Relationships between swelling temperature and shape memory properties of palmitic acid-based shape memory natural rubber

Abstract

This article investigates the effect of swelling temperature on palmitic acid-based shape memory natural rubber (SMNR). SMNR has high storage modulus and excellent energy absorption capability which is suitable to replace the electronic parts in the lightweight machine. Although the swelling process increased the trigger temperature of palmitic acid-based SMNR, high thermal energy in swelling process might accelerate the degradation of the SMNR. To verify the swelling effect, two rubber sources were adopted in the sample preparation and immersed into molten palmitic acid. A custom-made elongation device which is introduced in the methodology section was used to measure the shape memory parameters under different deformation strains (100%, 200% and 300%). It was found that both swollen rubber sources stood their own beneficial shape memory parameters. For example, high shape fixation ($$>90\%$$) was found in natural rubber latex film (NRLF) specimen, while natural rubber (NR) specimens had outstanding shape recovery (100%). Swelling experiment revealed that the solvent diffusion rate was increased in higher swelling temperature, but crosslink density of rubber specimen limited the penetration of palmitic acid and maximum solvent uptake amount. Strain control mode test indicated that the swelling temperature accelerated the chain scission process which decreased the crosslink density of rubber specimens, but shape fixation was increased by high void formation. The DSC test clearly showed that trigger temperature varied with the solvent contents in the rubber specimens. Scanning electron microscopy images illustrated that the precoated palmitic acid was formed on the rubber molecules. The relationship between the swelling temperature and shape memory parameters of SMNR was established and the trigger temperature of SMNR was successfully increased near the melting temperature of fatty acid.