Unplasticised PVC

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. 

Twin-screw extruders now dominate the extrusion field, particularly because of their positive pumping action which is so important with PVC in powder form. 

Because PVC evolves corrosive hydrochloric acid on heating, care should be taken in the choice of metals for machine construction and the use of plating and/ or special steels is widely practised. 

Extrusion blow moulding of bottles has been successfully accomplished in reeent years by attention to the points mentioned above. It is to be noted here that UP VC has a much lower average specific heat between the proeessing temperature and room temperature than polyethylene and, being essentially amorphous, no latent heat of fusion. This leads to much less heat needing to be removed on cooling of mouldings and very short cycle times are possible. 

As explained in Section 12.4.1 a paste is obtained when the voids between particles are completely filled with a plasticiser so that the polymer particles are suspended in it. It has also been pointed out that to ensure a stable paste there is 

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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. 

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

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. 

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. 

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 ... 

Shear rate (s 1) Poly(methyl methacrylate) 230 °C Acetal copolymer 200 °C Nylon 6,6 285 °C Propylene-ethylene copolymer 230 °C Low-density polyethylene 170 °C Unplasticised PVC 150 °C... 

The characteristics of organic based heat stabilisers used in PVC are outlined and a comparison is made of the performance of an organic based stabiliser one-pack with a traditional lead stabiliser one-pack in the injection moulding of an unplasticised PVC pipe compound. Spiral flow and colour development during injection moulding are discussed and the results of customer trials on a large... 

A study was made of the ability of viscoelastic models to describe the measured material functions of unplasticised PVC during extrusion and to determine whether it was possible to reproduce the elastic properties of the large entrance pressure drop and small extrudate swell during the extrusion of PVC using a capillary rheometer. Models used were the Phan-Thien and Tanner model and the K-BKZ-Wagner model with a single exponential damping... 

A continuous extrusion process that introduces molecular orientation to an unplasticised PVC pipe is described. Pipe design is discussed and it is shown how the relevant property improvements are utilised. Materials costs are reduced while short and long term performance is enhanced offering an outstanding opportunity for PVC pressure piping. 

EFFECT OF PROCESSING CONDITIONS OF UNPLASTICISED PVC COMPOSITIONS ON POLYMER STRUCTURE... 

The volumetric, elastic and dynamic properties of internally and externally plasticised PVC were studied and compared with those of unplasticised PVC. The glass transition temperature for the plasticised samples was markedly lowered and this decrease was more important for the externally plasticised ones. The positions of the loss peaks from dielectric alpha-relaxation measurements confirmed the higher efficiency of the external plasticisation. However, the shape of the dielectric alpha-relaxation function was altered only for the internally plasticised samples. The plasticisation effect was linked with a decrease in the intensity of the beta-relaxation process but no important changes in the activation energy of this process were observed. The results were discussed. 47 refs. 

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