Shape memory effects of poly(L-lactide) and its copolymer with poly(ε-caprolactone)

The thermal properties, crystalline structure and shape memory effects of poly(L-lactide) (PLLA) and its copolymer with poly(epsilon-caprolactone) (PCL) are systematically investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and tensile tests. The influences of composition and intrinsic viscosity on structure and shape memory effects are also revealed. It is found that the PLLA homopolymer and poly(L-lactide-co-epsilon-caprolactone) (PCLA) copolymers exhibit good shape memory effects. The existence of PLLA crystal and amorphous phase play very important roles for shape memory effects. The intrinsic viscosity obviously affects the crystallinity of polymers and further affects the shape memory effects. The shape recovery rate decreases with increasing deformation strain, which is relate to the deformation of PLLA crystal. The recovery stress increase with the increase of the epsilon-CL content and maximum recovery stress is 3.54MPa obtained in the PCLA804 (20wt% epsilon-CL content, M-w=304,400). With the increase of cyclic testing number, the shape recovery rates decrease and the shape retention rates increase at the beginning and then approach to a steady value.