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applications. Wu et al. (2009) studied cellulose/starch/lignin films and found that the content of both lignin and cellulose influence the mechanical properties of the film. Unmodified lignin decreased the mechanical properties when blended together with thermoplastics (Chung et al. 2013). More specifically, lignin addition into polyolefins decreased the elongation at break, while had no effect on tensile strength. Blends with more compatible polymers, e.g. , polyesters, can result in enhanced strength, stress at yield, and Young’s modulus (Pouteau et al. 2004). Modifications, such as esterification, etherification, and graft polymerization, enhance several properties of lignin/thermoplastics – dispersions (Chung et al. 2013). Likewise, the usage of additives ( e.g. , plasticizers) have been reported to improve the reinforcing effect of lignin (Pouteau et al. 2004). BARRIERS BASED ON MICROORGANISM-DERIVED BIOPOLYMERS PLA, PBS, and PHAs are all biodegradable thermoplastic polyesters, and each of them can be produced from biomass-based raw materials by fermentation (Gorrasi et al. 2008; Xu and Guo 2010; Bhatia et al. 2012; Bugnicourt et al. 2014; Harmsen et al. 2014). These potential biopolymers ARE bio-based alternatives to petroleum-based thermoplastics (Bhatia et al. 2012; Bugnicourt et al. 2014; Rastogi and Samyn 2015). All of these biopolymers are found in industrial scale production (Rizzarelli and Carroccio 2009; Rabu et al. 2013; Bugnicourt et al. 2014). The production routes of these materials are presented in Fig. 4. Different blends and composites have been studied both in order to improve mechanical, chemical, and thermal properties and to reduce the cost of these polymers (Dufresne et al. 2003; Lin et al. 2011; Bhatia et al. 2012; Gorrasi et al. 2014). In the following sections, PLA, PBS, and PHAs are introduced, together with their different blends and composites. Polylactide Polylactide (PLA) is a broadly available aliphatic and thermoplastic biopolyester (Liu 2006; Rhim et al. 2009; Bugnicourt et al. 2014; Rastogi and Samyn 2015) that was commercialized in the early 90s (Tang et al. 2012; Rabu et al. 2013). PLA is obtained from lactic acid, which is a bacterial fermentation product of starch-rich products, e.g. , corn, sugarcane (Yu et al. 2006; Gorrasi et al. 2008; Rhim et al. 2009; Papageorgiou et al. 2010; Tang et al. 2012; Rabu et al. 2013; Reddy et al. 2013), sulphite liquors, agro- wastes (Rastogi and Samyn 2015), or food industry wastes (Andersson 2008). It has been reported that with 1.6 kg of sugars, 1.0 kg of PLA can be obtained (Reddy et al. 2013). Lactic acid (LA) is the building unit of PLA and it exists as L- and D-lactic acid enantiomers. The most common stereoisomers of PLA are poly(L-lactide) (PLLA), poly(D-lactide) (PDLA), and poly(DL-lactide) (PDLLA) (Farah et al. 2016). The PLA can be produced via lactic acid polycondensation or via lactide ring-opening polymerization (Rhim et al. 2009; Rabu et al. 2013). The principles for the production process are presented in Fig. 4. Commercial, high molecular weight PLA is produced via the ring-opening method (Andersson 2008; Papageorgiou et al. 2010). PLA is biodegradable yet also compostable and recyclable (Andersson 2008; Picard et al. 2011; Golden and Handfield 2014). PLA has good mechanical (Yu et al. 2006; Arora and Padua 2010; Papageorgiou et al. 2010; Bhatia et al. 2012) and moisture
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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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