Analysis of curing of a sustained release coating formulation by application of NIR spectroscopy to monitor changes physical–mechanical properties

The focus of the study was to explore the physical–mechanical properties of curing films and use these properties as a reference for models that relate NIR spectra to the extent of curing. Cast films were cured at 40, 50, and 60 °C from 1 to 48 h before being scanned on an NIR Spectrometer and analyzed for physical–mechanical properties using an Instron® material testing system. The studies show clear dependence of the physical–mechanical properties on the time and temperature used for curing. Principal component analysis (PCA) and parallel factor analysis (PARAFAC) were performed to investigate the effect of curing on the films. Both PCA and PARAFAC analysis of the NIR spectra showed that spectral features could be directly related to the changes associated with the triethyl citrate (TEC), which directly affected the physical–mechanical properties during curing. Partial least squares (PLS) models were developed that related NIR spectra to the physical–mechanical properties. The use of the Young's Modulus as a reference for NIRS model development resulted in good prediction and was determined to be the best reference for model development. This study demonstrated the NIRS could predict the Young's Modulus which may be used to indicate the extent of curing.

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