PVA/PEG/graphene shape memory composites responsive to multi-stimuli

Commercially available low-cost polyvinyl alcohol (PVA)/polyethylene glycol (PEG) were used to develop nanocomposites containing different amounts of graphene using the solution casting technique. The shape-memory performance of the developed films was investigated using multiple types of actuations, including thermal heating and microwave (MW) irradiation for triggering the shape-memory effects (SMEs). The bending test was used to quantitatively characterize SMEs of PVA/PEG nanocomposites. The results show that the developed PVA/PEG blend and its nanocomposites show shape recoverability under both thermal and MW irradiation actuation. The nanocomposite containing 0.2 wt% graphene exhibits the best shape-memory performance. The maximal recovery ratio (Rr) is nearly 100% within 8 s. However, for the specimens with higher graphene loadings of 0.5 and 1.0 wt%, the Rr values are significantly lower with incomplete recovery (Rr ≈ 45%). The scanning electron microscopy (SEM) image of PVA/PEG/0.2 shows good uniformity and dispersion of graphene, while at higher loadings graphene sheets agglomerate. The nanocomposites also show positive results when subjected to water-induced shape recovery tests. The recovery data were fit using a sigmoidal-logistic-1 model with correlation factors of 0.999. Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis were used to evaluate the SMEs. The nanocomposites show improved thermal stability compared to that of the blend without graphene as indicated by the increase (by 10–30 °C) in the values of the degradation temperature. This study identified novel and flexible graphene-based SMP materials with a potential for a range of applications, such as actuations, tissue regeneration, wearable sensors, and thermal management The highlight of this study is using graphene to introduce additional cross-linked points in PVA/PEG composites to improve the shape memory properties under multiple types of actuations.