The Chemical and Mechanical Properties of Thiol Modified ABS

Abstract

The oxidative degradation (photo and thermal) of unstabilised and stabilised acrylonitrile-butadiene-styrene graft copolymer (ABS) has been studied using a viscoelastomeric technique (Rheovibron), falling weight impact tester and infra-red spectrometry to measure mechanical and chemical changes occurring in the polymer. Linear correlations were obtained between the loss of unsaturation in the polybutadiene segment of the polymer and loss of impact resistance. The parameters were also correlated with decrease in tan δ at -80°C. Stabilisers containing the thiol group, notably 3,5-di-tert-butyl-4-hydroxybenzyl mercaptan (BHBM), an antioxidant, and 4-benzoyl-3-hydroxyphenyl-1-O-ethyl thioglycollate (EBHPT), a UV stabiliser, have been bound to ABS in latex and during processing in a high temperature mixing operation through the thiol group by free radical addition to the double bond. The bound stabilisers produced in concentrated form (masterbatches) have been diluted to normal concentration (1%) with unstabilised ABS and their stabilising properties followed by the above techniques. The adducts were effective thermal and photo-oxidative stabilisers and their effectiveness was not substantially reduced by solvent extraction of the polymer. The presence of bound stabilisers in normal concentration did not affect the initial mechanical properties of ABS compared with unstabilised ABS. Furthermore, ABS containing synergistic combinations of the two stabilisers showed remarkable synergism in stabilising the mechanical properties of ABS towards photodegradation.