The Rheological Properties Of Polypropylene/Carbon-Based Nanocomposites In Microscale Channels

With the development of polymer micro forming technology changed rapidly, the research of polymer flow properties under the microscale channels has become an important direction of polymer processing rheology.In micro-channels, the melt has large SVR(surface volume ratio) as well as high pressure and shear rates. The micro-scale rheology research focused on the scale effect of viscosity and wall slip, pressure sensitivity of viscosity, etc. However, at present, a lot of research referring to microscale rheology only take the common pure polymer as objective, few study about the rheological properties of polymer nanocomposites in microcale channels has been reported. As a result, carbon nanotubes (CNT), carbon black (CB) and graphite piece (GNP) filled polypropylene (PP) composites were prepared by melt blending,its viscoelasticity, multi-scale flow channel size dependence of viscosity and pressure sensitivity of viscosity based on PVT (pressure volume-temperature) datas were investigated in this paper.Dynamic rheological parameters including storage modulus, loss modulus and complex viscosity of the three nanocomposites were measured by using rotation rheometer under a condition of 1% strain. The result show that both the modulus and viscosity increased with the nanoparticles content increasing, they also show a strong dependency on scanning frequency at low frequency area.The modulus of all three nanocomposites will be larger than that of PP significantly when mass fraction of particles are more than 2%. Rheological percolation threshold effect was observed in PP/CNT when CNT content was 2%.In capillary rheometer experimental study, the flow curves of three nanocomposites under three dies with different diameter but the same length-diameter ratio were obtained. Viscosity under the same shear rates decreases with the decrease of the die diameter.The viscosity deviation in the three dies at a shear rates of 1500s-1 were adopted to characrize the scale effect of viscosity.The viscosity scale effect of all three materials has a tendency of decrease with the particle content increase. A rise in temperature will strengthen the viscosity scale effect while a high shear rates weaken this effect. The slip phenomenon were also investigated in die, an exponential relationship exist between slip velocity and shear stress and the slip velocity will increase when melt temperature rise.The viscosity presure sensitivity of the three composites were studied combining the flow activation energy and PVT datas.The addition of nanoparticles did not significantly influence the flow activation energy of the composites.In PVT tests, a rise in pressure will increase the initial crystallization temperature of the samples.Finally pressure sensitivity coefficient of viscosity were calculated. Pressure coefficient of the three nanocomposites decreased gradually with the increase of particle content.In addition from the theoretical analysis and calculation formula,we can speculate that a temperature rise will increase the pressure sensitivity coefficient and a higher pressure will decrease the coefficient.