Two‐way multi‐shape memory properties of peroxide crosslinked ethylene vinyl‐acetate copolymer (EVA)/polycaprolactone (PCL) blends

Abstract

Rare studies have investigated on the 2‐way shape memory crosslinked blends with multiple shape memory behavior up to date. To consider the merit of commercial cost‐competitive crystalline polymers, ethylene vinyl‐acetate copolymer (EVA)/polycaprolactone (PCL) blends (60/40 and 30/70) were peroxide‐cured to form the 2‐way multi‐shape memory crosslinked blends using a melt‐blending method. Both resins were selected to have a similar controlled crosslinking degree, which allowed us to distinctly evaluate their actuation contributions from the cooling‐induced elongation (crystallization) and from the entropy‐driven elongation during cooling process, respectively. In the 2‐way process for the 60/40 system, 2 respective peaks contributed from the cooling‐induced crystallization of EVA and PCL in the cooling curves based on the strain derivate rates at various temperatures were observed. After the cooling process under the loading stress of 150 kPa, the 2‐step heating‐induced contraction process with increasing temperature started at 54.1°C above the melting temperature of PCL at 52.3°C and EVA at 78.3°C, demonstrating 2‐way multi‐shape memory behavior. The multi‐step behavior was more prominent at higher PCL composition and higher load for the 30/70 system. It was found that the entropy‐driven contribution to the overall actuation magnitude increased with increasing nominal loads due to the increased orientation of molecular networks in the blends. The current approach offers numerous possibilities in preparing 2‐way multi‐shape memory crosslinked blends.

Design of Ethylene-Vinyl Acetate Copolymer Fiber with Two-Way Shape Memory Effect

“…For example, Figure 5a,c show the shape memory process in the stretched and contracted states (relative to the initial length), respectively. Moreover, the significant MIC and CIE emerge during each heating-cooling cycle [55]. The R a,2W of EVA-6M was only 8.69% after five cycles, and there was a downward trend as shown in Figure 5a and Table 3.…”

Thermo‐responsive shape memory behavior of poly(styrene‐b‐isoprene‐b‐styrene)/ethylene‐1‐octene copolymer thermoplastic elastomer blends

“…10 Semi-crystalline polymer/elastomer blends are an effective and economical method for production of SMPs. [11][12][13][14] While the semi-crystalline polymer acts as a switch between permanent and temporary shape, the elastomeric polymer provides entropic elasticity to return the material to its permanent shape. Unlike conventional elastomers, thermoplastic elastomers (TPEs) are multi-phase polymers in which hard and soft phases are dispersed within each other.…”

Two‐Way Reversible Shape Memory Properties of Benzoyl Peroxide Crosslinked Poly(ethylene‐co‐vinyl acetate) under Different Stress Conditions

“…Several pioneering works have contributed to production of materials with two‐way shape memory behavior, including laminated composites, [ 28–32 ] liquid crystal elastomers, [ 33,34 ] and crosslinked crystalline polymers. [ 35–49 ] Laminated polymer composites comprising two layers bonded with an adhesive agent are limited by the weak interlayer strength and cyclicity. Furthermore, the complicated synthesis of liquid crystal elastomers is still challenge, which limits their mass production.…”