Plastics Materials 7 Episode 15 pptx

Polycarbodi-imide resins 807 Because of the high cross-link density of polyisocyanurates as prepared above, the resultant foams are brittle, so that there has been a move towards polyisocyanurate-polyurethane combinations. For example, isocyanurate-con- taining polyurethane foams have been prepared by trimerisation isocyanate- tipped TDI-based prepolymers. The isocyanurate trimerising reaction has also been carried out in the presence of polyols of molecular weight less than 300 to give foams by both one-shot and prepolymer methods. An alternative route involves the reaction of 1,2-epoxides with isocyanates to yield poly-2-oxazolidones (Figure 27.12). OCNRNCO + CH,-CH-R,-CH-CH, L co-0 C -coA Figure 27.12 Whilst reaction can take place in the absence of catalysts it is more common to use such materials as tetra-alkylammonium halides and tertiary amines such as triethylenediamine. A major side reaction leads to the production of isocyanurate rings, particularly in the presence of tertiary amines. The conventional polyisocyanurate may be prepared with a two-component system using standard polyurethane foaming equipment. It is usual to blend isocyanate and fluorocarbon to form one component whilst the activator or activator mixture form the second component. Typical properties of isocyanurate foam are given in Table 27.5. Table 27.5 Typical properties of polyisocyanurate foams Density Compression strength Shear strength Initial K value Equilibrium K value Resistance to elevated temperature distortion (DIN 53424) 2.1-3.01b 20-40 Ibf/in2 15-35 Ibf/in2 0.1 15 BTU in ftr'h-' "F' at 32°F 0.16 units 38-48 kg/m3 0.14-0.28 MPa 0.10-0.24 MPa 0.17 W/mK at 0°C 0.24 200°C 27.y POLYCARBODI-IMIDE RESINS Besides trimerisation, leading to the production of polyisocyanurates, iso- cyanates can react with each other to form polycarbodi-imides with the simultaneous evolution of carbon dioxide: 808 Polyurethanes and Polyisocyanurates When this is carried out in suitable solvents at temperatures in the range 75-120"C, soluble products will be obtained. Polymeric MDI is usually used as the isocyanate component and this results in a stiff chain molecule. One such product is reported to have a Tg of 200-220°C. In the absence of solvents and with suitable catalysts the evolution of carbon dioxide simultaneously with the polycarbodi-imide formation gives rise to a foamed product. These foams are cross-linked because of reactions between carbodi-imide groups and free isocyanate groups. Raw materials for such foams are now available from Bayer (Baymid). The polymers combine a high level of flame retardancy with good thermal insulation and sound absorption characteristics. Densities are somewhat high (16-20 kg/m'). Amongst applications reported are underfloor footfall sound insulation, thermal insulation between cavity walls and pipe insulation. 27.10 POLYURETHANE-ACRYLIC BLENDS Over the years many blends of polyurethanes with other polymers have been prepared. One recent example'* is the blending of polyurethane intermediates with methyl methacrylate monomer and some unsaturated polyester resin. With a suitable balance of catalysts and initiators, addition and rearrangement reactions occur simultaneously but independently to give interpenetrating polymer networks. The use of the acrylic monomer lowers cost and viscosity whilst blends with 20% (MMA + polyester) have a superior impact strength. 27.11 MISCELLANEOUS ISOCYANATE-BASED MATERIALS Because of their great versatility there continues to be a steady stream of developments of polymers made by reaction of i~ocyanates.'~ In addition to the materials discussed in this chapter there are, to name but three, the polyureas, the polyoxazolidinones and polybenzoxazinediones. There is also growing interest in multi-phase systems in which hard phase materials are dispersed in softer polyether diols. Such hard phase materials include polyureas, rigid polyurethanes and urea melamine formaldehyde condensates. Some of these materials yield high-resilience foams with load deflection characteristics claimed to be more satisfactory for cushioning as well as in some cases improving heat resistance and flame retardancy. Aqueous dispersions of polyurethanes have also become available which may be used instead of solutions in organic solvents for such applications as leather treatment, adhesives and surface coatings. The polycarbamylsulphonates are water-soluble reactive bisulphite adducts of polyisocyanates and are being investigated as possible materials to render woollen fabrics crease-resistant. References 1. WURTZ, A,, Ann., 71, 326 (1849) 2. HENTSCHEL, w., Ber., 17, 1284 (1884) 3. SAUNDERS, J. H., and FRISCH, K. G., Polyurethanes-Chemistry and Technology; Pt 1- Chemistry, Interscience, New York (1962) Technical Reviews 809 4. PHILLIPS, L. N., and PARKER, D. n. v., Polyurethanes-Chemistry; Technology and Properties, 5. ARNOLD, R. G., NELSON, J. A., and VERBANC, I. J., Chemistry of Organic Isocyanates, Du Pont 6. PINTEN, H., German Patent, Appl. D-90, 260 (March 1942) 7. BAYER, 0 MULLER, E, PETERSEN, S., PIEPENBRINK, H. E, and WINDEMUTH, E., Angew. Chem. 62, 57 Iliffe, London (1964) Bulletin HR-2 (1-20-56) (1950); Rubber Chem. Technol., 23, 812 (19.50) 8. HAMPTON, H. A., and HURD, R., Trans. Plastics Inst., 29, 204 (1961) 9. sursr, J. M., Trans. Plastics Inst., 29, 100 (1962) 10. FERRIGNO, T. H., Rigid Plastics Foams, Rheinhold, New York (1963) 11. BALL, c. w., BALL, L. s., WALKER, M. G., and WILSON, w. I., Plastics & Polymers, 40, 290 12. KIRCHER, K., and PIPER, R., Kunstoffe, 68, 141 (1978) 13. ELrAs, H NG., and VOHWINKEL, F., Chapter 13 in New Commercial Polymers-2, Gordon and (1972) Breach, New York, London (1986) Bibliography nRYDsoN, I. A,, Rubbery Materials and their Compounds, Elsevier Applied Science, London atirsr, J. M. (Ed.), Developments in Polyurethanes-Z, Elsevier Applied Science, London (1978) DoMmow, B. A., Polyurethanes, Reinhold, New York (1957) DUNNOLS, I., Basic Urethane Foam Manufacturing Technology, Technomics, Westport, Conn. FERRIGNO, T. H., Rigid Plastics Foams, Reinhold, New York, 2nd Edn (1967) FRISCH, K. c., ‘Recent Advances in the Chemistry of Polyurethanes’, Rubb. Chem. Technol., 45 FRISCH, K. c., Recent Developments in Urethane Elastomers and Reaction Injection Moulded (RIM) FRISCH, K. c. and REEGAN, s. L., Advances in Urethane Science and Technology (Vols. 1, 1972; 2, 1973; FRISCH, K. c., and SAUNDERS, J. H., Plastic Foams, Pt 1, Marcel Dekker, New York (1972) HARROP, D. J., Chapter 5 in Developments in Rubber Technology-3 (Eds WHELAN, A. and LEE, K. s.), HEALY, T. T. (Ed.), Polyurethane Foams, Iliffe, London (1964) LEE, L. I. Polyurethane Reaction Injection Moulding, Rubber Chem. Technol., 53, 542 (1980) MECKEL, w., GOYERT, w., and WIEDER, w., Chapter 2 in Thermoplastics Elastomers (Eds LEGGE, N. R., PHILLIPS, L. N., and PARKER, D. B. v., Polyurethanes-Chemistry Technology and Properties, Iliffe, SAUNDERS, I. H., and FRISCH, K. c., Polyurethanes-Chemistry and Technology; Pt 1 -Chemistry; WHELAN, A,, and BRYDSON, I. A. (Eds). Developments with Thermosetting Plastics. (Chapter 6 by A. Buyer-Polyurethanes, Handbook produced by Bayer AG, English language edition (1979) (1988). (1979) 1442-1466 (1972) Elastomers, Rubber Chem. Technol., 53, 126 (1980) 3, 1974; 4, 1976; 5, 1976; 6, 1978; 7, 1979), Technomics, Westport, Conn. Applied Science, London (1982) HOLDEN, G., and SCHROEDER, H. E., Hanser, Munchen (1987) London (1964) Pt 2-Technology, Interscience, New York (1962) Bamatt and Chapter 7 by J. B. Blackwell). Applied Science, London (1974) Technical Reviews UHLIG, K., and KOHORST, J., Kunstoffe, 66, 616-24 (1976) PALM, R., and SCHWENKE, w., Kunsroffe, 70, 665-71 (1980) MILLS, R., Kunstoffe, 77, 1036-8 (1987) LUDKE, H. Kunstoffe, 86, 1556-1564 (1996) 28 Furan Resins 28.1 INTRODUCTION The furan or furane resins mainly find use because of their excellent chemical and heat resistance. In the past they have mainly been used in applications peripheral to the plastics industry such as foundry resins, for chemically resistant cements and for binders. Recent developments have facilitated their use in laminates for chemical plant. 28.2 PREPARATION OF INTERMEDIATES The two intermediates of commercial furan resins are furfural and furfuryl alcohol. Furfural occurs in the free state in many plants but is obtained commercially by degradation of hemicellulose constituents present in these plants. There are a number of cheap sources of furfural, and theoretical yields of over 20% (on a dry basis) may be obtained from both corn cobs and oat husks. In practice yields of slightly more than half these theoretical figures may be obtained. In the USA furfural is produced in large quantities by digestion of corn cobs with steam and sulphuric acid. The furfural is removed by steam distillation. Furfural is a colourless liquid which darkens in air and has a boiling point of 16 1.7"C at atmospheric pressure. Its principal uses are as a selective solvent used in such operations as the purification of wood resin and in the extraction of butadiene from other refinery gases. It is also used in the manufacture of phenol- furfural resins and as a raw material for the nylons. The material will resinify in the presence of acids but the product has little commercial value. Catalytic hydrogenation of furfural in the presence of copper chromite leads to furfuryl alcohol, the major intermediate of the furan resins (Figure 28.1). 810 Resinification 8 11 CH-CH II [H21 CH-CH cq ,y Chromite - II Copper CH II II 0 CHO 0 CH,OH Figure 28.1 The alcohol is a mobile liquid, light in colour, with a boiling point of 170°C. It is very reactive and will resinify if exposed to high temperatures, acidity, air or oxygen. Organic bases such as piperidine and n-butylamine are useful inhibitors. 28.3 RESINIFICATION Comparatively little is known of the chemistry of resinification of either furfuryl alcohol or furfural. It is suggested that the reaction shown in Figure 28.2 occurs initially with furfuryl alcohol. + Furfuryl Alcohol - H,O Figure 28.2 The liberation of small amounts of formaldehyde has been detected in the initial stage but it has been observed that this is used up during later reaction. This does not necessarily indicate that formaldehyde is essential to cross-linking, and it would appear that its absorption is due to some minor side reaction. Loss of unsaturation during cross-linking indicates that this reaction is essentially a form of double bond polymerisation, viz Figure 28.3. Figure 28.3 812 Furan Resins This reaction, like the initial condensation, is favoured by acidic conditions and peroxides are ineffective. The polymerisation of furfural is apparently more complex and less understood. For commercial use a partially condensed furan resin is normally prepared which is in the form of a dark free-flowing liquid. Final cure is carried out in situ. The liquid resins are prepared either by batch or continuous process by treating furfuryl alcohol with acid. Initially the reaction mixture is heated but owing to the powerful exothermic an efficient cooling system is necessary if cross-linking is to be avoided. Water of condensation is removed under vacuum and the reaction stopped by adjusting the pH to the point of neutrality. Great care is necessary to prevent the reaction getting out of hand. This may involve, in addition to efficient cooling, a judicious choice of catalyst concentration, the use of a mixture of furfuryl alcohol and furfural which produces a slower reaction but gives a more brittle product and, possibly, reaction in dilute aqueous solution. The resins are hardened in situ by mixing with an acidic substance just before application. A typical curing system would be four parts of toluene-p-sulphonic acid per 100 parts resin. The curing may take place at room temperature if the resin is in a bulk form but elevated temperature cures will often be necessary when the material is being used in thin films or coatings. 28.4 PROPERTIES OF THE CURED RESINS The resins are cross-linked and the molecular segments between the cross-links are rigid and inflexible. As a consequence the resins have an excellent heat resistance, as measured in terms of maintenance of rigidity on heating, but are rather brittle. Cured resins have excellent chemical resistance. This is probably because, although the resins have some reactive groupings, most of the reactions occurring do not result in the disintegration of the polymer molecules. Therefore, whilst surface layers of molecules may have undergone modification they effectively shield the molecules forming the mass of the resin. The resins have very good resistance to water penetration. Compared with the phenolics and polyesters the resins have better heat resistance, better chemical resistance, particularly to alkalis, greater hardness and better water resistance. In these respects they are similar to, and often slightly superior to, the epoxide resins. Unlike the epoxides they have a poor adhesion to wood and metal, this being somewhat improved by incorporating plasticisers such as poly(viny1 acetate) and poly(viny1 formal) but with a consequent reduction in chemical resistance. The cured resins are black in colour. 28.5 APPLICATIONS The principal applications for furan resins are in chemical plant. Specific uses include the lining of tanks and vats and piping and for alkali-resistant tile cements. The property of moisture resistance is used when paper honeycomb structures are treated with furan resins and subsequently retain a good compression strength even after exposure to damp conditions. Bibliography 8 13 Laminates have been prepared for the manufacture of chemical plant. They have better heat and chemical resistance than the polyester- epoxide- phenolic- or aminoplastic-based laminates but because of the low viscosity of the resins were not easy to handle. Because they were also somewhat brittle, furan-based laminates have been limited in their applications. This situation may be expected to change somewhat with the advent of new polymers of greater viscosity (375-475 cP) (37.5-47.5 N s/m2) and generally easier handling qualities. Whilst patents (e.g. Ger. Pat. 1927 776) describe polymeric blends of UF and furane resins as being suitable for such laminating it has been stated that the commercially available polymers (e.g. Quacorr RP100A-Quaker Oats Co.) are basically furfuryl alcohol polymers not modified by PF or UF resins. They are cured by modified acid catalysts, giving a rather more gentle cure than the earlier catalyst systems. Furane resin-chopped strand mat laminates have tensile strengths in excess of 20 000 lbf/in2 (140 MPa), a heat distortion temperature of about 21 8°C and good fire resistance. Not only does the material have excellent resistance to burning but smoke emission values are reported to be much less than for fire-retardant polyester resin. The laminates are being increasingly used in situations where corrosion is associated with organic media, where corrosion is encountered at temperatures above 100°C as in fume stacks and where both fire retardance and corrosion resistance are desired as in fume ducts. One other substantial development of the 1960s was the use of ureaformalde- hyde-furfuryl alcohol materials as foundry resins, particularly for ‘hot-box’ operations. The furfuryl alcohol component of the resin is usually in the range Furane resins are useful in impregnation applications. Furfural alcohol resinified in situ with zinc chloride catalysts can be used to impregnate carbon (including graphite) products and be cured at 93-150°C to give products of greater density and strength and which have much lower permeability to corrosive chemicals and gases. The resins are also used for coating on to moulds to give a good finish that is to be used for polyester hand-lay up operations. Development work by Russian workers had led to interesting products formed by reaction of furfuryl alcohol with acetone and with aniline hydrochloride. The resins formed in each case have been found to be useful in the manufacture of organic-mineral non-cement concretes with good petrol, water and gas resistance. They also have the advantage of requiring only a small amount of resin to act as a binder. 25 -40%. Bibliography GANDINI, A. ‘FURAN RESINS’, Encyclopedia of Polymer Science and Technology (2nd Edition), Vol. 7, MCDOWALL, R., and LEWIS, P., Trans. Plastics Inst., 22, 189 (1954) MORGAN, P., Glass-reinforced Plastics, Iliffe, London, 3rd Edn (1961) RADCLIFFE, A. T. (Eds. WHELAN. A,, and BRYDSON. I. A,) Chapter 5 of Developments wifh Thermosetting pp. 454-73, John Wiley, New York (1987) Plastics, Applied Science, London (1975) See also various articles by Itinskii, Kamenskii, Ungureau and others in Plasticheskie Massy from 1960 onwards. (Translations published as Soviet Plastics by Rubber and Technical Press Ltd, London.) 29 Silicones and Other Heat-resisting Polymers 29.1 INTRODUCTION To many polymer chemists one of the most fascinating developments of the last 80 years has been the discovery, and the attendant commercial development, of a range of semi-inorganic and wholly inorganic polymers, including the silicome polymers. Because of their general thermal stability, good electrical insulation characteristics, constancy of properties over a wide temperature range, water- repellency and anti-adhesive properties, the silicone polymers find use in a very wide diversity of applications. Uses range from high-temperature insulation materials and gaskets for jet engines to polish additives and water repellent treatments for leather. The polymers are available in a number of forms such as fluids, greases, rubbers and resins. The possibility of the existence of organosilicone compounds was first predicted by Dumas in 1840, and in 1857 Buff and Wohler' found the substance now known to be trichlorosilane by passing hydrochloric acid gas over a heated mixture of silicone and carbon. In 1863 Friedel and Crafts2 prepared tetraethylsilane by reacting zinc diethyl with silicon tetrachloride. 2Zn(C,Hs), + SiC14 + Si(C2H5)4 + 2ZnC1, In 1872 Ladenburg' produced the first silicone polymer, a very viscous oil, by reacting diethoxydiethylsilane with water in the presence of traces of acid. C2H5 I I C,H, I H2O I C,H,-0 -Si- 0-C2H, - - (-0 -Si-)- + C,H,OH Acid C*H, C,H, The basis of modem silicone chemistry was, however, laid by Professor E S. Kipping at the University College, Nottingham, between the years 1899 and 1944. During this period Kipping published a series of 5 1 main papers and some 8 14 Introduction 8 15 supplementary studies, mainly in the Journal of the Chemical Society. The work was initiated with the object of preparing asymmetric tetrasubsituted silicon compounds for the study of optical rotation. Kipping and his students were concerned primarily with the preparation and study of new non-polymeric compounds and they were troubled by oily and glue-like fractions that they were unable to crystallise. It does not appear that Kipping even foresaw the commercial value of his researches, for in concluding the Bakerian Lecture delivered in 1937 he said ‘We have considered all the known types of organic derivatives of silicon and we see how few is their number in comparison with the purely organic compounds. Since the few which are known are very limited in their reactions, the prospect of any immediate and important advance in this section of chemistry does not seem very hopeful.’ Nevertheless Kipping made a number of contributions of value to the modern silicone industry. In 1904 he introduced the use of Grignard reagents for the preparation of chlorosilanes and later discovered the principle of the inter- molecular condensation of the silane diols, the basis of current polymerisation practice. The term silicone was also given by Kipping to the hydrolysis products of the disubstituted silicon chlorides because he at one time considered them as being analogous to the ketones. In 193 1 J. E Hyde of the Coming Glass Works was given the task of preparing polymers with properties intermediate between organic polymers and inorganic glasses. The initial objective was a heat-resistant resin to be used for impregnating glass fabric to give a flexible electrical insulating medium. As a result silicone resins were produced. In 1943 the Coming Glass Works and the Dow Chemical Company co-operated to form the Dow Coming Corporation, which was to manufacture and develop the organo-silicon compounds. In 1946 the General Electric Company of Schenectady, NY also started production of silicone polymers using the then new ‘Direct Process’ of Rochow. The Union Carbide Corporation started production of silicones in 1956. There are at present about a dozen manufacturers outside the Communist bloc. Amongst major producers, in addition to those already mentioned, are Bayer, Rhone-Poulenc, Wacker-Chemie, Toshiba, Toray and Shinetsu. During the 1970s growth rates for the silicones were higher than for many other commercial polymers, generally showing an annual rate of growth of some 10-15%. In part this is due to the continual development of new products, in part to the increasingly severe demands of modern technology and in part because of favourable ecological and toxicological aspects in the use of silicones. In the early 1980s world capacity excluding the Eastern bloc was assessed at about 270000 tonnes per annum, being dominated by the USA (41%) with Western Europe taking about 33% and Japan 17%. 29.1.1 Nomenclature Before discussing the chemistry and technology of silicone polymers it is necessary to consider the methods of nomenclature of the silicon compounds relevant to this chapter. The terminology used will be that adopted by the International Union of Pure and Applied Chemistry. The structure used as the basis of the nomenclature is silane SiH, corresponding to methane CH,. Silicon hydrides of the type SiH3(SiH,), SiH3 8 16 are referred to as disilane, trisilane, tetrasilane etc., according to the number of silicon atoms present. Alkyl, aryl, alkoxy and halogen subsituted silanes are referred to by prefixing ‘silane’ by the specific group present. The following are typical examples: Silicones and Other Heat-resisting Polymers (CH3)2SiH2 dimethylsilane CH3 Si*C13 trichloromethy silane (C,H, ), Si.C2Hs ethyltriphenylsilane Compounds having the formula SiH3*(OSiH2),0*SiH3 are referred to as disiloxane, trisiloxane etc., according to the number of silicon atoms. Polymers in which the main chain consists of repeating-Si-0- groups together with predominantly organic side groups are referred to as polyorganosiloxanes or more loosely as silicones. Hydroxy derivatives of silanes in which the hydroxyl groups are attached to a silicon atom are named by adding the suffices -01, -diol, -triol etc., to the name of the parent compound. Examples are: H,SiOH silanol H2Si(OH)2 silanediol (CH,),SiOH trimethy lsilanol (C6H,)2(C2H50)SiOH ethoxydiphenylsilanol 29.1.2 Nature of Chemical Bonds Containing Silicon Silicon has an atomic number of 14 and an atomic weight of 28.06. It is a hard, brittle substance crystallising in a diamond lattice and has a specific gravity of 2.42. The elemental material is prepared commercially by the electrothermal reduction of silica. Silicon is to be found in the fourth group and the second short period of the Periodic Table. It thus has a maximum covalency of six although it normally behaves as a tetravalent material. The silicon atom is more electropositive than the atoms of carbon or hydrogen. The electronegativity of silicon is 1.8, hydrogen 2.1, carbon 2.5 and oxygen 3.5. It has a marked tendency to oxidise, the scarcity of naturally occurring elemental silicon providing an excellent demonstration of this fact. At one time it was felt that it would be possible to produce silicon analogues of the multiplicity of carbon compounds which form the basis of organic chemistry. Because of the valency difference and the electropositive nature of the element this has long been known not to be the case. It is not even possible to prepare silanes higher than hexasilane because of the inherent instability of the silicon-silicon bond in the higher silanes. The view has also existed in the past that the carbon-silicon bond should be similar in behaviour to the carbon-carbon bond and would have a similar average bond energy. There is some measure of truth in the assumption about average bond energy but because silicon is more electropositive than carbon the C-Si bond will be polar and its properties will be very dependent on the nature of groups attached to the carbon and silicon groups. For example, the CH3-Si group is particularly resistant to oxidation but C6 H13-Si is not. The polarity of the silicon-carbon bond will affect the manner in which the reaction with ions and molecules takes place. For example, on reaction with [...]... Hz IS0 178 IS0868 IS0180 at -30°C IS04589 IEC695-2- 1 ASTM D2 57 IEC 250 1.18 20 MPa 25 MPa 110% D60 25 kJ/m2 15 kJ/m2 48 960°C at 3.2mm thickness >io15 n Rcm 0.010 Polymers for use at High Temperatures 29 .7 841 POLYMERS FOR USE AT HIGH TEMPERATURES The bulk of plastics materials are required to operate within the range of -30 to + 100°C There has, however, been a steadily increasing demand for materials. .. affected by temperature than with the corresponding paraffins (see Figure 29.2) 9 u 5 5- 3 4- 0 ' J- I w 5: 2: '1 o1 4;O ~ -25 3 6 5 5 3 4 3 J S 2 3 1 3 0 2 9 2-8 2 7 2 6 2 5 2 4 2 3 2.2 3,9) 87 _ 0 25 50 7EHPERATURf 21 -_ r- 7 7s 100 150 200 IN 'C Figure 29.2 Viscosity-temperature curves for four commercial dimethylpolysiloxane fluids and for liquid paraffin The numbers 1000, 300, 100 and 40 indicate... of 1000lbf/in2 (7 MPa) Of particular importance are the electrical properties of the laminates These are generally superior to P-F and M-F glass-cloth laminates, as may be seen from Table 29.3." Power factor (1 MHz) Dielectric strength V/O.OOl in kV/cm Insulation resistance (dry) Insulation resistance (after water immersion) P-F M-F Silicone BS11 37 BS11 37 0.06 150 -200 60-80 10000 0.08 150 -200 60-80 20000... gravity (25°C) Flexural strength 23OC 200°C Flexural modulus 23°C - 14 000 Ibf/in2 ( 97 MPa) 5000 Ibf/in2 (35 MPa) D .79 0 1.8 X 1@1bf/in2 12400MPa 0.9 X lOhlbf/in2 6200 MPa 200°C Tensile strength 23°C 200°C Dielectric constant 10'-IO6Hz Power factor 10'-106Hz 1.65 D .79 0 D.651 D.652 4400 Ibf/inz (30 MPa) 1300 Ibf/in2 (9 MPa) D .150 3.6 D 1 50 -0.005 Miscellaneous applications Like the fluids, the silicone resins... replaced the older traditional materials such as soap Similar fluids have also been found to be of value in the die-casting of metals Silicones have not found extensive application in the moulding of thermosetting materials since the common use of plated moulds and of internal lubricants in the moulding power obviate the need Their use has also been restricted with thermoplastics because of the tendency... laminates and 25-35% for low-pressure laminates The pieces of cloth are then plied up and moulded at about 170 °C for 30-60 minutes Whilst flat sheets are moulded in a press at about 1000 lbf/in2 (7 MPa) pressure, complex shapes may be moulded by rubber bag or similar techniques at much lower pressures ( -15 lbf/in2) (0.1 MPa) if the correct choice of resin is made A number of curing catalysts have been used,... of less than 0.5% after 24 hours at 150 °C 29.4.2 General Properties As a class dimethylsilicone fluids are colourless, odourless, of low volatility and non-toxic They have a high order of thermal stability and a fair constancy of physical properties over a wide range of temperature ( -70 °C to 200°C) Although Silicone Fluids 825 fluids have prolonged stability at 150 °C they will oxidise at 250°C with... dimethylsilicone fluids are summarised in Table 29.2 1 1.04 0.818 1.382 Value of n Viscosity (centistokes) Specific gravity d2525 Refractive index nDZ5 3 2.06 0. 871 1.390 6 3.88 0.908 1.395 14 10 0.9 37 1.399 90 100 0.965 1.403 350 lo00 0. 970 1.404 210 350 0.969 1.403 Barry" has shown that for linear dimethylsilicones the viscosity (q) in centistokes at 25°C and the number ( n ) of dimethylsiloxy groups... introduced commercially by the Olin Corporation in 1 971 as Dexsil The polymers have the essential structure SiR2- CB loH oC-(SiR2- 0-)x- - where CB,oHloC represents a rn-carborane group of structure shown in Figure 29 .7 Introduction of some vinyl groups in a side chain enables vulcanisation to take place It is claimed that when stabilised with ferric oxide the materials may be used operationally to 250°C and... catalysts used and the ambient conditions Typical catalysts include tin octoate and dibutyl tin dilaurate Addition-cured materials are particularly suitable for casting polyurethane materials, but require scrupulous cleanliness when processing since cure may be affected by such diverse materials as unsaturated hydrocarbon solvents, sulphur, organo-metallic compounds, plasticine and some epoxide resins . (1980) 3, 1 974 ; 4, 1 976 ; 5, 1 976 ; 6, 1 978 ; 7, 1 979 ), Technomics, Westport, Conn. Applied Science, London (1982) HOLDEN, G., and SCHROEDER, H. E., Hanser, Munchen (19 87) London. of new polymers of greater viscosity ( 375 - 475 cP) ( 37. 5- 47. 5 N s/m2) and generally easier handling qualities. Whilst patents (e.g. Ger. Pat. 19 27 776 ) describe polymeric blends of UF and. PALM, R., and SCHWENKE, w., Kunsroffe, 70 , 665 -71 (1980) MILLS, R., Kunstoffe, 77 , 1036-8 (19 87) LUDKE, H. Kunstoffe, 86, 155 6 -156 4 (1996) 28 Furan Resins 28.1 INTRODUCTION The