Determination of accelerators and antioxidants in vulcanized rubber by Fourier transform infrared spectrophotometry

During vulcanization, rubber is treated with different substances that have a marked influence on the properties of the end product. Identifying and determining the chemical species responsible for such properties is rendered difficult by the fact that some are incorporated into the vulcanizate or decompose during the process. In this work, we developed a new method for the determination of vulcanization accelerators and antioxidants based on Fourier Transform Infrared spectra of the CCl4 extracts of vulcanized rubber specimens. Calibration is performed by using Partial Least-Squares Regression (PLSR); the additive concentrations prior to vulcanization are related to the spectra of the fragments or decomposition products extracted from the polymer matrix following vulcanization. The effects of the spectral mode (absorbance or first-derivative) and wavenumber range were assessed by constructing various models to ensure accurate determinations. The proposed method was applied to two vulcanizates obtained by two different procedures; the results were quite satisfactory in both cases. (C) 1997 Elsevier Science B.V.