Mechanical Properties Of Shape Memory Polymer Research Articles

4D printing of shape memory polymer nanocomposites for enhanced performances and tunable response behavior

The emergence of four-dimensional (4D) printing introduces a novel approach to the design and manufacturing of high-performance multifunctional shape memory polymers (SMPs). Herein, two types of nanomaterials were blended or embedded into SMPs matrix to enable 4D printing of shape memory polymer composites (SMPCs) via photocuring. The incorporation of hexagonal boron nitride (HBN) nanoparticles enhanced the thermal stability and mechanical properties of SMPs, and accelerated their thermally responsive shape recovery speed. HBN nanoparticles also significantly improved the performance stability of SMPs, even after undergoing multiple shape memory cycles. Electrically responsive shape memory behavior in SMPCs was achieved by embedding a spray-coated polyaniline: polystyrene sulfonate /graphene (PANI: PSS/GR) electrothermal layer (ETL). The applied voltage, ETL resistance, HBN blend content, and sample thickness had a significant regulation effect on electrically responsive shape recovery behavior and shape recovery force. PANI: PSS improved adhesion between ETL and SMPCs matrix, filled the gaps between graphene platelets, which resulted in rapid, uniform, and stable heating upon energization. The presented electrically responsive gripper was capable of grasping objects of various shapes and sizes. This strategy broadens the potential applications of 4D printed SMPCs in challenging environments while propelling the advancement of 4D printing.

Temperature dependence analysis of mechanical properties and bending behaviors of shape memory programmable composites

Temperature significantly affects the mechanical properties of shape memory polymers (SMPs). The temperature dependence of mechanical properties and bending behaviors of shape memory polymer composites (SMPCs) was investigated in this study. Dynamic mechanical analysis and static mechanical tests were performed to investigate the temperature dependence on the mechanical properties of SMP and SMPC. The tensile strength and shear strength of SMP declined as the temperature rose, while the elongation at break increased first and subsequently reduced. SMPC exhibited brittle fracture at low temperatures and fiber buckling at high temperatures, respectively. Subsequently, a temperature-dependent model of the bending behavior of SMPC was developed. Theoretical model revealed the effect of temperature and fiber volume content on fiber buckling. The higher the temperature and fiber volume content is, the easier the fiber buckles. The effects of temperature, thickness and fiber volume content on critical buckling curvature, strain energy, half-wavelength and amplitude were investigated. Temperature and fiber volume content were positively related to critical buckling curvature, strain energy and amplitude, but negatively related to half-wavelength. Thickness was positively related to strain energy, half-wavelength and amplitude, but negatively correlated to critical buckling curvature, in which thickness does not determine whether SMPC buckling occurs. Eventually, the theoretical model was verified using the four-point bending test to ensure its credibility. The research results are expected to provide theoretical guidance for the design and application of SMPC.

Physical cross-linked aliphatic polycarbonate with shape-memory and self-healing properties

As one of the stimulus-responsive intelligent materials, shape memory polymers (SMPs) gained increasing attention for possessing the benefits of lightweight, low density, easy processing, and large shape variables. It is of great significance to enhance self-healing properties and mechanical properties of SMPs. Herein, we synthesized an aliphatic polycarbonate monomer named MMC (5-methyl-5-[(4-methoxy)-benzyloxycarbonyl]-1,3-dioxan-2-one) by a two-step method. The cross-linked network was constructed by ring-opening copolymerization of 5-methyl-5-benzyloxycarbonyl-1, 3-dioxan-2-one (MBC) and MMC with mPEG43 as an initiator and Sn(Oct)2 as a catalyst. The acquired elastomer achieves a stretchability of up to 777.7 %, which is significantly higher than that of the homopolymer of MBC. The elastomer presents a shape recovery rate of 97.8 within 42 s at 37 °C and can maintain excellent stretchability up to 772.0 % which is 99.3 % of the initial value after repair at 37 °C for 6 h. The introduction of MMC heightens the viscosity of the cross-linked network and effectively improves its stretching and self-healing performance, which offers new candidates for future body-sensors, stimuli-responsive materials, and wound healing.