On-line monitoring of alkali-free cloth/phenolic resin prepreg by near-infrared Spectroscopy

A Near-infrared (NIR) spectroscopy method was developed for the on-line analysis of the resin content, the solubility resin content and the volatile content during the manufacture of alkali-free cloth/phenolic resin prepreg. The partial least square (PLS) regression was used to develop the calibration models, which for the volatile content was preprocessed by 1st derivative (DER) + VN (R-2 = 98.84, RMSEC V = 0.120), for the solubility resin content by 1st DER + MSC (R-2 = 99.24, Root mean square error of calibration (RMSEC) V = 0.058) and for the resin content by spectral data preprocessing method (R-2 = 97.51, RMSEC = 0.357). Root mean square error of prediction (RMSEP) of the prediction model for the resin content was 0.605, for the solubility resin content was 0.101 and for volatile content was 0.127. The results of the paired t-test revealed that there was no significant difference between the NIR method and the standard method. The NIR spectroscopy method could be used to predict the resin content, the solubility resin content and the volatile content simultaneously. Besides, the prepreg was analyzed once within 1 min without sample destruction. The processing parameters of the prepreg during manufacture could be adjusted according to the results of the NIR spectroscopy method. The results indicated that the NIR spectroscopy method was sufficiently accurate and effective for quality control in alkali-free cloth/phenolic resin prepreg.