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PEER-REVIEWED REVIEW ARTICLE
Cellulose acetate In the preparation of CAs, acetic acid anhydride, together with a catalyst of zinc chloride or sulphuric acid, acts as a reagent to substitute the hydroxyls of the cellulose backbone in esterification (Kuusipalo et al. 2008). Found in applications in fields such as molding and extrusion (Gilbert 2017), cellulose acetate (CA) is currently the most commonly applied thermoplastic cellulose derivative. Likewise, many of the applications of CA and its forms are found in the food packaging industry, being used as rigid wrapping films (Paunonen 2013). Cellulose acetate can exist in several forms, some of the most common ones being cellulose acetate butyrate (CAB), cellulose triacetate (CTA), and cellulose acetate propionate (CAP). Out of these forms, CAB displays the lowest water absorption. However, the value is still high compared to its counterparts in today’s industry, vinyls, such as polyvinyl chloride (PVC). Several biodegradable CAs have been introduced in the 90s. They were marketed as Bioceta® and Biocellat®, the products of the former including eco-friendly hair brushes, etc . Likewise, the blends of CA have been marketed under the name Biodegrade® by FKuR. They are food-contact approved and applicable for injection molding and extrusion (Gilbert 2017). Uddin et al. (2016) found promising results as far as high oxygen barrier and interfacial adhesion, while combining CA with graphene oxide in order to produce a CA-based oxygen barrier material for biodegradable packaging applications. Dou et al. (2013) reported a drastic improvement in oxygen barrier by combining CA and layered double hydroxide nanoplatelets (LDH), after which thermal annealing treatment was carried out. Moreover, there have been several attempts to apply CAs as antimicrobial films, as well as matrix material for nanocellulose fibers (NCF) motivated by the solubility of CAs to organic solvents (Paunonen 2013). Kabiri and Namazi (2014) reported a maximum decrease of 47% in WVP with 0.8% of graphene oxide (GO) on a matrix of nanocrystalline cellulose acetate, where CA was used to link graphene oxide fillers with cellulose nanocrystals. Likewise, Grunert and Winter (2002) combined trimethylsilylated cellulose nanocrystals from bacterial cellulose (BC) with CAB acting as matrix material. Cellophane Cellophane exhibits potential barrier properties (Tome et al. 2011). Cellophane, regenerated cellulose in film form, is produced in the viscose process together with rayon fibers (Alén 2011; Paunonen 2013). Tome et al. (2011) studied the permeability of atmospheric gases, such as oxygen, and water vapor barrier properties of cellophane by esterifying with fatty acids. As a result, an improvement of 50% in water vapor barrier and 8% in oxygen barrier was reached. These studies encourage further investigation on the barrier properties of cellophane, which is biodegradable and fully suitable in food packaging. However, cellophane use has diminished given the emergence of several other alternatives for packaging. Environmental effects associated with carbon disulfide and other by-products of the viscose process are also important factors; however, cellophane itself is 100% biodegradable, a reason for its popularity as a food wrapping. Nanocellulose and Nano-lignocellulose There are several main reasons for the barrier properties of films comprising micro- or nanofibrillar cellulose or nanocrystalline cellulose. The degree of crystallinity, the length-to-width ratio of fibrils, the surface polarity, and the internal cohesion of the fibrillar suspension all play a role (Lagaron et al. 2004; Dufresne 2012; Hubbe et al. 2017). The uptake of moisture from surroundings is a significant drawback of
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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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