The global demand of safe, ecofriendly, biodegradable and sustainable packaging materials containing quality products have compelled the development of novel packaging solutions (Anukiruthika et al. 2020, Sanchez-Garcia et al. 2010). In this context with the aim of developing novel packaging materials with improved performance, fabrication of multilayered composite films that integrates the unique functionalities of different polymers is emerging (Anukiruthika et al. 2020). In general, customary packaging materials are derived from non-sustainable synthetic polymers like polyethylene (PE), polypropylene (PP), and polystyrene (PS) due to their relatively low cost, ease of processing and excellent mechanical and barrier properties (Anukiruthika et al. 2020, Sanchez-Garcia et al. 2010). However, non-economical plastic recycling processes and non-biodegradability of these petrochemical based plastics pose serious environmental issues. Hence, developing biodegradable packaging materials from biodegradable plastics (biopolymers) and resources is among the judicious strategies to mitigate or reduce the environmental impact of synthetic plastics.
Among various biopolymers, polysaccharides such as starch, chitosan, carrageenan, and galactomannans are most widely studied for the preparation of edible or biodegradable films. Guar gum (Gg), a heteropolysaccharide/galactomannan is the powdered endosperm derived from the seeds of Cyamopsis tetragonolobus. Structurally, it possesses a straight chain of mannose linked through a (1→4)-β-D-mannopyranose (Man) units and having branched galactose units linked through (1→6)-α-D-galactopyranose (Gal) units (Chudzikowski, 1971, Sharma et al. 2020) which is responsible for its thickening, emulsifying, binding, gelling and film forming properties in aqueous solutions (Thombare et al. 2016). However, Gg films exhibit relatively poor mechanical and barrier properties (Dai et al. 2017, Saurabh et al. 2015). Because of the moderately poor mechanical and rigidity properties of Gg, there is an incredible inspiration to improve the physicochemical properties of the Gg based films by amalgamating them with other biopolymers. The last decade signifies the tremendous interest in the use of cellulose nanomaterials, like cellulose nanocrystals (CNCs), as bio-based nano-reinforcement for improving the mechanical properties of various polymeric materials (Bilbao-Sainz et al., 2011, Nair et al., 2014, Yadav et al., 2018, Yadav et al., 2020). Furthermore, the rod-like, highly crystalline CNCs can form dense H-bonded network structure that results in the formation of a tortuous path restricting the diffusion of aroma, taint, or other gases, thereby presenting excellent barrier properties suitable for packaging applications (Bilbao-Sainz et al., 2011, Nair et al., 2014).
The LBL self-assembly technique introduced by Decher, Hong, and Schmitt (1992) for the functionalization of a solid surface has become one of the most prominently utilized process for the fabrication of multilayered composite films (Decher et al. 1991). The technique is based on the alternate adsorption of components, like a polymer, biomolecule, or inorganic particle, onto a substrate that allows the sequential formation of a nanostructured composite film (Ding et al., 2005; Costa et al., 2013). The fabrication of multilayered composite films through LBL self-assembly technique usually involves the deposition of oppositely charged polyelectrolytes via ionic interactions (Costa et al., 2013). However, LBL construction mechanism can be driven by several other interactions, including electrostatic interactions, H-bonds, charge transfer interactions, guest–host interactions, cation–dipole interactions, or the combined interactions of the above forces (Li, et al., 2012; Zhu et al., 2015). LBL technique offers advantage of adequate interfacial interaction by achieving proper dispersibility or miscibility of various polymers used (Sui et al., 2010). Hence, the multilayered functional composite films with well-defined thickness, composition, and structure can be easily fabricated from the aqueous solutions (Decher, 1997). The simple easy-to-apply methodology, flexibility in the use of materials with the possibility of using different active constituents and thickness control ability at the nanoscale level perhaps make LBL self-assembly technique a versatile surface-modification tool (Qi et al., 2012; Castleberry et al., 2014). The technique offers advantage of imparting unique physicochemical properties for preparing smart composite film surfaces and advanced coatings for various applications (Castleberry et al., 2014; Richardson et al., 2015). Such LBL structured composite films have a wide scope of utilization in packaging materials, electrochromic devices, optical sensors, super-hydrophobic surfaces, dye-sensitized solar cells, tissue engineering etc. (Lee et al. 2000; Ogawa et al. 2007; Kokubo et al. 2007, Richardson et al. 2015).
LBL self-assembly approach can comprise various approaches like spraying, immersion, spinning and casting (Richardson et al. 2015). Various research groups have reported the use of LBL technique for fabricating multilayered composites by combining anionic CNCs with various cationic polymers like poly (diallyldimethylammonium chloride) (Pillai et al. 2016), poly(allylamine) hydrochloride (Moreau et al. 2012), poly(ethylenimine) (Li et al. 2019) etc. As yet, very few research groups have reported the fabrication of Gg based multilayered composites using LBL technique. Dai et al. (2017) developed composite films by depositing alternating layers of CGg and anionic CNFs to fabricate robust multilayered films with good oil and gas barrier properties. In the present work, cationic guar gum (CGg), carboxylated cellulose nanocrystals (cCNCs) and hydroxypropylmethyl cellulose (HPMC) were used to fabricate multilayered composite films by employing LBL self-assembly technique. HPMC, a cellulose ether with excellent film forming properties, has been used here as a flexible interface in order to generate flexible transparent films with good optical, mechanical and barrier properties. The main objective of the presented work is to develop bio-based, sustainable and environmentally benign multilayered composite films with intended application as packaging materials.