Blends stabilisers

A high-impact polystyrene (polystyrene SBR blend) may have seven times the impact strength of ordinary polystyrene, but about half the tensile strength, a lower hardness and a softening point some 15°C lower. Because of the rubber content there may be a reduction in light and heat stability and stabilisers are normally incorporated. 

The use of stabilisers (antioxidants) may, however, have adverse effects in that they inhibit cross-linking of the rubber. The influence of phenolic antioxidants on polystyrene-SBR alloys blended in an internal mixer at 180°C has been studied. It was found that alloys containing 1% of certain phenolic antioxidants were gel-deficient in the rubber phase.The gel-deficient blends were blotchy in appearance, and had lower flow rates compared with the normal materials, and mouldings were somewhat brittle. Substantial improvements in the impact properties were achieved when the antioxidant was added later in the mixing cycle after the rubber had reached a moderate degree of cross-linking. 

P.V.C. plastisols P.V.C. plastisols are liquids which contain little or no solvent/diluent. They consist of a blend of polyvinyl chloride (p.v.c.) resins, plasticisers, stabilisers, viscosity depressants, pigments and sometimes fillers. 

For general aspects on sonochemistry the reader is referred to references [174,180], and for cavitation to references [175,186]. Cordemans [187] has briefly reviewed the use of (ultra)sound in the chemical industry. Typical applications include thermally induced polymer cross-linking, dispersion of Ti02 pigments in paints, and stabilisation of emulsions. High power ultrasonic waves allow rapid in situ copolymerisation and compatibilisation of immiscible polymer melt blends. Roberts [170] has reviewed high-intensity ultrasonics, cavitation and relevant parameters (frequency, intensity,... 

Whatever the approach, the result is a difficult-to-analyse system. Such options suit polymer producers better than additive suppliers. Aromatic polymers (PPO) have been mentioned as char-forming FRs. Polymeric UV absorbers, blended in proper proportions with commercial plastics, have potential use as stabilisers for fibres, films and coatings. Several monomeric stabilisers containing a vinyl group were homopolymerised and used as stabilisers for PE, PVC, acrylates, polystyrene, cellulose acetate and several vinyl polymers [55]. 

Other noteworthy developments are carrier materials, such as Stamypor (DSM) and Accurel (AKZO), for production of concentrates with liquid or low-melting additives and reactants (see Section 1.2.1). The biggest growth area for additive carriers is coming from liquid peroxides and silanes, due to related health and safety issues for shopfloor staff. The NOR HALS stabiliser Tinuvin 123-S (a non-interacting, low-MW liquid) for TPO, PP and some blends is delivered in a solid carrier (Accurel). 

Heat stabilisers for PVC act by HC1 scavenging and include organotins, mixed metal salt blends, and lead compounds. The latter account for nearly 64 % of volume (in 1994), followed by barium/cadmium and organotin compounds. Cadmium-based heat stabilisers are rapidly being replaced due to environmental concerns. Barium/zinc and calcium/zinc compounds show a high growth rate. It is expected that methyltin stabilisers will soon dominate the growing PVC pipe market. 

Desai et al. [86] reported on the photolytic degradation of the anti-viral, sorivudine, which formed the inactive Z-isomer. On the basis of extensive dmg-excipient compatibility studies it was found that the incorporation of iron oxide pigments into the blends (direct compression or wet granulated) stabilised the dmg to photodegradation indeed, so much so that the tablet was found not to require a film coat. The data are summarised in Table 2.6. 

Malic acid finds use in a variety of products, mostly in fruit-flavoured carbonates. It is the preferred acidulant in low-calorie drinks and in cider and apple drinks, enhancing flavour and stabilising colour in carbonated and non-carbon-ated fruit-flavoured drinks. Malic acid may also be used to mask the off-taste of some sugar substitutes. Blends of malic and citric acids are said to exhibit better taste characteristics than either acidulant individually. 

Figure 5.11 Infrared spectra of 50/50 PVC/NBR blends after mixing (a) for 5 minutes, (b) for 60 minutes (stabilised with tribasic lead sulfate) at 180 °C, (c) at 160 °C, (d) at...

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