The Stabilization of Acrylonitrile-Butadiene-Styrene Copolymers Against Heat and Light

Abstract

The thermal and photo-oxidative stability of acrylonitrilebutadiene- styrene copolymer (ABS) has been investigated in the presence of various stabilizers representative of two different mechanisms of antioxidant action; chain breaking and preventive. When present in the polymer as additives bis (3,5 ditert butyl 4 hydroxybenzyl) monosulphide and 4-benzoyl 3 hydroxyphenyl o-ethyl thioacid esters were more effective thermal and UV stabilizers than any commercially available stabilizers. Furthermore, they showed synergistic behaviour as photo-stabilizers. Stabilizers containing the above functional groups have been bound to ABS through the thiol group by free radical addition to the double bond. The antioxidant 3,5 ditert-butyl-4-hydroxy benzylmercaptan was found to inhibit adduct formation in the presence of residual monomer (styrene) remaining from the polymer manufacture. This has been overcome by (a) removing the monomer before reaction, (b) by using a water soluble azo-type initiator. The mechanism of. the inhibition process has been shown to be due to the oxidiation products derived from the antioxidant. The adducts were effective both thermal and photo-oxidative stabilizers for ABS and their effectiveness was not modified by solvent extraction of the polymer. Furthermore, ABS obtained by mixing latices containing the antioxidant and UV stabilizer adducts showed synergistic behaviour towards photo-oxidation. It. was found that latex—-bound antioxidants could be produced in concentrated form and that these, when diluted to normal concentration with unstabilized ABS latices were as effective as those obtained by reacting with total latices at lower concentrations.