Study On In Situ Alloy Of Polypropylene/Polystyrene Blends.

In this dissertation, PP-g-PS grafting copolymers by two different methods and precopolymer of hexadecyl acrylate(HA) and styrene(St) were prepared to compatibilize plolypropylene/polystyrene blend and polypropylene. The relationship between phase structure and mechanical properties has been investigated by scanning electron microscope(SEM), phase contrast microscopy (PCM), polarization microscope(POM) and Rheology.Evidence of the grafting of St onto PP was determined by FTIR. The grafting ratio and grafting efficiency of grafted copolymer by method (a) are higher than method (b). The grafting ratio showed linear relationship with the content of monomer with the concentration of monomer lower than18 wt%. The impact fracture morphology of blends has been investigated by means of SEM. The result showed that PP was incompatible with PS. The adding or PPg improved the interface strength. For the PP/PS/HA-St blends, the average dispersed phase size dp and average chord length L1 reduced with the increasing of the molar ratio of copolymer. But the higher concentration of HA resulted in poor interfacial adhesion. PCM patterns in real space were transformed into patterns in wave-number space by 2-dimensional Fourier transformation (2DFT). Some character parameters, such as correlation distance ac2 and the fractal dimension D, were calculated. The results showed that PPga and PPgb can lead to small disperse phase size and improve the compatibility between PP and PS with finer phase domains. The results accorded with those of SEM. The mechanical properties of the blends were studied. Youngs modulus improved with the addition of PPga and PPgb. The PP/PPga blend showed higher improvement in Youngs modulus in comparison with PP, while impact strength and tensile yield stress changed a little. The blends of PP/PS/HA-St and PP/HA-St showed significantly improved impact strength in comparison with PP/PS and PP, respectively. POM images confirmed that the addition of PS restrained the growth of spherulite of PP. However, the spherulite of PP formed better in PP/PS/PPg, PP/PS/HA-St and PP/HA-St blends than in PP/PS blend. It was found thatη* of compatibilized blends decreased in the presence of PPg, HA-St by dynamic rheology analysis, which lead to good process properties.