Increasing Cell Homogeneity of Semicrystalline, Biodegradable Polymer Foams With a Narrow Processing Window via Rapid Quenching

Biodegradable polymer foams have the potential to lessen environmental burdens caused by traditional petroleum-based plastics. One such family of alternatives, poly(hydroxyalkanoates), have tremendous potential in this regard, but have poor foamability owing to a narrow thermal processing window. Of particular interest for this study is poly(hydroxybutyrate-co-valerate) (PHBV). Two chemical blowing agents were tested for their ability to create low density, closed-cell PHBV foams, and it is shown here that sodium bicarbonate decreases the bulk density compared to azodicarbonamide blowing agents but with the loss of a closed-cell structure. To counter this, PHBV foams were quenched with water, leading to faster crystalline formation in the polymer matrix. As a result of faster solidification, a more uniform, closed-cell bubble morphology was entrapped in the final foam product, leading to high-expansion ratio foam. Thus, PHBV, a material with poor melt strength, has enhanced melt properties for foaming applications when crystallization is induced on the same time scale as cell coalescence. POLYM. ENG. SCI., 54:2877-2886, 2014. (c) 2014 Society of Plastics Engineers