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.
Laser scanning confocal fluorescence microscopy measurements were performed on thermoplastic polyolefin (TPO) substrates that were coated with chlorinated polyolefin (CPO). The TPO investigated was a blend of high modulus polypropylene with an ethylene-butene copolymer (EBR9) containing 9 wt% butene. The CPO was a maleated chlorinated polypropylene containing 20 wt% Cl. The purpose of these experiments was to obtain detailed mechanistic information about the CPO-TPO interaction. To achieve acceptable contrast in these measurements, a fluorescent dye was covalently attached to a small portion of the CPO. Solvent wiping of the TPO substrates with isopropyl alcohol followed by xylenes prior to coating with CPO increased the mean roughness of the TPO surface by more than 100 nm; but it had a much larger effect on the roughness of the (several micrometers) CPO-TPO interface after coating. The EBR component of the TPO was shown to be exclusively responsible for the roughness increase. We also found evidence of a diffuse interface between the CPO and ERB components that was localized to sites in which the EBR was present at the TPO surface. M any plastic automotive parts such as bumpers and fascia are fabricated from thermoplastic polyolefin (TPO). The term TPO refers to a family of polypropylene (PP) blends in which a second polyolefin, such as ethylene-propylene rubber (EP), ethylenepropylene-diene rubber (EPDM), or ethylene-butene rubber (EBR) serves as the impact modifier. Coating failure on thermoplastic polyolefin substrates has been a problem confronting the automotive industry for many years. The poor paintability of TPO substrates results from its low surface energy, the lack of active groups, and the chemical inertness of the main TPO components. Although the introduction of the impact modifier into the blend tends to improve the paintability of TPO, it is still difficult to obtain a strong coating directly on a TPO substrate. For proper paint adhesion to TPO, additional surface treatments are required. These include plasma or flame treatment or corona discharge to oxidize the surface in order to introduce polar groups. 1 Another major strategy for surface preparation is the application of a thin layer of adhesion promoter (AP) to the TPO surface to enhance the coating adhesion to TPO. Most adhesion promoters are formulations containing chlorinated polyolefin (CPO). The adhesion promoter is regarded as a coupling agent in the painted TPO system, and TPOs of different composition normally require different CPOs for optimum performance. Although CPO has been used as an adhesion promoter in the automotive industry for many years, knowledge about how CPO promotes coating adhesion to TPO is limitroducible results is challenging because of the complexity and variability of the underlying TPO substrate. 2 To appreciate some of the complexities, consider first that while paint will adhere to CPO-primed injectionmolded TPO, the adhesion is substantially poorer if the TPO of the same composition is compression-molded. 3...
The teaching process is a systematic project of the integration of teaching and learning, in which the relationship between the components has a direct impact on the teaching effect. The purpose of this paper is to explore the main problems existing in the teaching of engineering courses in colleges and universities, so as to provide solutions for improving teaching quality. The main contents include effective introduction of teaching content, optimization of teaching content framework, improvement of teaching language skills and timely summary of teaching content.
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