Monitoring Network and Interfacial Healing Processes by Broadband Dielectric Spectroscopy: A Case Study on Natural Rubber

Abstract

Broadband dielectric spectroscopy (BDS) is introduced as a new and powerful technique to monitor network and macroscale damage healing in an elastomer. For the proof of concept a partially cured sulfur-cured natural rubber (NR) containing reversible disulfides as the healing moiety was employed. The forms of damage healed and monitored were an invisible damage in the rubber network due to multiple straining and an imposed macroscopic crack. The relaxation times of pristine, damaged and healed samples were determined and fitted to the HavriliakNegami equation to obtain the characteristic polymer parameters. It is shown that seemingly full mechanical healing occurred regardless the type of damage, while BDS demonstrates that the polymer architecture in the healed material differs from that in the original one. These results represent a step forward in the understanding of damage and healing processes in intrinsic selfhealing polymer systems with prospective applications such as coatings, tires, seals and gaskets.

Giving a Second Opportunity to Tire Waste: An Alternative Path for the Development of Sustainable Self-Healing Styrene–Butadiene Rubber Compounds Overcoming the Magic Triangle of Tires

“…The data corresponding to the virgin and damaged state of SBR ( Figure 5a) do not differ between each other; the frequency where the maxima appear are the same, and the shape of the peak is similar. This could imply that the damaged produced in the network structure did not alter the overall relaxation dynamics of the rubber, although we were expecting less restricted dynamics due to the bond breakage and chain scissions occurring after cyclic deformation [19]. Nonetheless, clear differences in the shape of the spectra can be noticed in the repaired sample; a widening of the relaxation is observed.…”

“…The irreversible covalent crosslinked rubber network theoretically blocks its self-healing capability, since chain mobility is required for healing to take place. Consequently, the mechanical performance and healing efficiency are antagonistic properties, since the simultaneous improvement of both properties is a priori not achievable [19]. Overcoming this compromise is one of the actual challenges of the self-healing scientific community.…”

“…This powerful and sensitive tool for studying the dipolar relaxations of polymers offers the possibility of covering an extensive range of temperatures and frequencies. Therefore, it is possible to investigate dynamic processes that take place on different time scales [19,21]. BDS can also be considered an important practice for monitoring healing in polymers, considering that this technique is capable of analyzing and describing multilevel molecular mobility as a function of the structural state of the polymer [19,22].…”

“…Therefore, it is possible to investigate dynamic processes that take place on different time scales [19,21]. BDS can also be considered an important practice for monitoring healing in polymers, considering that this technique is capable of analyzing and describing multilevel molecular mobility as a function of the structural state of the polymer [19,22]. Hernández Santana et al studied, for the first time, the molecular dynamics evolution during the healing of both internal and macroscopic damages of a partially cured NR, demonstrating that the polymer structure in the different states (virgin and healed) diverges [19].…”

Permeation Damage of Polymer Liner in Oil and Gas Pipelines: A Review

“…Dielectric spectroscopy is used to measure the permittivity or dielectric constant of the polymeric materials as a function of frequency [ 106 , 107 ]. It can also be done by as a function of time or temperature at fixed frequencies to determine the physical and chemical properties of polymer.…”