Fluorescence and Raman Chemical Imaging of Thermoplastic Olefin (TPO) Adhesion Promotion

Abstract

Thermoplastic olefins (TPOs) are an important class of materials in the automotive industry. The surface properties of TPOs tend to prohibit adhesion of paints used to increase the longevity and enhance the cosmetic appearance of exterior TPO components. To increase adhesion, the TPO surface is coated with a chlorinated polypropylene (CPO) primer. The CPO thin film increases the TPO surface free energy and promotes paint adhesion. We have developed a generally applicable strategy for quantitative monitoring of CPO film uniformity, thickness, and adhesion based on the use of an environmentally sensitive fluorescence dye that is incorporated within the CPO adhesion promoter. The dye-tagged CPO thin film is analyzed in real time with a macroscopic imaging system employing novel liquid crystal tunable filter (LCTF) imaging spectrometers. The fluorescence chemical imaging approach is applicable to on-line monitoring of the TPO surface modification process. Controlled modification of the TPO surface is contingent on detailed understanding of the underlying TPO substrate. Raman chemical imaging is employed as a noninvasive approach to characterize TPO surface architecture. Specifically, we have developed a method for visualizing the surface to bulk distribution of CPO, polypropylene, and ethylene−propylene rubber phases in TPO without the use of dyes or stains. Blend components are visualized on the basis of their intrinsic vibrational spectrum. In general, Raman microscopy represents a powerful method for polymer characterization that is competitive with time-of-flight secondary ion mass spectrometry (TOF−SIMS) and transmission electron microscopy (TEM).