Thermal stability of cellulose nanomaterials and their composites with polyvinyl alcohol (PVA)

This study investigates the thermal stability of composites composed of polyvinyl alcohol (PVA) reinforced with biodegradable fillers: cellulose nanocrystals (CNC) or cellulose nanofibrils (CNF). Combinations of PVA with CNC and PVA with CNF at 2, 4, 6, and 8 % cellulose by weight underwent several different thermogravimetric analysis (TG) heating programs-constant heating rate, isothermal, and high resolution with a dynamic heating rate. The starting materials (PVA pellets, PVA film, aqueous CNC at 11.8 % solids, and aqueous CNF at 3 % solids) were also tested in the TG after drying. Temperatures at the onset of degradation and at maximum degradation for the principal pyrolysis stage were quantified. Kinetic parameters (activation energy, pre-exponential factor) were calculated using the Flynn-Wall-Ozawa (FWO) method. CNC or CNF incorporation in the PVA matrix did not markedly shift temperatures at the onset of degradation or at maximum degradation for the major stage of pyrolysis, compared to neat PVA. However, the inclusion of nanocellulose lowered the maximum rate of degradation, with larger reductions at higher filler contents. A larger portion of the composites' original mass remained intact following the major degradation peak. Incorporation of CNF in composites with PVA produced films with activation energies higher than the activation energy of neat PVA film.