Effect of pressure on the intensity of absorption bands in the IR spectra of compacted polyethylene powde

The investigation of the IR spectra of compacted reactor powders of ultra-high-molecular-weight polyethylene showed that the intensities of the absorption bands depend on the compaction pressure; namely, they decrease with increasing pressure. It is found that the ultimate pressure above which the absorption band intensity ceases to decrease depends on the spectral position of the band; the shorter the wavelength, the higher the ultimate pressure. This pressure is 5–10 MPa for bands in the long-wavelength spectral region (the band at 720 cm −1 ) and 100 MPa for the short-wavelength region (the band at 5875 cm −1 ). It is assumed that this phenomenon is related to a change in the size of pores d with pressing. Beams with wavelengths λ < d will undergo multiple diffuse reflections and reach a photodetector that is weaker than beams with λ > d . With increasing pressure, the size of pores decreases and the boundary between the two regions of the spectra shifts to short wavelengths.