Material Selection and Geometric Design for Few-filament Shape Memory Polymer Yarns for Force Generation

Integrating shape memory polymers (SMPs) directly into textiles embeds responsiveness into the structure, making these materials great candidates for applications such as compression stockings. Despite advancements in material performance and textile design, an investigation of the impact of twist on SMP performance and guidelines for SMP selection are needed to enable designers to leverage SMP performance in textiles. A material selection process for few-filament force generating SMP yarns evaluates material candidates by dynamic mechanical analysis, differential scanning calorimetry, and tensile testing. Although this material selection process is tailored to force generating yarns for compression garments, the method may be adapted to other applications. Two selected SMPs, polyamide and poly(lactic acid), were manufactured into few-filament yarns to enable a tailorable relationship between stress and strain beyond nominal material behavior. The strain programmed SMP twisted yarns recover up to 20% more programming force than straight filaments during stress recovery. The potential of SMP yarns in textiles is evaluated for compression garments by mapping the relationship between circumference, pressure, and active textile linear tension. The material selection process and evaluation of customizable mechanical performance through few-filament yarn structures will encourage and enhance the incorporation of SMPs into compression garments and other applications.