Plastics Materials 7 Episode 13 docx

687 CURING TIME IN min (g) volume resistivity; (h) surface resistivity; (i) power factor; (j) permittivity; (k) mould shrinkage; (1) after-shrinkage. The letters D, A and DA indicate the time of optimum cure indicated by the dye test D (see text by boiling in 10% HZS04 (A) and boiling in a mixture of 0.9% HISO, and 0.025% Kiton Red (DA). (After Morgan and Vale") 688 Aminoplastics In the early 1990s M-F moulding materials were estimated at about 7% of the total thermosetting moulding powder market in Western Europe. Although this percentage has remained virtually constant for many years (indicating a usage of about 11 000 tonnes), it has to be borne in mind that the importance of thermosetting moulding materials relative to thermoplastics has declined substantially over the past 40 years. It is an interesting point that because of its use in tableware, melamine-formaldehyde moulding materials are better known to the general public than any other moulding material of such limited consumption. 24.3.4 Laminates Containing Melamine-Formaldehyde Resin The high hardness, good scratch resistance, freedom from colour and heat resistance of melamine-formaldehyde resins suggest possible use in laminating applications. The use of laminates prepared using only melamine resins as the bonding agent is, however, limited to some electrical applications because of the comparatively high cost of the resin compared with that of P-F resins. On the other hand a very large quantity of decorative laminates are produced in which the surface layers are impregnated with melamine resins and the base layers with phenolic resins. These products are well known under such names as Formica and Warerite. Resins for this purpose generally use melamine-formaldehyde ratios of 1 :2.2 to 1:3. Where electrical grade laminates are required the condensing catalyst employed is triethanolamine instead of sodium carbonate. Decorative laminates have a core or base of Kraft paper impregnated with a phenolic resin. A printed pattern layer impregnated with a melamine- formaldehyde or urea-thiourea-formaldehyde resin is then laid on the core and on top of this a melamine resin-impregnated protective translucent outer sheet. The assembly is then cured at 125-150°C in multi-daylight presses in the usual way. Decorative laminates have achieved remarkable success because of their heat resistance, scratch resistance and solvent resistance. Their availability in a wide range of colours has led to their well-known applications in table tops and as a wall-cladding in public buildings and public transport vehicles. The electrical grade laminates are made by impregnating a desized glass cloth with a triethanolamine-catalysed resin (as mentioned above). The dried cloth is frequently precured for about 1 hour at 100°C before the final pressing operation. A typical cure for 15-ply laminate would be 10-15 minutes at 140°C under a pressure of 250-1000 lbf/in2 (1.7-7 MPa). Cloth based on alkali glass yields laminates with poor electrical insulation properties. Much better results are obtained using electrical grade glass which has been flame-cleaned. The use of certain amino silane treatments is claimed to give even better physical and electrical insulation properties. Glass-reinforced melamine-formaldehyde laminates are valuable because of their good heat resistance (they can be used at temperatures up to 200°C) coupled with good electrical insulation properties; including resistance to tracking. 24.3.5 Miscellaneous Applications In addition to their use in moulding powders and laminates, melamine- formaldehyde resins are widely used in many forms. Melamine-Phenolic Resins 689 Hot setting adhesives, prepared in the same way as laminating resins, give colourless glue lines and are resistant to boiling water. Their use alone has been limited because of high cost but useful products may be made by using them in conjunction with a urea-based resin or with cheapening extenders such as starch or flour. As already mentioned in Section 24.2.4 melamine is now widely used in conjunction with urea (and formaldehyde) to produce adhesives of good strength, reactivity and water resistance but with low ratios of formaldehyde to amine (i.e. urea and melamine). Melamine-formaldehyde condensates are also useful in textile finishing. For example, they are useful agents for permanent glazing, rot proofing, wool shrinkage control and, in conjunction with phosphorus compounds, flame- proofing. Compositions containing water-repellent constituents such as stearamide may also improve water repellency. Modified melamine resins are also employed commercially. Alkylated resins analogous to the alkylated urea-formaldehyde resins provide superior coatings but are more expensive than the urea-based products. Treatment of hexahydroxymethylmelamine with an excess of methanol under acid conditions yields the hexamethyl ether of hexahydroxymethylmelamine (HHMM). Not only will this material condense with itself in the presence of a strong acid catalyst to form thermoset structures but in addition it may be used as a cross-linking agent in many polymer systems. Such polymers require an active hydrogen atom such as in a hydroxyl group and cross-linking occurs by a trans-etherification mechanism. Typical polymers are the acrylics, alkyds and epoxides, HHMM having been particularly recommended in water-based coating resins. Paper with enhanced wet-strength may be obtained by incorporating melamine resin acid colloid into the pulp. Melamine resin acid colloid is obtained by dissolving a lightly condensed melamine resin or trihydroxymethylmelamine, which are both normally basic in nature, in dilute hydrochloric acid. Further condensation occurs in solution and eventually a colloidal solution is formed in which the particles have a positive charge. Careful control over the constitution of the colloidal solution must be exercised in order to obtain products of maximum stability. 24.4 MELAMINE-PHENOLIC RESINS Moulding powders based on melamine-phenol-formaldehyde resins were introduced by Bakelite Ltd, in the early 1960s. Some of the principal physical properties of mouldings from these materials are given in Table 24.1. The principal characteristic of these materials is the wide range of colours possible, including many intense bright colours. The melamine-phenolics may be considered to be intermediate between the phenolic moulding materials and those from melamine-formaldehyde. As a result they have better moulding latitude and mouldings have better dry heat dimensional stability than the melamine-formaldehyde materials. Their tracking resistance is not as good as melamine-formaldehyde materials but often adequate to pass tracking tests. The main applications of these materials are as handles for saucepans, frying pans, steam irons and coffee pots where there is a requirement for a coloured heat- 690 Aminoplastics resistant material. It was never likely that the melamine-phenolics would absorb much of the market held by melamine resins, irrespective of price, since this market is largely dependent on either the non-odorous nature of the good tracking resistance of the material used. Neither of these two requirements were fulfilled by the melamine-phenolics. Future developments thus seem to lie in the creation of new markets for a coloured, heat-resistant material intermediate in price between the phenolic and melamine materials. 24.5 ANILINE-FORMALDEHYDE RESINS22 Although occasionally in demand because of their good electrical insulation properties, aniline-formaldehyde resins are today only rarely encountered. They may be employed in two ways, either as an unfilled moulding material or in the manufacture of laminates. To produce a moulding composition, aniline is first treated with hydrochloric acid to produce water-soluble aniline hydrochloride. The aniline hydrochloride solution is then run into a large wooden vat and formaldehyde solution is run in at a slow but uniform rate, the whole mix being subject to continuous agitation. Reaction occurs immediately to give a deep orange-red product. The resin is still a water-soluble material and so it is fed into a 10% caustic soda solution to react with the hydrochloride, thus releasing the resin as a creamy yellow slurry. The slurry is washed with a counter-current of fresh water, dried and ball-milled. Because of the lack of solubility in the usual solvents, aniline-formaldehyde laminates are made by a ‘pre-mix’ method. In this process the aniline hydrochloride-formaldehyde product is run into a bath of paper pulp rather than of caustic soda. Soda is then added to precipitate the resin on to the paper fibres. The pulp is then passed through a paper-making machine to give a paper with a 50% resin content. Aniline-formaldehyde resin has very poor flow properties and may be moulded only with difficulty, and mouldings are confined to simple shapes. The resin is essentially thermoplastic and does not cross-link with the evolution of volatiles during pressing. Long pressing times, about 90 minutes for a 4 in thick sheet, are required to achieve a suitable product. Laminated sheets may be made by plying up the impregnated paper and pressing at 3000 lbf/in2 (20MPa) moulding pressure and 160-170°C for 150 minutes, followed by 75 minutes cooling in a typical process. A few shaped mouldings may also be made from impregnated paper, by moulding at higher moulding pressures. In one commercial example a hexagonal circuit breaker lifting rod was moulded at 7000 lbf/in2 (48 MPa). I 6 + CH,O + H2N @ CH,OH I %HN CH2% Figure 24.1 0 Resins containing Thiourea 691 As with the other aminoplastics, the chemistry of resin formation is incompletely understood. It is, however, believed that under acid conditions at aniline-formaldehyde ratios of about 1: 1.2, which are similar to those used in practice, the reaction proceeds via p-aminobenzyl alcohol with subsequent condensation between amino and hydroxyl groups (Figure 24.1 0). It is further believed that the excess formaldehyde then reacts at the ortho- position to give a lightly cross-linked polymer with very limited thermoplasticity (Figure 24.11). + CH,O + H,O Figure 24.11 Such condensation reactions occur on mixing the two components. The resultant comparative intractability of the material is one of the main reasons for its industrial eclipse. Some typical properties of aniline-formaldehyde mouldings are given in Table 24.2. Table 24.2 Typical properties of aniline-formaldehyde mouldings Specific gravity 1.2 Rockwell hardness M 100, 125 Water absorption (24 h) Tensile strength Impact strength Dielectric constant 3.56-3.72 (100Hz-100MHz) Power factor 100 Hz 0.00226 I MHz 0.00624 100 MHz 0.003 18 0.08% (ASTM D.570) 10 500 Ibf/in2 (73 MPa) 0.33 ft Ibf/in? notch (Izod) Upper Service Temperature -90°C Track resistance Resistant to alkalis, most organic solvents Attacked by acids between phenolics and U-Fs 24.6 RESINS CONTAINING THIOUREA Thiourea may be produced either by fusion of ammonium thiocyanate or by the interaction of hydrogen sulphide and cyanamide. NH4SCN * CS (NH,), NH2CN + H2S + CS(NH2)2 The first process is an equilibrium reaction which yields only a 25% conversion of thiourea after about 4 hours at 140-145°C. Prolonged or excessive 692 Aminoplastics wNH. CH,OH + HO . CH, . NHm L +m~~. CH, . NH- + CH,O + H,O wNH.CH,OH + NHw / \ / \ CShwNH.CH,.Nm CS + H,O Figure 24.12 heating will cause decomposition of the thiourea whilst pressure changes and catalysts have no effect on the equilibrium. Pure thiourea is a crystalline compound melting at 181-182°C and is soluble in water. Thiourea will react with neutralised formalin at 20-30°C to form methylol derivatives which are slowly deposited from solution. Heating of methylol thiourea aqueous solutions at about 60°C will cause the formation of resins, the reaction being accelerated by acidic conditions. As the resin average molecular weight increases with further reaction the resin becomes hydrophobic and separates from the aqueous phase on cooling. Further reaction leads to separation at reaction temperatures, in contrast to urea-formaldehyde resins, which can form homogeneous transparent gels in aqueous dispersion. Polymer formation is apparently due to hydroxymethyl-methyl and hydroxy- methyl-amino reaction (Figure 24.12.). In comparison with urea-based resins, thiourea resins are slower curing and the products are somewhat more brittle. They are more water-repellent the U-F resins. At one time thiourea-urea-formaldehyde resins were of importance for moulding powders and laminating resins because of their improved water resistance. They have now been almost completely superseded by melamine- formaldehyde resins with their superior water resistance. It is, however, understood that a small amount of thiourea-containing resin is still used in the manufacture of decorative laminates. References 1. British Patent 151,016 2. British Patent 171,094; British Patent 181.014; British Patent 193,420 British Patent 201,906; British Patent 206,512; British Patent 213,567; British Patent 238,904; British Patent 240,840 British Patent 248,729 3. British Patent 187,605; British Patent 202,651; British Parent 208,761 4. British Patent 455,008 5. BLAKEY, w., Chem. and Ind., 1349 (1964) 6. DINCLEY, c. s., The Story of B.I.P., British Industrial Plastics Ltd., Birmingham (1963) 7. BROOKES, A., Plastics Monograph No. 2, Institute of the Plastics Industry, London (1946) 8. KADOWAKI, H., Bull. Chem. Soc. Japan, 11, 248, (1936) 9. MARVEL, c. s., et al., J. Am Chem. Soc., 68, 1681 (1946) 10. REDFARN, c. A,, Brit. Plastics, 14, 6 (1942) 11. THURSTON, I. T., Unpublished paper given at the Gibson Island conference on Polymeric Materials 12. DE JONG, J. I., and DE JONGE, J., Rec. Trav. Chim., 72, 207 and 213 (1953) 13. ZICEUNER, G., Monatsh., 82, 175 (1951); 83, 1091 (1952); 86, 165 (1955) (1941) Reviews 693 14. VALE, c. P., and TAYLOR, w. G. K., Aminoplastics, Iliffe, London (1964) 15. HOFTON, J., Brit. Plastics, 14, 350 (1942) 16. MILLS, F. I., Paper in Plastics Progress 1953 (Ed. MORGAN, P.), IIiffe, London (1953) 17. GAMS, A,, WIDNER, G., and FISCH, w., Brit Plastics, 14, 508 (1943) 18. British Patent 738.033 19. MORGAN, D. E., and VALE, c. P., Paper in S.C.I. Monograph No. 5 The Physical Properties of 20. VALE, c. P., Trans. Plastics Inst., 20, 29 (1952) 21. BS 1322 22. Plastics (London), 15, 34 (1950) Polymers, Society of the Chemical Industry, London (1959) Bibliography BLAIS, I. F., Amino Resins, Reinhold, New York (1959) MEYER, B., Urea Formaldehyde Resins, Addison-Wesley, Reading (Mass.) (1979) UPDEGRAFF, I. H., Encyclopedia of Polymer Science and Technology (2nd edition), Vol. 1, pp 725-89 VALE, c. P., Aminoplastics, Cleaver-Hume Press, London (1950) VALE, c. P., and TAYLOR, w. G. K., Aminoplastics, IIiffe, London (1964) (1985) Reviews G~TZE, T., and KELLER, K., Kunstoffe, 70, 684-6 (1980) EISELE, w., and WITTMANN, o., Kunstoffe, 70, 687-9 (1980) GARDZIELLA, A,, Kunstoffe, 86, 1566-1578 (1996) 25 Polyesters 25.1 INTRODUCTION Polyesters are encountered in many forms. They are important as laminating resins, moulding compositions, fibres, films, surface coating resins, rubbers and plasticisers. The common factor in these widely different materials is that they all contain a number of ester linkages in the main chain. (There are also a number of polymers such as poly(viny1 acetate) which contain a number of ester groups in side chains but these are not generally considered within the term polyester resins.) These polymers may be produced by a variety of techniques, of which the following are technically important: (1) Self-condensation of o-hydroxy acids, commercially the least important route: HORCOOH + HORCOOH etc + mORCOORC00m (2) Condensation of polyhydroxy compounds with polybasic acids, e.g. a glycol with a dicarboxylic acid: HOROH + HOOCRICOOH + HOROH + mOROOCR1COORO~ + H20 (3) Ester exchange: R,OOCRCOOR1 + HOR20H __j ~OOCRCOOR,OO~ + R,OH (4) Ring opening of a lactone, e.g. of E-caprolactone with dihydroxy or trihydroxy initiators: c=o /\ R- 0 +-RCOOm 694 Introduction 695 (5) Alcoholysis of the acid chloride of a dicarboxylic acid with a polyhydroxy alcohol: ClOCROCl + HOR,OH + ~OCRCOOR1O~ + HC1 Credit for the preparation of the first polyester resin is given variously to Berzeliusl in 1847 and to Gay-Lussac and Pelouze in 18832 Their first use came about in the early years of this century for surface coatings where they are well known as alkyd resins, the word alkyd being derived somewhat freely from alcohol and acid. Of particular importance in coatings are the glyptals, glycerol- phthalic anhydride condensates. Although these materials were also used at one time for moulding materials they were very slow curing even at 200°C and are now obsolete and quite different from present day alkyd moulding powders. Linear polyesters were studied by Carothers during his classical researches into the development of the nylons but it was left to Whinfield and Dickson to discover poly(ethy1ene terephthalate) (BP 578 079), now of great importance in the manufacture of fibres (e.g. Terylene, Dacron) and films (e.g. Melinex, Mylar). The fibres were first announced in 1941. At about the same time, an allyl resin known as CR39 was introduced in the United States as a low-pressure laminating resin. This was followed in about 1946 with the introduction of unsaturated polyester laminating resins which are today of great importance in the manufacture of glass-reinforced plastics. Alkyd moulding powders were introduced in 1948 and have since found specialised applications as electrical insulators. With the expiry of the basic IC1 patents on poly(ethylene terephthalate) there was considerable development in terephthalate polymers in the early 1970s. More than a dozen companies introduced poly(butylene terephthalate) as an engineering plastics material whilst a polyether-ester thermoplastic rubber was introduced by Du Pont as Hytrel. Poly(ethy1ene terephthalate) was also the basis of the glass-filled engineering polymer (Rynite) introduced by Du Pont in the late 1970s. Towards the end of the 1970s poly(ethy1ene terephthalate) was used for the manufacture of biaxially oriented bottles for beer, colas and other carbonated drinks, and this application has since become of major importance. Similar processes are now used for making wide-neck jars. Highly aromatic thermoplastic polyesters first became available in the 1960s but the original materials were somewhat difficult to process. These were followed in the 1970s by somewhat more processable materials, commonly referred to as polyarylates. More recently there has been considerable activity in liquid crystal polyesters, which are in interest as self-reinforcing heat-resisting engineering thermoplastics. Such is the diversity of polyester materials that it has to be stressed that their common feature is only the ester (-COO-) link and that this often only comprises a small part of the molecule. Nevertheless it may influence the properties of the polymer in the following ways: (1) It is, chemically, a point of weakness, being susceptible to hydrolysis, ammonolysis and ester interchange, the first two reactions leading to chain scission. In some cases the reactivity is influenced by the nature of the adjacent groupings. (2) As a polar group it can adversely affect high-frequency electrical insulation properties. Its influence is generally lower below Tg unless the 696 Polyesters portion of the polymer containing the ester group has some mobility below the main Tg. (3) The polar ester group may act as a proton acceptor, allowing interactions with other groupings either of an inter- or an intramolecular nature. (4) The ester link appears to enhance chain flexibility of an otherwise polymethylenic chain. At the same time it generally increases interchain attraction and in terms of the effects on melting points and rigidity the effects appear largely self-cancelling. 25.2 UNSATURATED POLYESTER LAMINATING RESINS The polyester laminating resins are viscous, generally pale yellow coloured materials of a low degree of polymerisation (-%-lo), i.e. molecular weight of about 2000. They are produced by condensing a glycol with both an unsaturated and a saturated dicarboxylic acid. The unsaturated acid provides a site for subsequent cross-linking whilst provision of a saturated acid reduces the number of sites for cross-linking and hence reduces the cross-link density and brittleness of the end-product. In practice the polyester resin, which may vary from a very highly viscous liquid to a brittle solid depending on composition, is mixed with a reactive diluent such as styrene. This eases working, often reduces the cost and enhances reactivity of the polyester. Before applying the resin to the reinforcement a curing system is blended into the resin. This may be so vaned that curing times may range from a few minutes to several hours whilst the cure may be arranged to proceed either at ambient or elevated temperatures. In the case of cold-curing systems it is obviously necessary to apply the resin to the reinforcement as soon as possible after the catalyst system has been added and before gelation and cure occur. The usual reinforcement is glass fibre, as a preform, cloth, mat or rovings but sisal or more conventional fabrics may be used. Since cross-linking occurs via an addition mechanism across the double bonds in the polyesters and the reactive diluent there are no volatiles given off during cure (c.f. phenolic and amino-resins) and it is thus possible to cure without pressure (see Figure 25.1). Since room temperature cures are also possible the resins are most useful in the manufacture of large structures such as boats and car bodies. Small quantities of higher molecular weight resin in powder form are also manufactured. They are used in solution or emulsion form as binders for glass- fibre preforms and also for the manufacture of preimpregnated cloths. 25.2.1 Selection of Raw Materials 1,2-Propylene glycol is probably the most important glycol used in the manufacture of the laminating resins. It gives resins which are less crystalline and more compatible with styrene than those obtained using ethylene glycol. Propylene glycol is produced from propylene via propylene oxide. The use of glycols higher in the homologous series gives products which are more flexible and have greater water resistance. They do not appear to be used on a large scale commercially. Products such as diethylene glycol and triethylene glycol, obtained by side reactions in the preparation of ethylene glycol, are sometimes used but they [...]... of certain polyesters (ref 15) T,,, (“C) for n = Series 2 3 4 5 6 220 188 320 150 100 - 170 170 155 - - 230 175 86 67 53 125 185 170 84 30 55 181 240 90 47 52 57 1 67 160 7 10 - 1 2 3 4 5 6 7 8 9 10 11 12 254 254 265 125 270 273 82 17 122 66 188 220 190 160 - 115 213 - 29 - 150 - - - - 164 - - 135 125 - 182 98 61 74 53 156 - Series 1 Poly(ethy1ene alkylenedioxy-4,4‘-dibenzoates) -O.(CH2)Z*O*OC 2 Poly(alky1ene... 5.0-6.0 >lo16 78 -1 17 15-30 140-165 20-30 150-165 60-90 0.009 0.12-0.18 1.64 0.03-0.05 0.02-0.04 4.0-5.5 3.5-5.0 >lo16 1 17- 156 5-15 150-165 60-90 0.006 0.09-0 .13 1.8 "C 0.009 0 .13- 0.18 1 .7- 1.8 0.01-0.05 0.02-0.04 4.5-5.5 4.5-5.0 >lo16 94 -135 40 -70 Except where marked by am asterisk these results were obtained by tests methods as laid down in BS 771 S cm/cm ft Ib - 0.04-0.06 - 4.0-6.0 >10'6 1 17- 156 10-20... ethylene glycol (see Section 25 .7) The considerable success of PET for making bottles and similar products, together with continuing demand for PET film, had led to an upsurge in companies supplying PET materials By 19 87 nine companies were supplying PET materials in Western Europe for injection moulding, seven for bottle manufacture and eight for film As with many other plastics materials being manufactured... phenolic, aminoplastic and silicone resins is discussed elsewhere in this book World production of unsaturated polyester resins in 19 97 was of the order of 1 .7 X lo6 tonnes, with the USA accounting for about 45% and Western Europe 27% Over 75 % is used in reinforced plastics, with the rest being used for such diverse applications as car repair putties, ‘cultured marble’, wood substitution and surface... (60 Hz) (20°C) ( IO6 Hz) Power factor (60 Hz) (20°C) (106 Hz) Volume resistivity Water absorption (24 h immersion) Units Poly(ethy1ene terephthalate) Kodel - 1.39 17- 25 1 17- 173 50-1 30 4000 1580 3.16 2.98 0.002 0.014 10" 0.55 1.226 10- 17 69-1 17 45 >4000 >I580 3.1 2.9 0.005 0.014 10' Ibf/in2 MPa % V/O.001 in kV/cm n c/o - 0.30 The principal uses of poly(ethy1ene terephthalate) film are electrical, particularly... (at break) Izod impact strength Rockwell hardness ( M scale) z Dielectric constant IO6 H Dissipation factor lo" Hz lo6 Hz 1. 37- 1.38 250-255 0.02 0.10 26 1 71 .5 52.9 0.8 106 3. 37 0.0055 0.0208 O C % % "C MPa MPa ftlbf in-' notch Poly(ethy1ene terephthalate) Moulding Materials 72 1 and a back flow valve fitted to screw injection moulding machines Cylinder temperatures are about 260°C and mould temperatures... absorption (%) Press formed mat laminate 1.4-1.5 8- 17 55-1 17 10-20 69 -138 -0.5 3440 0.02-0.08 3.2-4.5 0.2-0.8 Fine square woven cloth laminate 1.5-1.8 18-25 124- 173 20- 27 138 -190 -0.6 4150 0.02-0.08 3.2-4.5 0.2-0.8 -2.0 30-45 210-3 10 40-55 2 67- 380 1-2 6890 -138 0 0.02-0.05 3.6-4.2 0.2-0.8 The most desirable features of polyester-glass laminates are: rovings I 2.19 150 1030 155 1100 6.6 45 500 - (1) They can be... (unoriented) Crystalline melting point (T,) Maximum rate o crystallisation-at f Glass transition temperature (T,) almost completely extended a = 4.56 A h = 5.94 A c = 10 .75 8, (chain axis) 1. 47 glcm3 1.33 g/cm3 1.38-1.39 g/cm3 -1.45 g/cm3 265°C 170 °C 67 C Poly(ethy1ene terephthalate) film is produced by quenching extruded film to the amorphous state and then reheating and stretching the sheet approximately three-fold... thermosetting polyester mouldings P-FGP 150- 170 Moulding temperature* 60 -70 Cure time (cup flow test)* Shrinkage 0.0 07 Impact strength 0.12-0.2 Specific gravity 1.35 Power factor (800 Hz) 0.1-0.4 Power factor ( lo6Hz) 0.03-0.05 Dielectric constant (800 Hz: 6-10 Dielectric constant ( lo6Hz) 4.5-5.5 Volume resistivity 1012-1014 Dielectric strength (90°C) 39- 97 Water absorption 45-65 DMC (GP) Polyester... Fibres are also available from poly-( 1,4-~yclohexylenedimethyleneterephthalate) and are marketed as Kodar (Kodak) and Vestan (Hiils) 72 0 Polyesters 25.5 POLY(ETHYLENE TEREPHTHALATE) MOULDING MATERIALS In 19 97 it was estimated that global production of PET was about 16 .7 X 106 t.p.a., of which 12 million tonnes was used in textiles, 2 million tonnes for audio and video film (with a small quantity for . Chim., 72 , 2 07 and 213 (1953) 13. ZICEUNER, G., Monatsh., 82, 175 (1951); 83, 1091 (1952); 86, 165 (1955) (1941) Reviews 693 14. VALE, c. P., and TAYLOR, w. G. K., Aminoplastics,. (%) (MPd) (MW (MW 1.4-1.5 8- 17 55-1 17 10-20 69 -138 -0.5 3440 0.02-0.08 3.2-4.5 0.2-0.8 Press formed mat laminate 1.5-1.8 18-25 124- 173 20- 27 138 -190 -0.6 4150 0.02-0.08 3.2-4.5. British Patent 248 ,72 9 3. British Patent 1 87, 605; British Patent 202,651; British Parent 208 ,76 1 4. British Patent 455,008 5. BLAKEY, w., Chem. and Ind., 134 9 (1964) 6. DINCLEY,