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PEER-REVIEWED REVIEW ARTICLE
PLA/30 wt% flax fiber composites with different additives, e.g. , kraft lignin, have also been studied. Good impact strength was achieved with (NaOH-treated) flax fiber addition, further enhanced with < 3wt% addition of pine kraft lignin (however, higher addition levels weakened the mechanical properties of the composite) (Johansson et al. 2012). PLA/ biopolymer blends PLA’s crystallinity was increased by mixing 25 wt% of poly(hydroxybutyrate) (PHB) and 5 wt% CNC. In addition, PHB enhanced the oxygen and water barrier properties, although it simultaneously impaired the transparency of PLA (Arrieta et al. 2014a). PLA/starch blends have been a topic of study (Yu et al. 2006; Johansson et al. 2012; Tang et al. 2012). Starch is a renewable and biodegradable hydrophilic polymer, which has been a common material in bioplastics (Yu et al. 2006). In order to reduce price and to enhance biodegradability, the aim has been to blend PLA together with starch (Johansson et al. 2012; Tang et al. 2012). Several studies have been carried out with different starches and additives, such as native corn starch together with a plasticizer, corn starch vs. high-amylose corn starch and gelatinized starch with water/glycerol (Tang et al. 2012). About 30 wt% to 50 wt% starch has been blended with PLA, subsequently causing a reduction in mechanical properties, such as in tensile strength and strain at break (Johansson et al. 2012). The crystallization rate of PLA has been increased with talc (1 volume %) and with starch (1.0 to 40% volume) addition. However, there are challenges involving the hydrophobic nature of PLA and the hydrophilic nature of starch, thus causing weak cohesion to each other and resulting in poor properties without additives or compatibilizers (Yu et al. 2006). Blending of enantiomeric polymers was reported to enhance thermal properties. Blending poly(L-lactide acid) (PLLA) together with poly(D-lactide acid) (PDLA) improved thermal stability compared to PLLA or PDLA alone. They achieved a 50 °C higher melting temperature by making the blend of PLLA/PDLA (Yu et al. 2006). The L and D isomers also have an effect on the crystallinity and mechanical properties of the polymer. High crystallinity can be achieved with L-form and amorphousness with copolymers of D and L isomers (Andersson 2008). PLA has been blended and copolymerized with biodegradable poly(caprolactone) (PCL) to decrease brittleness and improve the mechanical properties (Tang et al. 2012), such as impact strength. The PLA-based urethane blend was reported to increase impact strength when used as an additive. In comparison, PLA/ poly(butylene adipate-co- terephthalate) (PBAT) enhanced impact strength when the concentration on PBAT was 20 wt%. Harada et al. (2007) mixed PLA with PBS (90/10 wt%) by using a reactive processing agent, lysine triisocyanate (LTI). As a result, the impact strength was enhanced, from 18 kJ/m 2 to 50-70 kJ/m 2 at a LTI loading of 0.5 wt% (Harada et al. 2007). Poly(butylene succinate) Poly(butylene succinate) (PBS) is one of the most promising environmental- friendly aliphatic polyesters, which offers a great alternative for common polyolefins (Bhatia et al. 2012; Phua et al. 2012; Wang et al. 2013; Charlon et al. 2015). PBS was developed in Japan in the early 1990´s by Showa Polymer (Vroman and Tighzert 2009; Phua et al. 2012). The PBS is commonly produced from succinic acid and 1,4-butanediol
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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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