PROPERTIES AND CRYSTALLIZATION OF PLLA BIOPOLYMERS WITH CELLULOSE NANOCRYSTALS AND ORGANIC PLASTICIZER

Abstract

The paper deals with the research of ternary nanocomposites based on PLLA nucleated by lignin coated cellulose nanocrystals (L-CNC) and simultaneously modified with an acetyl tributyl citrate (ATBC) plasticizer. The potential synergistic effect of both additives on the crystallization and morphology of nanocomposites is evaluated by differential scanning calorimetry (DSC) and scanning electronic microscopy (SEM). Mechanical properties were evaluated by tensile tests and fracture toughness measurements. DSC analysis showed a synergistic effect of both additives on the crystallization of PLLA. Ternary composites which were plasticized by 10 mass% of ATBC and simultaneously nucleated by L-CNC (1 and 5 mass%) increased the degree of crystallinity up to 2.5 times and manage to eliminate undesired cold crystallization during reheating. A dramatic increase in ductility, associated with a decrease in tensile strength and modulus, was observed with the incorporation of ATBC at 10 mass%. The ductility of the PLLA/10ATBC and PLLA/10ATBC/1L-CNC composites increased from 3 % (PLLA) up to 160 % and 300 %, respectively. Furthermore, SEM analysis showed that higher concentrations of spray-dried L-CNC (5 mass%) are difficult to disperse by used technology. These agglomerates subsequently act as stress concentrators that initiate premature failure of the composites. Although a suitable combination of tensile characteristics was achieved, PLLA/10ATBC/1L-CNC composites still show relatively low Charpy impact strength (15 kJ/m2).

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