Biopolymers and Bioplastics

Biography

Biography: Warren Grigsby

Abstract

Substituting synthetic plastic additives with bio-derived materials has potential to improve plastic sustainability credentials. Esterified and native condensed tannins from Pinus radiata bark have been explored as functional plastic additives in petrochemical and biodegradable plastics. The presence of longer alkyl chain hexanoate esters promoted tannin miscibility in plastics whereas short chain acetate esters tended to remain as discrete domains, acting as fillers in the processed plastics. The presence of tannin esters at typical plastic additive loadings did not alter plastic mechanical properties, but greater (up to 10%) loadings can reduce both flexural and tensile properties. In assessing the functional equivalence provided by tannin additives, it was demonstrated that tannin esters inhibit the effects of UV and oxidative degradation. In polypropylene the use of tannin hexanoate acetate had greater UV inhibition efficacy than a typically used synthetic UV stabiliser at comparable loading. The tannin-additives likely provide a stabilising role through inhibiting UV penetration into the plastic, with analysis suggesting the tannin moiety itself was sacrificial and preferentially degrading. The degree of tannin esterification and retention of antioxidant capacity was crucial to inhibiting oxidative degradation and reducing plastic aging. Soil composting also revealed the tannin esters do not impact degradation of biodegradable aliphatic polyesters.