Comparison of Crystallinity and Molecular Orientation between Surface and Bulk of Some Polymers by FTIR-ATR and Transmission Spectroscopy.

Abstract : Fourier transform IR transmission and multiple internal reflection spectroscopy were used to characterize polyethylene and polypropylene surfaces and to compare with their bulk properties in regard to the degree of crystallinity and molecular orientation. Surface crystallinity of the cold drawn polyethylene and polypropylene samples is found to be similar to the bulk crystallinity values. In order to improve accuracy of the surface orientation measurement, a new rotatable sample holder, which utilizes a double-edged square parallelogram rather than conventional single-edged rectangular trapezoidal plates was designed. This enables the polymer film to be mounted and rotated orthogonally while maintaining identical contact. As a result, the three optical constants, kx, ky, and kz can be determined by using four equations, thus providing a check on the reliability of the data. Preliminary results obtained with this new sample holder indicate that the surface of cold drawn polyethylene has lower orientation than bulk, while similar orientation values were observed when comparing the surface with the bulk of cold drawn polypropylene. (Author)