Polystyrene-stabilisation

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. 

Stabilisers. Stabilisers prevent deterioration of the polymer due to environmental factors. Antioxidants are added to ABS, polyethylene and polystyrene. Heat stabilisers are required in processing polyvinyl chloride. Stabilisers also prevent deterioration due to ultra-violet radiation. 

GC is extensively used to determine phenolic and amine antioxidants, UV light absorbers, stabilisers and organic peroxide residues, in particular in polyolefins, polystyrene and rubbers (cf. Table 61 of Crompton [158]). Ostromow [159] has described the quantitative determination of stabilisers and AOs in acetone or methanol extracts of rubbers and elastomers by means of GC. The method is restricted to analytes which volatilise between 160 °C and 300 °C without decomposition. A selection of 47 reports on GC analysis of AOs in elastomers (period 1959-1982) has been published... 

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]. 

In a review of the course and mechanism of the catalytic decomposition of ammonium perchlorate, the considerable effects of metal oxides in reducing the explosion temperature of the salt are described [1], Solymosi s previous work had shown reductions from 440° to about 270° by dichromium trioxide, to 260° by 10 mol% of cadmium oxide and to 200°C by 0.2% of zinc oxide. The effect of various concentrations of copper chromite , copper oxide, iron oxide and potassium permanganate on the catalysed combustion of the propellant salt was studied [2], Similar studies on the effects of compounds of 11 metals and potassium dichromate in particular, have been reported [3], Presence of calcium carbonate or calcium oxide has a stabilising effect on the salt, either alone or in admixture with polystyrene [4],... 

Figure 2.17 Pair potentials calculated for 50 nm polystyrene particles in 0.1 moldm 3 electrolyte and with a -potential of —30mV. Curve a is the result for a simple polystyrene surface and curve b was calculated from the model of a 1 nm surfactant layer so that the -potential is taken as occurring at the outer edge of the adsorbed layer. A maximum in the potential of 8kBT is insufficient to provide long-term stability and the curves clearly shows how electrosteric stabilisation can achieve this...

The idea of the preparation of porous polymers from high internal phase emulsions had been reported prior to the publication of the PolyHIPE patent [128]. About twenty years previously, Bartl and von Bonin [148,149] described the polymerisation of water-insoluble vinyl monomers, such as styrene and methyl methacrylate, in w/o HIPEs, stabilised by styrene-ethyleneoxide graft copolymers. In this way, HIPEs of approximately 85% internal phase volume could be prepared. On polymerisation, solid, closed-cell monolithic polymers were obtained. Similarly, Riess and coworkers [150] had described the preparation of closed-cell porous polystyrene from HIPEs of water in styrene, stabilised by poly(styrene-ethyleneoxide) block copolymer surfactants, with internal phase volumes of up to 80%. 

Recent studies in our laboratory (3) using polystyrene latex dispersions stabilised by the above "comb" dispersing agent have shown that polymers such as poly(ethylene oxide) induce wealc flocculation above a certain critical concentration of free polymer which was dependent on the molecular weight of the chain. 

The technique involves first producing a seed latex by emulsifier-free emulsion polymerisation. A polystyrene latex of about 1 pva diameter is usually used. The seed particles are initially swollen using a microemulsion of a free radical initiator and a low molecular weight activating solvent , such as dibutyl phthalate, emulsified in water by sonication using sodium dodecyl sulphate as stabiliser. The seed... 

A number of reviews on polymer photostabilisation have appeared " as well as the stabilisation of ceramic paints clearcoats, wood finishes and car body paints . Hindered piperidine stabilisers (HALS) have also been reviewed in depth " and the surface stabilisation of polystyrene covered . ... 

Model suspoemulsions of polystyrene latex (mean volume diameter 1.84 pm) were prepared using the surfactant-free method, and then stabilised with Synperonic PE P94 (an ABA block of PEO-PPO-PEO with 47 PPO units and 42 PEO units) and isoparaffinic O/W emulsion (stabilised with Synperonic PE L92 with 47 PPO units and 16 PEO units). 

Model Suspoemulsion of Polystyrene Latex and IsoparafRnic Oil stabilised with Synperonlc PE (PEO-PPO-PEO A-B-A Block Copolymer)... 

A series of well-defined A-B block copolymers of polystyrene-block-polyethylene oxide (PS-PEO) were synthesised [6] and used for the emulsion polymerisation of styrene. These molecules are ideal as the polystyrene (PS) block is compatible with the PS formed, and thus it forms the best anchor chain. The PEO chain (the stabilising chain) is strongly hydrated with water molecules and extends into the aqueous phase where it forms the steric layer necessary for stabilisation. 

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