Crystallization, Morphology, and Enzymatic Degradation of Polyhydroxybutyrate/Polycaprolactone (PHB/PCL) Blends

Abstract

Two types of mixtures were prepared by solution blending: high molecular weight polyhydroxybutyrate (PHB)/poly(ε‐caprolactone) (PCL) and PHB/low molecular weight chemically modified PCLs (mPCL). The morphology, crystallization, and enzymatic degradation of the blends were studied by differential scanning calorimetry, polarized light optical microscopy, scanning electron microscopy, 1H NMR, and weight loss measurements. In addition, enzymatic degradation studies were performed by an exposure to Aspergillus flavus. High molecular weight PHB/PCL blends were found to be immiscible in the entire composition range. Phenomena such as PCL fractionated crystallization and a decrease in PHB nucleation density were detected. When PHB was blended with mPCLs, the blends were partially miscible; two phases were formed, but the PHB‐rich phase exhibited clear signs of miscibility through a depression of both the Tm and the Tg of the PHB component (which was stronger with lower molecular weight mPCL), and an increase in the growth rate of PHB spherulites in the blends as compared to neat PHB or to the PHB component in the PHB/PCL blends. The biodegradation by a exposure to A. flavus showed that the blends are synergistically attacked in comparison to the homopolymers. Two factors may influence the improved degradation rate of the blends: the dispersion of the components and their crystallinity that was reduced in view of the fractionated crystallization and impurities transfer. In the case of the PHB/mPCL blends, the increased miscibility between the components caused a reduction in the degradation rate.magnified image

Hollow fibers made from a poly(3-hydroxybutyrate)/poly-ε-caprolactone blend

“…In Figure 2 the cooling cycle for the pure components in comparison to several blends is shown. These measurements are in complete accordance with the findings of Lovera et al [19]: PHB crystallization temperature is shifted from 116°C to significantly lower temperatures (varying from 101-104°C for G specimens) when blended with PCL, demonstrating the disturbing effect of PCL on the PHB crystallization. This may be explained by a transfer of heterogeneities from PHB to PCL during blending.…”

“…Soft PCL droplets within the PHB phase did not lower the rigidity [18]. Contrary to these findings Lovera et al [19] showed an increased elasticity. Even though the aim of this study was rather the investigation of the degradation behaviour than the improvement of the mechanical properties of these solution cast blends, tensile tests demonstrated that a PHB/PCL 70/30 blend shows elongation values at break of about 50% whereas pure PHB tolerates a strain of 10% only, for nondegraded state, respectively.…”

“…The aim of blending is to achieve intermediate or even superior properties while preserving the major characteristics of the pure components. PHB has been blended with several other biocompatible and biodegradable polymers, for instance poly(ethylene oxide), poly (L-lactide), poly (L-lactic acid) or poly-!-caprolactone (PCL), in order to improve weak properties [18,19]. PCL in particular, a synthetic semicrystalline polyester also belonging to the category of biocompatible and biodegradable polymers, is considered as an interesting blend component due to the high ductility and thermal resistance.…”

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

“…Due to its high ductility, PCL offers attracting properties to PHB as it can reduce its low intrinsic fragility. PCL shows good miscibility behavior with a wide variety of polymers [21]; nevertheless, immiscibility with PHB has been reported in the literature together with different studies to increase compatibility between them [12,13,22,23].…”

“…Despite this, its high production cost in comparison to commercial plastics, its high fragility due to high crystallinity, its relatively low melt viscosity as well as its thermal instability at moderate temperatures restrict its use [2,7]. With the aim of improving some of its properties PHB has been blended with several biodegradable polymers such as poly(lactic acid)-PLA [2,8], poly(pdioxanone)-PPD [5], poly(butylene succinate) (PBS) [9,10], poly(ethylene succinate) (PES) [11] or poly(caprolactone)-PCL [12][13][14].…”