Thermally and Electrically Triggered Triple-Shape Memory Behavior of Poly(vinyl acetate)/Poly(lactic acid) Due to Graphene-Induced Phase Separation

Abstract

This work aimed to develop a facile and broadly applicable method for fabricating multistimuli responsive triple-shape memory polymers (SMPs). Hence, herein the SMPs were prepared through the simple physical blending of two commercially available biopolymers, poly(lactic acid) (PLA) and poly(vinyl acetate) (PVAc), in the presence of robust and conductive graphene nanoplatelets. Interestingly, atomic force microscopy observations and thermal analyses revealed that the presence of nanofillers led to phase separation and appearance of two well-separated transition temperatures in the blend of these two miscible polymers. Consequently, shape memory results showed that the unfilled blend of PLA/PVAc with a single thermal transition can only show moderate heat triggered dual-shape memory behavior. While, PLA/PVAc/graphene nanocomposite blends demonstrated excellent thermally and electrically actuated triple-shape memory effects besides their remarkable dual-shape memory behavior. In addition, electrical conductivity of the blend was enhanced by ∼14 orders of magnitude in the presence of graphene. More interestingly, electroactive shape recovery experiments exhibited that depending on the applied voltage, temporary shapes in each region of sample can be either individually or simultaneously recovered.

Designing triple‐shape memory polymers from a miscible polymer pair through dual‐electrospinning technique

“…While, the samples containing graphene have an excellent shape recovery behavior, as the R r (C → A) value for PLA‐G/PVAc‐G reached to 99.6% [Figure (d)]. These results are consistent with our previous observations that revealed excellent thermally actuated triple‐SM properties of the PLA/PVAc/graphene nanocomposite fabricated through solution blending method . Moreover, the R r (C → B) value of PLA/PVAc‐G is over 100%.…”

“…Additionally, it can be seen from Figure (b) and Table that embedding of graphene into the PLA and PVAc matrices led to a considerable reduction in the intensity (tan δ max ) and area of the loss factor peak of PLA, implying that less amount of energy can be dissipated during the deformation process and, as a result, more elastic energy can be stored in graphene‐loaded nanocomposite samples …”

“…In addition, Figure exhibits that the embedding of graphene nanoplatelets into the fibrous structures did not noticeably change the morphology of fibers, and the mean diameter of fibers slightly reduced in the presence of nanofillers. We have previously established that the incorporation of graphene nanoplatelets into the PLA, PVAc, and PLA/PVAc matrices leads to a significant increase in their electrical conductivity. Therefore, the electrical conductivity of polymer solutions can be increased in the presence of graphene and, as a result, net charge density on the surface of jet increases during the electrospinning process, which can account for the decrease in diameter of the nanofibers containing graphene …”

Electrospun hyperbranched polylactic acid–modified cellulose nanocrystals/polylactic acid for shape memory membranes with high mechanical properties

“…The shape fixation ratio determines the ability of the switch segment to be deformed or temporarily shaped. The shape recovery ratio determines the competence of the material to remember permanent shapes . As we can see from the figure, the fixed rate of neat PLA and its composite material was about 90%, which was not changed by the addition of H‐PLA‐CNCs.…”

Electroactive High‐Temperature Shape Memory Polymers with High Recovery Stress Induced by Ground Carbon Fibers

“…From the viewpoint of applications, electroactive SMPI (EASMPI) that can be activated conveniently with electricity is strongly desired, but the SMPIs reported are just activated with direct heat until now . During the exploration, we have observed that it is very difficult for some conductive fillers such as silver nanowires, carbon nanotubes, carbon black, and graphene to produce EASMPI, although they have produced other electroactive SMPs . Short carbon fiber is an attractive candidate for EASMPI, as it exhibits advantages including lower density than metal fibers, higher conductivity than carbon nanotubes, and less amount to form conductive network than carbon black and graphenes .…”