Reactive Extrusion

Reactive Extrusion

1. INTRODUCTION

As we are aware of the material called polymer and also knows that these are macromolecules which are form by linking together a much smaller molecules i.e. monomer and product called as polymer. The polymers/plastics are widely used in different fields as diverse as defense, radars and communications. These has been increasing acceptance of plastic for housing, electrical and electronics equipments leading to increased use of more general purpose plastics. Plastic has been widely accepted as packaging materials. The use of plastic films for wrapping bags and sacks is well known. The automobile industry is the major user of plastic and which is increasing year by year. In general area of medicine user range from spare parts of surgery such as hip-joints, syringe etc. We use this material in various forms in our daily life. Sheets, tubes, pipes, households, foams and many more. The different conventional processes are required for converting these polymeric materials into finished and shaped product. Major techniques are injection molding, compression molding, transfer molding, extrusion and so on. This seminar covers a special processing technique called as Reactive Extrusion.

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Reactive Extrusion

2. STATISTICAL DATA The consumption of plastic worldwide data is given as follows: WORLDWIDE PLASTIC CONSUMPTION Year 1995-96 1997-98 1999-2000 2001-2002

Quantity (million tons ) 112 130 146 160

Following table represents the data regarding plastic consumption in India year wise. PLASTIC CONSUMPTION IN INDIA Year 1995-96 1997-98 1999-2000 2001-2002 2006-2007

Quantity(million tones) 1.88 2.3 3.1 4.3 8

Following table represent the individual consumption of plastic in the country (India). INDIVIDUAL PLASTIC CONSUMPTION IN INDIA (In Metric tons) C.O.E. and T;Akola

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Reactive Extrusion Material

Year 1999-2000 515,496 649,000 789,480 175,382 723,860

HDPE PVC PP PS LDPE/LLDPE

2000-2001 540,000 700,000 905,000 193,300 820,000

The table below will gives percentage/data of processing techniques which has been used for converting the plastic into desired shape.

GLOBAL SCENARIO PLASTIC PROCESSING INDUSTRY. PROCESS Extrusion Injection molding Blow molding Calendaring Coating Compression molding Powder form Other process Total

PERCENTAGE 36% 32% 10% 6% 5% 3% 2% 6% 100

3. GENERAL EXTRUSION This is the oldest techniques developed from aluminium extrusion, which

is a continuous process in which the plastic or polymer material is fed from a hopper into heated cylinder. The screw inside the cylinder forces the molten material through a dia-orifice by means of pressure and gives required shape to molten material.

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Reactive Extrusion

Extrusion is one of the method available which comprises the forcing of plastic or molten material through a shape die by using pressure. The range of products produced by extrusion process includes pipes, films, sheets, filaments, wire coating, profiles and blow molded products. In the extrusion process the compounded plastic material is fed through the hopper of the extrusion machine as either powder or granules into a cylinder having provisions for electrical heating for softening of material. The hot plastic charge is further worked through the cylinder by a helically flighted revolving screw.

The temperature of the plastic material rises owing to the

frictional heat produced by the compression of charge between the rotating screw and the cylinder surface.

During its journey from hopper to die the plastic

material passes through distinct zone named feed zone, compression zone and metering zone. The final action of screw is to force the melted polymer through a die which determines its final size. The general extruder design consist of hopper, screw, nozzle, barrel and heating arrangements. There are three zones named as feed zone, compression zone, metering zone. Feed zone: This is the first zone where the raw material is fed to the extruder from hopper, from figure it is clear that maximum clearance is provided by screw

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Reactive Extrusion

to accept the raw material or granules. In this zone, preheating is done and with the help of screw movement the feed is conveyed to the compression zone.

Barrel Barrel

Heater

Screw

Die Metering zone

Compression zone

Compression zone:

Feed zone

At this zone material is heated and melt stream is formed by means of electrical heating on the surface of barrel, and by shearing heat which is provided by keeping minimum clearance between screw flight and internal surface of barrel. The material is melted by compression in this zone.

Metering zone: Another zone is metering zone. In this zone molten material from compression zone conveyed to the nozzle and die. The molten material is plasticized for final product of die. Different types of extruder designs are available namely single screw extrusion, twin screw extrusion, co-extrusion and vented extrusion. C.O.E. and T;Akola

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Reactive Extrusion

CO-EXTRUSION : In this technique two or more polymers are extruded simultaneously to form a single layer which makes a combination of properties with economics of that product.

VENTED EXTRUSION : This is equipped with vent port to remove moisture and other volatile harmful materials. Since some of the plastic materials are hygroscopic in nature and this tendency is removed by vented extrusion.

4. REACTIVE EXTRUSION This is a recent development of extrusion technique in which the extruder is used as mini reactor. “ Reactive extrusion is the name given to the process where by the plastic is manufactured in the extruder from base chemicals and once produced it passes through a die of the desire shape, which gives shape to the material.” C.O.E. and T;Akola

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Reactive Extrusion

Reactive processing Technology has now been established as an effective method for producing new polymer and polymer alloys. This system enable us to give various kinds of products from thermoplastic polymers alloys; as well as highly reactive material which are generally difficult to handle with conventional processing method such as injecting molding. This system is well suitable for many kinds of thermoplastic alloys, particularly for small lot production. The main reason lays that the continuous and low volume production and chemical composition control of polymers, their micro structure, physical properties are readily possible with this method. On the other hand, there are many plastic, currently being developed possessing excellent qualities in terms of functionality and reactivity, but having the difficulty to extrude/process them or else showing the poor fluidity necessary for processing due to the highly cross linking characteristics at molding temperature, Some kinds of polymeric material with significant thermo degradability requires to be quickly shaped after extrusion. These disadvantages leads the difficulties in commercial production using the conventional methods. Under these circumstances newly developed reactive extrusion and molding system can efficiently handle such materials as well as the conventional materials.

PROCESS: C.O.E. and T;Akola

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Reactive Extrusion

In a typical reactive extrusion process the reactants are fed into the extruder feed throat were the material is usually heated to initiate reaction or increase the reaction rate. The reactant mixer is conveyed through sequential barrel segments. Where degree of mixing and specific energy input bring the reaction to the desired degree of completion within the limit of residence time in the extruder. At this stage the reaction may be quenched or addition of catalyst quencher may be done where applicable. Volatile by- products or excess reactants may be removed. Feed

Polymerisation

Vent

Devolatization

Processing

Fig. REACTIVE EXTRUDER

Then molten polymer is extruded through the die and rapidly cooled by contact with a fluid medium such as water. After cooling and solidification quencher has been added to restrict further reaction. The mixing devices recently employed for both single and twin screw extruders are adequate for most reactive extrusion processes but some reaction for e.g. the co-polymerisation of two monomer of unequal reactivity, it is

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Reactive Extrusion

beneficial for a high degree of back mixing of the sort typically found in a well stirred batch reactor. Such mixing can be provided in reactive extrusion by employing a tangential counter-rotating twin screw extruder.

Mixing enhances desired

reactions and minimized side reactions.

MATERIALS 1. POLYETHEREMIDES : These materials can be manufactured in an extruder reactor by the condensation of Bis-phenol A dianhydride with different aromatic amines.

Chemistry : The condensation reaction of bisphenol-A dianhydride with a diamine such as phenylenediamine. The reaction can be shown as follows: Chemical Reaction: O ||

O

O O || O

CH3 | C | CH3

O + O NH2 O

O ||

O

N O C.O.E. and T;Akola

NH2 |

CH3 | C

N O 9

Reactive Extrusion || O

| CH3

O

+ 2 H2O Processing :

The reactor design consists of a twin-screw extruder with intermeshing screws and barrel length, Such that the average material. Residence time is 4.5 minute. A solid mixture of bisphenol-A-dianhydride, a diamine such as m-phenylenediamine, and a pthalicanhydride chain stopper is fed to the extruder throat, where the material melt in zone 2 and begins polymerisation. Zone 2 is only partially filled so that surface renewal allows removal of some of the water of reaction through the first vent maintained at atmospheric pressure. A vacuum vent at zone 4 removes the rest of the water. Fig. 2 shows the screw geometry in zone 3, which promotes melt sealing to prevent Back mixing of material between zone 2 and 4. Here a right handed (forward-conveying) screw element is followed by left handed (backward-conveying) screw element to retard the flow of material between zones.

Fig.1 Twin-screw extruder reactor for polyetherimide synthesis

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Fig. 2 Diagram of screw elements in zone 3 to promote melt sealing.

In procedure with better stoichiometry control the dianhydride and diamine are fed to extruder as separate melt streams via a concentric tube feed inlet fig. 3.

Diamine melt

Dianhydride melt

Fig.3 Concentric feed pipe for feeding molten reactants to extruder

Keeping the two molten reactants separate untill they can be mixed properly in the extruder promotes product homogeneity.

2. POLYURETHANE :Both polyurethane and polyurethaneureas have been prepared in extruder reactors. The chemical required as 9 parts butane 1,4 diol chain extender and 91 parts low molecular weight polyesters.

Chemistry : C.O.E. and T;Akola

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Reactive Extrusion

As these reactions proceed by step growth polymerisation. The stoichiometry control of the reactants is important for high molecular wt. polymers. The reaction is as follows Chemical Reaction: O O || || H – { O – C – (CH2)4 – C – O –(CH2)4 } OH + HO – (CH2)4 – OH + OCN – O H || | {O–C–N–

– CH2 –

– CH2 –

– NCO

H O | || – N – C – O – (CH2)4

etc.

Polyurethane

The reactants are often fed to extruder as melts or liquids. The functional groups – CN – and – OH – combines with each other through steps and tends to consume all the groups present in that molecule or reaction mixture. Processing : In this process 53mm twin screw extruder with co-rotating, selfwiping screws and 1855 mm in length is used as a reactor. A mixture of 9 parts Butane – 1, 4 diol chain extender and 91 parts low mol. wt. Polyester (OH number = 51.9) prepared from Adipic acid and butane – 1, 4 – diol and 35 parts 4, 4’- diisocynatodiphenylmethane are pumped separately as melts into the extruder entry Zone at 90-1200C.

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Reactive Extrusion

The middle section of extruder is held at 180-2600C and the last section of the extruder it 100-1800C. Operating at 70-300 rpm, the extruder produces polyurethane sheet through a sheet die at 30-100 kg/h throughput and 2.5 – 0.8 min residence time. The specific net energy requirement is 180-540 KJ/Kg of material. The key to the success of this process is the presence of at-least two or at-most three kneading zones each 240 mm long preceded by short metering segment. As shown in fig.4

Fig. 4 Extruder reactor design for polyurethane synthesis

5. COMPARISON GENERAL EXTRUSION REACTIVE EXTRUSION It requires granules or pellets as raw No granules or pellets are required as raw material

or

feed

i.e.

polymeric material i.e. monomer is fed to the

material in the granules form. extruder It leads to high heating history in a It leads to less heating history as there is polymer-polymer alloy as compare to no remelting

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Reactive Extrusion

Reactive. Processing for a heat sensitive or Processing of a heat sensitive/highly highly reactive material is quite reactive raw material can be done difficult. efficiently and smoothly. These type of technique is used It’s not in global use for manufacturing universally. process. Morphology control is difficult or it No morphology changes.

Obtained by

may change during the process. this to the min level. Manufacturing process are more Manufacturing process are simplified and costly comparatively cost reduction can be realized. It can be used for large production of It posses many advantage is research and thermo plastic product.

development activities on new plastic material.

6. ADVANTAGES The main advantages of the Reactive extrusion techniques are as follows. 1) Enclosed Tubular Reactor :An extruder may be considered to be horizontal reactor with one or two internal screws conveying reactant polymer/monomer in the form of solid or slurry, melt or liquid. 2) Product Purity :The most common reactant are polymers or polymers melts and gaseous liquid or molten low mol. Wt. compound. A particular advantages of the

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Reactive Extrusion

extruder as a chemical reactor in this context is the absence of solvent as the reaction medium.

No solvent, stripping or recovery process is required and

product contamination by solvent impurities is avoided. 3) Easy Control of Process:Because of their versatility, most extruder reactors are twin screw extruders, which posses a segmented barrel, each segment can be individually cooled or heated externally. In addition to external heating shear heat is develop by motion of screw.

4) Temperature and Residence time :The entire range of temperature may extend over the length of an extruder, the temperature differential between adjacent barrels segment is often < 1000C because of slow heat transfer to and from reactant material.

Typical

extruder residence time 10-600 sec. These values will vary for different reactions and reactants as well.

5) Flexible Design of Reactor or Extruder :By providing individual barrel segment with external opening its possible to introduce solid, liquid or gaseous reactants at specific point in the chemical process. Volatile bi-products from chemical reactions or excess reactant C.O.E. and T;Akola

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Reactive Extrusion

may be removed easily by applying a vacuum to the appropriate barrel segment and providing the appropriate screw segment with proper flight depth and geometry to ensure efficient surface renewal and exposure of the reaction mixture to low pressure.

The individual reaction zones at different pressure may be

segregated from one another by melt seals formed by restricting the flow of material both before and after the zone. Melt seals are commonly formed by using reverse flight and/or shallow screw flight segment that prevent back mixing of materials in adjacent zone, such technique used for high pressure differential between adjacent zones. Typical pressure encountered in reactive extrusion process are 50 mpa (500 atmp, i.e. 7250 psi ). 6) Efficient mixing: As it is possible to arrange the kneaders in reactive extruder for better mixing and high heat transfer for viscous material. Running of two or more extruder is possible in this technique , which increases the rate of reaction and process.

7) Continuous/ one line process: As we know without remelting/ palletizing one pass molding is done. So it reduces the time, heat losses requirement and leads to the economy. This Process/ technique increases product quality respectively.

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Reactive Extrusion

7. DISADVANTAGES Some of the disadvantages of this process are as follows: 1) Limited residence time: The limited residence time available in an extruder is often a disadvantage, although when applicable, catalysis frequently shortens the time required for reaction, but a large number of reactions are not rapid enough to be performed in extruders on commercial scale. 2) Parameter stability: The beneficial effect on rate and outcome of reaction often observed in organics and polymers reactions by changing solvent polarity, hydrogen

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Reactive Extrusion

bonding stability, boiling point and other parameter are not duplicated in a melt process. 3) Inefficient heat transfer: Most reactive extrusion processes may make heat transfer inefficient and difficult to control in exothermic chemical reactions, because most polymer melts have low thermal conductivity especially when limited amounts of valuable starting materials are involved most commercial reactive extruder involve simple one step chemical reaction between inexpensive and Readily available starting material.

4)Process limitation: Small commercial continuous extruder requires a minimum of 1001000gm of material for a typical experiment, such extruder reactions may not be convenient for running a large matrix of screening experiment. to optimize processing conditions especially when limited amounts

of valuable starting

materials are involved. Most commercial reactive extruder involve simple one step chemical reaction between inexpensive and readily available starting material.

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Reactive Extrusion

8. APPLICATIONS The important applications where the reactive extrusion technique can be used are as follows. Stampable sheet fabrication: If inorganic fillers or glass fibre are fed into a twin screw extruder or a fabricated fibre material is inserted into the mold, fiber reinforced composites can be obtained from this result this system can be applicable to more complicated polymer alloy composite.

Online monitoring device:

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Reactive Extrusion

This system is not only suitable for research and development but also utilized as a useful in online-monitoring device for quality assurance as well as for evaluation of processability and flow character of a product.

Large size products manufacturing: It can also be applied to special kinds of processing methods such as large size products and hybridized composites. Also to form a polymer alloy of thermoset material like unsaturated polyester by micro dispersion of elastomeric compound to improve its low impact strength can be easily possible by this method. New material for special application: ‘Innovative Polytetraflouroethylene’ polyamide material.

A new

material has been developed by reactive extrusion combining the excellent sliding properties of PTFE with the very good material and processing properties of polyamides.

During the melt modification reaction, the coupling between

polyamide and PTFE was realized by a transmidation reaction as a result polyamide – PTFE block copolymers were founded.

Starch foam products: It is used to develop and manufacture starch foam products having the resilience and compressibility of foam polystyrene, using water as the C.O.E. and T;Akola

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Reactive Extrusion

plasticizer and blowing agent.

Which are commercialized through one of

company, KTM for arts and crafts and for toy application.

9. SCOPE AND CONCLUSION The reactive extrusion processing and manufacturing can be used not only for highly reactive materials but also for thermally unstable materials to the development of new thermoplastic polymers and alloys, and to the recycling of used plastic product. In future it could be the part of commercial and mass, production line. As it is economical as compared to other extrusion techniques. It is also used in research and development areas. So in future the manufacturing of new materials can be possible at comparatively lower cost.

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Reactive Extrusion

BIBLIOGRAPHY 1) Mark,Bikales, Overberger, Menges. “Encyclopedia of Polymer science and Engineering”, Second Edition, Volume 14, Wiley Inter-science Publication,1991, Page no. 169-177. 2) Michael L. Berins, “SPI Plastic Engineering Handbook”, Fifth Edition, Chapman and Hall,Newyork and London,1991, Page no. 79-93. 3) Allan L. Griff, “Extrusion Technology”, Second Edition, Robert E. Krieger Publication Co.,1981, Page no. 1-13. 4) A. S. Athaley , “Handbook of Packaging”, 1995, Page no. 28-35. 5) Dr. J. S. Anand, “International Plastic Engineering and Technology”, Volume 2 No.1, New Age International Limited Publication, Nov.1995, Page no.33-44. 6) Popular plastic and packaging , July 2001. Page no. 51-52.

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Reactive Extrusion 7) www.nap.edu

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