Investigation On The Miscibility And The Interfacial Properties Of Thermoplastic Olefins And Clorinated Polyolefins

Thermoplastic polyolefins (TPO) have become increasing popular alternatives tosteel-made automotive parts such as painted bumper, fascia, filler, panels and otherinterior and exterior parts because of its lightweight, low cost, good mechanicalproperties and recyclability. However, this kind of painted automotive parts madefrom TPO has the disadvantage of paint failure. An important method to overcomethis problem is the application of a layer of adhesion promoter (AP), oftenchlorinated polyolefins (CPO). Although AP can promote the adhesion of paint toTPO effectively, paint failure during the period of guarantee is still a serious problemin automotive industry. So, the research on the interface of CPO and TPO, and howCPO promote coating adhesion to TPO substrate will lay a technical foundation onthe solving of the problem of the wear of automotive parts.In this study, the experimental investigations and theoretical analysis on themiscibility, the interface, and the adhesion between iPP/EBR thermoplasticPolyolefins and chlorinated polypropylene (CPO) were carried out by many advancedanalytical instruments and experimental technics, such as pulse force mode-atomicforce microscopy (PFM-AFM), laser scanning confocal fluorescence microscopy(LSCFM), wide angle X-ray diffrection（WXRD）, scanning electronic microscope(SEM), dynamic mechanical analysis (DMA), differrential scanning calorimeter(DSC), polarized optical microscopy (POM), lap-shear test and tensile test, etc.The morphology and the miscbility of iPP, EBR and CPO binary blends wereanalyzed by binary interaction energy density (Bij-Bc). The theretical analyzed resultswere further verified by LSCFM, SEM and DMA, etc. The conclusion was obtainedthat iPP/EBR and iPP/CPO blends are immiscible, EBR/CPO blend is miscible inmelt and partially miscible in solid state. The further inverstigation on themorphology of iPP/EBR blend showed that there was some improvement on themiscbility of iPP/EBR blend with the increasing of EBR content. The phase structuremodel of iPP/EBR blend was established.The composition at the surface of the injection-molded TPO plaques wascharacterized by attenuated total reflectance-Fourier transform infrared (ATR-FTIR).The result shows that although the amount of EBR content in TPO plaque is stable,the EBR content at surface of TPO12plaque changes with position of TPO plaque.The EBR content at the surface of TPO12plaque increases from near gate to far fromthe gate, but there is no obvious difference in EBR content at surface of TPO25plaque with respect to the gate. The morphology at the surfce and the near surface of TPO plaques was studied.The result shows there exists a skin layer with hundreds of micrometers thickness inTPO plaque. Within the skin layer, there is a pronounced transcrystalline layer andsignificant amounts of EBR. The thickness of the skin layer decreases and thedimension of EBR phase at the surface of TPO plaque increases from near the gate tofar from the gate.The interfacial structure of TPO/CPO/TPO lap shear joints was investigated byhigh resolution PFM-AFM. The results revealed a sharp interface (21nm) betweeniPP and CPO, a wider interface (28nm) between TPO and CPO without annealing,and an even broader interface (58nm) between TPO and CPO subjected to annealingat120°C for20min. These results are in accord with the idea that CPO interactspreferentially with the impact modifier as it promotes adhesion to TPO. A novelobservation from the PFM-AFM results was the presence in TPO/CPO samples of atransition zone of very different stiffness with a width on the order of600to1500nm.The interfacial adhesion mechanism of CPO to TPO and the interfacial structuralmodel were proposed, too.The adhesion of CPO to injection-molded TPO plaques and the fracture mode oflap joints varied both with the composition of TPO plaques and the compositiondistribution at the surface of TPO plaques. The fracture mode of the adhesion jointschanged from interfacial failure to mixed failure with the increasing of EBR contentin TPO plaque or from near the gate to far from the gate of TPO plaque. The fracturestrength and adhesion energy increased with the increasing of EBR9content in TPOblends, they increased from near the gate to far from the gate, too. The analyzedresults shows that the changing of the fracture strength and the adhesion energy withthe composition of TPO plaques was correlated to the EBR content in TPO plaqueand the cohesive force of TPO plaque, the changing of the fracture strength and theadhesion energy with the position at the surface of TPO plaques was correlated to theEBR content (also the composition distribution) at the surface of TPO plaques andthe thickness of skin layer, which were actually correlated to the folw field of themelt.The crystallization of CPO and its correlation to the adhesion of CPO to TPOsubstrate were investigated. CPO is a low-crystallinity polymer with two meltingpeaks. Both the crystallinity Xcand the glass transition temperature Tgof CPOincrease with the ageing time, three types of linear relationship were revealed relatedto CPO: Tgof CPO to the crystallinity Xcof CPO, the yield stress of CPO to XcofCPO, and the fracture strength to the clorine content of CPO. Based on these results,the adhesion force model of CPO/TPO was established. The predicted results from this model met very well with the experimental results. The methods to improve theadhesion of CPO to TPO were proposed, too.