Synergistic Reinforcement of Composite Hydrogels with Nanofiber Mixtures of Cellulose Nanocrystals and Chitin Nanofibers.

Simultaneous incorporation of cellulose nanocrystals (CNCs) and chitin nanofibers (ChNFs) into a polyvinyl alcohol (PVA) matrix opens possibilities for customization of more environmentally friendly composite materials. When used in tricomponent composite hydrogels, the opposite surface charges on CNCs and ChNFs lead to the construction of beneficial nanofiber structures. In this work, composite hydrogels containing CNCs, ChNFs, or their mixtures are produced using cyclic freeze-thaw (FT) treatments. When considering different compositions and FT cycling, tricomponent composite hydrogels containing a specific ratio of CNCs/ChNFs are shown to have promising mechanical performance in comparison to other samples. These results together with results from water absorption, rheological, and light scattering studies suggest that the CNC/ChNF structures produced property improvement by concurrently accessing the stronger interfacial interactions between CNCs and PVA and the longer lengths of the ChNFs for load transfer. Overall, these results provide insight into using electrostatically driven nanofiber structures in nanocomposites.

Controlling Barrier and Mechanical Properties of Cellulose Nanocrystals by Blending with Chitin Nanofibers.

Chitin nanofibers (ChNFs) and cellulose nanocrystals (CNCs) have been proposed as materials for renewable packaging with low O2 transmission that protect food, medicine, and electronics. A challenge in biomass-derived functional materials is tuning both barrier and mechanical properties, while minimizing process steps. A concept that merits additional study in this field is tuning of the barrier and mechanical properties by use of oppositely charged biomass-derived fibers, through interactions that support dense film formation. We report free-standing films formed by solution casting of blends of aqueous suspensions of CNCs and ChNFs with either low degree of acetylation (LChNFs, higher charge) or high degree of acetylation (HChNFs, lower charge). While neat CNC films had the highest O2 permeability (OP), the OP was lowered by 91% by addition of at least 25 wt % LChNFs to CNCs to an OP value near 1.7 cm3 µm/m2/d/kPa. Interestingly, blends of CNCs with less highly charged, larger HChNFs had equivalently lower OP as with LChNFs. The tensile strength and strain at break of blended ChNF/CNC films was optimal compared to neat cellulose or chitin when at least 50 wt % LChNFs or HChNFs were blended with CNCs. We show that the ability to tune properties of ChNF/CNC blends was coincident with the formation of aggregates of chitin and cellulose nanomaterials, which appear to support formation of dense layers of tortuous fiber networks.

Increasing efficiency of the homogenization process for production of chitin nanofibers for barrier film applications.

Chitin nanofibers (ChNFs) are of interest for barrier materials but are often extracted by high pressure homogenization (HPH) with high energy utilization. We studied the influence of deacetylation (DA) and pressure on HPH of shrimp chitin and the resulting solution cast films. Deacetylation to 72% DA resulted in improved ChNF suspension and film light transmission, strain at break, and tensile strength compared to chitin with DA of 89%. The oxygen permeability (OP) of the films was not affected by the modification and remained at low values of 1.9-2.4 cm3 µm/m2/day/kPa. We also show that deacetylation enables HPH intensity to be reduced during extraction of ChNFs from crab shell chitin (63% lower pressure and 73% reduction in number of passes), while achieving a low OP. Deacetylation pretreatment reduces HPH process intensity required to achieve oxygen barrier properties in ChNF films.

Multifunctional Bio-Nanocomposite Coatings for Perishable Fruits.

Hunger and chronic undernourishment impact over 800 million people, which translates to ≈10.7% of the world's population. While countries are increasingly making efforts to reduce poverty and hunger by pursuing sustainable energy and agricultural practices, a third of the food produced around the globe still is wasted and never consumed. Reducing food shortages is vital in this effort and is often addressed by the development of genetically modified produce or chemical additives and inedible coatings, which create additional health and environmental concerns. Herein, a multifunctional bio-nanocomposite comprised largely of egg-derived polymers and cellulose nanomaterials as a conformal coating onto fresh produce that slows down food decay by retarding ripening, dehydration, and microbial invasion is reported. The coating is edible, washable, and made from readily available inexpensive or waste materials, which makes it a promising economic alternative to commercially available fruit coatings and a solution to combat food wastage that is rampant in the world.