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PEER-REVIEWED REVIEW ARTICLE
barrier properties (Weber et al. 2002; Liu 2006; Shalini and Singh 2009), great transparency and printability (Arrieta et al. 2014a), and it has shown promising results as a barrier of hydrophobic aroma compounds (Ducruet et al. 2011). PLA has great processability (Rhim et al. 2009; Arrieta et al. 2014a; Golden and Handfield 2014; Rastogi and Samyn 2015) with several techniques, for example by extrusion, thermoforming (Picard et al. 2011) and blow molding (Turalija et al. 2016); in addition to these applying techniques bar coating and solution casting have been used (Rastogi and Samyn 2015). Commercialized PLA is currently used for several packaging applications (Weber et al. 2002) and food service products (Andersson 2008; Fortunati et al. 2012; Rabu et al. 2013; Reddy et al. 2013). Challenges in PLA utilization include its high brittleness (Harada et al. 2007; Andersson 2008; Kuusipalo et al. 2008; Rhim et al. 2009; Vroman and Tighzert 2009; Ducruet et al. 2011; Bhatia et al. 2012; Ojijo et al. 2012; Tang et al. 2012; Chung et al. 2013; Gordobil et al. 2014), relatively low thermal stability (Yu et al. 2006; Rhim et al. 2009; Vroman and Tighzert 2009; Fortunati et al. 2012; Tang et al. 2012; Chung et al. 2013; Gordobil et al. 2014), poor gas barrier properties (Andersson 2008; Rhim et al. 2009; Arora and Padua 2010; Picard et al. 2011; Johansson et al. 2012; Chung et al. 2013; Gordobil et al. 2014; Rastogi and Samyn 2015), low resistance against UV light (Chung et al. 2013) and, relatively high cost (Arora and Padua 2010; Papageorgiou et al. 2010; Bhatia et al. 2012; Chung et al. 2013; Golden and Handfield 2014; Gordobil et al. 2014; Gorrasi et al. 2014). In addition, the degradation rate of PLA is rather slow (Golden and Handfield 2014; Farah et al. 2016; Turalija et al. 2016) and reactive side- chain groups are desirable for this purpose (Golden and Handfield 2014; Farah et al. 2016). In order to improve properties or to lower the price of the product, efforts have been made by blending and developing composites with other polymers and fillers (Bhatia et al. 2012) as well as other additives, such as thermal stabilizers and plasticizers (Gorrasi et al. 2014). For example, the brittleness of PLA has been addressed by plasticization, blending with tough polymers, and rubber toughening (Nampoothiri et al. 2010). Plasticization with 10-20 wt% ester-like plasticizers, such as poly(ethylene glycol, PEG), is effective but lowers the stiffness. When added up to 10 wt%, impact modifiers, such as ethylene-based copolymers, reduce the brittleness and maintain acceptable levels of stiffness. The main disadvantage has been their non-biodegradability, which have limited their use in large volumes. Biodegradable options for impact modifiers of PLA have been introduced, including poly(ε -caprolactone, PCL), poly(-butylene succinate, PBS) and poly(-R-3-hydroxybutyrate, PHB). The amount required to reach acceptable toughness has been reported to be 20 to 40wt% (Notta-Cuvier et al. 2014). The PLA based coatings are widely used in food-packaging where food safety is the major driver, for example, the migration of additives and toxicological properties of the blend need to be checked (Johansson et al. 2012). PLA/filler composites Many studies have involved layered silicates and reported to improve gas barrier properties by 50% to 60% (23 °C, RH 50%). However, for products with a high barrier demand, the improvement is not enough (Johansson et al. 2012). Several other filler options have been studied in addition to layered silicates, such as metal oxides ( e.g. , TiO 2 , ZnO), carbon nanotubes, and metal nanoparticles ( e.g. , Ag, Au) to achieve
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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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