Gas chromatography: A new method of non contact NDE for cure monitoring of carbon-phenolic composites for determination of the gelation region for pressure application

We report the use of gas chromatography as a non contact Non destructive method for online cure monitoring of the carbon-phenolic composites during autoclave curing process to identify the gelation region for pressure application. Experimental trials are made on the laminates prepared by hand lay-up process in autoclave. During curing process methylol-phenol (M-phenol) and water are evolved as reaction by-products and the concentrations of the evolved byproducts are monitored by on-line gas chromatograph connected to autoclave facility. Experimental parameters like sample injection method, sample volume and time of injection have been optimized and M-phenol and water evolution concentrations are monitored as a function of component temperature. M-phenol evolution is more consistent compared to water evolution and therefore based on the falling trend of the methylol phenol concentration a broad region of gelation for pressure application is identified. The region thus identified is further narrowed down based on the diminishing trend of the M-phenol concentration and the experimental analysis of the laminates focusing on resin content and void content. Finally the on-line pressure application criterion was established based on the resin content and void content data.