeld, L. and miller, B., “Using Liquid Flow to Quantify the Pore Structure of Fibrous Materials”, J.Text.Inst., 2, 241-251, 1995 12. Nield, D.A, Bejan, A, Convection in a Porous Media second edition, Springer-Verlag, New York, 1-7, 1999 13. Chatterjee, P.K and Nguyen, H.V., “Mechanism of Liquid Flow and Structure property Relationships”, Absorbency, Elsevier Science Publishers, New York, 42-46, 1985 14. Ariadurai, S.A. and Potluri, P., “Modeling the In-Plane Permeability of Woven Geotextiles”, Textile 15. Adams, K.L., Miller, B., and Rebenfeld, L., “Forced In-Plane Flow of an Epoxy Resin in Fibrous, Networks”, Polymer Engineering and Science, 32, 1434-1441, 1986 16. Montgomery, S.M., Adams, K.L., and Rebenfeld, L., “Directional In-Plane Permeabilities ofGeotextiles”, Geotextiles and Geomembranes, 7,275-292, 1988 17. Adams, K.L, Russel, W.B., and Rebenfeld, L., “Radial Penetration of a Viscous Liquid into a Planar Anisotropic Porous Medium” 2, 203-215, 1988. 18. Adams, K.L, and Rebenfeld, L., “In-Plane Flow of Fluids in Fabrics: Structure/Flow Characterization”,Textile Research Journal, 11, 647-653, 1987. 19. Adams, K.L., Miller, B., and Rebenfeld, L., “Forced In-Plane Flow of an Epoxy Resin in Fibrous Networks”, Polymer Engineering and Science, 32, 1434-1441, 1986

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20. Montgomery, S.M., Miller, B., and Rebenfeld, L., “Spatial Distributions of Local Permeabilities in Fibrous Networks”, Textile Research Journal, 3, 151-161, 1992 21. Nederveen, C.J, “Absorption of Liquid in Highly Porous Nonwovens”, TAPPI Journal, 12, 174-180, 22. Development of a modified Inplane wicking Tester and To study the inplane wicking in Nonwovens, Project Report, B.Muthuram,IIT, NewDelhi, May 2006 23. Confederation of Indian Industry (CII) – Web News Report 24. Absorbency, Edited By Pronoy.K.Chatterjee New jersy, USA P-41

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