Fast shape recovery by changing the grafting ratio in polyurethane/montmorillonite–poly(methyl methacrylate) composites

We report a study on synthesizing fast, recoverable polyurethane/montmorillonite–poly(methyl methacrylate) (PU/MMT–PMMA) composites and understanding the influence of the grafting ratio of PMMA on the shape memory effect. PMMA was grafted on an exfoliated MMT surface via surface-initiated atom-transfer radical polymerization, which rendered a homogeneous dispersal of MMT in the PU matrix. The morphology and structure of the composites were characterized by scanning electron microscopy, transmission electron microscopy and powder X-ray diffraction. The mechanical, thermal and shape memory properties were characterized by dynamic mechanic analysis and temperature-modulated differential scanning calorimetry. Both tensile strength and strain at break for the composites increased with the introduction of MMT–PMMA, exhibiting 35 and 44% higher strength and strain than those of pure PU, respectively. The PU/MMT–PMMA composites showed high performance on shape memory behavior, with a shape fixity ratio of 100% and a shape recovery ratio of 99% in the first shape memory cycle. The composites also presented a higher shape recovery speed than both PU and PU/MMT. The best performance was obtained with a grafting ratio=3, with a recovery rate of 21.1° per second at 60 °C.