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PEER-REVIEWED REVIEW ARTICLE
Tang et al. 2012; Arrieta et al. 2014a; Bugnicourt et al. 2014; Follain et al. 2014; Rastogi and Samyn 2015) and its copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) (Pardo Ǧ Ibáñez et al. 2014). PHAs have been shown to be renewable and biodegradable under anaerobic and aerobic environments and are compostable biopolymers (Bugnicourt et al. 2014). PHA is a promising oxygen, water vapor, and UV-light barrier material (Bugnicourt et al. 2014; Rastogi and Samyn 2015). Compared to PLA, PHAs provide a better UV light barrier (Arrieta et al. 2014a). In addition, PHAs display better WVTR properties compared to other common extrudable biopolymers, such as PLA and PBS (Kuusipalo et al. 2008). Furthermore, there have been studies about the biodegradability of PHAs compared to other biopolymers, and this order was reported as PHB > PBS > PLA (Bugnicourt et al. 2014). PHAs display good film formability and coating ability (Tang et al. 2012). PHAs have been processed by several different techniques, such as extrusion, injection (Bugnicourt et al. 2014; Koller 2014) and compression molding (Rastogi and Samyn 2015), thermoforming (Koller 2014), solvent and spin casting (Thellen et al. 2008). PHBV-coated paperboards have been reported to handle creasing and to be heat sealable to itself and to paperboard within a temperature range of 190 °C to 230 °C (Andersson 2008). PHAs have been utilized as surface-sizing agents on paper with promising results on mechanical properties and the water resistance of the paper (Rastogi and Samyn 2015). PHB has also been used in other applications, e.g. , food and other types of packaging (Weber et al. 2002), in the manufacture of ropes, bank notes, and cars (Reddy et al. 2013) and in biomedical products (Misra et al. 2006). Challenges of PHAs involve, for example, the production cost (Valentin et al. 1999; Weber et al. 2002; Dufresne et al. 2003; Liu 2006; Andersson 2008; Gandini 2008; Kuusipalo et al. 2008; Mousavioun et al. 2010; Tang et al. 2012; Bugnicourt et al. 2014), low acid and base resistance, poor thermal processability (Rastogi and Samyn 2015), and the fact that the raw materials that are currently used compete with food sources (Bugnicourt et al. 2014). The PHAs have weak thermal stability above the melting point (~175 °C), although this aspect can be controlled by using additives (Johansson et al. 2012). Due to PHAs’ tendency to be brittle, they are often blended with additives or other polymers (Bugnicourt et al. 2014). Moreover, there is potential for improvement in terms of the gas barrier properties of PHAs (Andersson 2008; Tang et al. 2012). PHAs have been blended with other polymers and fillers to enhance their properties and to reduce the cost (Dufresne et al. 2003; Yu et al. 2006; Mousavioun et al. 2010). PHAs/filler composites Sanchez Ǧ Garcia and Lagaron (2010) investigated PHBV/organomodified clay composite. Compared to neat PHBV, its composite with 5 wt% clay resulted in a reduction of permeability levels to water (by 76%), to oxygen (by 32%), and to oil (limonene) (by 78%). The PHB/nanoclay composites have been studied but challenges still exist in the formation of the composite material due to PHB degradation behavior and instability. Improvements in mechanical and thermal properties have been achieved by combining nanoclay with PHB (Tang et al. 2012). Pardo Ǧ Ibáñez et al. (2014) improved the barrier properties of PHBV by adding keratin fibers. The PHBV with 1.0 wt% of keratin fiber blend improved water, limonene, and oxygen barrier properties as well as elastic modulus compared to pure PHBV. Dufresne et al. (2003) applied cellulose flour (up to 70 wt%) as reinforcement filler into a PHBV polymer matrix in order to reduce its price while still maintaining its
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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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