Study On In-situ Compatibilized Polypropylene/Polystyrene Blends Catalyzed By Nonhydrous Aluminum Chloride

The polypropylene/polystyrene blends were prepared in a twin screw extruder and a typical lewis acid, namely anhydrous aluminum (AlCl3) was used as the catalyst to compatibilize the blends by in-situ Friedel-Crafts alkylation. The small angle light scattering (SALS) and online-sampling-microscope were applied to study the morphology of the blends.The Tg of the PP and PS in the blends obtained by dynamic mechanical analysis (DMA) were closed up and this indicates the blends were compatibilized. The blends after selective Soxhlet solvent extraction were studied to insure the graft copolymer (PP-g-PS) was formed at the interphase by in-situ Friedel-Crafts alkylation and the formed PP-g-PS behaved as the compatibilizer in the blends.Phase morphology of PP/PS blends was observed by scanning electron microscope (SEM). The dispersed phase was distributed in the continuous phase in the shape of roundness particles. A method of digital analysis was applied to the SEM images to get corresponding structure parameters– average characteristic length Lm, distribution width of characteristic lengthσand fractal dimension DL. The results show that the main morphology development occurs during the phase dispersion, the dimension of the dispersed particles and the distribution of it decreased at the same time. The AlCl3 decreased the dimension of the dispersed particles, but because the dimension of the dispersed particles is little the decrease of it was not marked. To PP/PS blends with different composition the morphology changed with AlCl3 and the change was marked when the PS was the continuous phase.The images obtained by SALS were digitally analyzed by means of Debye-Bueche scattering theory to get the corresponding structure parameters– correlation distance ac and interface layer thickness d. ac was used to describe the dimension of the dispersed particles and d can prove the compatibilization of the blends. The results of the SALS changed with the content of AlCl3 and the composition of the blends and the current of it were same as the results of the SEM. Mechanical properties of PP/PS blends were tested. The addition of AlCl3 has very little effect on the Youngs modules when the composition of the blends was different. When PS was the continuous phase the addition of AlCl3 increased the yield stress of the blends marked. The change of mechanical properties of the PP/PS blends with content of AlCl3 is complex. The homopolymer chain scission happened in the in situ compatibilization and it affected the mechanical properties of the blends. The influences of the compatibilization and the homopolymer chain scission are contrary and one will increase the mechanical properties and the other will decrease it. The two reactions compete and when they reach a balance the blends will have better mechanical properties.