Autonomic Self-Healing in Epoxidized Natural Rubber

The development of polymers that can repair damage autonomously would be
useful to improve the lifetime of polymeric materials. To date, limited attention
has been dedicated to developing elastomers with autonomic self-healing ability,
which can recover damages without need for an external or internal source of
healing agents. This work investigates the self-healing behavior of epoxidized
natural rubber (ENR) with two different epoxidation levels (25 and 50 mol %
epoxidation) and of the corresponding unfunctionalized rubber, cis-1,4-
polyisoprene (PISP). A self-adhesion assisted self-healing behavior was revealed
by T-peel tests on slightly vulcanized rubbers. A higher epoxidation level was
found to enhance self-healing. Self-healing of rubbers following ballistic damages
was also investigated. A pressurized air flow test setup was used to evaluate the
self-healing of ballistic damages in rubbers. Microscope (OM, SEM, and TEM)
analyses were carried out to provide further evidence of healing in the impact
zones. Self-healing of ballistic damages was observed only in ENR with 50 mol %
epoxidation and it was found to be influenced significantly by the cross-link
density. Finally, self-healing of ballistic damages was also observed in
ENR50/PISP blends only when the content of the healing component (i.e., ENR50) was at least 25 wt %. From an analysis of the results, it was concluded that a
synergistic effect between interdiffusion and interaction among polar groups leads
to self-healing in ENR.