Microcellular Foaming Process Research Articles

Depressurization induced morphology control in solid-state microcellular batch foaming process

This research article describes the impact of the depressurization rate change on the morphology of microcellular polycarbonate foams (PCMFs) using batch-wise foaming with carbon dioxide as a physical blowing agent. It was expected that the depressurization rate will affect the foaming behavior of microcellular foamed polycarbonate (PCMFs). While keeping other variables constant and changing depressurization rate, the depressurization rate affects the cell size, cell density, cell size distribution, and expansion ratio. The result showed cell diameter 5 ± 0.5, 7 ± 0.8, 9 ± 1.2, and 9.5 ± 1.5 µm and expansion ratio 5.2, 5.5, 6.0, and 6.3 at depressurization rate of 0.5 (D1), 0.05 (D2), 0.01 (D3), and 0.005 (D4) MPa/Sec, respectively. The cell area distribution showed that a higher depressurization rate leads to the more regular distribution of cells. The cell densities were observed as 2.6 × 1010, 4.6 × 109, 2 × 109, and 8.2 × 108 cells/cm3 at D1, D2, D3, and D4. It is investigated that as compare to depressurization rate other variables such as saturation pressure, foaming temperature and foaming time has more impact on properties of PCMFs.

Reflectance According to Cell Size, Foaming Ratio and Refractive Index of Microcellular Foamed Amorphous Polymer.

Microcellular foamed plastic has a cell size of approximately 0.1 to 10 microns inside a foamed polymer and a cell density in the range of 109 to 1015 cells/cm3. Typically, the formation of numerous uniform cells inside a polymer can be effectively used for various purposes, such as lightweight materials, insulation and sound absorbing materials. However, it has recently been reported that these dense cell structures, which are induced through microcellular foaming, can affect the light passing through the medium, which affects the haze and permeability and causes the diffused reflection of light to achieve high diffuse reflectivity. In this study, the effects of cell size, foaming ratio and refractive index on the optical performance were investigated by applying the microcellular foaming process to three types of amorphous polymer materials. Thus, this study experimentally confirmed that the advantages of porous materials can be implemented as optical properties by providing a high specific surface area as a small and uniform cell formed by inducing a high foaming ratio through a microcellular foaming process.

Fabrication of open‐porous PCL/PLA tissue engineering scaffolds and the relationship of foaming process, morphology, and mechanical behavior

Tissue engineering scaffolds should provide a suitable porous structure and proper mechanical strength, which is beneficial for the delivery of growth factor and regulation of cells. In this study, the open‐porous polycaprolactone (PCL)/poly (lactic acid) (PLA) tissue engineering scaffolds with suitable porous scale were fabricated using different ratios of PCL/PLA blends. At the same time, the relationship of foaming process, morphology, and mechanical behavior in the optimized batch microcellular foaming process were studied based on the single‐factor experiment method. The porous structures and mechanical strength of the scaffolds were optimized by adjusting foaming parameters, including the temperature, pressure, and CO2 dissolution time. The results indicated that the foaming parameters influence the cell morphology, further determine the mechanical behavior of PCL/PLA blends. When the PCL content is high, with the increase of temperature and time, the cell diameter and the elastic modulus increased, and the tensile strength and elastic modulus increased with the increase of the average cell size, and decreased as the increase of the cell density. While when the PLA content was high, the cell diameter showed the same trend, and the tensile strength and elastic modulus were higher, and the elongation at break was lower, and tensile strength and elastic modulus decreased with the increase of the average cell size and increased with the increase of cell density. This work successfully fabricated optimized porous PCL/PLA scaffolds with excellent suitable mechanical properties, pore sizes, and high interconnectivity, indicating the effectiveness of modulating the batch foaming process parameters.

Warpage Reduction of Glass Fiber Reinforced Plastic Using Microcellular Foaming Process Applied Injection Molding.

This study analyzes the fundamental principles and characteristics of the microcellular foaming process (MCP) to minimize warpage in glass fiber reinforced polymer (GFRP), which is typically worse than that of a solid polymer. In order to confirm the tendency for warpage and the improvement of this phenomenon according to the glass fiber content (GFC), two factors associated with the reduction of the shrinkage difference and the non-directionalized fiber orientation were set as variables. The shrinkage was measured in the flow direction and transverse direction, and it was confirmed that the shrinkage difference between these two directions is the cause of warpage of GFRP specimens. In addition, by applying the MCP to injection molding, it was confirmed that warpage was improved by reducing the shrinkage difference. To further confirm these results, the effects of cell formation on shrinkage and fiber orientation were investigated using scanning electron microscopy, micro-CT observation, and cell morphology analysis. The micro-CT observations revealed that the fiber orientation was non-directional for the MCP. Moreover, it was determined that the mechanical and thermal properties were improved, based on measurements of the impact strength, tensile strength, flexural strength, and deflection temperature for the MCP.

Method of Calculating the Fluid Permeability of Machined Skin-Covered Porous Sheets from Experimental Flow Data

Abstract Porous polymer sheets created by the “solid state microcellular foaming process” possess an impermeable solid skin on the boundary. In order to experimentally determine the internal structure's fluid permeability, the skin is removed by machining a pattern of holes or channels so that fluid flow can be established when applying a pressure difference across the faces. In this work, a fluid flow model for this particular geometry assuming a Newtonian fluid and isotropic internal porous structure is established. This yields formulae used to compute the structure's Darcy permeability from experimental flow data. Experimental verification of the model is provided for a sample of Polyetherimide (PEI) nanoporous polymer sheet whose skin was drilled in various hole patterns, thus establishing the mathematical foundation for future work in investigating this class of porous materials.

Experimental research on swelling and glass transition behavior of poly(methyl methacrylate) in supercritical carbon dioxide

The glass transition temperature (Tg) reduction of polymer by plasticization is a paramount thermodynamic property in polymer/diluent systems, thus effecting microcellular foaming process. Experiment was conducted in a high-pressure cell furnished with an optical channel. In this research, the swelling ratios (ΔV/V0) of polymethyl methacrylate (PMMA) in carbon dioxide (CO2) with pressures ranging from 2 to 22MPa were measured, thus the Tg data of PMMA was determined in the same pressure range. It was found that the swelling ratio increases with temperature but reaches the maximum at 12MPa, instead of 22MPa. And the glass transition temperature decreases from 380.5 to 311.4K within the pressure range of 0.1–12MPa but increases gradually to 323.1K from 12 to 22MPa. Additionally, the change of maximum saturation temperature as a function of CO2 pressures agrees well with Tg of the polymer-CO2 system.

Die opening-induced microstructure growth in extrusion foaming of thermoplastic sheets

Abstract In this study, the influence of die opening gap on foam attributes during a microcellular extrusion foaming process was investigated. Lower die openings developed higher pressure drops on the foams, as a result of which greater thermodynamic instability was stimulated and, consequently, higher cell density foams along with enhanced expansion ratios were achieved. Further investigations were performed to study the synergistic influence of altering die opening with critical process parameters, namely, screw rotational speed and die temperature, on the foam expansion ratio and morphological transformations. Higher screw rotational speed induced shear nucleation phenomenon, which further enhanced the foaming process significantly. Also, an optimum die temperature was observed, which developed maximum expansion ratio at the lowest die opening gap. This study intends to enhance the understanding of extrusion foam processing among academia as well as among industries.

Physical properties of microcellular polymeric foams with supercritical CO2

Microcellular polymeric foams possess characteristics of thermal insulation and lightweight and impact resistant in comparison to their solid counterparts. The physical properties (i.e. glass transition temperature and CO2 solubility and diffusivity) of CO2–polymer mixtures play important roles in determining microcellular foaming parameters, and subsequently affect cell diameter and density. In this paper, an evaluation of the current state of understanding of the physical properties of microcellular foaming process was reviewed. The effects of these three physical properties on foaming were explained. In addition, this study focused on visual measurement and the prediction of these three properties. For measurement, visual observation at high pressure is of great significance, providing a reference for further study.

Fabrication of polylactic acid/polyethylene glycol (PLA/PEG) porous scaffold by supercriticalCO2foaming and particle leaching

PLA/PEG/NaCl blends were melt‐blended followed by gas foaming and particle leaching process to fabricate porous scaffold with high porosity and interconnectivity. A home‐made triple‐screw compounding extruder was used to intensify the mixability and dispersion of NaCl and PEG in the PLA matrix. Supercritical carbon dioxide was used as physical blowing agent for the microcellular foaming process. Sodium chloride (NaCl) was used as the porogen to further improve the porosity of PLA scaffold. This study investigated the effects of PEG and NaCl on the structure and properties of the PLA‐based blend, as well as the porosity, pore size, interconnectivity, and hydrophilicity of porous scaffolds. It was found that the incorporation of PEG and NaCl significantly improved the crystallization rate and reduced viscoelasticity of PLA. Moreover, scaffolds obtained from PLA/PEG/NaCl blends had an interconnected bimodal porous structure with the open‐pore content about 86% and the highest porosity of 80%. And the presence of PEG in PLA/NaCl composite improved the extraction ability of NaCl particles during leaching process, which resulted in a well‐interconnected structure. The biocompatibility of the porous scaffolds fabricated was verified by culturing fibroblast cells for 10 days. POLYM. ENG. SCI., 55:1339–1348, 2015. © 2015 Society of Plastics Engineers

Investigation of Cell Structure and Expansion Ratio of Microcellular Polypropylene Nanohomocomposites Prepared by a Solid-State Process

Microcellular poly(propylene-ethylene) random copolymer (r-PP-PE)/nanoclay (nanocomposite) and r-PP-PE/nanoclay/polypropylene fibers (nanohomocomposite) were autoclave-foamed via a solid-state microcellular foaming process using supercritical N2 as a foaming agent. Polypropylene grafted with maleic anhydride (PP-g-MA) was used as a compatibilizer. Amount of PP-g-MA to nanoclay was 3:1. This study investigated the effects of clay content and the presence of polypropylene fiber on the expansion ratio and cell morphology of the samples. The results indicated that nanoclay increased the expansion ratio of the samples, but the expansion ratio for nanohomocomposites was slightly lower than the nanocomposites. In addition, scanning electron microscopy (SEM) observation showed that the nanoclay decreased the cell size and increased the cell density, except for the nanocomposite with the highest nanoclay content, 3 wt%, which had larger cell size compared to the samples with 1.5 wt% nanoclay and less. On the other hand, the simultaneous presence of nanoclay and polypropylene fibers synergistically increased the cell nucleation effect; thus there was a dramatic increase in cell density. The Differential scanning calorimetry (DSC) analysis showed that the microcellular foaming process decreased the crystallinity of both types of samples.

Diffused Reflection Performance of Microcellular Foamed Polyethylene Naphthalate

Due to the increasing demand for high-performance diffuse reflectors in applications including LCD displays and lighting, many studies on the manufacturing of high-performance reflectors have been conducted. Microcellular foamed plastics are characterized as having a structure with a cell size of 10 µm or less along with a cell density of at least 109 cells/cm3. Since the structural characteristics of these materials were determined to result in diffused reflection, the use of polymers as diffuse reflectors has been studied. In this study, a diffuse reflector specimen was manufactured by applying a microcellular foaming process to polyethylene naphthalate (PEN). The optimum foaming conditions of PEN were determined through preliminary experiments using the Batch process and the specimen was manufactured using supercritical CO2. Additionally, to improve the low productivity, which is one of the disadvantages of the Batch process, additional specimens were manufactured while varying the saturation conditions. Through observation of the cross-sections of the specimens, the cell morphology depending on the process conditions was confirmed and then, the diffusion reflectivity was measured.

Factors That Affect Diffuse Reflection Performance of Microcellular Foamed Plastics

The structure of microcellular foamed plastics causes optical, acoustic, and electrical properties. The diffuse reflection performance of microcellular foamed plastics can be applied as a high performance diffuse reflector. To improve microcellular foaming process, a simulation was conducted. It was to analyze the factor affecting when microcellular foamed plastics realized the diffuse reflection performance. Cell morphology of microcellular foamed plastics can be expressed through four factors. From result of simulation made a data base about cell morphology and diffuse reflectance. And the statistical method was used for identify contributions by factors.

Strategy To Produce Microcellular Foamed Poly(lactic acid)/Wood-Flour Composites in a Continuous Extrusion Process

In microcellular foaming process of wood/plastic composites, the alterations in melt viscosity induced by the addition of wood-flour into the plastic matrix play an important role during the growth and stabilization of nucleated cells. This study examined the effects of wood-flour and low molecular weight rheology modifier addition levels on the melt flow index, shear viscosity, and extensional viscosity of PLA/wood-flour composites. From the results, an effective strategy is proposed to successfully and continuously produce microcellular foamed PLA/wood-flour composites with cellular structures similar to those achieved in neat PLA foams. It consists of matching the composites’ melt index value (or melt viscosity) to that of neat PLA by using a rheology modifier. Lowering the melt index of the composites from the matching value resulted in unprocessable foaming conditions owing to the increased melt viscosity, whereas cell structures slightly deteriorated by increasing the melt index of the composite above its optimum value.

Effect of intrinsic viscosity on solid-state microcellular foaming of polyethylene terephthalate

Abstract

The effect of polymer hardness, pore size, and porosity on the performance of thermoplastic polyurethane-based chemical mechanical polishing pads

Abstract

A study on the foaming ratio and optical characteristics of microcellular foamed plastics produced by a repetitive foaming process

Microcellular foaming technology has had a great influence on the polymer progress. According to the previous studies, polymer material has the same mechanical strength as general plastic molding products but it can have a lighter weight, and it has the features of insulation and noise suppression. In addition, it shows excellent diffused reflectivity since it has micro-sized cells. This study intends to determine the change microcellular foaming process conditions; it also intends to determine the optical characteristics, And the results of this experiment are shown through foaming ratio, diffused reflectivity, and cell morphology. We examined changes in cell morphology in the inner regions of polycarbonate (PC) samples and the resulting changes in foaming ratios. We also examined the optical characteristics that result when a repetitive foaming process is performed using polymer samples that have already undergone an initial microcellular foaming process. Polycarbonate is an amorphous material with exceptional optical characteristics. The saturation pressure was varied during both the first foaming process and the repetitive foaming process, and the results of the experiment were expressed in terms of foaming ratio, diffused reflectivity, and cell morphology.

Microcellular foam processing of biodegradable polymers — review

Polymers are the most widely used materials because of their ease of processing, low cost, and low density. But many of these materials are not easily recyclable and are difficult to degrade completely in nature, creating environmental problems. Considerable researches are underway to make naturally synthesized and biodegradable materials that are easily degraded and less likely to cause environmental pollution. As improved, lower-cost biodegradable polymers become available, we expect that research on foaming processes will be undertaken to further reduce the cost and weight and to improve function, ultimately increasing applicability. In this article, we review the microcellular foaming process as a thermoplastic forming process. We divide the microcellular foaming process into batch, injection, and extrusion processes and review the purpose and result of each. Easier-molding foamed biodegradable polymer will enable the substitution of most current foamed polymer products with products made of foamed biodegradable polymers.

Ultrasound assisted cyclic solid-state foaming for fabricating ultra-low density porous acrylonitrile–butadiene–styrene foams

In this research article, novel porous microcellular ABS foams were fabricated and subsequently investigated for their morphological attributes. Initial research focuses on developing ultra-low density closed cell foams through cyclic microcellular foaming process. First stage foaming process develops microcells which affect the second stage of the batch foaming process. Hence, the effect of repeated foaming process on foam density and its morphology are discussed. Subsequently, ultrasound excitations were utilized to rupture the closed cell walls, thereby developing porous structure. The combined cyclic solid-state foaming and ultrasound excitation provides a way to fabricate ultra-low density porous polymers.

Structure and mechanical properties of polystyrene foams made through microcellular injection molding via control mechanisms of gas counter pressure and mold temperature

In this study we developed a foaming control system using Gas Counter Pressure (GCP) combined with mold temperature control in the microcellular foaming (MuCell) process. The effects of the skin thickness, cell size, and cell morphology resulting from the three control mechanisms (including GCP control alone, mold temperature control alone, and GCP combined with mold temperature control) and process parameters on the mechanical properties of foamed polymer were investigated. In addition, the mechanical properties of foamed specimens molded from these three control mechanisms were also compared. It was found that skin thickness, cell size, and cell shape had significant influences on the mechanical properties of specimens depending on the molding conditions of gas counter pressure, holding time, and mold temperature. By increasing gas counter pressure, holding time, and decreasing the mold temperature, the tensile strength increased. In addition, by increasing gas counter pressure, holding time, and mold temperature alone, impact strength decreased. But, there were no clear relationships for processing parameters when GCP combined with dynamic mold temperature control was used because the effects of the skin thickness, cell size, and cell shape on the impact strength were unclear. Under experimental condition at mold temperature of 60°C combined with appropriate GCP control system, better tensile strength and impact performance were achieved and specimens with thin skin, small and uniform cell size as well as better surface quality were produced.

Changes in the Reflectivity and Color Characteristics of Microcellular Foamed Plastics

As the use of plastics has increased in various industries, research on microcellular plastics has increased as well. The microcellular foaming process helps produce lighter plastic and reduces material consumption. This process also affects the optical properties. The primary purpose of this study is to measure the visible changes occurring in polymer samples by comparing changes in the samples before and after the microcellular foaming process. To measure the changes in color characteristics, colored PC samples were utilized for the experiments. Changes in the color characteristics were indicated using the Munsell color system.