The effect of melt temperature, ultrasonic oscillations, and induced ultrasonic oscillations modes on weld line strength of polystyrene (PS) and polystyrene/polyethylene (PS/HDPE)(90/10) blend was investigated. The results show that the increase of melt temperature is beneficial to the increase of weld line strength of PS and PS/HDPE blend. Compared with PS, the increase of melt temperature can greatly enhance the strength of PS/HDPE blends. For PS, the presence of ultrasonic oscillations can enhance the weld line strength of PS at different melt temperatures. But for PS/HDPE blends, the presence of ultrasonic oscillations can improve the weld line strength when the melt temperature is 230℃, but when the melt temperature is 195℃, the induced ultrasonic oscillations hardly enhance the weld line strength. Compared with Mode I (ultrasonic oscillations were induced into the mold at the whole process of injection molding), the induced ultrasonic oscillations as Mode II (ultrasonic oscillations were induced into the mold after injection mold filling) is more effective at increasing the weld line strength of PS and PS/HDPE blends. The mechanism for ultrasonic improvement of weld line strength was also studied. POLYM. ENG. SCI., 45: 1666-1672, 2005.

The effects of nine kinds of transition metal oxides on the elimination kinetics of hydrogen chloride (HCI) during thermal decomposition of polyvinyl chloride (PVC) at 210℃ were investigated using online measurement of conduc-tivity. It was found that the presence of TiO2, V2O5, Cr2O3, and MoO3 obviously decreases the elimination rate of HCI and the amount of HCI released by a factor of 10-20 times, indicating that they have a strong inhibiting effect on the release of HC1. The presence of MnO2, ZnO, CuO, C0203, and Fe203 promotes the elim-ination of HCI during thermal decomposition of PVC. The maximum elimination rate of HCI in PVC/ZnO, especially, is ca.10 times as high as that of PVC. In this work, the LnLn kinetic model, Ln(l-X)=-ktn, describes the kinetics of elimin-ation of HCI during thermal decomposition of PVC. The elimination rate of HC1 during thermal decomposition of PVC increases with the rise of the apparent order of reaction, n, in this model nvalue well describes the elimination kinetics of HC1 during thermal decomposition of PVC.

The effects of ultrasonic oscillations on properties and structure of extruded highdensity polyethylene (HDPE) were studied. The experimental results show that ultrasonic oscillations can improve the surface appearance of the HDPE extrudates; increase the productivity of the HDPE extrudates; and decrease the die pressure, melt viscosity, and flow activation energy of the HDPE. The processing properties of the HDPE improve greatly in the presence of ultrasonic oscillations. Linear viscoelastic properties tests show that dynamic shear viscosity and zero shear viscosity decrease in the presence of ultrasonic oscillations. Ultrasonic oscillations can improve crystal perfection and thermal stability of HDPE. At appropriate ultrasound intensity, ultrasonic scillations could also increase the mechanical strength of extruded HDPE. The gel permeation chromatography (GPC) results show that at high ultrasound intensity and low rotation speed of extrusion, ultrasonic oscillations causes chain scission of HDPE, which result in a decrease of molecular weight and an increase of melt flow index.

The effeect of weld line on the morphology and mechanical properties of 70/30 polystyrene and polyamide-6 blends with various amounts of poly (styrene-co-maleic anhydride)(SMA) as compatibilizer was investigated. For blends without or with low content of SMA, the dispersed domains near the weld line were elongated parallel to the weld line; and the dispersed domains in weld line were spherical. But for blend with high content of SMA, the isotropic morphology was observed. And the dierence of morphology at weld line caused the distinction of fracture mechanism. The tensile strength of the blend is greatly influenced by the morphology of dispersed domains at weld line. While the morphology has only slight effect on impact strength of the blends.

The linear rheological properties of highdensity polyethylene (HDPE), polystyrene (PS), and HDPE/PS (80/20) blends were used to characterize their structural development during extrusion in the presence of ultrasonic oscillations. The master curves of the storage shear modulus (G) and loss shear modulus (G) at 200℃ for HDPE, PS, and HDPE/PS (80/20) blends were constructed with time-temperature superposition, and their zero shear viscosity was determined from Cole-Cole plots of the outof-phase viscous component of the dynamic complex viscosity versus the dynamic shear viscosity. The experimental results showed that ultrasonic oscillations during extrusion reduced G and G as well as the zero shear viscosity of HDPE and PS because of their mechanochemical degradation in the presence of ultrasonic oscillations; this was con-firmed by molecular weight measurements. Ultrasonic oscillations increased the slopes of log G versus log G for HDPE and PS in the low-frequency terminal zone because of the increase in their molecular weight distributions. The slopes of log G versus log G for HDPE/PS (80/20) blends and an emulsion model were used to characterize the ultrasonic enhancement of the compatibility of the blends. The results showed that ultrasonic oscillations could reduce the interfacial tension and enhance the compatibility of the blends, and this was consistent with our previous work.