Effects of recycling on polystyrene shape memory polymers for in-situ resource utilization

Abstract

One-way, thermoplastic shape memory polymers (SMPs) used as actuators for self-folding origami are typically single-use materials that would be decommissioned upon completion of mission objectives. As a result, there exists an abundance of unutilized, single-use SMP waste. In-situ resource utilization (ISRU) and recycling offer solutions for the use and integration of sustainable SMP material infrastructures on Earth and for long-duration space missions. Unfortunately, mechanical recycling causes degradation of material properties. Therefore, it is imperative to quantify the effects of recycling on SMP properties. Herein, we utilize a thermo-mechanical recycling method applied to polystyrene SMPs. After recycling, we conduct Fourier transform infrared spectroscopy, differential scanning calorimetry, and dynamic mechanical analysis to investigate changes to the chemical structure, viscoelastic properties, and shape recovery response of the polymer. The results indicate negligible changes to the viscoelastic and shape recovery properties of the recycled material from one to six recycling sequences (extrusions) when compared to the non-recycled material. The most evident form of deterioration occurred in the physical appearance of the material. Otherwise, the shape recovery performance and thermo-mechanical properties remained consistent after recycling. Therefore, the recovery characteristics (recovery ratio, recovery time, and actuation stress) do not change significantly after six recycling sequences, making this material viable for ISRU applications in space environments.