Investigation of cellulose nanocrystals (CNC) and cellulose nanofibers (CNF) as thermal barrier and strengthening agents in pigment-based paper coatings

In response to food packaging improvements, this study investigates changes in mechanical and thermal barrier properties of pigment-based paper coatings when cellulose nanocrystals (CNC) and cellulose nanofibers (CNF) are added to the formulation. Stable dispersions of all coating components were formed between pH 7-9 (zeta potential > |30 mV|) except CNF, which favored stable dispersions at higher pH. Hydrodynamic diameters (D-h) of CNC and CNF decreased when interacting with calcium carbonate ions (Ca2+ and CO32-); however, latex binder and dispersant diameters were unaffected by the presence of CaCO3 in solution. Thermal barrier performance was quantified by measuring Delta T across coated samples, with and without nanoparticle additives. Both CNC and CNF additives significantly contributed to the Delta T measured, with the best result recorded for 2 wt% CNF, pH 7, and a drying rate of 25 degrees C/min. This sample recorded 37 +/- 6 degrees C higher than the Delta T for baseline coatings (without additive). Dynamic mechanical analysis (DMA) showed a higher storage modulus for all samples containing CNC and/or CNF compared with the baseline coating, suggesting a material with greater resistance to deformation from applied load. Higher dissipation energy was also observed; however, lower tan delta values suggest improved mechanical properties with both additives.