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PEER-REVIEWED REVIEW ARTICLE
biodegradability. They observed poor interaction between the filler and PHBV, poor mechanical properties, and an increased degree in crystallinity. Nevertheless, the mechanical properties were enhanced at higher temperatures (above glass – rubber transition of PHBV). Dubief et al. (1999) studied nanocomposites, where the matrix polymer was poly( E -hydroxyoctanoate) (PHO) and nanofillers were starch microcrystals and cellulose whiskers. As a result, the addition of nanofillers enhanced the mechanical properties of the matrix polymer. The PHB has been used in plasticized PLA/CNC nanocomposite to increase the crystallinity of PLA. Consequently, the resulting composites were transparent and compostable (Arrieta et al. 2015). PHAs/biopolymer blends The mechanical and thermal properties as well as the processability of PHB were enhanced by low and high molecular weight plasticizers. By adding 20 wt % plasticizer (blend of dioctyl phthalate and di-2-ethylhexylphthalate), Erkske et al. (2006) achieved enhanced strength, elongation, and decreased brittleness. In addition, the melting temperature was lowered and, overall, the processing window was expanded considerably. The authors also added 20-60 wt% of starch to a PHB/ plasticizer blend. The elongation and strength properties of the composite decreased by increasing the starch content, whereas water vapor barrier increased (the optimal starch content 25 to 40 wt%). PHB has been blended with starch-adipate and grafted starch-urethane derivatives, resulting in limited mechanical properties (Tang et al. 2012). In another study, PHB was blended with starch acetate (SA) to change the crystallization, e.g. , lower temperature and enthalpy of non-isothermal crystallization of PHB. PHB/SA blends were found to be immiscible (Zhang et al. 1997). PHB was blended with cellulose propionate (CP), which resulted in higher ductility. The components of the PHB and CP blend were miscible. Likewise, a miscible blend of PHB and cellulose acetate butyrate (CAB) expanded the processability of the system by lowering the degree of crystallinity and the melting temperature. Additional studies have considered chitin and chitosan blended with PHB (Yu et al. 2006). Ikejima and Inoue (2000) compared PHB/chitin and PHB/chitosan blends and found an improvement in the biodegradability compared to neat chitosan and chitin. In addition, they observed that 25wt% PHB containing PHB/chitin blend degraded more rapidly than neat PHB or chitin as a result of decreased crystallinity of PHB. A PHB/poly(hydroxybutyrate-co-hydroxyhexanoate) (PHBHHx) blend was found to strengthen the elongation at break significantly when the PHBHHx content in the blend was increased from 40% to 60% (Zhao et al. 2003). The PLA/PHB films were brittle and rigid without plasticizing with, for example, poly(ethylene glycol) (PEG). The PLA/PHB based films in the Arrieta et al. (2014b) study displayed a compostable character. Abdelwahab et al. (2012) studied PLA/PHB blends with a plasticizer (5 wt% and 7 wt%). The elongation at break increased by the addition of the plasticizer. Olkhov et al. (2003) investigated PHB/poly(vinyl alcohol) (PVA) blends, where the PHB content varied from 0% to 100%. The highest water vapor permeability was observed when the PHB content was 40 wt%.
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Helanto et al. (2019). “ Bio-based barriers ,” B io R esources 14(2), Pg #s to be added.
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