Morphology, Structure And Properties Of PC/PE Blend Compatibilized By In-situ Macromolecular Reaction

The study on polyolefin-based engineering plastics is an important research field of polymeric materials and science at present because it allows the optimization of the properties compared with the single components. But like most polymer blends, the immiscibility of engineering plastics such as polycarbonate (PC) and high-density polyethylene (HDPE) in the melt state leads to poor interfacial adhesion, the coalescence of the minor phase and the drop of final properties. For compatibilization of PC/PE blend, block or graft copolymer is commonly used as compatibilizer, which is formed in-situ in reactive blending. A commercial ethylene-acrylic acid copolymer (EAA) was employed to compatibilize the PC/PE blends because the PC-g-EAA copolymer generated in-situ by the reaction between ester groups in PC and acid groups in EAA during the processing can be used as compatibilizer.To confirm the in-situ generation of the grafted copolymer (PC-g-EAA) as a compatilizer during processing by ester and acid reaction between PC and EAA in the presence of dibutyl tin oxide (DBTO), the EAA/PC binary blend was firstly studied. The ~1H-NMR analyses show that the reaction does take place in PC/EAA blend and grafted copolymer (PC-g-EAA) was in-situ generated during processing. The reaction peak in Haake torque curves and the changes from the SEM micrographs proved the generation of the grafted copolymer indirectly. As a catalyst, DBTO is an important factor to influence the reaction between PC and EAA, so the effect of DBTO on the generation of the PC-g-EAA copolymer under different temperatures and DBTO contents was investigated in this thesis. It is found that the catalyst not only accelerates the reaction between PC and EAA, but also hastens the chain-broken of PC and EAA with higher processing temperature and DBTO content.Then, the PC/PE/EAA ternary system blended by the one-step method in a twin-screw extruder was studied using SEM and DSC. These results indicated that the generation of PC-g-EAA copolymer by one-step blending was too little to improve the morphology and mechanical properties of PC/PE blend.The reactive compatibilized PC/PE/EAA blend was perpared using a two-step blending method (method B) in this thesis and the mechanical properties, morphology and structure of the blend were studied by the DSC, SEM, DR and DMA analysis. The results showed that the compatibilization of PC/PE blend by this method had unconspicuous increase, and the morphology of this blend from SEM micrographs is special in which the phase morphology showed a composite dispersed phase structure. It was found that the crystallinity of PE decreased due to the compatibilization of PC-g-EAA copolymer, which hindered the crystallization of PE phase. Dynamic mechanical analysis showed that the temperature of relaxation a and y of PE both decreased, because of the decrease of the crystallinity of PE phase. The dynamic rheology anylysis showed that the dynamic elastic modulus, viscous modulus and complex viscosity were all increased along with the generation of PC-g-EAA copolymer, which indicated that the reactive compatibilizaion with EAA could improve the interface interaction of PC/PE blend.The processing of the polymer is a structure tailoring process, so different blending methods bring different properties. As the system discussed is a reactive compatibilization system, so, the blending procedure is very important. Four different methods were investigated to blend PC/PE/EAA system. For all the four compatibilized blends, it could be found that the method D was better than others and the double-yield phenomena of PC/PE/EAA blend by method D was found in the tensile test. From the experiment datas by DSC, SEM, DR and DMA, it could be found that the crystallinity and the temperature of the melting peak in the blends by method B, C and D were lower than that by method A due to the better reactive compatibilization. Using dynamic mechanical and dynamic rheology analysis, the results showed that the miscibility of PC/PE/EAA blends by C and D methods was improved and the interface adhension was enhanced.