In situ monitoring the manufacturing process of polymer composites with highly flexible and sensitive GNP/ MWCNT film sensors.

Highlights • This paper proposes a new GNP/MWCNT sensor, because of its unique mesoporous structure, the GNP/MWCNT film has good compatibility with the composite. • During the manufacturing process, the sensor can effectively capture the change of the resin phase, which is characterized by resistance change. As the resin changes from a rubbery state to flowing liquid state, the resin infiltration sensor changes the conductive structure. It causes the resistance increase. When resin cross-links, the matrix contraction leads to the electrical structure recovery and resistance drop. Once the resin cured basically, the resistance rises slowly due to its negative temperature coefficient. • With a standard curing system, the gel point was demonstrated in the curve of the real-time resistance change of the sensor. Compared with DMA results, results are basically same. However, DMA is laboratory method under certain conditions. It requires specific samples that are small size and/or lightweight. The GNP/MWCNT film sensor can monitor gel points in different locations and thicknesses in real time. Therefore, this method readily be applied to the in-situ monitoring of composite curing on the industrial scale and results are more accurate. Abstract In this study, we developed a film sensor composed of multi-walled carbon nanotubes (MWCNTs) and graphene nanoplates (GNPs) via a simple mixing and spray-vacuum filtration. This highly flexible and sensitive GNP/ MWCNT film sensor can be embedded into polymer composite to in situ monitor the resin phase changes and gel point during the composite manufacturing process. The resistance of the GNP/MWCNT film sensor was obtained using two-terminals method by Fluke 2638 A, and the resistance changes could be related to phase changes of the resin matrix. Dynamic mechanical analysis (DMA) was performed to obtain the gel point of the composite as a baseline to compare with the GNP/MWCNT film sensor output. Experimental results show that the GNP/MWCNT film sensor embedded in the composite laminates can effectively capture the change of the resin phase, which is characterized by resistance. As the resin changed from the rubber state to the flow state, the resistance increased from 2.5 × 10−3 to 1.04. When the resin was cross-linked, the resistance dropped from 1.04 to 0.88. Once the resin is substantially cured, the resistance rises from 0.88 to 0.97 slowly. GNP / MWCNT films have a good ability to respond to changes in the resin state. The gel point of resin obtained from the GNP/ MWCNT film sensor is 134℃, which is consistent with 137℃ from the DMA results. The accurate gel point can optimize the curing system and improve the quality of composite products. The GNP/MWCNT film sensor has great potential to establish and optimize manufacturing processes and to improve the cure quality of fibre-based resin composites. [ABSTRACT FROM AUTHOR]