Polyesters

1. Polyesters • Polyesters are among the more versatile synthetic polymers. • The common methods of synthesising simple esters are used to make polyesters. • These include direct esterification (1), transesterification (2) and the reaction of alcohols (3) with acyl chlorides or anhydrides (4). CORPORATE TRAINING AND PLANNING

2. Commercially important Polyesters • Poly(ethylene terephthalate) (PET) Poly(trimethylene terephthalate) Poly (ethylene napthalate-2,6-dicarboxylate) (PEN) CORPORATE TRAINING AND PLANNING

3. Commercially important Polyesters Poly (butylene terephthalate) (PBT) Poly (4-hydroxybenzonate) Polycarbonate CORPORATE TRAINING AND PLANNING

4. Polyethylene Terephthalate (PET) • Linear polyesters were studied by Carothers during his classical researches for development of Polyamides. • But it was Whinfield and Dicson who developed PET at Calico Printers Association, England I 1941 (As Fibres, Terylene and Dacron and as Film, Melinex and My lar, with the expiry of the basic ICI patents on PET there was considerable development in terephthalate polymers in the early 1970’s. • More than a dozen companies introduced PBT as an Engineering Plastics during this time. • The fiber in the name of Kodel and Film in the name of Kodar was developed by Kodak. • . CORPORATE TRAINING AND PLANNING

5. Polyethylene Terephthalate (PET) • PET was also the basis of glass filled engineering polymer (Rynite) introduced by DuPont in 1970’s. Towards the end of 1970’s PET was used for the manufacture of biaxial oriented bottles . CORPORATE TRAINING AND PLANNING

6. Monomer Ingredients for PET • The ingredients which are used for PET are ethylene glycol and dimethyl teraphthalate. HO – CH2 – CH2 – OH Ethylene glycol • Dimetyl terephthalate CORPORATE TRAINING AND PLANNING

7. Chemistry of Preparation of PET • The PET polymers is produced by the reaction of ethylene glycol and Terephthalic acid or Dimethyl terephthalate in the presence of metal acetate catalyst. This process is called ester exchange process. • In this process, a low molecular weight diester, known as the monomer is first produced by reacting 1 mol. or dimethyle terephthalate with about 2.1 – 2.2 mol ethylene glycol at 150°C in the presence of catalysts, such as antimony trioxide and cobaltous acetate. CORPORATE TRAINING AND PLANNING

8. Chemistry of Preparation of PET • In addition to this diester, di-2-hydroxyethyl terephathalte, some oligomers of following general structure, are also produced. • HO-(CH2) 2 -O[O-C- O -COO-(CH2 ) 2 -O] n-H • When n = 1, 2, 3 • Methanol formed during the condensation is removed using a distillation column. The monomer is then heated to 270° - 280°C with removal of volatiles under reduced pressure down to 1 mm Hg. Heat and vacuum are employed to increase the molecular weight with concurrent removal of volatile products such as water /alcohol and glycol. • n CH3OOC - O - COO CH3 + n HO - CH2 - CH2 - OH • O O • - [C - O - C - O -CH2- CH2 - O -] n + 2n CH3 OH CORPORATE TRAINING AND PLANNING

9. Manufacturing of PET • PET Polymers are manufactured by a stage-wise melt polymerization process consists of transesterification, pre-polymerization and finishing polymerization steps. Continuous melt polycondensation process for PET manufacture. CORPORATE TRAINING AND PLANNING

10. Manufacturing of PET • In the transesterification stage dimethyl temphthalate (DMT) or terephthalic acid (TPA) is converted into bishydroxy ethyl terephthalate in the presence of metal acetate catalyst. • Ethylene glycol (EG) DMT, and catalyst are fed at a molar ratio of 1.7 to 2.0:1 (with TPA this ratio is 1-3 to 1.5:1) and a temperature of 100-180°C. This stage takes 3-4 hr. • The reaction byproduct methanol (Water When TPA) is used is separated from EG vapors in a reflux column. CORPORATE TRAINING AND PLANNING

11. Manufacturing of PET • After adding stabilizer and additives, the prepolymer is forced through a superfine fitter to the second (pre-poly condensation) stage. • The poly condensation reaction is performed under vacuum (15-25 torr) and elevated temperature. (280 – 300°C). • The resulting EG is removed by a vacuum pump while the prepolycondensation product – a low molecular weight (DP= 30) relatively non-viscosity material (40 poise) is pumped to the finishing poly condensation stage after a residence time of about 2 hrs. CORPORATE TRAINING AND PLANNING

12. Manufacturing of PET • The finishing polymerization stage, which is operated at 0.5 – 1 torr, requires special wiped film or extruder type reactor in order to handle the high viscosity of the polymer ((DP = 100), few thousand poise). • Many manufacturer have devised their own proprietary agitation systems to minimize the build-up of the solidifying polymer layers. • The EG vapours contaminated with oligomers are drawn off through a special condensing system and sent to a recovery unit • The polymers melt can be sent to a direct spinning plant or transformed into pellets. CORPORATE TRAINING AND PLANNING

13. Relations of Structure and Properties of PET • There are various classes of linear polyesters. • The concentration of ester groups has predominant effect on the properties of linear polyesters. • For the aromatic classes of linear polyester, decreasing the concentration of ester groups apparently leads to a reduction in melting point. • However, in such aromatic linear polyester the decrease in concentration of ester group is accompanied by the p-phenylene group concentration. • It is found from aliphatic polyester that the ester group concentration has little effect on the melting point. • In fact a decrease in ester group concentration leads to a slight increase in the melting point. CORPORATE TRAINING AND PLANNING

14. Relations of Structure and Properties of PET • It is found that in an ester group the in chain ether link –C-O-C- increase the chain flexibility compared with a polyethylene chain to decrease the heat of fusion. • At the same time there will be some increase in inter chain attraction via the carbonyl group which will decrease the entropy of fusion. • Since these two effects almost cancel each other out there is almost no change in ester group concentration. • With all linear series of polyester as the no. of methylene groups in the repeating unit increases so the polymer becomes more like a linear polyethylene (polymethylene). CORPORATE TRAINING AND PLANNING

15. Relations of Structure and Properties of PET • It is also observed that Tm (melting point) of a polymer with an odd no. of methylene groups in the aliphatic portion of the repeat unit is lower than for the polymer with one more but an even no. of methylene groups. • Generally, the highest melting points are obtained where the in-chain aromatic ring is of the p-phenylene type. • The materials have a disadvantage of sensitivity to water and alkaline solution. • These materials are crystalline and only proton donors that are capable of inter action with the ester groups are effective solvents. CORPORATE TRAINING AND PLANNING

16. Characteristics of PET (For Identification) • The PET is a semicrystalline material, normally amorphous with low crystallinity and high transparency. • It is identified by sweet smell, when burns, orange flame, soot forming and melt drips. • It is scratch resistant • Melting point is 220°C • It is having short and long term thermal limit temperature respectively 135°C and 100°C CORPORATE TRAINING AND PLANNING

17. Characteristics of PET • Outstanding chemical resistance to organic and inorganic liquids • Water repellent • Sterilizable by ethylene oxide and X-rays • Inherent good electrical property • Ability to orient • Good tensile strength • Superior strength and stiffness • Excellent dimensional stability • Excellent melt strength with slower crystallization rate • Good impact strength even at low temperature • High tear strength • Heat resistant • Flame retardant • Outstanding clarity • High gloss CORPORATE TRAINING AND PLANNING

18. Properties of PET Properties UnitsValues Specific gravity ---- 1.40 Tensile strength MPa 51 Tensile modulus MPa 175 Flexural modulus Mpa 204 Elongation at break % 7 Impact strength izod, Notched, kg.cm/cm 9.25 Hardness R 105 Deflection temperature under load 0C 205-210 (1.82 Mpa) Vicat softening point °C 75 Coefficient of linear expansion mm/mm/ 0C 6.0 x 10-5 Water absorption, 24hrs % < 0.1 Refractive index 1.62 Dielectric strength KV/mm 26 Dielectric constant 10-6 Hz 3.3 Power factor 0.03 Volume resistivity Ohm.m 1013 Melting point 0C 265 Glass transition temperature °C 67 CORPORATE TRAINING AND PLANNING

19. Properties of PET Mechanical Properties PET exhibits a high modulus up to 75°C, when it is crystalline and 40°C, when it is amorphous even when they are mechanically stressed for a long period. Thermal Properties PET has excellent dimensional stability. Electrical Properties PET has high dielectric strength and high volume resistivity. The dielectric properties are adequate for many electronics applications. CORPORATE TRAINING AND PLANNING

20. Properties of PET • Water Absorption • PET is hygroscopic and in its melt states the resin hydrolyses. • Optical Properties • The light transmission of PET differs greatly according to chemical composition. CORPORATE TRAINING AND PLANNING

21. Properties of PET • Permeability to water vapour and Gases • PET is less permeable than PVC-U. • The permeability of film is 40µm/1.58 mil. • The permeability to water vapour is higher than that of the polyolefins but lower than that of PC, PA, POM. PET films are largely odor-proof which leads to their frequent use in packaging materials in combination with PE films CORPORATE TRAINING AND PLANNING

22. Properties of PET • Chemical Properties • PET is resistant to weak acids and alkaline solutions, oils, fats, aliphatic and aromatic hyrocarbons, carbon tetrachloride. • It is not resistant to strong acids and alkaline solutions, phenol, long exposure to hot water. • The crystalline polyalkyle terephthalates are susceptible to hydrolysis which precludes their use in aqueous solution temperatures above 70°C for in steam. • PET does not show any pronounced tendency to stress cracking. CORPORATE TRAINING AND PLANNING

23. Properties of PET • Weathering Resistance • The relatively high resistance to weathering can be increased by the use of carbon black to protect against UV. • Resistance to High energy Radiation • PET is relatively resistant to high energy radiation. It is degraded more strongly only at absorbed energies of more than 100 KJ/ Kg. After 7 to 8 MJ/Kg it decomposes into powder. CORPORATE TRAINING AND PLANNING

24. Properties of PET • Flammability • PET burns with a sooty orange-yellow flame, it drips and smells sweetly aromatic. Flame retardant grades donot drip and meet the requirements of UL 94 V-0. • Toxicity • PET is suitable for applications involving contact with food stuffs and is physiologically inert. • Sterilization • PET can be sterilized in an ethylene oxide atmosphere or by irradiation. CORPORATE TRAINING AND PLANNING

25. Additives of PET 1. Functional additives 2. Fillers 3. Reinforcements CORPORATE TRAINING AND PLANNING

26. Functional Additives 1. Anti-oxidants 2. UV absorbers 3. Flame retardants CORPORATE TRAINING AND PLANNING

27. Fillers and Reinforcements 1. Mica - Fillers 2. Thermoplastics glass fiber - Reinforcements CORPORATE TRAINING AND PLANNING

28. Grades of PET • The PET is available in the following grades. • Injection moulding grade • Extrusion grade • Stretch blow moulding grade CORPORATE TRAINING AND PLANNING

29. Processing considerations of PET • PET can be processed by the following techniques : • Injection moulding • Stretch blow moulding • Thermoforming • Extrusion CORPORATE TRAINING AND PLANNING

30. Processing considerations of PET • PET resins are primarily for injection moulding. • PET is hygroscopic and in its melt state the resin hydrolyzes. • PET resin supplied in moisture porof containers can have a moisture content upto 0.04%, but hydrolysis can occur at a moisture level above 0.02%. • Therefore, even virgin PET directly from suppliers containers, as well as regrind, should be dried to level of less than 0.02% and maintained at that level. • Dehumidifier hopper is recommended with injection moulded PET. • Drying time values from 4 hrs. for wet resin to 2 hrs. for virgin resin at 135°C. CORPORATE TRAINING AND PLANNING

31. Processing considerations of PET • The moulding must be carried out with dried material and because of the free flowing nature of the melt, restricted nozzles should be used and a back flow valve fitted to screw injection moulding machine. • Cylinder temperature are about 260 – 290°C.and mould temperature as high as 140°C to promote a controlled crystallization. • A significant degree of crystallinity occurs in the mould. Therefore, mould temperature should be selected carefully in order to enhance crystalline formation. • Mould temperature also influence cycle time and products quality, particularly warpage shrinkage, surface gloss depth or colour and chemical resistance. CORPORATE TRAINING AND PLANNING

32. Processing considerations of PET • Although resin grades from the same supplier show the same melt temperature, PET from different suppliers shows different melt temperature ranging from 260 – 290°C .The recommended typical injection moulding cylinder temperature also differ between suppliers. • An interesting feature of PET is that according to the moulding conditions two quite dissimilar products one amorphous, the other transparent, may be obtained, this beings a consequence of having a Tg of about 80°C. • Because of the low melt viscosity injection moulding screw for PET should be fitted with back flow valves and the barrel nozzles should have shut-off-valves. CORPORATE TRAINING AND PLANNING

33. Surface Finishing of PET • The high chemical resistance of the polyalkylene terephthalates necessitates the use of special purpose lacquers to ensure good adhesion. • The same applies to hot embossing (temperature range of the die 140 - 200°C). • PET can be polished easily. Metallization can be only be carried out by high vacuum deposition. • Where high gloss surfaces are required on filled and reinforced product, an intermediate lacquer must be used. CORPORATE TRAINING AND PLANNING

34. Machineability of PET • Cutting • Cutting can be possible in PET with suitable equipments in a specified speed. • Joining • Welding • Moldings and semi-finished products can be welded and bonded. Unreinforced moldings can be joined by hot gas and heated tool welding. With increasing glass fiber and the flame retardant content, the welded joints decrease in strength. Friction and ultrasonic welding are efficient joining methods. • The conditions for heated tool welding are • Heated tool temperature - 260°C • Contact pressure at start of heating - 0.5 bar • Contact pressure at start of welding - 0.5 bar • Heating up time (according to wall thickness) - 10 to 30 s CORPORATE TRAINING AND PLANNING

35. Applications of PET • Appliances • Automotive • Electrical/Electronics • Films • Furniture • Packaging • Miscellaneous CORPORATE TRAINING AND PLANNING

36. Applications of PET Appliances : Oven and appliance handles, coil forms for microwave oven transformers, small appliance structural framers, panels, chassis and housing and instrument covers. CORPORATE TRAINING AND PLANNING

37. Applications of PET Automotive: Structural parts such as luggage racks and grills, fuctional housing such as windshield, wiper motor housing , fuel filters, blade supports and bells, sensor, lamp sockets, relays, switches and solenoids Grill opening retainer Door module CORPORATE TRAINING AND PLANNING

38. Applications of PET Electrical/Electronics: Lamps sockets , coil forms for audio/video transformers, terminal blocks, electrical. Electronic connectors and thrust washers. Electricals Connectors CORPORATE TRAINING AND PLANNING

39. Applications of PET Films: X-ray films, photographic films, magnetic tapes and printing sheets. Food packaging CORPORATE TRAINING AND PLANNING

40. Applications of PET Furniture: Pedestal bases, sent pans, chair arms and castes. CORPORATE TRAINING AND PLANNING

41. Applications of PET Packaging : Carbonated soft drink containers, distilled spirits, toiletries, food products, mustard, pickle foods, peanut butter, spices, edible oil cocktail mixer and syrups. Containers CORPORATE TRAINING AND PLANNING

42. Applications of PET Miscellaneous: General purpose pumps housing , mirror housings three dimensional circuit boards and structural components in office automation equipment, computer housing and structural components, containers, trays, blisters and drinking cups. CORPORATE TRAINING AND PLANNING

43. Applications of PET Automobile engine cover Heat shield Gear box Door washers CORPORATE TRAINING AND PLANNING

44. Blends of PET • PET/PC • Partially miscible blends (miscibility is controlled by the level of transesterification) with co-continuous morphology show improved processability, chemical resistance, crystallinity, elongation, low temperature impact and tensile strength. • Blends also show decreased shrinkage and high heat deflection temperature. • These blends are especially interesting for reinforced products because the warpage is significantly decreased. CORPORATE TRAINING AND PLANNING

45. Blends of PET • PET/Elastomers • These blends are formulated for extrusion, injection, compression, blow and transfer molding. • The blends contain up to 35 wt. of glass fiber. • They show good processability rigidity impact and tensile strength as well as excellent weatherability. CORPORATE TRAINING AND PLANNING

46. List of Manufacturers/Suppliers of PET CORPORATE TRAINING AND PLANNING CORPORATE TRAINING AND PLANNING