Papers by Keyword: Polymer Melt

Abstract: Introduced a experiment measuring method of polymer melt bulk modulus. This method based on the PVT reciprocity principle of polymer melt. Depending on liquid attribute of polymer melt, which means pressure changing caused micro variety of volume of certain quality melt in sealed container, polymer melt bulk modulus under the different temperature and pressure could be measured. According with the Polymer Free Volume Theory, the result proved the scientificity of this method.

Abstract: Temperature of the polymer melt is one of the most important parameters for the polymer continuous extrusion molding process. There are many factors influence the distribution of the melt temperature, these factors have the coupling and nonlinear relationship which is difficult to measure accurately by the traditional measuring method. In this study, a BP neural networks-based model approach is presented in which the effects of the die wall temperature and screw speed and the wall temperature of the transition section and the measurement section in the continuous extrusion molding are investigated. Comparison of the BP neural networks model predictions with the experimental data yields very good agreement and demonstrates that the BP neural networks model can predict the polymer melt temperature field with a high degree of precision (the mean square error within 0.03)

Abstract: Experimental observations indicate that the viscosity of polymer melt flowing through micro channel is altered with variation of characteristic size of micro channels. The explanation about the trend of various viscosity is inconsistent. In this paper, the micro channel dies of 1000μm ,500μm and 350μm diameter were developed and with several polymers, including PP , PS and HDPE, depending on the capillary flow model, the measurement experiments of polymer melt viscosity were investigated at various shear rate. Test results show that with micro-channel size decrease, the percentage reduction in viscosity increases and the difference of viscosities in different micro channels reduces with increasing shear rate.

Abstract: Electromagnetic dynamic plasticating extrusion, as one of main novel forming methods, has many important benefits to the forming process and the properties of its products. Here a visualization technique of flow induced birefringence was used to study the effects of the vibration parameters of screw on the extensional stress in contraction die. It is shown that , the extensional stress vibrate with the screw vibration at the same frequency; the amplitude of the extensional stress increases with the amplitude of the screw increasing; the average extensional stress at dynamic extrusion is less than that without vibration force, and it decreases with the screw vibration frequency or amplitude increasing.

Abstract: An understanding of flow behavior of polymer melts through a slit die is extremely important for optimizing die design. In this paper numerical simulations have been undertaken for the flow of linear low-density polyethylene through Coat-hanger sheet dies. A new finite element method is proposed to simulate the flow in slit channel using Wagner constitutive model. This is one kind of finite element semi-analytical method by which the velocity distributions in thickness direction is approach by Fourier series. Numerical results of volumetric flow and pressure in coat-hanger dies are given to compare to the three-dimensional simulation using the finite element method. It appears that numerical solutions are as accurate as the complete 3D calculations and the computing time can be saved.

Abstract: With the rapid development of micro injection molding, the determination of melt rheological behavior within micro mold cavity is very important for the accurate simulation modeling. Yet several investigations show the viscosity of melt decreases with the reduction of micro channel characteristic size, but there has been no sufficient experimental data for the conclusion. In this paper, depending on the capillary flow model, the measurement experiments of polymer melt viscosity were investigated when Polymethyl Methacrylate (PMMA) was extruded through the micro channel dies of 1000μm ,500μm and 350μm diameter. Test results show that, as micro-channel size decreases, the viscosity increases and the difference of viscosities in different micro channels reduces with increasing shear rate. This indicates microscopic scale melt rheological behavior of PMMA is different from that of other materials.

Abstract: In the Present Contribution the Atomistic Structure of the Polymer Melt at 300 K Is Simulated by Means of Molecular Dynamics. the Agreement with an Experimental Density Is Obtained with a Deviation Lower than 1%. the Free Volume Is Analyzed in 1,000 Structures and 6.5 X 108 Cubic Å of Molecular Space. a Model for the Free Volume Cavities Is Proposed. in the Model the Size and Number of the Cavities Can Be Scaled by Three Parameters: Probe Radius, Cavity Depth and Cavity Threshold Volume. the Experimental Values of the Nano-Sized Cavity Volumes as Well as Ortho-Positronium Lifetimes Are Obtained, as Compared to Models with Cylindrical and Spherical Geometry. a Typical Value of the Number Density of Free Volume Cavities at 0.001 Å-3 Is Obtained. the Cavities Have Typically Elongated Shape with a Side-to-Length Ratio 1:2.

Abstract: New shear and extensional viscosity models based on Fredrickson kinetic equation coupled with Dewitt constitutive equation were established to predict viscosities of polymer melts. The experimental data of 125°C LDPE and LDPE filled with 35% glass beads reported from references were compared with the model predictions. The predictions showed good agreement with the measurements. The models are simple and easy to use. Because they contain no structure parameter, they are capable to describe the viscosities of pure polymer and polymer composites.

Abstract: The viscoelastic flow and swell behaviors of polymer melts in the profile extrusion process can significantly influence the performance and dimension of the final products. In the study, the viscoelastic flow pattern of a commercial low density polyethylene (LDPE) extruded through out of the hollow profiled extrusion die is investigated by means of finite element simulation. The mathematical model of three-dimensional viscoelastic flow and swell of polymer melts is established with a differential Phan-Thien and Tanner (PTT) constitutive model. A penalty method is employed to solve the non-linear problem with a decoupled algorithm. The computation stability is improved by using the discrete elastic-viscous split stress (DEVSS) algorithm with the inconsistent streamline-upwind (SU) scheme. A streamface-streamline method is introduced to adjust the swelling free surface of the extrudate. The essential viscoelastic flow characteristics of LDPE flowing through out of the hollow profile extrusion die is investigated based on the proposed numerical scheme. Both the redistribution of flow velocity and the release of stress are found to be the reasons for the swell phenomenon.

Abstract: The rheological characteristics of four polymer melts (PS, PMMA, PP and HDPE) are investigated by a capillary rheometer with the die diameters from 1.5mm to 0.5mm.The effects of temperature on shear viscosity and the effects of both temperature and shear rate on non-Newton exponent of melts are discussed when the die diameter is 0.5mm. The results show that the shear viscosity of four polymers decreases with the rise of shear rate. The shear viscosity of PS and PMMA increases with the decrease of die diameter, the shear viscosity of PP and HDPE decreases with die diameter and minute differences of shear viscosity with different die diameters are observed with the growth of shear rate. When the die diameter is 0.5mm, Arrhenius equation is found to be suitable to describe the relations between shear viscosity and temperature for four polymer melts. The non-Newton exponents of four polymer melts increase with the temperature and decrease with the rise of shear rate.