Enhancing Polymer Composites with Triboluminescent Materials

Fiber-reinforced polymer composites (FRPCs) have a variety of applications in diverse industries. However, predicting the failure of FRPCs is more difficult than predicting the failure of more traditional materials like steel. Furthermore, composites can suffer extreme internal damage, but show little if any external indication that damage has occurred. This study investigated the potential for integrated structural health monitoring and self-healing for polymer composites utilizing triboluminescent (TL) materials. This study followed three phases. In Phase 1, the effects of enhancing resins with TL zinc sulfide manganese (ZnS:Mn) and europium dibenzoylmethide triethylamine (EuD4TEA) phosphors were investigated, including optimization of the EuD4TEA synthesis process and development of a model for tensile modulus based on TL inclusion and type of resin. EuD4TEA should be synthesized using at minimum 80 mmol/L europium nitrate and 260 mmol/L DBM, with at least 80 mmol/L TEA. ZnS:Mn was observed to increase elastic modulus of vinyl ester and light-curable polyurethane, by 103% and 60%, respectively. The larger EuD4TEA crystals decreased vinyl ester’s (VE’s) elastic modulus by 11%, at least partly due to particle size. EuD4TEA-enhanced light-curing polyurethane suffered a 95% decrease in elastic modulus, mostly due to incomplete cure. Inclusion of EuD4TEA in the VE resin resulted in the formation of voids, approximately the size of the EuD4TEA crystals. Protecting the EuD4TEA crystals from the heat of cure reduced the formation of bubbles, and improved TL emissions. Thermogravimetric analysis indicated the NHEt3 group was lost as EuD4TEA was heated above 100 °C. In Phase 2, a new measurement system was developed to evaluate luminescence and longevity of TL-enhanced resins. Optical fibers with a tip coating of TL-enhanced resin both provided a stage for the sample and directed the TL emissions into a light sensor. This tip-coated optical fiber method results in less variation in TL signal for ZnS:Mn-enhanced VE and sucrose-enhanced VE samples than impacts on loose ZnS:Mn and sucrose crystals. The intensity of TL emissions may be increased sevenfold by exposing the TL-enhanced sample to ultraviolet light immediately prior to TL testing. In Phase 3, the potential for TL-induced polymerization (and, by extension, TL-induced healing) was assessed. The results show polymers may be cured with visible light, even low-intensity photoluminescence, indicating feasibility of TL-induced healing.