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PEER-REVIEWED REVIEW ARTICLE
biodegradation, yet they possess a relatively resistance to oil and fat (Andersson 2008). For packaging purposes and compared to cellulose esters, cellulose ethers can be substituted regio-selectively since the substituents, the ethers, are located closer to the main group of the cellulose polysaccharide (Fox et al. 2011). However, while comparing with starch, Andersson (2008) concludes that cellulose ethers are expensive to produce in large-scale as coating materials due to their costly derivatization process associated with their recalcitrant crystalline structure. Methyl cellulose Methyl cellulose (MC) is a non-thermoplastic, water-soluble cellulose ether (Khan et al. 2010) with high oxygen barrier ability. As its hydrophilic nature would suggest, the water vapor barrier performance of MC is modest (Paunonen 2013). Liu et al. (2018) improved the water vapor barrier by grafting a coating of polyethylene- reinforced graphene oxide on a MC substrate. Lagarón and Fendler (2009) obtained a high water barrier by combining methyl cellulose with two types of fillers, either montmorillonite (MMT) or mica. A high water barrier by increasing MMT content was also found by Tunç and Duman (2010). MC is used as a viscosity modifier in fields such as food packaging and pharmaceutical industry, where it is applied as an edible film. In addition, MC is used as a thickener, emulsifier, and water-containing substance, and can be applied as a film or coating material (Paunonen 2013). It has been investigated for drug delivery, antimicrobial materials, and regenerative applications (Liu et al. 2018). A potential blend of polycaprolactone (PCL) and methyl cellulose (MC) was proposed by Khan et al. (2012), which exhibited low water vapor permeability. Carboxymethylated cellulose Carboxymethylated cellulose (CMC) is prepared by an alkali-catalyzed reaction aided by chloracetic acid. The CMC is a hydrophilic, non-thermoplastic, water-soluble polymer which displays decent thermal gelatinization. The hydrophilic nature of CMC has been reported to increase along with its DS, which in turn is linked to alkali concentration in the alkalization step used for preparation. Thus, the DS is directly proportional with the WVP, although after a certain alkaline concentration, the DS and WVP reach their maximum and start to decrease. In industry, including papermaking (Paltakari 2009), CMC is used as viscosity modifier, thickener, water-retention agent and as a structural or adhesive component. Likewise, in the packaging field CMC is used for edible films (Paunonen 2013). Mazhari Mousavi et al. (2017) coated nanocellulose (e.g. nanofibrillated cellulose, NFC) with CMC as an additive for paperboard. As a result, the barrier properties were improved. The CMC allowed a higher NFC solids content while also reducing NFC flocculation and blocking pores. He et al. (2008) demonstrated the procedure of producing CMC from paper sludge as a more cost-effective method than conventional CMC production methods, which utilize cotton linters as precursor material. Hydroxypropyl cellulose Hydroxypropyl cellulose (HPC) is a thermoplastic polymer that provides a good water vapor barrier and satisfactory grease resistance (Thielking and Schmidt 2006). It displays a liquid crystalline behavior with cholesteric, nematic, and smectic phases, which affect both its barrier and mechanical properties, the latter of which are strongly dependent on the measured direction (Andersson 2008). Leminen et al. (2015) studied HPC-based dispersion barrier coatings on paperboard to improve its oil resistance. He
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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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