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PEER-REVIEWED REVIEW ARTICLE
has been cited in many publications (Dufresne 2013). Moreover, superhydrophobic paper has been topical and with high potential demand (Rastogi and Samyn 2015). Arbatan et al. (2012) successfully coated NFC together with precipitated calcium carbonate (PCC) as two separate layers on filter paper while applying the dip-coating method. In addition, they applied alkylene ketene dimer to render the paper superhydrophobic. Nanocellulose/biopolymer blends Lindström and Aulin (2014) raised the issue of compatibility between a thermoplastic and non-thermoplastic material, which would need to be tackled prior to industrial-scale implementation. The difficulty of blending nanocellulose with thermoplastic, hydrophobic materials, such as PLA, has been discussed. Attempts to resolve this issue have so far involved the application of surfactants or emulsions. To date, the challenge has not yet been resolved. Nair et al. (2018) presented a solution in the form of nanocellulose fibrils with high lignin content (NCFHL), which were wet mixed with PLA. A strong compatibility was found between the fibrils and PLA. In addition, the NCFHL fibrils increased the mechanical, thermal, and water vapor barrier properties. Song et al. (2014) applied a blend of nanocellulose fibrils and polylactic acid (NCF/PLA) on paper by a cast-coating process. To disperse it conveniently in the hydrophobic PLA, NCF was rendered hydrophobic by grafting hydrophobic monomers via free radical polymerization. Consequently, the WVTR of paper was reduced. We note, however, that to render them hydrophobic or compatible with a hydrophobic matrices, the surface treatment of nanomaterials, such as nanocelluloses, which have a very high area per unit mass, imply a high treatment cost. Jonoobi et al. (2010) improved the processability of NFC while blending it with PLA. The improvement was due to the enhanced mechanical and thermal properties. The improvement in storage modulus of the blend was attributed to nanofibers restricting PLA segmental mobility. Espino-Pérez et al. (2013) obtained a satisfactory composite, despite some thermal stability issues, by blending cellulose nanocrystals (CNC) with PLA by grafting with n-octadecyl isocyanate. As a result, this hydrophobic, long-chain aliphatic molecule was noted to decrease WVTR, yet OTR remained unchanged. Nano-lignocellulose Nano-lignocellulose (NLC) or ligno-nanocellulose, is a form of nanocellulose produced from mechanical pulp, as displayed in Fig. 3. Mechanical pulp typically contains more lignin than chemical fibers. Therefore, the prepared nanocellulose also inherently contains lignin. Due to the presence of lignin, the mechanical properties of NLC are somewhat lower than those of chemical pulp nanocellulose (Osong et al. 2014). One benefit of using NLC instead of chemical pulp nanocellulose is the more economical production of mechanical pulp compared to that of chemical pulp (Osong et al. 2016). According to Spence et al. (2010), the presence of lignin increased water vapor permeability, due to increased porosity that compensates its hydrophobic nature. However, hot-pressing appears to increase material density and thereafter impart an improved oxygen barrier and surface hydrophobicity. Rojo et al. (2015) reported a reduction in oxygen permeability and surface wettability due to increase in material density as a consequence of hot-pressing of NLC films. Likewise, while adding lignin, the reduced wettability was found to correlate with a decrease in the dispersive component of NFC surface energy.
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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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