Polymer processing

1. POLYMER PROCESSING
The main goal of polymer processing is to produce a usable
object.

2. NECESSARY PARAMETERS FOR PROCESSING.
i. Flow or Deformation (i.e.., rheology).
ii. Transfer of heat and Thermal behavior.
iii. Transfer of mass.
iv. Chemical reaction.

3. EXTRUSION
 Extrusion can be defined as the act of shaping a
material by forcing it through a die.
 Polymer conversion operation.
Principle:
It comprises of forcing of a plastic material through
an orifice(die) by means of pressure.

4. APPLICATION
 For compounding plastics
 Production of tubes ,pipes ,sheets ,film , wire
coating and other continuous profiles.
 It is generally used in case of thermoplastic
polymers and some thermo sets too.
 Commonly used polymers are
PE,PP,PV,PS,PVC,polyamide,polyster

5. EXTRUDER
 Extruders are basically helical screw pumps that
convert solid polymer material into melt , which is
then delivered to the die.
TYPES:
 Single screw extruder
 Twin screw extruder

6. TYPES OF SCREWS

7. SINGLE SCREW EXTRUDER

8. VARIOUS SECTIONS
FIG. SHOWS VARIATION IN CHANNEL DEPTH.

9. ZONES/SECTIONS IN S.S.E
 Feed zone
 Compression/ plasticizing zone
 Melt/Metering zone
 Die zone

10. SCHEMATIC DIAGRAM OF VARIOUS ZONES

11. FEED ZONE
 In this 1st zone, the polymer pellets are conveyed to
the subsequent zone.
 Main function is to preheat the polymer.
 Here the screw depth is constant.

12. COMPRESSION ZONE
 Here the screw depth increases.
 It repels the air gap between the granules.
 Heat transfer from the barrel wall is improved.
 Density change is accommodated.

13. METERING ZONE
 Here screw depth is constant.
 It homogenizes the melt and supply it to the die.

14. DIE ZONE
 The final zone where the screen pack is located.
 It usually comprises of the perforated steel plate called
breaker plate and a sieve pack.
 It sieves out the extraneous materials(foreign particles).
 It removes the turning memory from the polymer melt.
 It allows head pressure to develop by providing a
resistance for pumping action of metering zone.

15. VENTED EXTRUDER
 The polymers being processed should be
devolatilized or degassed . Such an operation can
be carried out by an vented extruder.
 As a result the air bubbles are removed.
 It is nothing but an addition of an decompression
zone to the already existing screw.

17. ADVANTAGES
 Low cost tooling and short lead time.
 Low cost products.
 Reinforcement can be done easily.
 Use of multiple parts in varieties.
 Slow maintaining.
 Also used in co-extrusion , tubular flows, crossway
extruder in similar process.

18. MAJOR PROBLEMS
 Die swelling
 Melt Fracture
 Spiraling
 Bam booing
 Regular ripple
 Random fracture

19. WAYS TO REDUCE DIE SWELLING
 Decrease the extrusion rate
 Increase the length of the die end
 Increase the draw down ratio without affecting the
output
 By improving design factors

20. EXTRUSION BASED PROCESS
 Cross head
 Co-extrusion
 Tubular blown films

21. BLOWN FILM EXTRUSION
 Used for specialized plastic films for packing
industry.
 It consists of a extrusion tube with thermoplastic
material and is inflated to form thin tubular product.
 There is fixed orientation due to inflation and
pulling.
 Commonly used HDPE,LLDPE.,

23. CO-EXTRUSION
 Simultaneous extrusion of two or more polymers
through a single die.
 Allows multiple layers extrusion of
films,sheets,pipes and mostly in packing industry.
ADVANTAGES:
• Reduced material
• Processing cost improved
• Moreuniform distribution temperature.

25. INJECTION MOULDING
 The basic principles is that to inject the molten
polymer into a closed cooled mould where it
solidifies to give the product. The moulding by
opening the mold to release it.
TWO SECTIONS:
I. Injection unit
II. Clamp /Press unit
TWO PHASES:
I. Plasticizing phase
II. Injection phase

26. FEATURES
 The difference here is that the screw does not
rotate but it reciprocates to and fro thereby injecting
the melt into the mold.
 In addition here there is no breaking plate or sieve
plate instead there is chevk valve.
 Gating is important in flow systems as they resist
the flow.(Edge,disk,ring,submarine gates)
Parts:
i. Cavity or impression
ii. Channels
iii. Cooling channels
iv. Ejector pins

27. MOULDING CYCLE
 Mold is closed and a shot of melt is ready in
injection unit.
 Valve opens and screw forces the melt through
nozzle into mold.
 Hold on stage,where pressure is maintained and
released when freezing commences.
 Valve closes and reciprocation starts.Pressure
develops against nozzle and screw accumultes new
slot of melt.
 When mold is cooled,press is opened and moulding
removed.

31. CONTROL PARAMETERS IN IM
 Temperature of melt
 Temperature of mold
 Pressure and speed of injection
 Hold on pressure
 Timings of various parts of process cycle
DEFECTS IN IM:
• Short shots
• Voids and sinks
• Weld lines
• Orientation
• Shrinkage

32. SPECIALIZED IM PROCESS
Spruless moulding:
• Inorder to reduce scrap:
• The nozzle locates directly to mold cavity.
• For complex single impression molding.
Sanwich moulding:
• The technique injects skin and core melt seperately.
• Skin polymer is generally normal one,
• Core polymer is onewhich contains lubricating
agents.

33. STRUCTURAL FOAM MOULDING
 SFM is development of IM where stiffness becomes
prerequistic
 Stiffness ,S=E(t)3
 Suitable for full product
 Here the melt is expandable,contains dissolved gas
which decomposes at melt temperature to give foam.
 A short shot leaves space into which foam expands.The
pressure becomes driving force to fill mold,which is less
than 3Mpa.
Advantages:
 Producing large and flexible products;
 low process energy:

35. REACTION INJECTION MOULDING[RIM]
 The technique combines two metered ,well mixed
reactive sreams.(urethane)
 One stream contains polyether backbone,a catalyst
and a cross linking agent.
 Other stream contains has isocynate,blowing agent
ADVANTAGES:
 Conducted at low temperature(60-90C) for
polyvinyl.
 Processing and preparing takes place
simultaneously.

37. REINFORCED INJECTION MOULDING[RRIM]
 It is an extesion of RIM where there is inclusion of a
reinforced glass fibre.
 Here ,two fast reacting liquid streams are precisely
metered and mixed using high pressure
impingement mixing with polymer blowing agents.
ADVANTAGES:
 Moulding ranges from rubbery flexible to semi
flexible materials to rigid unyielding products by
suitable deformation of reactants.
 Internal mould pressures are low.

39. COMPESSION MOULDING
 The technique consists of forcing a combination of
a resin and a cross linking agent by means of
pressure.
 Pre heating enables the cycle time to be
reduced,which is by convection ,infrared
lamp,dielectric heating.
ADVANTAGE:
 Low waste & finishing cost;
 Useful for bulky products.
DISADVANTAGE:
 Poor tolerance
 Not useful for intricate shapes

41. TRANSFER MOULDING
 Similar ,to compression moulding but differs in a way
that the mix of resin and curing agent is first raised in
both temperature and pressure in a holding
device,plasticizing pot or loading well.
 Outgassing by venting is done by orifices at the parting
line.
 Typical size:0.64cm wide & 0.0025-0.0075cm deep.
ADVANTAGES:
 Rapid production rate and faster;
 Good dimensional accuracy and intricate parts .
DISADVANTAGES:
 Expensive moulds;
 Large material loss and size limitation.

43. BLOW MOULDING
 Polymer processing operation that produces hollow
objects(bottles).
 Used for producing large volume products.
TYPES:
i. Extrusion blow moulding
ii. Injection blow moulding
iii. Stretch blow moulding

44. EXTRUSION BLOW MOULDING
 The semi molten tube called,parison,which is formed
directly from extruder ready hot & soft.
 Parison is allowed to descend into mould cavity.
 Mold is closed, blowing is carried followed by
inflation and cooling .
 The mold opens and hollow product is taken.
 Intermittent blow moulding is faster than continuous
extrusion operation

46. INJECTION BLOW MOULDING
 The technique injects melt into one or more
preheated,preform cavities aroud a given core pin.
 Preform mold is opened and heated polymer is
moved using core pin where it is inflated and
ejected.
 Drying cycle time is 1.5 s,which includes opening of
mold ,movement of mold unit and close time.
 This is followed by exhausting and a blowing during
cycle.

48. STRETCH BLOW MOULDING
 In this method,the molded preform is once
again,molded into a very cooled mold along with
refrigrant coolant.
 This quench the amorphous state,the preform is
reheated above it’s glass transition temperatureand
stretch blown.
 This stretches the preform downwards and
simultaneously blowing in radial direction.
 Ex:Stretch blow molding of PET bottles.

50. THERMOFORMING & VACCUMFORMING
 The preform in form of extruded sheet of polymer is
heated untill soft and deformed by a shaping force
into the mold where it is allowed to cool.
4 main methods in variants of thermoforming
 Matched mold forming
 Slip forming
 Air blowing
 Vaccum forming.

52. 4 main techniques in variants of vaccum forming
 Straight vaccum forming
 Vaccum snap back forming
 Vaccum drape forming
 Plug assists vaccum forming

53. .

54. ROTATIONAL BLOW MOLDING
 The powdred polymer is loaded into a closed
mold,which is heated while rotating biaxially.
 The polymer coats the inner wall of the mold to a
uniform thickness.
 After which it is cooled and removed as finished
product.
 Four stages:loading,molding,cooling,unloading
Unique features:
 Ratio of major & minor axis 1:4
 Heating temperature=>250-350C
 P.E,Polycarbonate,polystyrene,polyurethane.

55. ADVANTAGES
 Producing large hollow products
 Uniform thickness achieved
 No waste scrapes
 Slow heating and melting of the thermoplastic
powder in a biaxially rotating mold to produce
seamless products(without markings)
DISADVANTAGES
• Marix cost high due to fine granules
• Not used wall thickness less than 0.003 inches.
• Not suitable for small products.
• Cycle time longer;no complex shapes can be made.

57. CALEDERING
 It involves laminar flow with heat transfer in a roll
system.
 These are process applied to rubbery polymers;&
production of continuous sheet and film.
SPECICATIONS:
 1.5 meter in length
 1mm thickness
 Diameter 0.5-1m
 Thickness rate of rotation 1m/s

58. STEPS INVOLVED
i. Weighing of polymer,additives and ingredients
ii. Compounding them using bambury mixer
iii. Transferring the melt to calendar rolls
iv. Feeding them in between rolls
v. Enclosing can be done
vi. Cooling and winding up

59. ADVANTAGES:
 Very little thermal degradation
 Open process
 For processing of thermally unstable materials
DISADVANTAGES:
 Long time
 Capital investment is higher
 Economically suitable for larger particles and not
possible for smaller ones.

61. SPINNING PROCESS
 Spinning is that a polymer melt is forced through a
small orifice,called spinner jet which shapes it into a
fibre form.
 After this it undergoes a phase transformation to
solid form after which it is wound up or taken up in
a babbin and processed to spun yarn.
TYPES:
a) Melt spinning
b) Dry spinning
c) Wet spinning