Interrelated shape memory and Payne effect in polyurethane/graphene oxide nanocomposites

We report the fabrication of graphene oxide (GO) based polyurethane (PU) nanocomposites by a simple method of mixing and their shape memory properties at different temperatures. Both the polymer and the filler were synthesized in the laboratory by simple and easy methods - PU by pre-polymer method and GO by improved graphene oxide synthesis method. High molecular level dispersion of GO platelets within the PU matrix and thus good mechanical properties were maintained by the improved PU/GO interfacial interaction. The structure of the polymer composites was investigated by scanning electron microscopy and X-ray diffraction studies revealed a highly dispersed morphology of graphene oxide sheets in PU. The improvement in shape memory obtained for the nanocomposites was then quantitatively analysed using the Payne effect. The crosslink density calculated using the Maier and Goritz model (Payne effect) was found to be dependent on the thermal transitions of the composites and it varied with the filler concentration. Accordingly a nice correlation was established between the temperature dependence of shape memory and the crosslink density. Composite behaviour was further analysed by the dynamic measurements such as rheology, stress relaxation and Mullins effect. To the best of our knowledge, the quantification of shape memory in terms of physical crosslinks and filler-polymer entanglements of the PU/GO nanocomposite system has not been addressed before and is introduced in this work.