Four-dimensional printing of continuous glass fiber-reinforced thermoplastics

Shape memory polymers (SMPs) are a new class of materials in which their shapes can be changed over time. Despite their lightness and ease of fabrication, SMPs have very low recovery forces and are therefore inefficient when high loads are applied. To improve the mechanical properties of polymeric materials, glass fiber (GF) is commonly used as a reinforcement. The purpose of this study was to demonstrate a four-dimensional (4D) printing process using material extrusion additive manufacturing on both polylactic acid (PLA) and thermoplastic polyurethane (TPU). The goal was to improve the recovery forces in SMPs. GF roving was fed continuously into the nozzle of a three-dimensional (3D) printer to fabricate composite specimens. Also, multi-layer PLA/TPU specimens were printed. There was a measurement of shape fixity, shape recovery, and force recovery ratios. A multi-objective function analysis was performed to determine the optimum material based on recovery force priority in this study. In terms of recovery force, GF showed a superior effect. For composite specimens, shape fixity and recovery ratios decreased and increased, respectively. According to the result of optimization, PLA with 6.62 % GF proved to be the best material. PLA's recovery force has been improved by annealing heat treatment. Furthermore, cyclic experiments up to three cycles were conducted to evaluate the performance of the optimum material.