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PEER-REVIEWED REVIEW ARTICLE
improvements, for instance, in mechanical, thermal, gas barrier, antibacterial, and UV barrier properties (Papageorgiou et al. 2010; Gorrasi et al. 2014). Several researchers have reported improvements in barrier and mechanical properties of biodegradable materials by 1.0 wt% to 5 wt%, by adding montmorillonite (MMT) (Sanchez Ǧ Garcia and Lagaron 2010). Picard et al. (2011) mixed PLA together with 4 wt% organically modified montmorillonite (OMMT), subsequently achieving enhance gas barrier properties. Ojijo et al. (2012) studied the blend of (PLA/PBSA)- organically modified clay composite. The ratio of polymers was kept constant at 70:30 (PLA/PBSA), while organically modified clay content was varied between zero wt% and 9 wt%. As a result, an improvement of 29% in elongation was obtained by a blend of PLA/PBSA/2 wt% organically modified clay compared to plain PLA. Moreover, other mechanical properties were also good in the blend, and reduction in thermal stability was only moderate (Ojijo et al. 2012). Rhim et al. (2009) investigated how different nanoclay types and concentrations in PLA films influence the mechanical, barrier, and antimicrobial properties of the film. The behavior varied among the types of nanoclays and concentrations. Promising improvement against water vapor (6% to 33% decrease) was noticed with organically modified clay. However, tensile strength and elongation decreased due to the filler addition (Rhim et al. 2009). While blending 5 wt% of organo- modified mica-based clay grade with PLA, Sanchez Ǧ Garcia and Lagaron (2010) achieved 54% lower water permeability, 55% lower oxygen permeability, a 75% decrease in UV light transmission (wavelength 250 nm), and a 32% reduction in visible light transmission (wavelength 650 nm) than with neat PLA. Gorassi et al. (2014) obtained upgraded water vapor barrier properties by mixing 6 wt% and 12 wt% of silane-treated halloysite nanotubes (HNT) with PLA matrix. Filler content was the main factor influencing the barrier properties. One filler option is the main byproduct, gypsum, from the PLA production. Gypsum is a calcium sulfate and can improve the mechanical properties of PLA. Furthermore, the filler size and content had the biggest influence on the water vapor resistance of a PLA/calcium sulfite hemihydrate biocomposite (Gorrasi et al. 2008). A good compatibility between PLA and modified kaolinite have been achieved, which resulted in improved oxygen resistance (50%) (Arora and Padua 2010). Due to the addition of nanoclays, PLA/nanoclay and PLA/PCL/nanoclay films have been reported to have improved oxygen and water vapor barrier properties (Andersson 2008). Fortunati et al. (2012) achieved a 34% improvement in water vapor barrier properties with PLA matrix together with 1 wt% surfactant modified cellulose nanocrystals (s-CNC). In addition, they obtained good gas barrier properties and low overall migration levels in solvent casted PLA/s-CNC and PLA/unmodified cellulose nanocrystal (pristine, CNC) biocomposite films. Active food packaging materials from PLA, together with 1.0 wt% CNC and 1.0 wt% silver (Ag) nanoparticles, indicated a 46% reduction in the oxygen transmission rate. Similar improvement was obtained with a biocomposite of PLA/5wt% CNC/1wt% Ag. Fortunati et al. (2013) have reached acceptable levels in overall migration with PLA-based CNC/Ag-biocomposites, but they noticed that silver was easily released from them. By applying alcohols, Turalija et al. (2016) modified PLA surface properties to make it more hydrophilic and antimicrobial. Glycerol and polyethylene glycerol, chitosan, and silver nanoparticles were also considered. Enhancement in hydrophilicity with alcohols and chitosan decreased the water contact angle from 70° to 40-45°. Silver was applied on PLA-based films by plasma deposition. Turalija et al. (2016) noticed increased hydrophilicity and a noteworthy enhancement in the antimicrobial properties of PLA-based films with silver.
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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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