Shape memory properties of melt-blended polylactic acid (PLA)/thermoplastic polyurethane (TPU) bio-based blends

PLA and TPU were melt-blended to form shape memory bio-based blends in order to improve the shape memory effect of PLA. The shape memory behaviors of PLA/TPU blends predeformed under three different predeformation temperatures (25, 80, 120 °C) were investigated at various recovery temperatures. At the predeformation temperature of 25 °C, the addition of TPU significantly increased the shape recovery ratio of PLA up to 93.5 ± 0.4 % at 160 °C for the PLA/TPU (50/50) blends. With the increase of predeformation temperatures, the shape fixing ability enhanced, but the ability of shape recovery decreased. In order to consider both fixing and recovery ratios together, an additional denotation of shape memory index to couple both ratios by the multiplication of fixing ratio (R_f) and recovery ratio (R_r) was also considered. The sharp increases in the shape memory index curves against recovery temperatures for blends predeformed near the glass transition temperature of PLA were observed in comparison with the gradual, and earliest or latest, increases in the shape recovery curves for those predeformed at room temperature or high temperature. The recovery stress peak temperatures largely corresponded to the predeformation temperatures and increased with increasing the predeformation temperatures, indicating a unique “memory” effect for this type of bio-based blends in terms of recovery stress.