Towards Development of a Self-Healing Composite using a Mendable Polymer and Resistive Heating

Abstract

Mendomers are a group of polymers that are mendable upon heating. Specifically, cracks in these polymers have been shown to heal themselves when heated close to the glass transition temperature. The main mechanism behind the healing is the thermally reversible Diels—Alder reaction, where a dicyclopentadiene unit in the polymer backbone breaks apart into two cyclopentadiene terminal groups, which then reunite upon heating. The present study investigates the feasibility of using a mendomer as a matrix for re-mending composites reinforced with graphite fibers. The graphite fibers are used as electrical conductors to provide the necessary heat to the polymer. Specimens were prepared by spreading a monomer, called mendomer, powder on a graphite/epoxy laminate substrate and curing in a vacuum oven. Microcracks were introduced by bending the substrate coupon, and the latter was heated by applying electric currents. The healing behavior was confirmed by disappearance of microcracks that were observed with an optical microscope and a scanning electron microscope (SEM).

Cyclopentadiene‐functionalized polyketone as self‐cross‐linking thermo‐reversible thermoset with increased softening temperature

“…The decrease in the rDA DSC integrals of cyclopentadiene may be related to the presence of different trimer/dimer units ratio (Scheme ) or simply loss of thermo‐recovery efficiency. Indeed, trimers of cyclopentadienyl display a different rDA temperature than dicyclopentadienyl units . The same considerations outlined above are actually valid for DSC measurements of the higher conversion cyclopentadiene polymer ( PKCPD2 ) (Figure ).…”

“…These results are in agreement with what observed by X. Chen and E. Ruckenstein, who found, for a similar system, a sharp reduction in viscosity (taken as indication of thermal reversibility) in the range of 150–170°C. Moreover, other authors determined the same de‐cross‐linking temperature values (i.e., around 150°C) for monomeric units of di‐cyclopentadienyls linked by ester moieties. Recently, a study showed that, by submerging the cross‐linked network in toluene for 14 h, the detaching of the dicyclopentadiene units can occur at temperatures as low as 90°C.…”

“…This is in agreement to what observed for cyclic dicyclopentadienyl connected through ester bonds to aliphatic spacers . In particular, a study showed that the rDA exothermal peak is dependent on the heating rate (i.e., from 2°C min −1 till 15°C min −1 ) with a clear shift towards higher temperatures (in the range 190–210°C) for measurements performed at lower heating rates. Shifts towards the upper range limit or even the appearance of shoulders in the DSC can be related to the formation of trimers of cyclopentadiene .…”

An addressable conducting network for autonomic structural health management of composite structures

“…The contact resistance needs to be considered at the interface between conducting lines and the substrate laminate when the pair resistance is measured. The contact resistance was estimated using resistance measurements between two electrodes on the same surface at various distances and the intercept of their linear approximation [5,6]. This contact resistance model has been shown to be effective in simulating resistive heating [6].…”

“…Supplying a high electric current to the graphite fibers generates resistive heating in the polymer matrix. It has been successfully shown that a thermally mendable polymer can be healed by using resistive heating when used as a matrix [5][6][7]. In addition, the conductive property allows in-service health monitoring systems by the electrical resistance change method (ERCM) .…”