Study of the Molecular Orientation Heterogeneity in Polypropylene Injection-Molded Parts by Raman Spectroscopy

Polarized Raman microspectroscopy has been used to study oriented-skin layers induced in injection-molded isotactic polypropylene (iPP) parts. A method based on the intensity sensitivity of several Raman bands to laser light polarization was employed to estimate the degree of molecular orientation in iPP. The skin-core molecular orientation heterogeneity in injection-molded iPP is then evaluated via two different experimental methods. Results show that an in-depth profile using micro-Raman confocal technique is as valuable as an edge profile performed on a sample cross-section because both are correlated with optical microscopy measurements. Both Raman measurements are in good agreement with optical microscopy measurements. The skin development was found to be narrowly related to the shear strain rate at the mold walls. POLYM. ENG. SCI., 50:138-143, 2010. (C) 2009 Society of Plastics Engineers