EMBRITTLEMENT AND REJUVENATION OF BACTERIAL POLY[(R)-3-HYDROXYBUTYRATE]

A major drawback of bacterial poly[(R)-3-hydroxybutyrate] (PHB) is its intrinsic brittleness. Although as-moulded PHB shows ductile behaviour, upon storage at ambient temperature a detrimental ageing process embrittles the material and limits its application possibilities. This remarkable embrittlement is delineated in the present study and could be attributed to progressive crystallization. Up to now, most attempts to improve the mechanical properties of PHB have focussed on incorporating comonomers, such as 3-hydroxyvalerate, but then the mechanical improvements are at the expense of the production costs. Alternatively, we found that by using a simple annealing treatment PHB homopolymer can be toughened while subsequent ageing is prevented to a large extent.