Pilling Textile Testing By Abubakkar Marwat

Abu Bakkar Marwat (05-NTU-05)

By:

Abu Bakkar Marwat 05-NTU-05 Section A Semester VIII NTU Faisalabad 0313-6660505 [email protected]

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1-Introduction: Ever since the invention of the loom, fabric producers have observed the phenomenon known as fabric “pilling,” a process that results in the formation of small fuzzy balls or “pills” on the fabric surface. In the short term, pilling may lead to unattractive “fuzzy” fabric; over time, especially with natural fabrics, it can lead to a complete wear-through of the fabric. A pill’s evolution involves three major steps: first, abrasion on the fabric—the fibers rubbing against themselves or another surface— causes a “fuzz.” Further agitation then causes a collection of fiber to appear as clinging balls, anchored to the fabric much like a burr’s tiny hooks (see Figure 1). Finally, as mechanical and physical action weakens the pill’s ability to cling over time, it falls off the fabric in its last stage known as depletion or removal. Figure 1: Fiber Ends Entangle to Create “Pill” on Fabric (50x magnification). Although pilling has been with us for some time, it wasn’t a significant problem with wool and cotton fibers. With the invention of synthetic fibers, however, consumers and manufacturers began to take note of the undesirable pilling syndrome. The rest of this paper explains why pilling has been such a challenge to the synthetic fiber and fabric industry and what DuPont has done to meet that challenge. 2-Causes: Pills are formed by a rubbing action on loose fibres which are present on the fabric surface. Pilling was originally a fault found mainly in knitted woolen goods made from soft twisted yarns. The introduction of man-made fibres into clothing has aggravated its seriousness. The explanation for this is that these fibres are stronger than wool so that the pills remain attached to the fabric surface rather than breaking away as would be the case with wool. The initial effect of abrasion on the surface of a fabric is the formation of fuzz as the result of two processes, the brushing up of free fibre ends not enclosed within the yarn structure and the conversion of fibre loops into free fibre ends by the pulling out of one of the two ends of the loop. Gintis and Mead consider that the fuzz

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formation must reach a critical height, which is dependent on fibre characteristics, before pill formation can occur. The greater the breaking strength and the lower the bending stiffness of the fibres, the more likely they are to be pulled out of the fabric structure producing long protruding fibres. Fibre with low breaking strength and high bending stiffness will tend to break before being pulled fully out of the structure leading to shorter protruding fibres. The next stage is the entanglement of the loose fibres and the formation of them into a roughly spherical mass of fibres which is held to the surface by anchor fibres. As the pill undergoes further rubbing, the anchor fibres can be pulled further out of the structure or fatigued and eventually fractured depending on the fibre properties and how tightly they are held by the structure. In the case of low-strength fibres the pills will easily be detached from the fabric but with fabrics made from high-strength fibres the pills will tend to remain in place. This factor is responsible for the increase in the propensity for fabrics to pill with the introduction of synthetic fibres. Low twist factors and loose fabric structures such as knitwear have a rapid fibre pull-out rate and long staple length resulting in the development of numerous large pills. The life of these pills depends on the balance between the rate of fibre fatigue and the rate of roll-up. Pill density can increase steadily, reach a plateau or pass through a maximum and decrease with time depending on the relative rates of pill formation and pill detachment. The pill density is also governed by the number of loose fibre ends on the surface and this may set an upper limit to the number of pills that will potentially develop. This has important implications for the length of a pilling test because if the test is carried on too long the pill density may have passed its maximum. Fibres with reduced flex life will increase the rate of pill wear-off. Because the fibres that make up the pills come from the yarns in the fabric any changes which hold the fibres more firmly in the yarns will reduce the amount of pilling. The use of higher twist in the yarn, reduced yarn hairiness, longer fibres, increased inter-fibre friction, increased linear density of the fibre, brushing and cropping of the fabric surface to remove loose fibre ends, a high number of threads per unit length and special chemical treatments to reduce fibre migration will reduce the tendency to pill. The presence of softeners or fibre lubricants on a fabric will increase pilling. Fabrics made from blended fibres often have a greater tendency to pill as it has been found [3] that the finer fibres in a blend preferentially migrate towards the yarn exterior due to the difference in properties. 3-Adverse effects: Pilling is an important problem not only for textile and clothes manufacturers but also for users. The effect of the pilling process

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results in a significant decrease in fabric quality and a negative influence on the user’s comfort. It also affects the fabric appearance very badly. 4-Determination: After rubbing of a fabric it is possible to assess the amount of pilling quantitatively either by counting the number of pills or by removing and weighing them. However, pills observed in worn garments vary in size and appearance as well as in number. The appearance depends on the presence of lint in the pills or the degree of colour contrast with the ground fabric. These factors are not evaluated if the pilling is rated solely on the number or size of pills. Furthermore the development of pills is often accompanied by other surface changes such as the development of fuzz which affect the overall acceptability of a fabric. It is therefore desirable that fabrics tested in the laboratory are assessed subjectively with regard to their acceptability and not rated solely on the number of pills developed. Counting the pills and/or weighing them as a measure of pilling is very time consuming and there is also the difficulty of deciding which surface disturbances constitute pills. The more usual way of evaluation is to assess the pilling subjectively by comparing it with either standard samples or with photographs of them or by the use of a written scale of severity. Most scales are divided into five grades and run from grade 5-no pilling, to grade 1-very severe pilling. 4.1-Random D3512):

tumble

pilling

test

(ASTM

• What This Test is Used For: This test is used to cover the resistance to the formation of pills and other related surface changes on the textile fabrics using the random tumble pilling tester. The procedure is generally applicable to all types of woven and knitted fabrics. • How This Test Works: Textile samples are placed into the random tumble pill tester for a specified amount of time and tumbled. The samples are then evaluated for the degree of pilling. • Scientific Testing Requirements: Bring specimens to moisture equilibrium for testing in standard atmosphere for testing textiles according to ASTM D-1776, conditioning Textiles for Testing.

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4.1.1-Equipment Needed: • Random Tumble Pilling Tester • Cork Cylinder Liners: about 5 3/4” wide by 17.81” long cut from 0.063” thick flat sheets of Type P2117A material conforming to Classification System F104, Appendix X2. • Air Injection Device to give 14-21 kPa (2-3 psi) air pressure in each test chamber • Adhesive: white all-purpose, for sealing the edges of the specimen • Twelve 4.13” squares cut on the bias approximately at a 45° angle to the warp and filling 4.1.2-Sampling: A lot sample is selected at random from the consignment. From this sample after removing first 2 meter fabric, 2 meter laboratory sample is cut. Preparing test specimen: • Cut a 4.13” square on the bias at approximately a 45° angle to the warp and filling directions. One sample needed per person. (Avoid cutting samples in areas with wrinkles & other distortions. • Avoid getting oil, water, grease, etc. on the sample while handling.) 4.1.3-Conditioning: Condition sample and cork liners by bone drying and then bring them to moisture equilibrium in the controlled chamber 4.1.4-Test Procedure: • Place Specimen and a 25 mg of a 5 mm (0.2”) gray colored cotton fiber into the test chamber. • Place the cover on the chamber and set the timer for a running time of 30 minutes. (10 minute intervals for up to 30 minutes may be more indicative for certain knits or soft-woven fabrics.) • Turn the motor switch to “on,” and push the “start” button, and start the airflow. • During the run check each chamber at frequent intervals. (If the specimen becomes wedged around the impeller without tumbling or lies on the bottom or side of the chamber, shut off the air, stop the machine, remove the face plate, and free the specimen. • Record on a data sheet any abnormal behavior or hang ups of the specimen. • After each run, rake out each specimen and clean off excess cotton fiber using the vacuum cleaner.

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4.1.5-Preparation for Evaluation • Place each specimen on the double faced tape in the viewing cabinet. 4.1.5.1-Evaluation • Using suitable rating standards, and the apparatus for fabric evaluation, subjectively rate the face of each specimen, looking down on the specimen at a 45° angle and using the rating standard and the following scale. When the appearance of a test specimen falls between that of 2 rating standards, assign the half value (i.e. 3.5). 5 - no pilling 4 - slight pilling 3 - moderate pilling 2 - severe pilling 1 - very severe pilling • Average the ratings for the 3 specimens from each laboratory sampling unit and the average for the lot. • Take note if one strip in either fabric direction, or in any one portion of a specimen, report this condition. This indicates that different yarns may have been used in the construction of the fabric being tested. • Check the pilled specimens for evidence of irregular tumbling. If specimens show a high concentration of pills in a general line not parallel to either fabric direction, assume a specimen is wedged around the impeller for one or more periods during the test. Discard these and repeat test with new specimens. • Evaluate the fabric for other surface effects such as fuzzing. It is advisable to have a separate set of in-house fabric rating standards for each surface effect to be rated. 4.2- ICI Pill box: Specimens are mounted on polyurethane tubes and tumbled randomly in a cork-linked box at a constant rotational speed. Fuzzing and pilling is assessed visually after a defined period of tumbling. Any special treatment of the laboratory sample, i.e. washing, cleaning, has to be agreed upon and shall be stated in the test report. 4.2.1-Equipment and material: • Pill testing box • Polyurethane specimen tubes

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• Mounting jig, used to mount specimens on the tubes • Self-adhesive polyvinyl chloride tape, 19 mm wide • Sewing machine • Viewing cabinet 4.2.2-Sampling and test specimen: A lot sample is selected at random from the consignment. From this sample after removing first 2 meter fabric, 2 meter laboratory sample is cut. From this sample, cut four test specimens, each 125 mm x 125 mm. on each test specimen mark the back of the fabric and the length direction. A seam allowance of 12mm is marked on the back of each square. In two of the samples the seam is marked parallel to the warp direction and in the other two parallel to the weft direction. The samples are then folded face to face and a seam is sewn on the marked line. 4.2.3-Conditioning: The specimens are then conditioned in standard temperate atmosphere conditions at 20±2oC and relative humidity of 65±4%. 4.2.4-Test procedure: • Each specimen is turned inside out and 6mm cut off each end of it thus removing any sewing distortion. • The fabric tubes made are then mounted on rubber tubes so that the length of tube showing at each end is the same. • Each of the loose ends is taped with poly (vinyl chloride) (PVC) tape so that 6mm of the rubber tube is left exposed as shown in Fig. • All four specimens are then placed in one pilling box. • The samples are then tumbled together in a cork-lined box as shown in Fig. 7.5. The usual number of revolutions used in the test is 18,000 which take 5 h. • Some specifications require the test to be run for a different number of revolutions.

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4.2.5-Assessment: The specimens are removed from the tubes and viewed using oblique lighting in order to throw the pills into relief. The samples are then given a rating of between 1 and 5 with the help of the descriptions in Table.

5-Conclusive remarks: • A pilling problem is related to fiber type, strength, and extensibility. • Natural fibers like cotton exhibit some pilling, but it goes unnoticed because of its inherent weakness:  the pills are tiny and fall off quickly • The balance between pill formation and depletion was changed with the introduction of stronger, man-made fibers. Synthetics like polyester and acrylics contain strong “anchor” fibers for the pills to cling to—so strong that fewer pills fall away. The formation rate is also higher, making the problem even more pronounced. • Synthetic knits exhibit pilling problems because of their loose construction, and knits of synthetic staple fibers contain numerous eligible free fiber ends that begin the pilling process. • Filament fabrics have no free ends to migrate, so no pills can form. • Some believe that reducing the denier (yarn thickness) in blends of polyester and natural fibers affects pilling rates, or that less polyester content will decrease pilling. In fact, denier has little to do with pilling and the presence of any polyester staple will contribute to pilling.