Poly(L-lactic acid) and poly(ε-caprolactone) based ultra-strong and tough thermoplastic polyurethane-urea with multi-urea segments and oriented microstructures

Although poly(L-lactic acid) (PLA) has been widely studied and used in biomedical areas because of its well-known biocompatibility, degradability and renewability, its potential application is still greatly limited by its brittleness and poor ductility. In this work, we, for the first time, reported a series of multi-urea linkage segmented ultra-strong thermoplastic polyurethane-urea (PUU) copolymers using PLA and poly(epsilon-caprolactone) as the mixed soft segments and water as an indirect in situ chain extender. The tensile strength, elongation at break and tensile modulus of the obtained PUU copolymers are 45-52 MPa, 380-540% and 180-430 MPa, respectively. After a simple one-step uniaxial tensile deformation was applied to these PUU copolymers, their tensile strength and tensile modulus could be dramatically increased to 200 and 630 MPa, respectively, while maintaining enough good ductility (elongation at break >50%). Scanning electron microscope and Wide-angle X-ray Diffraction results showed that the dramatically improved mechanical performance should be mainly attributed to their more oriented microstructures. This study provided an easy strategy to pursuing synthetic PLA based biopolymers combining with ultrahigh mechanical strength and biocompatible and degradable properties.