Blends of poly(ester urethane)s and polyesters as a general design approach for triple‐shape memory polymers

4D Printing of Electroactive Triple-Shape Composites

Triple-shape polymers can memorize two independent shapes during a controlled recovery process. This work reports the 4D printing of electro-active triple-shape composites based on thermoplastic blends. Composite blends comprising polyester urethane (PEU), polylactic acid (PLA), and multiwall carbon nanotubes (MWCNTs) as conductive fillers were prepared by conventional melt processing methods. Morphological analysis of the composites revealed a phase separated morphology with aggregates of MWCNTs uniformly dispersed in the blend. Thermal analysis showed two different transition temperatures based on the melting point of the crystallizable switching domain of the PEU (T_m~50 ± 1 °C) and the glass transition temperature of amorphous PLA (T_g~61 ± 1 °C). The composites were suitable for 3D printing by fused filament fabrication (FFF). 3D models based on single or multiple materials were printed to demonstrate and quantify the triple-shape effect. The resulting parts were subjected to resistive heating by passing electric current at different voltages. The printed demonstrators were programmed by a thermo-mechanical programming procedure and the triple-shape effect was realized by increasing the voltage in a stepwise fashion. The 3D printing of such electroactive composites paves the way for more complex shapes with defined geometries and novel methods for triggering shape memory, with potential applications in space, robotics, and actuation technologies.

Influence of Spinning Method on Shape Memory Effect of Thermoplastic Polyurethane Yarns

Shape memory polymers are gaining increasing attention, especially in the medical field, due to their ability to recover high deformations, low activation temperatures, and relatively high actuation stress. Furthermore, shape memory polymers can be applied as fiber-based solutions for the development of smart devices used in many fields, e.g., industry 4.0, medicine, and skill learning. These kind of applications require sensors, actors, and conductive structures. Textile structures address these applications by meeting requirements such as being flexible, adaptable, and wearable. In this work, the influence of spinning methods and parameters on the effect of shape memory polymer yarns was investigated, comparing melt and wet spinning. It is shown that the spinning method can significantly influence the strain fixation and generated stress during the activation of the shape memory effect. Furthermore, for wet spinning, the draw ratio could affect the stress conversion, influencing its efficiency. Therefore, the selection of the spinning process is essential for the setting of application-specific shape-changing properties.

Trans-Polyisoprene/Poly (Ethylene-co-Vinyl Acetate) Polymer Composites as High-Performance Triple Shape Memory Materials

The performance and programming conditions of the triple shape memory of crosslinked trans-polyisoprene/poly (ethylene-co-vinyl acetate) (TPI/EVA) composites with different contents of dicumyl peroxide (DCP) were investigated. The effect of triple shape memory in the TPI/EVA composites was studied by tensile loading, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and dynamic thermomechanical analysis (DMA). It was demonstrated that the content of DCP increased, the crystallization temperature of TPI decreased from 55.2 to 38.3 °C, and the crystallization temperature of EVA decreased slightly. The SEM results showed that DCP, as an initiator, could form a graft copolymer of TPI-g-EVA at the interface of the two phases, which could improve the adhesion of the two phases. The DMA showed that the higher the content of DCP, the higher the first-stage shape recovery ratio. Moreover, the composites exhibited favorable shape fixity ratio (R_f) and shape recovery ratio (R_r) with the incorporation of 0.4 phr DCP. At the same time, it was demonstrated that the TPI/EVA composites showed excellent mechanical strength, including tensile strength up to 24.3 MPa, as well as elongation at break reaching 508%.