Stress‐Induced Melting of Crystals in Natural Rubber: a New Way to Tailor the Transition Temperature of Shape Memory Polymers

Abstract

Lightly cross-linked natural rubber (NR, cis-1,4-polyisoprene) was found to be an exceptional cold programmable shape memory polymer (SMP) with strain storage of up to 1000%. These networks are stabilized by strain-induced crystals. Here, we explore the influence of mechanical stress applied perpendicular to the elongation direction of the network on the stability of these crystals. We found that the material recovers its original shape at a critical transverse stress. It could be shown that this is due to a disruption of the strain-stabilizing crystals, which represents a completely new trigger for SMPs. The variation of transverse stress allows tuning of the trigger temperature T(trig) (σ) in a range of 45 to 0 °C, which is the first example of manipulating the transition of a crystal-stabilized SMP after programming.

Shape‐Memory Natural Rubber: An Exceptional Material for Strain and Energy Storage

“…As recently reported, the trigger temperature increases with rising programming temperature 23–25. We propose that this is possibly due to the growing crystal size.…”

“…Secondly, SMNR is the first example of a semi‐crystalline SMP with a significantly tunable trigger temperature 23. Thirdly, even after programming the trigger temperature can be adjusted by mechanically manipulating the stress transverse [stress‐induced melting (SIM)]24 and parallel [stress‐induced stabilizing (SIS)]25 to the elongation‐stabilizing direction. Finally, SMNRs have the capability to store extremely large strains of up to 1000% 23.…”

Recent progress in shape memory polymer: New behavior, enabling materials, and mechanistic understanding

“…Intriguingly, recent study has shown that polymer crystals formed via strain-induced crystallization can be manipulated to precisely tune the melting temperature [312][313][314]. This may open up new ways to induce 2W-SME.…”

Environmental Memory of Polymer Networks under Stress

“…[ 19 ] Particularly interesting are polymer networks that not only respond to but also memorize an environmental signal. [ 22,23 ] Further, programmed SMNR strongly responds to liquids and gases by resuming its original shape. We hypothesize that this behavior might be found for those semi-crystalline networks where the change of the amorphous phase has a signifi cant impact on the stability of the crystals.…”