bioresources. com
PEER-REVIEWED REVIEW ARTICLE
Lignin/biopolymer blends In spite of native lignin being generally hydrophobic, its hydrophobic nature is not sufficient to provide paperboard with a hydrophobic barrier (Antonsson et al. 2008). However, the derivatives, blends, and composites of lignin have achieved promising results as far as water resistance (Antonsson et al. 2008; Spiridon et al. 2010; Bhat et al. 2013; Hult et al. 2013a,b). Furthermore, while examining acetylated lignin blended with PHB, lignin was found to lower the crystallinity of PHB and to enhance its thermal stability in TGA analysis by increasing T 5% 22 °C, T 50% 19 °C, and T max 17 °C (Bertini et al. 2012). In addition, Mousavioun et al. (2010) studied PHB/bagasse soda lignin (up to 40 wt%) blends. Soda lignin enhanced the overall thermal stability of the PHB matrix. Kovalcik et al. (2015) made films from poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) together with lignin (up to 10 wt%). The addition of lignin enhanced the thermo-oxidation stability as well as oxygen and carbon dioxide resistance of the films. These films were recommended to be used as packaging materials (Kovalcik et al. 2015). Shankar et al. (2015) studied agar/lignin films where the lignin content was 1wt% to 10wt%. The authors noticed a positive difference in water vapor barrier, UV-light barrier, and mechanical properties compared to the neat agar films. They proposed food packaging film end-use for the agar/lignin films due to their UV-light barrier properties (Shankar et al. 2015). Antimicrobial activity against Gram (+)ve and Gram (-)ve bacteria of chitosan/lignin films has also been examined. Clear activity against the bacteria was detected and found suitable for active food packaging applications (Rai et al. 2017). Antioxidants can be used in active packaging and as a product protector against oxygen and gas. In this context, owing to the polyphenolic structure of lignin, its antioxidant behavior has been examined (Gordobil et al. 2014; Ye et al. 2016). Domenek et al. (2013) studied antioxidant activity of two different alkali lignins blended with a PLA matrix. As a result, the oxygen barrier properties were improved while the mechanical properties decreased slightly (Domenek et al. 2013). Indeed, some PLA/lignin blends have resulted into decreased mechanical performance, including tensile strength and elongation. Furthermore, Chung et al. (2013) enhanced the UV barrier properties of PLA by blending in 10 wt% of synthesized lignin-g-PLA copolymers. Moreover, Gordobil et al. (2014) studied two types of lignins at different content blended together with PLA. In the study, commercial alkaline lignin and almond shell extracted lignin were acetylated and compared. Finally, the addition of both lignins enhanced thermal stability, yet the crystallinity of PLA remained unchanged. Both acetylated lignins seemed to inhibit the hydrolytic degradation of PLA. In terms of mechanical properties, the elongation at break was enhanced with the addition of lignins, yet the other mechanical properties did not improve. If the lignin was not acetylated, the mechanical properties decreased (Gordobil et al. 2014). Lignin has been reported to improve thermal stability, tensile strength, and hydrophobicity in starch-lignin blends. However, it has also been reported to impair elongation and transparency (Spiridon et al. 2010; Miranda et al. 2015). Indeed, lignin has been used as a filler in thermoplastic starch (TPS) blends. It has been reported to enhance mechanical and thermal properties, as well as moisture resistance (Gordobil et al. 2014). In addition, lignin has been reported to enhance plasticity in starch/lignin blends, to reinforce cellulose and to work as a compatibilizer in cellulose/starch blends. Bhat et al. (2013) improved the properties of starch-based films thought the addition of 1% to 5% lignin. The main improvement was in water and water vapor resistance and in the heat seal-ability of the film. The film was seen suitable for food packaging
22
Helanto et al. (2019). “ Bio-based barriers ,” B io R esources 14(2), Pg #s to be added.
Made with FlippingBook - Online catalogs