ROLL-TO-ROLL PROCESSING OF PAPER-BASED PACKAGING MATERIALS USING CELLULOSE NANOCRYSTALS AND CHITOSAN

The objective of this work is to investigate the feasibility of a scalable fabrication process for single- and multi-layer coatings of biopolymers applied to paper that is super-calendared and lightly silicone-converted to reduce fluid penetration through the paper. A single or dual layer slot die, integrated within a roll-to-roll system, was used to uniformly coat thin films of chitosan, and anionic cellulose nano-crystals (CNC) on the paper at a flow rate and web velocity within the process window. Chitosan was coated alongside CNC either simultaneously using a dual-layer slot die or sequentially with a single layer slot die to yield bilayer coatings that improved the barrier properties of the substrate material. Barrier properties were examined by carrying out oxygen transmission rate (OTR) tests at a relative humidity of 50%. Furthermore, the effects of the molecular weight of the cationic phase and the pH of the CNC suspension on the barrier and mechanical properties were examined. Coatings with high molecular weight of chitosan produced materials that exhibited good barrier properties as indicated by their low OTR values (i.e., ~ 7 cm³/m²/day). This effect was attributed to the CNC crystallinity as well as hydrogen bonding and strong electrostatic attraction between the cellulosic coating components and chitosan. Samples coated with lower molecular weight of chitosan performed similarly to higher molecular weight chitosan coated materials. The pH of the CNC suspension did not present a significant impact on the OTR results, albeit CNC suspensions with lower pH produced thinner coatings due to their higher charge density enabling thin layer adsorption on the substrate. Furthermore, samples with lower pH performed poorly in substrates with higher porosity. Bilayer coatings fabricated using the dual layer slot die produced more flexible materials compared to samples coated sequentially, based on their TAPPI kit numbers. In summary, coating paper-based substrates with biopolymers helped to enhance both the mechanical and barrier properties and could prove to be a useful alternative to plastics.