Tailoring the physical properties of poly(lactic acid) through the addition of thermoplastic polyurethane and functionalized short carbon fibers

The elevated brittleness of commercial grades of poly(lactic acid) (PLA) may limit their use in several engineering applications. Therefore, the aim of this work is to develop a PLA-based material possessing well-balanced stiffness and toughness. Composites were prepared by blending PLA with increasing contents (from 10 to 30 wt%) of a thermoplastic polyurethane (TPU) and a fixed concentration (5 wt%) of carbon fibers (CFs), to tune the mechanical properties of the resulting materials. In order to increase the interfacial adhesion between CFs and polymeric phase, CFs were subjected to an acidic modification, by treating them in solution of H2SO4 and HNO3. The prepared composites were characterized from a chemical, rheological, morphological, and thermo-mechanical point of view. Fourier transform infrared spectroscopy showed that the fiber surface reactivity was significantly enhanced by the acid treatment, with the introduction of reactive functional groups on CFs. Rheological and dynamic-mechanical tests confirmed that the introduction of acid-treated CFs implied strong fiber-matrix interactions. Thanks to the presence of the acid treated CFs, an important increase in tensile modulus and maximum stress was obtained for all the compositions. In particular, samples containing 10 wt% of TPU showed +74% tensile modulus and +43% maximum stress with respect to the unfilled blends. Moreover, the elongation at break of PLA was significantly improved (+81%) with the addition of 30 wt% of TPU. It was therefore demonstrated that the adopted approach could be effective for the preparation of novel PLA-based materials with tailorable and well-balanced properties that could find application in various technological fields.