Comparison between Far-IR and IR Absorption Spectroscopy for Estimating Vinyl Acetate Content in Ethylene-vinyl Acetate Copolymer

Far-IR absorption spectra at frequencies from 0.5 to 21.0 THz were obtained for sheets of ethylene-vinyl acetate copolymer (EVA) containing different contents of vinyl acetate (VA) from 12 to 60% with different thicknesses from 1.0 to 3.0 mm. As a result, EVA exhibits absorption at 2.5, 6.7, 10.5, 11-17, and 17-20 THz. Especially, the 2.5-THz intensity with a good proportionality up to 60% of VA content exhibits comparable accuracy to the IR method and is applicable for estimating the VA content in EVA sheets 2.0 or 3.0 mm thick, for which IR method is difficult to be applied.