UNPLASTICISED

In the case of a crystalline polymer the maximum service temperature will be largely dependent on the crystalline melting point. When the polymer possesses a low degree of crystallinity the glass transition temperature will remain of paramount importance. This is the case with unplasticised PVC and the polycarbonate of bis-phenol A. 

When dipoles are directly attached to the chain their movement will obviously depend on the ability of chain segments to move. Thus the dipole polarisation effect will be much less below the glass transition temperature, than above it Figure 6.4). For this reason unplasticised PVC, poly(ethylene terephthalate) and the bis-phenol A polycarbonates are better high-frequency insulators at room temperature, which is below the glass temperature of each of these polymers, than would be expected in polymers of similar polarity but with the polar groups in the side chains. 

Since the incorporation of plasticisers into a polymer compound brings about a reduction in glass temperature they will also have an effect on the electrical properties. Plasticised PVC with a glass temperature below that of the testing temperature will have a much higher dielectric constant than unplasticised PVC at the same temperature (Figure 6.6). 

Energy to break per unit width of sample. (In notched specimens this is taken as the energy to break unit width of notch. In this case the results are quoted in such units as ft lb per inch of notch or joules per millimetre. The values obtained depend on the notch width. For example, it has been found that on reducing the notch width from V" to X the impact strength of a polycarbonate increased by a factor of 5.4 and that of unplasticised PVC by 3.1.)... 

Flow properties of polyethylene have been widely studied. Because of the wide range of average molecular weights amongst commercial polymers the viscosities vary widely. The most commonly used materials, however, have viscosities lower than for unplasticised PVC and polyfmethyl methacrylate) and higher than for the nylons. 

In the case of unplasticised polymer the main concern is with control of gelation and ensuring processability and adequate stabilisation. The formulation selected thus depends almost as much on the actual processing equipment used as on the end-product. Formula 8 gives a typical rigid opaque formulation suitable for pipes and Formula 9 a transparent calendering compound. 

Unplasticised PVC Vinyl chloride-vinyl acetate copolymer (sheet) PVC + 50 p.h.r. DIOP... 

Figure 12.22. Effect of copolymerisation of vinyl chloride with other monomers on the properties of unplasticised compounds. (After Weldon )...

Due consideration of these principles has made it possible to process unplasticised PVC by all the standard melt processes, including injection moulding and bottle blowing, a state of affairs hardly conceivable in the 1950s. 

Unplasticised latexes will not form a coherent film on drying and about 25% plasticiser is required before such a film is produced. As with paste it is necessary to flux the compound at about 150-160% in order to produce a useful product. 

Over 80% of the market is accounted for by suspension homopolymer, 13% by emulsion and paste-forming homopolymer, and the rest is mainly bulk homopolymer and vinyl chloride-vinyl acetate copolymer. In Western Europe about two-thirds of consumption is in the field of unplasticised PVC. 

This chapter has so far dealt with the major fields of use of vinyl chloride polymers, namely plasticised PVC homopolymer, unplasticised PVC, including impact-modified grades, and copolymers particular based on vinyl acetate. There are, however, five particular special forms of vinyl chloride polymer which merit separate consideration, namely crystalline PVC, after-chlorinated PVC (often known as CPVC) and certain graft copolymers and two vinyl-chloride-based copolymers. 

Figure 14.6. Relation between tensile strength and degree of hydrolysis for unplasticised poly(vinyl alcohol) film. (After Davidson and Sittig )...

Blending of ABS with other polymers is not restricted to the aim of raising the distortion temperature. Blends with PVC are made for various purposes. For example, 80 20 ABS/PVC blends are used to produce fire-retarding ABS-type materials, as already mentioned, while 10 90 blends are considered as impact-modified forms of unplasticised PVC. ABS materials have also been blended with plasticised PVC to give a crashpad sheet material. 

Blending of ABS with an acrylic material such as poly(methyl methacrylate) can in some cases allow a matching of the refractive indices of the rubbery and glassy phases and providing that there is a low level of contaminating material such as soap and an absence of insoluble additives a reasonable transparent ABS-type polymer may be obtained. More sophisticated are the complex terpolymers and blends of the MBS type considered below. Seldom used on their own, they are primarily of use as impact modifiers for unplasticised PVC. 

Perhaps the greatest resistance to development with these materials is the strong competition offered by the clear impact-modified grades of unplasticised PVC which are generally less expensive. 

Some typical properties of polyester-glass laminates are given in Table 25.1. From these figures it will be seen that laminates can have very high tensile strengths. On the other hand some laminates made by hand lay-up processes may have mechanical properties not very different from those of thermoplastics such as the polyacetals and unplasticised PVC. 

The low-HV unplasticised grades are the most critical to process, requiring the higher processing temperatures. Conditions are slightly less critical with the higher HV and plasticised grades. 

Plastic pipes Pipes made from plastic materials such as unplasticised p.v.c.. Polythene, ABS and GRP are now widely used for carrying domestic cold water, wastes and rain water. Joining varies according to pipe diameter and service condition, but is generally relatively simple (see Section 18.6). 

Rod Anodes These consist of solid or copper-cored titanium rod, portions of which can be platinised. They range from 6 to 25 mm in diameter and are normally supplied pre-assembled in a steel or unplasticised p.v.c. mount ready for screwing into prepared bosses on the plant under protection. Electrical connections are made via cables in the usual way. The anodes are spaced to give even current distribution. 

Acrylic Sheet (e.g. Perspex) Acrylonitrile Butadiene Styrene Resins (1) Nylon 66 Fibre (m) Nylon 66 Plastics (m) PCTFE PTFE (n) PVDF (y) Rigid Unplasticised PVC Plasticised PVC ... 

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