A new method for estimating the content of vinyl acetate in ethylene-vinyl acetate copolymer

A new method for estimating the content of vinyl acetate (VA) in ethylene-vinyl acetate copolymer (EVA) is proposed. It is a kind of optical absorption spectroscopy in a frequency range from 0.5 to 21.0 THz. Comparison of absorption spectra among sheets of EVA with differing contents of VA from 12 to 60% by weight and a sheet of low-density polyethylene containing no VA revealed that the EVA sheets exhibit relatively sharp absorption at 2.5, 6.7, and 10.5 THz and rather broad absorption at 11 to 17 THz and 17 to 20 THz. All these absorption intensities are in proportion to the content of VA, up to certain contents, which enables us to estimate the content of VA in EVA quantitatively. Among them, the absorption at 2.5 THz measured by THz time-domain spectroscopy shows the best accuracy.