Determination of gel time and gel point of epoxy-amine thermosets by in-situ near infrared spectroscopy.

Abstract A method of near-infrared spectroscopy combined with wavelet transform was proposed to determine in-situ the gel time and gel point of epoxy resin simultaneously. The reconstructed spectra of the low-frequency wavelet coefficients were used for determination of gel time, and the reconstructed spectra of some detail coefficients which are dominated by chemical information for determination of epoxy conversion. In-situ determination of gel point has been achieved using evolutionary near infrared spectra of epoxy curing. The accuracy of gel point achived to 0.01. Compared with the traditional determination method of gel point, in which TMA and DSC are respectively used for gel time and conversion, this method not only can determine in-situ gel time and conversion degree simultaneously, and remarkably improve accuracy of the gel point result but also is of low cost, and fast and easy to operate. Highlights • Gel time and gel point of epoxy curing can be determined simultaneously by in situ NIR spectroscopy combined with WT. • Accuracy of gel point has been remarkably improved using the reconstructed NIR spectra by WT detail coefficient. • Gel time can be easily monitored using the reconstructed NIR spectra by WT approximate coefficient. • The epoxy curing reaction has been interpreted at molecular level using the evolutionary NIR spectra. • The NIR method is obviously superior to the method of DSC combined with TMA because of low cost, fast and easy to operate. [ABSTRACT FROM AUTHOR]