The toughening effect of a small amount of poly(ε-caprolactone) on the mechanical properties of the poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)/PCL blend

To improve the mechanical properties of bacterial poly(3-hydroxybutyrate) [P(3HB)] and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(3HB-co-3HH)], the materials were blended with poly(epsilon-caprolactone) (PCL). The P(3HB-co-7 mol% 3HH) cast film and the P(3HB-co-11 mol% 3HH) melt-pressed film show brittleness after aging, although unaged samples show ductile behavior. However, the addition of a small amount of PCL was found to greatly improve the toughness of the P(3HB-co-7 mol% 3HH) cast film and the P(3HB-co-11 mol% 3HH) melt-pressed film. Reduction in the whitening of the elongated P(3HB-co-7 mol% 3HH) film by blending with PCL indicates that a transition in the deformation mechanism of the film was induced. In P(3HB-co-11 mol% 3HH)/PCL melt-pressed films, a cloud of craze initiation created by the dispersed PCL was observed. Differential scanning calorimetry thermograms and scanning electron microscopy images of the blended films indicated that finely dispersed PCL, the crystallization of which was restricted, and/or voids formed during preparation contribute to the delocalization of the applied stress and ductile deformation of P(3HB-co-3HH) films. In conclusion, the transition in the deformation mechanisms and the delocalization of the applied stress are expected to be important for enhancing the toughness of aged P(3HB-co-3HH)s, and blending with a small amount of PCL is a simple way to improve the mechanical properties of P(3HB-co-3HH) s. Polymer Journal (2011) 43, 484-492; doi:10.1038/pj.2011.12; published online 23 February 2011