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Dye-labeled samples of a chlorinated (21.8 wt % Cl), maleated polypropylene (CPO), and a dye-labeled sample of poly(ethylene-co-butene) (EBR28, with 28 wt % butene) were synthesized and characterized. The dye was a functional benzothioxanthene related to the commercial dye Hostasol Yellow 3G. These substances were introduced as tracers into blends of CPO with polypropylene (PP) and with EBR9 (9 wt % butene) as well as ternary blends of CPO + PP + EBR9. The morphology of the blends was examined by laser scanning confocal fluorescence microscopy. Control experiments at 5 wt % tracer showed that the dye-labeled CPO was fully miscible with its unlabeled precursor and that dye-labeled EBR28 was fully miscible with pure EBR9. The blend experiments showed that this particular CPO was much more miscible with EBR9 than with PP. Ternary blend experiments intended to mimic the composition of a thermoplastic polyolefin (TPO, with 25% EBR9 as the impact modifier) showed that the EBR formed micron size droplets in the PP matrix and that the CPO completely engulfed the EBR droplets to form a core−shell morphology. Center cross sections of these droplets showed the CPO layer to be uniform in thickness, with a sharp interface with the PP matrix. The inner interface, between the CPO and EBR, was noticeably broader, with a thickness on the order of 0.5 μm, indicating only weak segregation between these two components of the blend.

In the automotive industry, ethylene−propylene rubber (EPR) is mixed with polypropylene (PP) to form a thermoplastic olefin (TPO) for use as car bumpers and fascia. An adhesion promoting primer, chlorinated polyolefin (CPO), is spray coated onto the TPO surface to increase adhesion of the base and clear coat paints to the low surface free energy TPO substrate. The surface morphology of rubber domains within the CPO-coated TPO substrate contributes strongly to the material characteristics, including impact resistance and adhesion properties. However, elastomer-phase analysis is challenging using traditional microanalysis imaging techniques. We employ fluorescence and Raman chemical imaging to characterize the TPO architecture in order to better understand the surface properties of coated TPO. Fluorescence imaging makes use of Nile red (NR), a fluorescent solvatochromic dye, solvated in the primer, which is effective in differentiating rubber from polypropylene on the basis of large variations in the fluorescence quantum efficiency. Confocal fluorescence chemical imaging performed on TPO coated with NR-doped CPO shows a thin (2−3 μm) layer of elastomer that has migrated to the TPO surface. Raman chemical imaging is in direct agreement with the fluorescence experiments by measuring the intrinsic vibrational signatures of CPO, EPR, and PP without the need for dyes or stains. Raman contrast is enhanced using cosine correlation analysis, a novel multivariate processing technique that provides chemical contrast on the basis of differences in spectral shape.

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).