Investigation of the crystallinity and orientation of polypropylene with respect to temperature changes using FT-IR, WRD, and Raman techniques

Abstract

Having good mechanical and barrier properties, polypropylene films are widely used in food-packing industry. The relation of crystallinity and orientation of polypropylene with these properties are well known. Temperature increase has an important effect on the crystallinity and orientation of polypropylene. The purpose of this study is to understand better crystallinity and orientation changes of the cast and bi-axially oriented polypropylene films with respect to temperature effect. These changes were investigated using especially in-situ FT-IR and dichroism as well as XRD and Raman spectroscopy. For this purpose, an in-situ variable temperature set-up is developed and adapted for FT-IR studies. Accordingly, the changes in the peaks related to the amorphous and crystalline contents of the films as well as the peaks reflecting the orientation of the films were investigated over the temperature range from 120-170o C. Temperature cycle was also applied. Moreover, the films were investigated after application of additional stress at 120o C for various durations.

The crystallinity and orientation of the films are affected significantly when the films were analyzed at higher temperature (>150o C). The crystallinity content of the film recovers after returning back to room temperature whereas orientational loss are permenant.