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

Abstract

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(e-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 2011Keywords: blend; mechanical property; polyhydroxyalkanoate; poly(e-caprolactone); tensile test INTRODUCTION Several kinds of polyhydroxyalkanoates (PHAs) are biosynthesized by various bacteria as energy-storage materials. 1-5 They may be produced from renewable natural resources and have biodegradability. Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(3HB-co-3HH)] is part of the PHA family. 6 Doi et al. 7 have found that the content of the 3HH unit greatly affected the thermal and mechanical properties of P(3HB-co-3HH), but had little effect on the crystalline structure of 3HB-rich P(3HB-co-3HH)s because of the formation of the P(3HB)-homopolymer-type crystalline phase and the exclusion of the 3HH unit from the crystalline lattice. P(3HB-co-3HH) was found to show improved mechanical properties and thermal plasticity over those of known PHAs. 8,9 One of the notable advantages of P(3HB-co-3HH)s is their adjustable mechanical properties, from soft to hard material, depending on the comonomer-unit composition; this allows for the tailoring of P(3HB-co-3HH) to various societal applications, such as in green and sustainable polymeric materials.However, P(3HB-co-3HH) becomes brittle after aging at room temperature, thus restricting its practical applications. Although

Biocompatibility studies and characterization of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)/polycaprolactone blends

“…Katsumata et al27 similarly reported enhanced toughness in solvent cast PHBHHx/PCL blends with less than 20 wt % of PCL. Additionally, they suggested that addition of more than 20 wt % of PCL leads to a reduction in ductility due to the localization of stress around voids, which increase in size as more PCL is present.…”

Crystallization properties of polycaprolactone composites filled with nanometer calcium carbonate

“…Biodegradable polymers have been widely used for the production of bags, sacks, and food packaging because these polymers, prepared from renewable resources, can undergo biodegradation upon disposal. 6 Recently, a number of studies on the fabrication and characterization of inorganic particle-filled PCL composites have been made. Since the 1990s, PCL blend systems have been studied extensively; these have included poly(vinyl chloride)/PCL, 2 styrene acrylonitrile/PCL, 3 poly(butylene terephthalate)/PCL, 4 and polystyrene/PCL 5 binary blend systems, and poly(epsiloncaprolactone)/poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)/PCL blend systems.…”

Processing and characterization of binary poly(hydroxybutyrate) (PHB) and poly(caprolactone) (PCL) blends with improved impact properties

“…5 it is clearly detectable the generalized lack of interactions between the two polymers. With the aim of analyzing the surface morphology, a selective extraction process was done with acetone for a period of 24 h to selectively dissolve PCL [24]. In Fig.…”

“…Cryofractured samples of each blend were subjected to a selective extraction of PCL with acetone. Firstly, all samples were dried in an air circulation air oven at 40 ºC for 24 h and subsequently immersed in acetone for additional 24 h at room temperature to selectively remove the PCL portion which allows a better distinguish of the phase distribution in the blend [24]. Prior to sample observation of the samples before and after selective extraction, surfaces were covered with a thin layer of platinum in vacuum conditions with a sputter coater.…”