Oligomeric Curing Activators Enable Conventional Sulfur-Vulcanized Rubbers to Self-Heal

Abstract

When introducing self-healing properties to elastomers, it is often difficult to balance their ability to recover properties after damage with a good mechanical strength prior to damage. We demonstrate that by replacing the activator system used in conventional accelerated vulcanization (CV) chemistry, from the traditional zinc oxide (ZnO) and stearic acid to a complex formed between ω-propenyl functional oligomers of poly(zinc methacrylate) (pZnMA/ZnO), the self-healing properties of vulcanized natural rubbers are enhanced while maintaining good tensile strengths. The pZnMA oligomers, as synthesized by catalytic chain transfer polymerization (CCTP), act as an activator for the sulfur curing system, while also forming an ionic network in the rubber. The addition of 20 phr of pZnMA/ZnO to a CV system resulted in a cured natural rubber with a tensile strength of 7.47 ± 0.64 MPa, which recovered 86.7% after self-healing at 80 °C for 2 h. Further addition of 40 phr of carbon black N234 unexpectedly enhanced the self-healing efficiency of these vulcanized rubbers to 92.2% under the same conditions and also improved the self-healing at room temperature. Finally, dynamic mechanical thermal analysis indicated that the natural rubber formulations containing pZnMA/ZnO showed improved wet traction but with higher rolling resistance to a standard formulation. These results point to an interesting direction for further research into the performance of self-healing composites in vehicle tire applications.

Effective and Fast-Screening Route to Evaluate Dynamic Elastomer-Filler Network Reversibility for Sustainable Rubber Composite Design

“…The CV system contains a higher sulfur content (2.0–3.5 phr) and lower accelerator:sulfur ratio (0.1–0.6) as compared to SEV and EV and generates higher amounts of poly- and disulfide bonds in the cured rubbers, therefore providing better mechanical strength and fatigue resistance, but lower thermal and reversion resistance . By reducing the sulfur content in the CV system, thermally triggered self-healing behavior was observed in vulcanized NR. , …”

A new strategy for improving high‐temperature mechanical properties of HNBR/ZDMA composites through polymerization of ZDMA promoted by zinc methylmercaptobenzimidazole

“…Finally, the total crosslinking density (V e ) of the vulcanizated rubber was calculated using the following Flory‐Rehner equation (), 19–21 where V s and χ were the molar volume of butanone (91.6 cm 3 /mol) and Flory‐Huggin's polymer‐solvent interaction parameter (0.34), respectively 17,22 . V r represented the volume fraction of rubber at swelling equilibrium, which was calculated using following the equation (), 23,24 where m 1 and m 2 were the masses of the swelling sample before and after drying, respectively. ρ 1 and ρ 2 were the densities of butanone (0.805 g/cm 3 ) and rubber, respectively.…”

“…where V s and χ were the molar volume of butanone (91.6 cm 3 /mol) and Flory-Huggin's polymer-solvent interaction parameter (0.34), respectively. 17,22 V r represented the volume fraction of rubber at swelling equilibrium, which was calculated using following the equation (2), 23,24…”

Design of Vulcanization Intermediates with Low Steric Hindrance Contributing to Vulcanization Network Formation

“…Rubbers are widely used in everyday life, such as automobile tires, airplane tires, and seismic isolation materials. − Sulfur cross-linking, known as vulcanization, is an extraordinarily important process to endow rubbers with practical performances in the rubber industry. − For the vulcanization reaction, the widely agreed pathway is that stearic acid and zinc oxide (ZnO) produce vulcanization intermediates, further initiating the formation of vulcanization networks. , However, the steric hindrance of such vulcanization intermediates often hinders the formation of vulcanization networks, limiting the property enhancement of vulcanized rubbers. , How to further promote the formation of vulcanization network is still a challenge in the rubber industry.…”