Non-destructive analysis of photodegradation of poly(methyl methacrylate) by near infrared light-fibre spectroscopy and chemometrics

Photo-degradation of poly(methyl methacrylate) (PMMA) has been analysed in situ by the use of near infrared (NIR) light-fibre spectroscopy. Fourier transform (FT) NIR spectra have been measured for PMMA plates irradiated by a high-pressure mercury lamp (450 W) for 0, 30, 60, 90, 120, 150, 180 and 210 min. Principal component analysis (PCA) has been carried out for the FT-NIR spectra pretreated by multiplicative scatter correction (MSC) or second derivative. A principal component (PC) weight loadings plot of factor 1 shows that the irradiation time is strongly correlated with the band due to the second overtone of the C=O stretching mode. Partial least squares (PLS) regression has enabled us to propose a calibration model which predicts the irradiation time of the PMMA plates, with a correlation coefficient and the mean square error of cross validation (RMSECV) of 0.995 and 7.2 min, respectively.