Multiple-shape memory behavior of nanocomposite based on polymethylmethacrylate/poly (lactic acid)/graphene nanoplatelets (PMMA/PLA/GNP)

In this study, nanocomposite samples based on polymethylmethacrylate/poly (lactic acid)/graphene nanoplatelets (PMMA/PLA/GNP) were prepared via melt mixing method and thermal multiple shape memory was induced. Dynamic mechanical thermal analysis results showed that two polymers are miscible in the selected blend ratio (70/30, 50/50, 30/70 w/w; PLA/PMMA) and was not affected by the presence of GNP (1 and 2 phr). The dispersion and distribution status of GNP were observed by scanning electron microscopy (SEM). The co-continuous morphology was dominant in all samples due to complete miscibility of two phases. Multi-shape memory was induced using a tensile test machine equipped with the hot oven at 65 and 100 °C. The results revealed that shape recovery was affected by the presence of GNP at high temperature(for example increasing from 93.34% in neat PLA/PMMA(50/50 w/w) to 96.67% in the sample containing 1 phr of GNP) while there was no considerable effect at low temperature. At high temperature, amorphous phases of two polymers are extended and un-melted chains of PMMA can be as hard segment and leads to good recovery. Due to nucleation and reinforcement effects of GNP, the higher degree of crystallization of PLA and higher storage modulus were obtained and caused to the enhancement of the shape fixity values at the presence of GNP.