Roles of Chitosan as Bio-Fillers in Radiation-Vulcanized Natural Rubber Latex and Hybrid Radiation and Peroxide-Vulcanized Natural Rubber Latex: Physical/Mechanical Properties under Thermal Aging and Biodegradability.

Although natural rubber was regarded as biodegradable, the degradation is a time-consuming process that could take weeks or months for any degradation or substantial weight loss to be observable, resulting in the need for novel processes/methods to accelerate the rubber degradation. As a result, this work investigated the potential utilization of chitosan (CS) as a biodegradation enhancer for radiation-vulcanized natural rubber latex (R-VNRL) and hybrid radiation and peroxide-vulcanized natural rubber latex (RP-VNRL) composites, with varying CS contents (0, 2, 4, or 6 phr). The R-VNRL samples were prepared using 15 kGy gamma irradiation, while the RP-VNRL samples were prepared using a combination of 0.1 phr tert-butyl hydroperoxide (t-BHPO) and 10 kGy gamma irradiation. The properties investigated were biodegradability in the soil and the morphological, chemical, mechanical, and physical properties, both before and after undergoing thermal aging. The results indicated that the biodegradability of both the R-VNRL and RP-VNRL composites was enhanced with the addition of CS, as evidenced by increases in the percentage weight loss (% weight loss) after being buried in soil for 8 weeks from 6.5 ± 0.1% and 6.4 ± 0.1% in a pristine R-VNRL and RP-VNRL samples, respectively, to 10.5 ± 0.1% and 10.2 ± 0.1% in 6-pph CS/R-VNRL and 6-pph CS/RP-VNRL composites, respectively, indicating the biodegradation enhancement of approximately 60%. In addition, the results revealed that the addition of CS could increase the value of tensile modulus by 119%, while decrease the values of tensile strength and elongation at break by 50% and 43%, respectively, in the specimens containing 6-phr CS. In terms of the color appearances, the samples were lighter and yellower after the addition of CS, as evidenced by the noticeably increased L* and b* values, based on the CIE L*a*b* color space system. Furthermore, the investigation into the effects of thermal aging showed that the overall tensile properties for both curing systems were reduced, while varying degrees of color change were observed, with the pristine R-VNRL and RP-VNRL samples having more pronounced degradation/changes for both properties. In conclusion, the overall results suggested that CS had great potential to be applied as a bio-filler in R-VNRL and RP-VNRL composites to effectively promote the biodegradability, environmental friendliness, and resistance to thermal degradation of the composites.