Modulation of shape memory properties of trans-polyisoprene by sulfur

Abstract In this paper, TPI/S composites were prepared by a simple physical melt blending method, and the composites were hot-pressed and molded using a vulcanization system. The effect of cross-linking on the vulcanization properties, mechanical properties, crystalline properties, and shape memory properties of trans-1-4 polyisoprene (TPI) was investigated by varying the amount of sulfur (S). It was shown that with the increase of sulfur dosage, both TPI scorch time and orthoclave time were shortened and the mechanical properties decreased; The melting peak area and melting temperature of the crystalline region of TPI decreased with the increase of sulfur content, and the cross-linking density increased while the crystallinity tended to decrease and the heat resistance deteriorated; In addition, with the increase of sulfur content, the shape return rate of TPI/S composites was increasing and the shape fixation rate was decreasing. When the TPI/S composites were used as shape memory materials, the sulfur dosage of 1 phr had the best shape memory performance, at which time the shape fixation rate of the composites reached 96.9% and the shape recovery rate reached 86.2%. When the sulfur content was elevated to 2 phr, the shape memory fixation rate was significantly decreased, indicating that the shape memory properties were severely compromised. This study reveals that the quantity of sulfur exerts a significant influence on the application of TPI/S composites. An appropriate amount of sulfur can facilitate the preparation of thermoplastic elastomers for utilization in shape memory materials. Nevertheless, an excessive amount of sulfur will substantially enhance the internal cross-linked structure of the composite and deteriorate the shape memory performance.