Impact strength polymerisation processes

Today the common practice is first to dissolve the rubber in the styrene monomer and then to polymerise the styrene in the usual way. By this process the resultant blend will contain not only rubber and polystyrene but also a graft polymer where short styrene side chains have been attached to the rubber molecules. This gives a marked improvement in the impact strengths that can be obtained. 

PHA polymers are thermoplastics that are soluble in halogenated solvents such as chloroform and dichloromethane. Depending on their chemical composition (homo- or copolymer, the hydroxy fatty acids contained), they differ in their physical properties, eg, ductility and elasticity. PHA can be processed on conventional processing equipment. The processability as well as some mechanical properties like impact strength and flexibility can improve when a monomer/comonomer with longer aliphatic chain is used in polymerisation. One of the commercially available types of PHA is polyhy-droxybutyrate (PHB). PHB is similar to polypropylene in some characteristics like melting temperature, tensile strength, moismre resistance, and odour barrier properties (Pouton and Akhtar, 1996). 

BR is a raw material (a raw rubber) which has two main markets the rubber goods industry and the plastics producers. The former blend it with other types of rubber and mix it with reinforcing fillers, oil and vulcanising chemicals to produce rubber compoimds. The rubber compound is then shaped and vulcanised under heat and pressure to produce the finished rubber article. The latter incorporate a small amount (5 to 8 %) during their polymerisation processes to enhance the impact strength of the finished plastic. The most widely produced material is high impact polystyrene, HIPS. 

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