Guangshun Chen

Studies on Rheological Behavior and Structure Development of High‐Density Polyethylene in the Presence of Ultrasonic Oscillations During Extrusion

The effects of ultrasonic oscillations on properties and structure of extruded high‐density 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 oscillations 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.

Modification of a Theoretical Model for the Prediction of the Thermal Expansion Behavior of Particulate Composites: Application to Poly(vinyl chloride)/Talc Composites

The coefficients of thermal expansion (CTE) of poly(vinyl chloride) (PVC)/talc composites were tested and the experimental data showed that the CTE of PVC/talc composites were closely related to the talc particle size and its distribution; for a given talc volume fraction, the smaller the talc particle size, and the lower the CTE of the PVC/talc composites. The theoretical equations proposed by Sideridis and Papanicolaou and by Lombardo, which were based on a single, spherical particle size, were found to predict well the CTE of PVC/talc composites, but with the obtained interphase thicknesses were too large to be believed. In order to overcome the shortcomings of these equations, being without variation of filler particle size and its distribution, a modified model was proposed. It was found that the modified model can predict well the CTE of PVC/talc composites, with almost the same and more reliable interphase thicknesses for different talc particle sizes, confirming the correctness of the modified model to some extent.

Effect of the Material of Construction of Die on Processing Behavior of Metallocene-Catalyzed Linear Low Density Polyethylene

Abstract 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 mLLDPE 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.

Effect of the morphology on the anisotropic light scattering of polycarbonate (PC)/poly(styrene-co-acrylonitrile) (SAN)(70/30) blend

The polycarbonate (PC)/poly(styrene-co-acrylonitrile) (SAN) (70/30) anisotropic light scattering sheet with controllable anisotropic degree was prepared by blending and hot stretching process. The morphological evolution of the dispersed particles for PC/SAN (70/30) blend during hot stretching was observed by a scanning electron microscope (SEM) and the effect of stretching deformation on the light scattering properties was investigated. The SEM photographs revealed that SAN particles deformed into ellipsoid during hot stretching. The scattering properties analysis results revealed the appearance of anisotropic light scattering for PC/SAN (70/30) blends with various deformations, and with the increase of stretching deformation, the anisotropic scattering degree increased, verifying the correctness of geometrical optical scattering theoretical analysis.

The Peculiar Temperature Response of Dynamic Rheological Behaviors of Poly (Vinyl Chloride)/trioctyl Trimellitate (100/70) System

The dynamic rheological behavior, application of time-temperature superposition (TTS) and the failure mechanism of TTS are studied for the poly(vinyl chloride) (PVC)/trioctyl trimellitate (TOTM) (100/70) system. The Arrhenius equation, Williams–Landel—Ferry (WLF) equation, mathematical non-linear fitting and manual shift are applied to TTS fitting. For the PVC/TOTM (100/70) system, none of those methods can give well-superimposed master curves with either single horizontal shift or two-dimensional (horizontal and vertical) shift. The failure reason is attributed to the thermorheological complexity of the PVC/TOTM (100/70) system. Curves of the storage modulus versus the frequency can be well fitted with an empirical equation (G′=G′0+Kω n ) usually used to describe filled polymer systems, indicating the multilevel flowing unit characteristic in this system. With the increase of test temperature, the structure of the PVC/TOTM (100/70) system changes and an apparent transition appears in the rheological behavior. Differential scanning calorimetry (DSC) results reveal that for the PVC/TOTM (100/70) system there are microcrystallites present below 220°C, but above the rheological transition temperature (190°C) the bulk of the microcrystallites melted, which corresponds to the appearance of viscous flow participating in the rheological behavior. It verifies the fact that the gel networks crosslinked by microcrystallites dominate the rheological behavior below the transition temperature in the PVC/TOTM (100/70) system. The quantity of microcrystallites remaining in the melt determines the perfection of the physical gel networks. With the increase of test temperature, the microcrystallites melted gradually and the gel networks are broken up.