(545a) Spray Coating Chitin & Cellulose Nanomaterials for Enhancement of Barrier Properties

Chitin is an abundantly occurring biopolymer like cellulose. The annual natural chitin production is estimated to be around 10¹⁰ - 10¹² tons per year (Barikani et al., 2014) and is about the same order of magnitude as cellulose, whose annual bio-production by photosynthesis is estimated to be of the order of 10¹¹-10¹² tons per year (Klemm et al.,2004). Similar to cellulose, chitin can also occur as chitin nanofibers (ChNFs) and when it is subjected to high shear treatment, nanofibers of 10-20 nm diameter and several microns in length are obtained (Wu et al., 2014; Ifuku & Saimoto, 2012). Wu et al. (2014) were able to produce chitin nanofibers in suspension from purified crab α-chitin, and when these suspensions were cast into films the resultant films had O₂ & CO₂ gas permeabilities of 0.006 & 0.018 barrer respectively. These good barrier properties as well as chitin’s natural bacterial resistance make chitin an excellent candidate for sustainable barrier packaging applications. But packaging materials are generally multilayered, and a good method for incorporating these chitin films in continuous multilayer packaging processing needs to be developed. Spray coating is one of the most versatile methods of applying liquid onto surfaces. Due to its frequent use in painting, spray coating processes are widely encountered in everyday life (McKeen, 2016). One of the main features of a spray coating process is the contactless delivery of the material to be coated onto the surface. This implies that the actual delivery process is not influenced by the surface topography and thus uneven, or delicate surfaces can be coated. The delivered load of coated material is independent of the surface and the lack of a metering gap leads to decreased sensitivity to defects and especially helps in reduction of web breaks in roll to roll process (Czerwonatis, 2008). Beneventi, et al. (2014) were able to coat slurries of micro fibrillated cellulose (MFC) onto wet highly porous papers allowing complete retention of MFC on the surface of the substrate and improved barrier properties of the final product. In the present study we demonstrate the successful spray coating of chitin nanofiber & cellulose nanocrystal (CNC) suspensions onto polylactic acid films. The spray coating of these materials was found to lead to a reduction in the oxygen barrier properties of the final composite film by as much as 75 % of its original value depending on the loading and the material used (CNC, Chitin or both). Unlike the study by Beneventi, et al. the substrate in this case is non porous and the suspensions do not wet the surface. The resulting de-wetting problems were successfully solved by heating the substrate surface. This process could open up a path for the use of more sustainable polymers with otherwise excellent properties but are lacking in barrier properties. Addition of a ChNF or CNC layer could also lead to a reduction in the amount of the more expensive polymer in the multilayer (with the sole function of providing oxygen barrier) all the while increasing the sustainability.