Study of annealing and orientation effects on physical properties of PLA based nanocomposite films

PLA-sepiolite and PLA-halloysite nanocomposites prepared by melt blending were systematically characterized in terms of mechanical, thermal and barrier properties. Annealing and unidirectional stretching techniques were used with the aim to improve matrix performances of nanocomposite based films; a preliminary study on the production of PLA-halloysite composites via film blowing has been also considered. Addition of unmodified clays did not significantly alter PLA properties mainly because of the lack of an adequate filler-matrix interface due to the absence of compatibilizer between polymer and reinforcements that limited clays effect as nucleating agents. Instead matrix crystallinity, mechanical and barrier properties resulted to be strongly affected by physical aging and orientation. Annealing and orientation are reported to be dominant over clay addition: only slight variations are reported to occur in presence of clay after these treatments. Fiber-like clays application in unidirectional orientation process led to important improvements in samples properties. Good results were obtained especially after unidirectional stretching: increased crystallinity, improved mechanical properties and reduced water absorption were achieved in presence of only 0.5%-wt of sepiolite. Further investigation will take place to systematically study the effect of different stretching conditions on PLA-sepiolite samples.