Plasticised PVC materials

In many international museum collections, degradation of plasticised PVC materials, in the form of clothing and footwear, furniture, electrical insulation, medical equipment, housewares, vinyl records and cassette tapes, toys and packaging materials used to store objects, has been detected as early as five years after acquisition. 

Degradation of plasticised PVC materials in museums is frequently observed as migration of the plasticiser from the bulk phase to surfaces. From there, plasticiser evaporates at a rate dependent on its vapour pressure. This process may be detected as a tacky feel to the plastic, increasing brittleness and subsequent discolouration of the PVC polymer itself. The mechanism by which... 

The very low density materials (VLDPEs) introduced in the mid-1980s are generally considered as alternatives to plasticised PVC (Chapter 12) and ethylene-vinyl acetate (EVA) plastics (see Chapter 11). They have no volatile or extractable plasticisers as in plasticised PVC nor do they have the odour or moulding problems associated with EVA. Whilst VLDPE materials can match the flexibility of EVA they also have better environmental stress cracking resistance, improved toughness and a higher softening point. 

A substantial part of the market for the ethylene-vinyl acetate copolymer is for hot melt adhesives. In injection moulding the material has largely been used in place of plasticised PVC or vulcanised rubber. Amongst applications are turntable mats, base pads for small items of office equipment and power tools, buttons, car door protector strips and for other parts where a soft product of good appearance is required. Cellular cross-linked EVA is used in shoe parts. 

Until comparatively recently the bulk of general purpose phthaiate plasticisers have been based on the branched alcohols because of low cost of such raw material. Suitable linear alcohols at comparative prices have become available from petroleum refineries and good all-round plasticisers are produced with the additional advantage of conferring good low-temperature flexibility and high room temperature resistance to plasticised PVC compounds. A typical material (Pliabrac 810) is prepared from a blend of straight chain octyl and decyl alcohols. 

In plasticised PVC the main function of a lubricant is to prevent sticking of the compound to processing equipment. This is brought about by selecting a material... 

Plasticised PVC, referred to below as PPVC, is used in a wide variety of applications. Originally a substitute for natural rubber when the latter material became difficult to obtain during World War II, it is frequently the first material to consider where a flexible, even moderately rubbery, material is desired. This arises from the low cost of the compounds, their extreme processing versatility, their toughness and their durability. 

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. 

It may also be argued that plasticised PVC may be considered as a thermoplastic elastomer, with the polymer being fugitively cross-linked by hydrogen bonding via the plasticiser molecules. These materials were, however, dealt with extensively in Chapter 12 and will not be considered further here. The ionomers are also sometimes considered as thermoplastic elastomers but the commercial materials are considered in this book as thermoplastics. It should, however, be kept in mind that ionic cross-linking can, and has, been used to fugitively crosslink elastomeric materials. 

If polypropylene is too hard for the purpose envisaged, then the user should consider, progressively, polyethylene, ethylene-vinyl acetate and plasticised PVC. If more rubberiness is required, then a vulcanising rubber such as natural rubber or SBR or a thermoplastic polyolefin elastomer may be considered. If the material requires to be rubbery and oil and/or heat resistant, vulcanising rubbers such as the polychloroprenes, nitrile rubbers, acrylic rubbers or hydrin rubbers or a thermoplastic elastomer such as a thermoplastic polyester elastomer, thermoplastic polyurethane elastomer or thermoplastic polyamide elastomer may be considered. Where it is important that the elastomer remain rubbery at very low temperatures, then NR, SBR, BR or TPO rubbers may be considered where oil resistance is not a consideration. If, however, oil resistance is important, a polypropylene oxide or hydrin rubber may be preferred. Where a wide temperature service range is paramount, a silicone rubber may be indicated. The selection of rubbery materials has been dealt with by the author elsewhere. ... 

Infrared spectroscopy is a major tool for polymer and rubber identification [11,12]. Infrared analysis usually suffices for identification of the plastic material provided absence of complications by interferences from heavy loadings of additives, such as pigments or fillers. As additives can impede the unambiguous assignment of a plastic, it is frequently necessary to separate the plastic from the additives. For example, heavily plasticised PVC may contain up to 60% of a plasticiser, which needs to be removed prior to attempted identification of the polymer. Also an ester plasticiser contained in a nitrile rubber may obscure identification of the polymer. Because typical rubber compounds only contain some 50% polymer direct FUR analysis rarely provides a definitive answer. It is usually necessary first... 

The enforcement in Denmark of EU Directives on food packaging materials is discussed. Enforcement activities considered include studies of total migration from food contact materials, migration from kitchen-and tableware made of melamine plastics and migration of di(2-ethylhexyl)adipate from plasticised PVC films. Activities which need to be undertaken to increase the effectiveness of enforcement activities in the field of migration are described, including development of selfinspection programmes in industry, European network of enforcement, more rapid analysis and provision of information to the consumer. 2 refs. 

In the wall thickness fluctuations up to 5 % may occur. As a result of the uneven temperature in the molten polymer during rotation, and also by the not always exactly reproducible rate of cooling, deviations in the dimensions of the finished product may amount to 5 %. Requirements are, that the materials can be molten completely, that the melt is sufficiently low-viscous, and that the molten polymer does not degrade too rapidly. Besides plasticised PVC, HDPE and LDPE are often used, as well as copolymers of PE such as EVA (ethylene - vinyl acetate copolymerj.Because the shear stresses in this process are extremely low, a narrow molar mass distribution is to be recommended, as discussed in 5.4. Cycle times vary between 3 and 40 minutes, dependent on the wall thickness. Cycle times can be reduced considerably by using machines with multiple moulds, since the cycle time... 

Since infrared (IR) spectroscopy is one of the most widely used techniques for the identification of materials at the molecular level, it has been extensively used to characterise the rubbery materials. In this chapter the rubbery materials encompass PE, plasticised PVC, thermoplastic elastomers and ionomers. 

Different types of interaction in rubbery materials, which include PE, plasticised PVC, TPE, ionomeric polyblends, and blends of plastics and rubbers can be characterised by different types of IR spectroscopic techniques. 

Castle, L., Mayo, A, Gilbert, J., 1990, Migration of epoxidised soya bean into foods from retail packaging materials and from plasticised PVC film used in the home. Food. Add. Contam. 7 (1) 29-36. 

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