In this work, the effect of ultrasonic irradiation on molecular structure development of metallocene-catalyzed linear low density polyethylene (mLLDPE) was studied. GPC results show that ultrasonic irradiation have influence on molecular weight and molecular weight distribution of mLLDPE. Molecular weight of mLLDPE decreases slightly at the initial 30s of ultrasonic irradiation and then increases obviously; its distribution becomes wider with the increase of ultrasonic irradiation time. The power and frequency of ultrasonic irradiation have the distinct influence on molecular weight and its distribution of mLLDPE. DSC results show that ultrasonic irradiation has distinct influence on multiple step crystallizing behaviors of mLLDPE because of the change of branched chain in mLLDPE molecules. Thermal stability of mLLDPE is improved greatly because of micro-crosslinking structure in mLLDPE molecule, which is formed in the presence of ultrasonic irradiation. A possible mechanism for molecular structure development of mLLDPE in the presence of ultrasonic irradiation is also proposed in this paper.

The ultrasonic degradation of polyamide 6 (PA6) melt was conducted in a specially designed reactor. The effects of initial molecular weight of PA6, irradiation time, ultrasonic intensity as well as ultrasonic irradiation distance on the ultrasonic degradation of PA6 melt were investigated. Some surprising experimental results show that for low molecular weight PA6 (LPA6), the viscosity-average molecular weight of LPA6 increases in the presence of ultrasonic oscillations due to extension reaction of end groups (eCOOH and eNH2), while for high molecular weight PA6 (HPA6), the viscosity-average molecular weight of HPA6 decreases with irradiation time, and passes through a minimum, then increases with irradiation time, up to a limiting molecular weight. Ultrasonic degradation kinetics of HPA6 melt obey the equation: Mt% MNCAe kt: FTIR analysis and a microtitration method confirm that the chain scission of HPA6 under ultrasonic irradiation occurs at CeN bonds. A plausible ultrasonic degradation model of the polymer melt based on molecular movement is proposed. Published by Elsevier Ltd.

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 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 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.

Polypropylene/montmorillonite nanocomposites (PPCNs) with 3% organophilic montmorillonite (OMMT) content were prepared via ultrasonic extrusion. The objective of present study was to investigate the effects of ultrasonic oscillations in processing on the morphology and property development of PPCNs. XRD and TEM results confirmed the intercalated structure of OMMT in conventional nanocomposite (without ultrasonic treatment) and ultrasonicated nanocomposite, but ultrasonic oscillations could make silicate layers finely dispersed and a little exfoliated. According to SEM, the OMMT particles were evenly and finely dispersed in the ultrasonicated nanocomposite via ultrasonic oscillations, and the aggregation size of clay particles was about 100nm, which is less than that in conventional nanocomposite. The crystalline dimension, crystalline morphology and the growth rate of crystallization in PPCNs were investigated by DSC and PLM, it was found that the OMMT particles and ultrasonic oscillations played an important role in the nucleation rate, crystallization temperature and spherulite size of PP matrix in nanocomposites. Compared with conventional nanocomposite, the mechanical properties of the ultrasonicated nanocomposite increased due to the improved dispersion of OMMT and diminished spherulite size. The thermal stability and the rheological behavior of PP and its nanocomposites were both studied by thermogravimetry and high pressure rheometer, respectively.

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.

Three kinds of polymer/layered nanocomposites were prepared via ultrasonic extrusion. Experimental results showed that ultrasonic oscillations could mostly decrease the size and its distribution of clay particles in polymer matrix. Therefore, crystal size of polymer matrix decreases. For PA6-based nanocomposites with higher compatibility, the ultrasonic oscillations can also affect the microstructure of clay, causing more regions of exfoliated clay. Due to better dispersion of clay and smaller crystal size, the elongation at break of polymer/layered nanocomposites ultrasonically treated got greatly increased, meanwhile ultrasonic oscillations also improved their other mechanical properties, such as tensile and impact strength.

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.