Application of NIR Spectroscopy and Fluorescence Spectroscopy for Monitoring of Curing of Sustained Release Coatings

Abstract

Objectives: The aim of this study was to investigate the application of NIR spectroscopy and fluorescence spectroscopy to the monitoring of curing of sustained release coating formulations. Methods: Films of coating formulations were prepared by casting method and were monitored during the curing process using a Thermal Analysis differential scanning calorimeter, an Instron? System for physical-mechanical analysis, a Foss NIR spectrometer, and an ISS Inc. Fluorescence Spectrometer. Methods were developed for the NIR spectrometer using data as reference acquired from examining glycerl monostearate and physical-mechanical properties. The NIR methods were developed using chemometric processing including principal component analysis (PCA), parallel factor analysis (PARAFAC), and partial least squares (PLS) regression. Results: Three methods were developed for monitoring the curing of coating formulations, two NIR spectroscopy methods and one fluorescence spectroscopy method The first NIR spectroscopy method was developed using the melting endotherm of glyceryl monostearate (GMS) as a reference. The developed PLS method provided excellent prediction of the state of GMS within the matrix indicative of a homogenous film and extent of curing. The second NIR spectroscopy method was developed after examination of physical-mechanical properties during the curing process. The Young's Modulus was found to be the best reference for PLS calibration and provided good prediction of the extent of the curing process Three different fluorescence probes were used in the development of a fluorescence spectroscopy method for detecting changes in the microenvironment during the curing process. Monitoring the fluorescence intensity and the fluorescence anisotropy of DPH and DMA-DPH within the polymer matrix successfully reported on changes of the physical and chemical state during the curing process. Conclusion This study demonstrated that NIR spectroscopy and fluorescence spectroscopy are methods that can be applied to the monitoring of curing of coating formulations. The study successfully demonstrated the use of NIR spectroscopy for predicting the state of GMS within a polymer matrix. Furthermore, to our knowledge, this study is the first application of NIR spectroscopy for prediction of the physical-mechanical properties of polymer films. The studies also developed and applied a novel approach for monitoring curing of coating formulations by application fluorescence spectroscopy.