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Graphical abstract Highlights • Developed Poly(N-Isopropylacrylamide)-Cellulose Nanocrystal hydrogel films. • Achieved unique thermo-responsivity and tunable optical performance. • Developed a hybrid materials system to modulate LCST and moisture content for thermo-responsivity and optical tunability. • Demonstrated a ∼ 15 °C reduction of the LCST relative to pure PNIPAm hydrogel films. • Below the LCST, PNIPAm/CNC hydrogel films exhibit transparency or semi-transparency. Abstract A hybrid materials system to modulate lower critical solution temperature (LCST) and moisture content for thermo-responsivity and optical tunability was strategically developed by incorporating cellulose nanocrystals (CNCs) into a poly(N -isopropylacrylamide) (PNIPAm) hydrogel matrix. The PNIPAm/CNC hydrogel films exhibit tunable optical properties and wavelength bandpass selectivity as characterized by PROBE Spectroscopy and Dynamic Light Scattering (DLS). Importantly, the micro/nano structures of the PNIPAm/CNC hydrogel films were completely different when dried below and above the LCST. Below the LCST, PNIPAm/CNC hydrogel films exhibit transparency or semi-transparency due to the uniform bonding of hydrophilic PNIPAm and CNC through hydrogen bonds. Above the LCST, the hydrogel films engage in both hydrophobic PNIPAm and hydrophilic CNC interactions due to changes in PNIPAm conformation which lead to light scattering effects and hence opacity. Furthermore, the incorporation of CNC induces a ∼ 15 °C reduction of the LCST relative to pure PNIPAm hydrogel films. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A new pathway for sustainable packaging materials was engineered by formulating multilayer CNF/CNC barrier coatings. • CNF and CNC synergistically enabled high oil and grease resistance (a kit rating of 11) comparable to fluorochemicals. • A significant reduction in oxygen transmission rate was demonstrated (∼by a factor of about 260) compared to uncoated paper. • Sustainable biomaterials are relevant to society's ongoing efforts to improve health, safety, and environmental stewardship. Abstract Cellulose derivatives such as cellulose nanofibers (CNF) and cellulose nanocrystals (CNC) have enormous potential to reduce or replace petroleum and fluorochemicals for food and other packaging applications. CNFs have been studied for their excellent oxygen and gas barrier properties; however, their performance rapidly decreases in the presence of moisture and higher humidity. CNCs are less sensitive to moisture due to their highly crystalline nature; however, coatings and films made of CNCs are much more prone to fracture due to their high brittleness. Our work demonstrates a unique composite barrier coating system of CNF and CNC that synergistically enables oil and grease resistance (a kit rating of 11) comparable to fluorochemicals. It also demonstrates a significant increase in air resistance (∼by a factor of about 300), and a reduction in oxygen transmission rate (∼by a factor of about 260) compared to uncoated paper. The improvements in oil and gas barrier properties were evaluated with respect to the molecular, chemical, and structural properties of the developed coatings. [ABSTRACT FROM AUTHOR]

Abstract: A sustainable packaging system with excellent liquid- and gas-barrier properties and enhanced strength properties was highlighted by a composite coating containing a mixture of cellulose nanocrystals (CNC), a high-aspect ratio nano-filler montmorillonite clay, an amphiphilic binder soy protein, and a surface-active agent alkyl ketene dimer. They were tested on various surfaces of commercially available packaging papers and compared with the appropriate control (i.e., CNC-only coating) to determine surface morphology, chemical composition, barrier, and mechanical properties. Scanning electron microscopy image analysis showed a compact matrix whose defects (cracks) were significantly attenuated compared to the control while FTIR showed fewer exposed hydroxyl (-OH) groups. The compact structure and reduced proportion of -OH groups are attributed to the plate-like structure, high aspect ratio of clay, and uniform distribution of additives to help inhibit gas, moisture, water, oil, and grease permeation. The base paper used also had a significant impact on how coatings interacted with various fluids. Overall, sustainable CNC-composite barrier coatings with relatively low-cost additives were fabricated and showed improved barrier and strength characteristics with a strong potential as barrier coatings for packaging.Graphical Abstract: [ABSTRACT FROM AUTHOR]