Chemical imaging of thermoplastic olefin (TPO) surface architecture

In the automotive industry, ethylene-propylene rubber (EPR) is mixed with p olypropylene (PP) to form a thermoplastic olefin (TPO) for use as car bumpe rs and fascia. An adhesion promoting primer, chlorinated polyolefin (CPO), is spray coated onto the TPO surface to increase adhesion of the base and c lear coat paints to the low surface free energy TPO substrate. The surface morphology of rubber domains within the CPO-coated TPO substrate contribute s strongly to the material characteristics, including impact resistance and adhesion properties. However, elastomer-phase analysis is challenging usin g traditional microanalysis imaging techniques. We employ fluorescence and Raman chemical imaging to characterize the TPO architecture in order to bet ter understand the surface properties of coated TPO. Fluorescence imaging m akes use of Nile red (NR), a fluorescent solvatochromic dye, solvated in th e primer, which is effective in differentiating rubber from polypropylene o n the basis of large variations in the fluorescence quantum efficiency. Con focal fluorescence chemical imaging performed on TPO coated with NR-doped C PO shows a thin (2-3 mu m) layer of elastomer that has migrated to the TPO surface. Raman chemical imaging is in direct agreement with the fluorescenc e experiments by measuring the intrinsic vibrational signatures of CPO, EPR , and PP without the need for dyes or stains. Raman contrast is enhanced us ing cosine correlation analysis, a novel multivariate processing technique that provides chemical contrast on the basis of differences in spectral sha pe.