Morphological, thermal, and mechanical properties of cellulose nanocrystal reinforced poly(lactic acid) and poly(butylene adipate-co-terephthalate): A comparative study on common and novel solvent casting methods

The mechanical and thermal properties of semicrystalline (sc) and amorphous (a) poly(lactic acid), PLA, and poly(butylene adipate-co-terephthalate), PBAT, and their nanocomposites containing 1 and 3 wt% CNCs, prepared through solvent casting methods using one (N,N-dimethylformamide [DMF]) or two (dimethyl sulfoxide (DMSO), and tetrahydrofuran (THF)) solvents were analyzed. Differential scanning calorimetry (DSC) showed that the total amount of crystals of the scPLA/CNC nanocomposites increased, whereas it decreased in the PBAT/CNC systems. In both cases, the crystallization temperature increased with CNC content. In tensile experiments, the Young modulus and yield strength of all nanocomposites were found to increase by incorporating CNCs, more significantly for the samples prepared using one solvent. The elongation at break of both PLA nanocomposites increased when prepared via one solvent, while it decreased for the two solvent methods as well as for PBAT nanocomposites prepared by both methods. The impact properties of the samples prepared by the two solvent methods decreased. In contrast, for the one solvent method, incorporating 3 wt% CNCs improved the impact properties by 32% and 9% in scPLA and aPLA, respectively, but decreased by 4% in PBAT nanocomposites. Also, in dynamic mechanical thermal analysis (DMA) the storage modulus of scPLA and PBAT/CNC systems increased significantly, especially in the rubbery region (5-85 MPa and 105-155 MPa, respectively). Using a percolation model, the strength of the percolating CNC was found to be dependent on temperature and affected by traces of solvent mostly in the scPLA nanocomposites.