Study Of Structure And Properties Of Plasma Induced Polypropylene Polystyrene In-situ Alloy

A new method was applied to prepare Polypropylene-graft-Polystyrene (PP-g-PSt)and its in-situ alloy PP/PSt of different proportions on the basis of low temperatureplasma surface modification. At the same time, PP/PS blend of the same proportion asPP/PSt alloy were prepared by a torque rheometer for comparison.Different kinds of plasma, such as nitrogen (N2), air, carbon dioxide (CO2), argon (Ar)plasma, was used to treat PP surface and further lead to the styrene monomer graftpolymerization on the treated PP surface, characterized by DPPH method todetermine the concentration of free radicals on the treated PP surface. Surface elementproportion and the presence of oxygen-containing groups before and after plasmatreating was characterized by X-ray photoelectron spectroscopy (XPS). Fouriertransform infrared spectroscopy (FTIR) was used to characterize the effect of thegrafting reaction. Combining the tests above and the graft ratio of PP-g-PSt together,argon gas (Ar) was chosen as the plasma gas source, and plasma treating conditionshould be40V and10min, and120℃was chosen as the temperature of thegrafting reaction. Scanning electron microscopy (SEM) was used to characterize themorphology of the PP/PSt alloys and PP/PS blends. A rotary rheometer was used toaquire the viscosity, storage modulus, loss modulus and complex modulus of the twogroups of samples. PP/PS blends as well as the compatibility of the PP/PSt alloys andthe crystallization process were investigated by SEM and rheometer. SEM showedthat the interface of PP/PSt alloys were not sharp, thus it can be concluded that thetwo phases in alloy are partially compatibility. Static rheological tests showed thatcrystallization rate of the PP/PS blends was faster than that of pure PP sample, and itspeeding up as the PS component increases, however, the crystallization rate of thePP/PS blends decreased after PS occupied more than50wt%, while the crystallizationrate of the PP/PSt alloys turned slower than pure PP.Cole-Cole plots made from rheological dynamic frequency scanning was used tocharacterize the compatibility of the two phases, and the results showed that theinternal structure of the alloy is more complex, which matched the result of SEM.Constant frequency oscillation test showed that the crystallization rate of PP/PSblends turned faster as PS content increasing，however the crystallization ratedecreased when PS content exceeds50wt%, which matched the result of steadyshear.