Raman spectroscopy determination of the thermoplastic content within epoxyresin-copolyethersulfone blends

The possibility of using Raman spectroscopy to determine the local thermopl astic content within blends of epoxy resins and copolyethersulfone was stud ied. The required calibration of the Raman data is presented here. It was o btained by multivariate methods and was based on homogeneous samples of kno wn content in amine-ended thermoplastic (expressed in weight %). Blends cur ed with two types of diamine curing agents were separately studied, the cur ing agents being the methylene bis(2,6-diethylaniline) (MDEA) and the 4,4'd iaminodiphenylsulfone (DDS). Partial least-squares (PLS) regressions with e xternal validation were performed. With MDEA, root mean square error of pre diction (RMSEP) values at validation were 3.2, 3.7, and 3.0% (depending on the spectral pre-treatment and on the wavenumber selection). RMSEP values w ere 2.4 or 3.0% with DDS (depending on the wavenumber selection). The appli cability of the calibrations to blends containing chlorine-ended copolyethe rsulfone is discussed. Results obtained with small or large Raman confocal holes are also compared.