Tricomponent composites with cellulose nanocrystals and chitin nanofibers - Exploring potential synergy through component interactions

Bio-based materials are being investigated increasingly as alternatives for synthetic materials in a variety of application areas, including composite materials. Among the options for bio-based materials, cellulose and chitin are abundant and increasingly available in different forms, including nanofibers. Due to their anticipated mechanical properties and anisotropic structure, nanofibers of cellulose and chitin lend themselves naturally for use as reinforcing fillers in polymer matrix composites, and the use of each in composites has been studied. However, composites containing both nanofillers has been explored to a lesser extent, and this composite design may provide benefits beyond those seen when the nanofibers are used separately. Therefore, the objective of this work is to examine how nanoscale forms of cellulose and chitin may be used separately and together in composite constructs. Specifically, we are preparing and characterizing composites composed of cellulose nanocrystals (CNCs) and/or chitin nanofibers (ChNFs) in a poly(vinyl alcohol) (PVA) matrix to understand more fully how component interactions affect the structure-property relationships in these materials and how these interactions may be used to produce synergistic improvements. For the specific CNCs and ChNFs used in this work, the nanofillers have opposite surface charge, with CNCs having a negative surface charge and ChNFs having a positive surface charge. Additionally, the components have an ability to interact through hydrogen bonding. These different types of interactions are anticipated to play a role in the structural development in the composites through the processing steps. To probe the effect of these interactions further, we have studied consolidated films as well as hydrogels. The results of these studies indicate that composites containing certain CNC/ChNF ratios possess better mechanical properties than composites containing only one type of nanofiber. Additionally, composites containing CNC/ChNF ratios where surface charges are more evenly balanced experience increased aggregation, presumably due to charge-driven association between the fillers. Mechanical property trends in consolidated films and hydrogels were qualitatively similar, suggesting a general behavior resulting from the component interactions. References 1. C.W. Irvin, C.C. Satam, J.C. Meredith, and M.L. Shofner, “Mechanical reinforcement and thermal properties of PVA tricomponent nanocomposites with chitin nanofibers and cellulose nanocrystals”, Composites Part A: Applied Science and Manufacturing, 116, 147-157 (2019)

Applications of chitin and cellulose based materials as sustainable plastics

Plastics waste is a land management and logistical problem, with difficulties in recycling packaging being of particular concern. A composite barrier material was developed by spray coating chitin nanofibers (ChNFs) and cellulose nanocrystals (CNCs) onto poly(lactic acid) (PLA). The resulting renewable flexible film had similar barrier properties to poly(ethylene terephthalate), with oxygen permeability of 19.6 cm3-µm/m2/day/kPa, resulting from structures driven by synergistic interactions of ChNFs and CNCs. Films formed from blended ChNF and CNC aqueous suspensions were investigated in order to determine whether synergy between the components leads to optimal mechanical and barrier properties. Solution cast films from CNCs were found to have higher oxygen permeability (OP) than deacetylated ChNF films. Addition of 25 wt. % ChNFs to CNCs resulted in an OP reduction by 87 % to a value of 1.7 cm3-µm/m2/day/kPa similar to that of pure deacetylated ChNF films. These developments allow lowering the amount of ChNFs used in the ChNF-CNC formulations without significant impact to barrier properties if deacetylated ChNFs were used. Additionally, the homogenization process for the ChNF manufacture was optimized through controlled deacetylation. The resulting surface cationization allowed ChNFs to be homogenized in 8 passes as opposed to 30 passes at a lower pressure of 551 bar. Deacetylated material had similar barrier properties, higher light transmission (up to 85 %T) and showed 164 % and 162 % improvement in tensile strength and strain at break, respectively. Finally, a hybrid film was produced using chitosan, cellulose derived poly(glucuronic) acid and polyethylene glycol, which exhibited high oxygen barrier (0.2 cm3-µm/m2/day/kPa) and polymer-like water vapor permeation (8.2 g-mm/m2/day). This material takes advantage of reactions between chitosan and carboxylic acid groups on poly(glucuronic acid) that could form the basis for a new class of biodegradable materials. In summary, these developments contribute to optimization of renewable bio-based nanomaterial blends to produce alternative barrier packaging that could be produced in a circular manner at a lowered cost.Ph.D

Spray-Coated Multilayer Cellulose NanocrystalChitin Nanofiber Films for Barrier Applications

Chitin is an abundant biopolymer whose natural production is second only to cellulose. Similar to cellulose nanocrystals (CNCs) or nanofibers (CNFs), chitin nanofibers (ChNFs) can be isolated and used as sustainable O₂ barrier materials for food, electronics, and pharmaceutical packaging. These bioavailable nanomaterials are readily dispersed in water enabling spray-coated films to be deposited at high rates onto uneven or delicate surfaces. In the present study, we demonstrate the successful layer-by-layer spray coating of cationic ChNF and anionic CNC suspensions onto poly­(lactic acid) (PLA) films. ChNF/CNC multilayers were found to lead to a reduction in the O₂ permeability of the final composite film by as much as 73% with the largest effects seen in composites with three alternating layers (ChNF-CNC-ChNF). Multilayer ChNF/CNC coatings were found to have lower O₂ permeability and lower haze than those coated with ChNF or CNCs alone (72% and 86% lower haze, respectively), pointing to a synergistic effect. The composites had a water vapor transmission rate similar to the PLA substrate