Stratification in thermoplastic olefins (TPO); photoacoustic FT-IR depth profiling studies

Photoacoustic Fourier Transform infrared (PA FT-IR) depth profiling experim ents ranging from 3 to 50 mu m into the surface of thermoplastic olefin (TP O) show that the crystalline polypropylene (PP) phase resides at approximat ely 7-9 mu m below the TPO surface, while ethylene-polypropylene rubber (EP R) layer is present at 15 mu m, and extends into the bulk. In an effort to determine the distribution of PP and EPR components, a calibration method w as developed by ratioing pure PP and EPR bands at 2953 and 2849 cm(-1) at 1 0/90, 25/75, 50/50, 75/25, and 90/10 ratios. Comparison of this numerical d ata and the experimental results allows determination of the distribution o f EPR and PP components across the film thickness. It appears that the EPR region is predominantly present at 15 mu m below the surface, while PP is l ocated at shallower depths. Concentration variations of talc can be also fo llowed by monitoring the band at 1019 cm(-1) caused by Si-O stretching mode s and its content is higher near the TPO surface. Based on these studies, a stratification model for TPO is proposed. (C) 1999 Elsevier Science Ltd. A ll rights reserved.