The ultrasonic degradation of polystyrene (PS) and ethyleneepropylene diene monomer (EPDM) melts was conducted in a specially designed reactor. A degradation model of polymer melts was proposed to explain the ultrasonic degradation, and degradation of polymer melts is treated as a mechanochemical process. Ultrasonic degradation kinetics obeys the equations: MTZMNCA e kt or ½h tZ½h NC ½h 0 ½h N e kt. The experimental results show that the molecular weight or intrinsic viscosity of polymer melts decreased with ultrasonic irradiation time and approached a limiting value, below which no further degradation took place. Dierent from ultrasonic degradation of polymer solutions, the scission of chains in polymer melts is random in the initial stage, and then non-random. FTIR spectra of samples ultrasonically treated and untreated confirmed that the initial product of ultrasonic degradation in polymer melts is a macroradical. The effects of ultrasonic intensity and reaction temperature on degradation of PS and EPDM melts were also investigated. The significant results showed that the degradation rate, the limiting value and degradation extent are correlated greatly with the experimental conditions.

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.

The effects of interfacial interaction between nano-CaCO3 andPVCon mechanical properties and morphology of PVC/nano-CaCO3 composites were studied. Nano-CaCO3 was treated with vibromilling in the presence of PVC and coupling agents. The mechanical properties of PVC/treated nano-CaCO3 are remarkably improved. Transmission electron microscopy results revealed that vibromilled nano-CaCO3 particles are well dispersed in PVC matrix with good homogeneity and well adhered to PVC matrix. Molau test indicated that chemical reaction between newly formed surface of nano-CaCO3 and PVC or coupling agent took place. Theoretical calculation results show that the interfacial interaction between PVC and nano-CaCO3 are substantially improved through vibromilling treatment of nano-CaCO3 in the presence of PVC and coupling agent. Molau test results of the samples in THF.

The effects of die materials on die pressure, productivity of extrusion, melt viscosity, and melt fracture of metallocene-catalyzed linear low density polyethylene (mLLDPE) as well as their mechanism were studied in a single screw extrusion system. Die materials used in our experiment include steel, brass, and polytetrafluoroethylene (PTFE). The experimental results show that die materials have great influence on the processing behavior of mLLDPE. The PTFE die can greatly inhibit the occurrence of melt fracture or surface distortion of mLLDPE extrudate. The surface appearance of raLLDPE extrudate is greatly improved. The PTFE die can greatly increase the productivity of mLLDPE extrudate and decrease the die pressure and the melt viscosity of mLLDPE. A possible mechanism For the improved processability of mLLDPE is proposed.

The effects of ultrasonic oscillations on the rheological and viscoelastic properties and morphology of high-density polyethylene (HDPE)/Illite (70/30) composites were studied. The experimental results showed that the die pressure and apparent viscosity of the HDPE/Illite (70/30) composites were reduced greatly, and so the mass-flow rate significantly increased in the presence of ultrasonic oscillations during the extrusion. Scanning electron microscopy and linear viscoelasticity tests showed that ultrasonic oscillations improved the dispersion of the Illite particles into the HDPE matrix. The aggregation of the Illite particles disappeared on the fractured surfaces of HDPE/Illite (70/30) composites extruded in the presence of ultrasonic oscillations, and this indicated that ultrasonic oscillations promoted the homogeneous dispersion of Illite particles into the HDPE matrix. Ultrasonic oscillations caused the permanent reduction of the dynamic viscosity and zero-shear viscosity of HDPE/Illite (70/30) composites.