Effect of crystallinity, crystal polymorphism, and graphene oxide nanosheets on the barrier properties of poly (L-lactic acid)

In this study, the effects of crystallinity, crystal polymorphism, and graphene oxide nanosheets (GONS) on the oxygen and water vapor permeability of PLLA were investigated. It was revealed that for the pristine PLLA with a crystallinity degree of 40%, the oxygen and water vapor permeability decreased by about 48% and 30%, respectively. Also, by changing the crystal form from alpha' to alpha in a constant crystallinity ratio, the oxygen and water vapor permeability decreased by about 10% and 28%, respectively. PLLA/GO nanocomposites with various compositions were prepared by solution coagulation. Results of the permeability analysis on nanocomposites showed that in the presence of 1 wt% GONS, the oxygen and water vapor permeability of PLLA films decreased by about 80% and 30% respectively. In addition, the simultaneous effect of crystallinity and the presence of GONS was investigated, demonstrating that the simultaneous presence of crystalline structures with nanosheets caused the gas pathways to prolong immensely, and for the sample containing 1 wt% nanosheets with about 35% of crystallinity, the rate of oxygen permeation and water vapor transmission decreases by about 90% and 60%, respectively. The Nielsen, Bharadwaj, Duan & Thomas, and Tan & Thomas models were used for comparing these results.