Mechanical and thermo-oxidative resistance properties of natural rubber film reinforced by orange peel-based carbon dots

Bio-based carbon dots (CDs) have a wide range of precursor sources, abundant chemical functional groups, and good free radical scavenging ability. This makes them an excellent candidate for modifying natural rubber (NR). In this work, CDs were synthesized from orange peels using a hydrothermal process and were utilized to reinforce NR latex. The structure and properties of both the CDs (including morphology, functional groups and fluorescence emission spectra) and NR/CDs films (including crosslinking density, morphology, functional groups, and mechanical properties) were comprehensively investigated. The results indicate that the inclusion of CDs led to improvements in tensile and tear strength while maintaining undamaged elongation at break. The tube model results indicate that the Ge (the elastic modulus brought by entangled chains) is significantly higher than the Gc (the elastic modulus contributed by chemical crosslinking) in this system, suggesting that the physical entangled network play a more significant role than chemical cross-linking; and the trend of Gc+Ge with the amount of CDs aligns completely with the cross-linking density measured by swelling method. Additionally, it was observed that CDs exhibited excellent thermo-oxidative resistance properties for NR. After 24 hours of thermal aging, the aging coefficient increased from 20.7% (NR-0) to 65.8% (NR-7). Furthermore, with an increase in thermal aging time, the tensile strength and crosslinking density of NR-0 decreased at a faster rate compared with NR-5. At an aging time of 40 hours, the tensile strength of NR-0 was reduced to 0.53 MPa and almost completely failed; whereas the tensile strength of NR-5 was still maintained at 8.2 MPa. Overall, the addition of CDs dramatically improved the thermo-oxidative resistance and mechanical properties of the NR film. Simultaneously, a novel way involving the utilization of orange peel with high value is being proposed. • Orange peel was selected as the raw material for preparing carbon dots without any passivation or purification treatment. • The dispersion solution of carbon dots was directly utilized to modify natural rubber latex. • The tube model was employed to elucidate the reinforcing mechanism of carbon dots on NR; • The thermo-oxidative resistance of carbon dots on NR has been revealed.