Improved Processability and the Processing-Structure-Properties Relationship of Ultra-High Molecular Weight Polyethylene via Supercritical Nitrogen and Carbon Dioxide in Injection Molding

The processability of injection molding ultra-high molecular weight polyethylene (UHMWPE) was improved by introducing supercritical nitrogen (scN2) or supercritical carbon dioxide (scCO2) into the polymer melt, which decreased its viscosity and injection pressure while reducing the risk of degradation. When using the special full-shot option of microcellular injection molding (MIM), it was found that the required injection pressure decreased by up to 30% and 35% when scCO2 and scN2 were used, respectively. The mechanical properties in terms of tensile strength, Young’s modulus, and elongation-at-break of the supercritical fluid (SCF)-loaded samples were examined. The thermal and rheological properties of regular and SCF-loaded samples were analyzed using differential scanning calorimetry (DSC) and parallel-plate rheometry, respectively. The results showed that the temperature dependence of UHMWPE was very low, suggesting that increasing the processing temperature is not a viable method for reducing injection pressure or improving processability. Moreover, the use of scN2 and scCO2 with UHMWPE and MIM retained the high molecular weight, and thus the mechanical properties, of the polymer, while regular injection molding led to signs of degradation

Conventional and Microcellular Injection Molding of a Highly Filled Polycarbonate Composite with Glass Fibers and Carbon Black

Conventional solid injection molding (CIM) and microcellular injection molding (MIM) of a highly filled polycarbonate (PC) composite with glass fibers and carbon black were performed for molding ASTM tensile test bars and a box-shape part with variable wall thickness. A scanning electron microscope (SEM) was used to examine the microstructure at the fractured surface of the tensile test bar samples. The fine and uniform cellular structure suggests that the PC composite is a suitable material for foaming applications. Standard tensile tests showed that, while the ultimate strength and elongation at break were lower for the foamed test bars at 4.0–11.4% weight reduction, their specific Young’s modulus was comparable to that of their solid counterparts. A melt flow and transition model was proposed to explain the unique, irregular “tiger-stripes” exhibited on the surface of solid test bars. Increasing the supercritical fluid (SCF) dosage and weight reduction of foamed samples resulted in swirl marks on the part surface, making the tiger-stripes less noticeable. Finally, it was found that an injection pressure reduction of 25.8% could be achieved with MIM for molding a complex box-shaped part in a consistent and reliable fashion

An XML Based Knowledge Management System for e-Collaboration and e-Learning

This paper presents the development, key features, and the implementation principles of a sustainable and scaleable knowledge management system (KMS) prototype for creating, capturing, organizing, and managing digital information in the form of Extensible Markup Language (XML) documents and other popular file formats. It is aimed to provide a platform for global, instant, and secure access to and dissemination of information within a knowledge-intensive organization or a cluster of organizations through Internet or intranet. A three-tier system architecture was chosen for the KMS to provide performance and scalability while enabling future development that supports global, secure, real-time, and multi-media communication of information and knowledge among team members separated by great distance. An XML Content Server has been employed in this work to store, index, and retrieve large volumes of XML and binary content

FEM of Gas-Assisted Injection Molding Based on 3D Model

The gas-assisted injection molding (GAIM) process is so complicated that increasing reliance has been placed on CAE (Computer Aided Engineering) as a tool for both mold designers and process engineers. In this paper, a 3D theoretical model and numerical scheme is presented to simulate the GAIM process, in which an equal-order velocity-pressure formulation method is employed to eliminate the pressure oscillation. In addition, the whole flow field including the gas and melt regions is calculated using a uniform momentum equation with the viscosity of gas raised to a certain order of magnitude, and a 3D control volume scheme is employed to track the flow front of the melt and gas. Finally, the validity of the model has been tested through case studies and experimental verification