Publication: Thermoresponsive shape memory blend of polylactic acid/styrene-butadiene-styrene copolymer with fillers or crosslinker
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Date
2023-08-01
Authors
Fathin Hani Binti Azizul Rahim
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Abstract
Shape memory polymers from biodegradable polymer blends have captured interest among researchers. However, there are some issues especially, related with responsive rate and repeatability that need to be considered. To solve the issue, a study of thermoresponsive shape memory polymer blend was prepared from the melt-blending of polylactic acid/styrene-butadiene-styrene copolymer (PLA/SBS) and morphology, thermal, shape memory, tensile, rheological and viscoelastic properties were evaluated. With the variation in the compositions, two-phase morphologies were observed due to the immiscibility of the blend. 70PLA/30SBS blend which possesses intermediate storage and loss moduli indicated optimum shape fixity ratio (Rf) and recovery ratio (Rr) with good tensile properties due to the formation of SBS droplets in the continuous PLA phase. In the second stage, 5 wt.% of erbium oxide (Er2O3), halloysite nanotube (HNT) and tungsten carbide (WC) was added separately into the binary blends of 70PLA/30SBS. 70PLA/30SBS-HNT has the highest tensile strength due to the reinforcing feature of the HNT but caused the reduction in Rf with the increasing immersion time. 70PLA/30SBS-Er2O3 showed an improvement in Rf and Rr possibly due to the spherical structure of Er2O3 and low viscosity that facilitates the chain movement during the deformation and recovery phase. The introduction of WC in 70PLA/30SBS blend led to high crystallinity and the optimum recovery time for Rr of 5 min. Meanwhile, the crosslinked 70PLA/30SBS blend was prepared by introducing different dicumyl peroxide (DCP) contents (i.e. 0.5, 1.0, 1.5 and 2.0 wt.%). The gel content and swelling density were measured to investigate the crosslinking density in the crosslinked 70PLA/30SBS blends. The presence of DCP led to high gel content value indicated the crosslinking reaction happened in the 70PLA/30SBS blends. The SBS droplet phase elongated in PLA domain as more DCP was added. The shape memory behavior was examined in three cycles. The Rf of the uncrosslinked blend increased with shape memory cycles. However, for crosslinked 70PLA/30SBS blend exhibited a reduction of Rr with test cycles. For this part, 70PLA/30SBS/1.5DCP blend is considered as the best system with optimum tensile properties, highest Rf value and intermediate Rr value. To summarize, thermoresponsive shape memory PLA/SBS blend properties were influenced significantly by the various composition, the presence of different fillers and the amount of crosslinker.