Effect Of Ultrasound Irradiation On PS And PP As Well As PP Based Blends

The effects of ultrasound on extrusion processing, structure and properties of polystyrene (PS), polypropylene (PP), PP/ethylene-propylene-diene monomer terpolymer (EPDM) blends and PP/inorganic-fillers were studied. The molecular conformation and structure of the polymers were analyzed by positron annihilation, infrared dichroism, GPC and thermal analysis, etc. And the mechanism of ultrasound effect on the viscoelasticity and viscous of polymer melt were explored. The relationships between phase structures and mechanical properties of polypropylene blends and composites with ultrasound irradiation were also investigated. The main experimental results show that:The die pressure, apparent viscosity and die swell of PS and PP are reduced remarkably and the melts fracture are postponed in presence of ultrasound during extrusion. Ultrasound irradiation can also reduce the viscosity of the blends and composites based on PP effectively during extrusion.Ultrasound applied to the entrance of the die disturbs the convergent flow of the melt in the entry zone so much that it changes the stream pattern to a way there is lesser elastic tensile strains happen. It also e activates the molecular chains, so that elastic tensile strains can be recovered very quickly. That is why the measured is reduced, and so the apparent viscosity reduced. Ultrasound irradiation reduces the recoverable shear strain, the shear stress at the wall of the die, the first normal stress and the relaxation time of the polymer melt. It reduces the dependence of polymer viscosity on the shear rate, the viscosity of the melt decrease exponentially as ultrasound intensity increases. Ultrasound vibration cooperates with the shear in disentangling the molecular network to increase the flowability of polymer melt. Analyzed Ultrasound irradiation increases the free volume of PS, reduces the molecular entanglements of polymer melt. As the ultrasound intensity is increased, the molecular weight of PP is reduced and the molecular-weight distribution narrow down. Infrared dichroism analysis indicates the orientation of PP molecules to the flow direction reduces and crystallinity of PP reduces. When ultrasound is applied, its powerful vibration, shatter and cavitations help to cut and disperse EPDM in PP matrix, and make EPDM deform and orient to the flow direction. The particles size of EPDM and the interfacial tension of the two phases are reduced by ultrasound irradiation. The molecular structure characterization indicates that PP degrades, EPDM cross-links and the PP-EPDM copolymers are formed at the interface of the two phases by ultrasound irradiation. Introduction of ultrasonic vibration into extrusion is capable of improving the compatibility of EPDM and PP matrix, toughening PP/EPDM blends without harming rigidity excessively.Inorganic fillers with different shapes response in different way in the PP melt to ultrasound vibration. Ultrasound vibration breaks up the agglomerated particles of spherical fillers, increases the orientation degrees of acicular-fillers to the flow direction, and induces sheet-fillers orient with its surface perpendicular to the direction of the ultrasound vibration. Ultrasound helps to enhance the mechanical properties of PP/inorganic-fillers composites, prefer to the direction that the fillers are oriented to.