Extrusion processing of low-density microcellular foams

grantor: University of TorontoA continuous extrusion process for the manufacture of low-density, microcellular foams is presented. Microcellular polymers are foamed plastics characterized by a cell density greater than 109 cells/cm3 and a fully grown cell size on the order of 10 [mu]m. Previous research on the continuous processing of microcellular polymers has focused on the control of microcell nucleation in extrusion. This thesis presents an effective means for the control of cell growth by freezing the foam skins in order to achieve a desired expansion ratio in microcellular foam processing that uses CO 2 as a blowing agent, a means of lowering the melt temperature to prevent deterioration of the cell-population density via cell coalescence, and a means of employing lubrication to suppress the melt fracture observed on the extruded foams. Promotion of a desired volume expansion ratio and prevention of cell coalescence while suppressing the melt fracture in microcellular foam processing were experimentally verified. The influences of processing parameters such as melt temperature, nozzle temperature, amount of injected CO2, and amount of injected lubricant on the final foam morphologies were investigated. By tailoring the extrusion processing parameters, microcellular HIPS and HDPE foams with a cell density of 108-1010 cells/cm3 and a controlled expansion ratio in the range of 1.5 to 25 were successfully obtained.Ph.D

Effect of filler material and foaming agent on practical properties of wood plastic composites

In this study, feasibility of foaming wood plastic composites using injection molding process was investigated. The effect of lignocellulosic raw material (Poplar saw dust and soybean straw flour) on the properties of composites was examined. Wood plastic composite boards with 3.2 mm thickness, 105 mm width and 105 mm length were prepared using high density polyethylene granules.  The foaming agent (Azodicarbonamide) at 2 wt % was also used. The scanning electron microscope micrographs confirmed that foaming process has been successfully carried out. The Results showed that all mechanical properties (except the impact strength) decreased while water absorption increased as the microcellular foaming method was used. Adding soybean straw flour to the foam structure led to​​ the decrease in flexural strength, flexural modulus of elasticity and tensile strength. Water absorption and thickness swelling were negatively affected with the addition of soybean straw flour

Investigation of energy absorption performances of a 3D printed fiber-reinforced bio-inspired cellular structure under in-plane compression loading

This article proposes glass-fiber-reinforced bone-inspired cellular structures to enhance energy absorption capability. The elastic modulus of the bone-inspired unit cell is obtained analytically based on the energy method and then employed in Particle Swarm Optimization algorithm to get optimized cellular structures. In the optimized cellular structure, the stiffness is optimized and the energy absorption capacity is investigated. A Fused Filament Fabrication 3D printing process is used to fabricate the cellular structures with continuous glass fiber-reinforced polylactic acid (PLA). In-plane compression tests are performed to investigate the mechanical performance of cellular structures. Finite Element Modeling (FEM) is conducted to analyzed the mechanical performance of the structures. In FEM, the failure criterion is determined using the maximum stress and VUSDFLD subroutine, and the damage growth is modeled by decreasing the mechanical properties. A good agreement between numerical and experimental results was observed. Results demonstrated that the energy absorption in glass-fiber-reinforced PLA is ∼250% higher than in the un-reinforced structure. The optimized cellular structure exhibits a stable prolonged plateau stress region and very high specific energy absorption parameters