Physicochemical, Thermomechanical, and Swelling Properties of Radiation Vulcanised Natural Rubber Latex Film: Effect of Diospyros peregrina Fruit Extracts

A range of radiation vulcanised natural rubber latex (RVNRL) films were prepared using various concentrations of aqueous extracts of mature Diospyros peregrina fruit, which acted as a cross-linking agent. The surface of the RVNRL films exhibited an aggregated morphology of the rubber hydrocarbon with increasing roughness due to increasing fruit extract contents in the latex. An improvement in tensile strength, tensile modulus, and storage modulus of RVNRL films was observed with the addition of fruit extracts compared to the control film due to their cross-linking effect. The glass transition ( ) temperature of all the RVNRL films was found to be at around ？61.5°C. The films were also observed to be thermally stable up to 325°C, while the maximum decomposition temperature appeared at around 375°C. The incorporation of fruit extracts further revealed a significant influence on increasing the crystallinity, gel content, and physical cross-link density of the RVNRL films. 1. Introduction Virgin natural polymers like rubber latex, an elastic macromolecular polymer (polyisoprene), have inherently low mechanical and thermal stability properties. Natural rubber is highly sensitive to thermal decomposition and autooxidation and, therefore, undergoes thermal aging when exposed to heat, air, and ozone resulting in poor mechanical, thermal, and swelling properties. In order to improve their mechanical properties the rubber molecules are being processed with different types of antioxidants and particulate fillers, such as silica [1, 2], clays [3], carbon black [4], and carbon nanotubes [5, 6] to expand their applications in various fields. Radiation vulcanisation is also being employed to improve the mechanical properties of natural rubber [5, 7, 8]. Some nonwater soluble amino acids, such as cystine, asparagines, and alanine, were also used as antioxidant in radiation vulcanised natural rubber latex (RVNRL) films and showed good antiaging effect on RVNRL films with tensile strength retentions ranging from 70% to 80% after accelerated aging at 100°C for 24？h compared to RVNRL film containing no antioxidant (tensile strength retention ~35%) [9]. They also reported Keratin from chicken feather as a potential antioxidant (tensile strength retention ~60%) for RVNRL film. Tris(nonylated phenyl)phosphite (TNP) [10–12], polyfuran, polythiophene [13], polyamines [3, 14], and pyridazine derivatives [15] were also reported to be effective antioxidants to prolong the life of natural and synthetic rubber films. Ko？íková et al. [16] investigated sulphur free lignin (10–30？phr)