Electrical Resistance Sensing of Epoxy Curing Using an Embedded Carbon Nanotube Yarn

Abstract

Curing effects were investigated by using the electrical response of a single carbon nanotube yarn (CNTY) embedded in an epoxy resin during the polymerization process. Two epoxy resins of different viscosities and curing temperatures were investigated, varying also the concentration of the curing agent. It is shown that the kinetics of resin curing can be followed by using the electrical response of an individual CNTY embedded in the resin. The electrical resistance of an embedded CNTY increased (~9%) after resin curing for an epoxy resin cured at 130 °C with viscosity of ~59 cP at the pouring/curing temperature (“Epon 862”), while it decreased (~ −9%) for a different epoxy cured at 60 °C, whose viscosity is about double at the corresponding curing temperature. Lowering the curing temperature from 60 °C to room temperature caused slower and smoother changes of electrical resistance over time and smaller (positive) residual resistance. Increasing the concentration of the curing agent caused a faster curing kinetics and, consequently, more abrupt changes of electrical resistance over time, with negative residual electrical resistance. Therefore, the resin viscosity and curing kinetics play a paramount role in the CNTY wicking, wetting and resin infiltration processes, which ultimately govern the electrical response of the CNTY immersed into epoxy.

Monitoring of Curing and Cyclic Thermoresistive Response Using Monofilament Carbon Nanotube Yarn Silicone Composites

“…During the temperature programs, specimens were equilibrated for 15 min at RT in stabilization zone (S). In order to evaluate the signal noise level, the signal to noise ratio (SNR) of the fractional change in electrical resistance was calculated according to [10]:…”

“…In addition, the high porosity of the CNTYs may promote infiltration of liquids between the CNT bundles affecting the stiffness, toughness, and electrical conductivity of the yarn by separating the adjacent CNT bundles and increasing the contact electrical resistance [3,[7][8][9]. It was observed that C 2021, 7, 60 2 of 14 the thermoresistive properties of the embedded CNTY strongly depend on the chemical structure of the polymeric matrix, temperature range, porosity, and capillary diffusion of polar liquids [3,8,[10][11][12][13][14][15]. Rodríguez-Uicab et al [10] investigated the effect of the curing kinetics of epoxy resins with different viscosities on the thermoresistive response of the CNTY monofilament composites at different curing temperatures.…”

“…It was observed that C 2021, 7, 60 2 of 14 the thermoresistive properties of the embedded CNTY strongly depend on the chemical structure of the polymeric matrix, temperature range, porosity, and capillary diffusion of polar liquids [3,8,[10][11][12][13][14][15]. Rodríguez-Uicab et al [10] investigated the effect of the curing kinetics of epoxy resins with different viscosities on the thermoresistive response of the CNTY monofilament composites at different curing temperatures. The results showed that the fractional change in electrical resistance of the CNTY/epoxy resin increased (~9%) during the curing process of an epoxy resin with a viscosity of 59 cP cured at 130 • C, while it decreased (~−9%) for another epoxy with viscosity of 115 cP cured at 60 • C. It was observed that the curing kinetics of epoxy resin has a dominant role on the electrical resistance of CNTY monofilament composites due to the resin infiltration, electrochemical charge transfer, chemical and thermal shrinkage, and thermal stresses.…”

Monitoring Strain Response of Epoxy Resin during Curing and Cooling Using an Embedded Strain Gauge

“…Strain responses of curing stress have been studied by scientists by using carbon fibers [ 17 , 18 , 19 , 20 ], glass fibers [ 21 ], and carbon nanotube yarn [ 22 ]. For example, Y. Huang et al used Raman spectroscopy to study the residual stress in carbon fiber/epoxy resin composites and made it clear that this technology is an excellent scientific tool for determining the residual stress in composites [ 23 ].…”

“…For example, Y. Huang et al used Raman spectroscopy to study the residual stress in carbon fiber/epoxy resin composites and made it clear that this technology is an excellent scientific tool for determining the residual stress in composites [ 23 ]. Omar Rodríguez-Uicab et al have investigated the curing effects and development of residual stresses during epoxy resin curing through the electrical response of a single carbon nanotube yarn embedded in the epoxy polymer [ 22 ]. These landmark works boost the development of multifunctional smart materials integrated into structural composites, and have made extraordinary contributions to the study of resin curing kinetics.…”