Programing polyurethane with systematic presence of graphene-oxide (GO) and reduced graphene-oxide (rGO) platelets for adjusting of heat-actuated shape memory properties

We fabricated shape memory composites based on thermoplastic polyurethane (TPU) containing three types of graphene, that is, graphene-oxide (GO), reduced graphene-oxide (rGO) and hybrid GO:rGO (ratio 1:1) to study their mechanical and shape memory properties. Tailoring a bridge between microstructure and macro-properties of TPU composites comprising 1, 2 and 5 wt% filler concentration was the primary aim of this work. Incorporation of GO and rGO platelets into the TPU matrix augmented the modulus, elongation at break and breaking stress compared to that of pristine TPU. Besides, the TPU/rGO composites revealed greater young modulus, %elongation, storage modulus, and %crystallinity compared to TPU/GO composites at similar filler content. In particular, the TPU/GO:rGO composites displayed the synergic improvement in dynamic and static mechanical properties owing to the systematic localization GO and rGO platelets in hard and soft segments of TPU, respectively. Interestingly, this localization was thermodynamically predicted by the solubility parameter of components and approved with microscopic observation. The TPU composite behavior was further examined by relaxation stress analysis. While the GO platelets have no significant influence on shape recovery behavior as compared to rGO filled composites, on the other hand, the shape fixation is deteriorated by adding the rGO platelets. The shape memory assessment clarified that the simple TPU composites comprising GO(2 wt%) and rGO(5 wt%) have the highest value in shape fixity and shape recovery, respectively. Noteworthy, both shape fixity and recovery of TPU composites improved when simultaneously using the rGO and GO platelets (GO:rGO) as hybrid filler. The shape recovery and fixity value of 5 wt% TPU composite containing hybrid GO:rGO is 96.7% and 99.1%, respectively, which it has increased up 1.12, 1.05 and 1.02-fold in shape recovery that of neat TPU, 5 wt% TPU composite containing GO and rGO, respectively. This study proves that incorporation of hybrid GO:rGO into shape memory TPU matrix can be employed effectively to attain superior mechanical strength, the excellent shape fixity and high actuation value.