Blowing Agent Content Research Articles

Optimization of Mg Blowing Agent Content for Foaming Aluminum

Optimization of Mg Blowing Agent Content for Foaming Aluminum

Study of the Mechanical, Sound Absorption and Thermal Properties of Cellular Rubber Composites Filled with a Silica Nanofiller.

This paper deals with the study of cellular rubbers, which were filled with silica nanofiller in order to optimize the rubber properties for given purposes. The rubber composites were produced with different concentrations of silica nanofiller at the same blowing agent concentration. The mechanical, sound absorption and thermal properties of the investigated rubber composites were evaluated. It was found that the concentration of silica filler had a significant effect on the above-mentioned properties. It was detected that a higher concentration of silica nanofiller generally led to an increase in mechanical stiffness and thermal conductivity. Conversely, sound absorption and thermal degradation of the investigated rubber composites decreased with an increase in the filler concentration. It can be also concluded that the rubber composites containing higher concentrations of silica filler showed a higher stiffness to weight ratio, which is one of the great advantages of these materials. Based on the experimental data, it was possible to find a correlation between mechanical stiffness of the tested rubber specimens evaluated using conventional and vibroacoustic measurement techniques. In addition, this paper presents a new methodology to optimize the blowing and vulcanization processes of rubber samples during their production.

Influence of Gas Pressure and Blowing Agent Content on the Formation of Aluminum Alloy Foam

Apart from density and alloy composition, the structure of solid metallic foams determines their mechanical performance. Herein, the effect of ambient pressure on the foaming behavior of AlSi6Cu4 precursors is studied. In situ X‐ray radioscopy is applied while foaming in a furnace chamber pressurized up to 40 bar. The content of the blowing agent (TiH2) is varied for each of the pressures chosen. The foam density and morphology are analyzed quantitatively using time‐resolved X‐ray radioscopy sequences and postsolidification X‐ray tomography data. The optimal content of blowing agent as well as the pore sizes and distributions is found to depend strongly on the ambient pressure. At high pressures very small, round, and uniformly distributed pores are formed and crack formation is avoided during the gas nucleation stage, which helps to prevent structural defects. Adjusting the ambient pressure allows for better control of the foam structure and density, which is relevant for commercial production and application.

Near-Infrared Spectroscopic Monitoring Technique of Physical Blowing Agent Concentration in Foam Injection Molding Processes

Near-Infrared Spectroscopic Monitoring Technique of Physical Blowing Agent Concentration in Foam Injection Molding Processes

The Relationship between the Morphology and Elasticity of Natural Rubber Foam Based on the Concentration of the Chemical Blowing Agent.

Concentrated natural latex was used to produce a rubber foam that is porous, elastic and well ventilated. The mechanical properties can be either soft or firm, depending on the formulation of the latex used. Briefly, concentrated natural latex was mixed with chemical agents to make the rubber foam on a laboratory scale using the Dunlop process. In this work, we changed the concentration of the chemical blowing agent in the latex. The morphological properties of the rubber foam were characterised using scanning electron microscopy, and the mechanical properties, or elasticity, were studied using compression experiments and the Mooney–Rivlin calculation. The results show that the concentration of the chemical blowing agent affects the morphological properties of the rubber foam but not the mechanical properties, indicating the heterogeneous structure of the rubber foam. The thermodynamic parameters (∆G and ∆S) and the internal energy force per compression force (Fu/F) of the rubber foam with various amounts of chemical blowing agent were also investigated. This study could be applied in the foam industry, particularly for pillow, mattress and insulation materials, as the present work shows the possible novel control of the morphological structure of the rubber foam without changing its mechanical properties. The difference in cell sizes could affect the airflow in rubber foam.

Viscoelastic Polyurethane Foams for Use in Seals of Respiratory Protective Devices.

A key factor in effective protection against airborne hazards, i.e., biological and nonbiological aerosols, vapors, and gases, is a good face fit of respiratory protective devices (RPDs). Equally important is the comfort of use, which may encourage or discourage users from donning RPDs. The objective of the work was to develop viscoelastic polyurethane foams for use in RPD seals. The obtained foams were characterized using scanning electron microscopy, infrared spectroscopy, thermogravimetry, and differential scanning calorimetry. Measurements also involved gel fraction, apparent density, air permeability, elastic recovery time, compression set, rebound resilience, and sweat uptake. The results were discussed in the context of modifications to the foam formulation: the isocyanate index (INCO) in the range of 0.6–0.9 and the blowing agent content in the range of 1.2–3.0 php. FTIR analysis revealed a higher level of urea groups with increasing water content in the formulation. Higher INCO and water content levels also led to lower onset temperatures of thermal degradation and higher glass-transition temperatures of the soft phase. A decrease in apparent density and an increase in mean pore sizes of the foams with increasing INCO and water content levels was observed. Functional parameters (air permeability, elastic recovery time, compression set, rebound resilience, and sweat uptake) were also found to be satisfactory at lower INCO and water content levels.

Characterization of chemically foamed poly(lactic acid)

This paper presents the characterization of poly(lactic acid)-based chemically foamed foam structures. We used extrusion grade, high molecular weight poly(lactic acid) as matrix material and azodicarbonamide as foaming agent. The resulting foams were characterized by foam density, cell population density, scanning electron microscopy, and based on the fracture surface of the foam cross-section, we calculated cell size distribution. The obtained distributions were fitted with the use of log-normal distribution in each case. We presented the effect of chemical blowing agent content (0.5 wt%, 1 wt%, 2 wt%, 4 wt% and 8 wt%) on the PLA-based foam structure and the effect of processing temperature (190 °C, 210 °C and 230 °C) on cell size distribution.

Gas transport properties of cellular hollow fiber membranes based on LLDPE/LDPE blends

The production of foamed hollow fiber membranes (HFMs) is presented based on polymer blends using various concentrations of linear low-density polyethylene (LLDPE) and low-density polyethylene (LPDE) combined with azodicarbonamide (chemical blowing agent) to prepare samples via twin-screw extrusion. In particular, the blowing agent concentration as well as the stretching speed were found to be the most important parameters to achieve a good cellular structure for membrane application. From the samples obtained, a complete set of morphological, thermal, and gas transport characterization was performed. The results show that LLDPE/LDPE blends compared to neat LLDPE lead to higher cell density at high stretching speed, which is appropriate for membranes having higher gas permeability and selectivity due to lower cell wall thickness. The results also show that the developed cellular structure has high potential for the continuous production of HFMs for different gas separation, especially for hydrogen recovery.

A lightweight, thermal insulation and excellent weatherability foam crosslinked by electron beam irradiation

Thermal insulation and excellent weatherability microcellular foams based on lightweight polymer are successfully developed from chlorinated polyethylene rubber/polyvinyl chloride (CM/PVC) compounds through electron beam irradiation cross-linking and chemical foaming technology. The effect of electron beam irradiation on the blends of CM/PVC foam prepared with different compositions starting from 70:30 to 50:50 (CM:PVC) with varied radiation doses from 30 to 70 kGy and varied chemical blowing agent contents from 10 to 20 phr has been studied. The aim was to investigate the influence of the different blending ratio, the chemical blowing agent content and the irradiation dose on physical and mechanical properties and morphology of the cellular structure in the produced foams. Thermal conductivity of CM/PVC compounds foams achieved in this study is as low as 0.0374W/mK.

Microstructural analysis and blowing agent concentration in aged polyurethane and polyisocyanurate foams

Over the last few years, new environmental protection regulations have promoted the adoption of new blowing agents for the production of foam materials. Understanding how these new blowing agents influence the characteristics of the foams is critical in thermal engineering applications. The cell structure of a foam and the concentration of the blowing agents in it are the main factors affecting the thermal conductivity of foams. Recent studies have revealed the risks of condensation of some of the new environmentally friendly blowing agents at temperatures below 10 °C. Meanwhile, many blowing agents tend more easily to escape the foam structure when subject to temperature cycles; this aging increases the thermal conductivity of too, since the blowing gas is replaced by air. In this paper, to understand the loss of thermal performance of aged foams, a microstructure and chemical characterization was performed together with thermal conductivity tests of both pristine and laboratory-aged foams. The aging behaviour was analysed by SEM imaging and by measuring the blowing agent concentration in both open cell and closed cell foams. Changes in the polymer physical attributes were identified. Results prove that aged foams show cellular elongation and increase in the cell wall thickness. The results of gas chromatography helped to quantify the changes in the concentration of pentane in aged polyisocyanurate foams. A decrease of the blowing agent between 11% and 85% for the aged polyisocyanurates was measured. Finally, this study highlights the importance to analyse the in-service characteristics of both polyurethane and polyisocyanurate foams to avoid considering their thermal conductivity as a constant property.

Microstructure and blowing agent concentration analysis in accelerated aged polyurethane & polyisocyanurate insulation

Some closed cell foam insulation products show an increase in thermal conductivity at low temperatures. This reduction in thermal performance has been attributed to the diffusion of air and blowing agent through the foam and to the condensation of the blowing agent. Aging processes and polymer degradation further increase the thermal conductivity of foams. The initial cell structure plays a role in dictating the thermal performance and changes with foam aging which is rarely investigated. To understand the loss of thermal performance in closed cell foams, a microstructure and chemical characterization of pristine and aged samples was performed in this study. The aging behaviour was analyzed by SEM imaging and by measuring the blowing agent concentration in the foam. Changes in the polymer physical attributes were identified. This study also used gas chromatography and quantified changes in pentane concentration in aged polyisocyanurate foams. Results show that aged foams undergo change in their polymer appearance and cellular elongation. Gas chromatography quantified a decrease in blowing agent in the range of 11-85% for polyisocyanurate foams after aging.

The effect of resin formulation on the cellular morphology and mechanical properties of phenolic foams

ABSTRACTIn the present study, the effects of blowing agent concentration, surfactant, and resin viscosity on the cellular structure, density, and compressive strength of phenolic foams were investigated. The mechanism of foaming was studied by thermal analyses, as well. The scanning electron microscopy was performed to investigate the morphology of foams. The presence of surfactant was essential to obtain a foam structure. By increasing the amount of blowing agent in the formulation, the bubbles became larger. The variation of the resin viscosity had the sharp effect on the cell size and its distribution so that the cell size dropped from 108 to 77 μm in the sample with the highest viscosity. The mechanical properties were significantly affected by foam structure as well as the cell uniformity. By decreasing the average cell sizes, the compression strength and modulus were improved up to more than 60%. Finally, the optimum values for viscosity of resin and, blowing agent, and surfactant concentrations were obtained. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2020,137, 48331.

Prediction of Foaming Process in the Production of Aluminium Foams

The paper deals with the physical-chemical effects of a blowing agent on production the cellular metal systems (in this case aluminium foams). Based on the isothermal concertation and pressure curves for the H-Ti system and by using the maximum gas volume obtained from equation of state, there was applied the blowing agent to 1 kg of AlSi12 aluminium alloy. Moreover, using relation to determine aluminium foam relative density (ρ REL) from alloy AlSi12, there was done prediction to determine density of 1 kg metal foam from AlSi12 alloy at different blowing agent contents from 0.1 up to 1.5 wt% of titanium hydride TiH 2. These isothermal calculations were compared with the density of aluminium foal from alloy AlSi12, which was produced by an industrial process. Basic mechanical properties were subsequently measured on the produced foam samples.

Synthesis and characterization of high temperature resistant thermal expansion microsopheres with P(acrylonitrile/methacrylic acid/N,N-dimethylacrylamide/n-butylacrylate) shell

High temperature resistant microspheres were prepared via Pickering suspension polymerization. Acrylonitrile (AN), methacrylic acid (MAA) and N,N-dimethylacrylamide (DMAA) were used as monomers, and n-butylacrylate (BA) was used as modified monomer to improve the expansion properties of the microspheres. Morphology of the microspheres was characterized by scanning electron microscopy (SEM) and polarizing optical microscope (POM) respectively. The average diameter of the prepared microspheres was 51.9 μm, and the maximum expansion volume was 4 times of the original volume. The expansion performance and blowing agent content of the microspheres were characterized by thermal mechanical analysis (TMA) and thermogravimetric analysis (TGA) respectively. The onset expansion temperature of the microspheres was 159.5 °C, the maximum expansion temperature was 213.9 °C, and the encapsulation content of the blowing agent was 14.62%. Fourier transform infrared (FTIR) showed that the adjacent chains of AN and MAA form imide ring structure during the thermal expansion process of the microspheres.

Viscoelastic epoxy foams by an aqueous emulsion foaming process

The research proposed an aqueous emulsion foaming process to produce a viscoelastic epoxy foam having a density of 0.33–0.36 g/cm3 from the polyamide–epoxy adduct, which uses a reverse ratio of epoxy and polyamide hardener. The process is simple, economical and uses no surfactant, thanks to the emulsifying ability of polyamide hardener. Firstly, the mixture of excess polyamide, epoxy and sodium bicarbonate was emulsified with distilled water using high-speed stirring to form dispersed epoxy droplets in water. Secondly, a solution of ammonium chloride was added, which reacted with sodium bicarbonate to produce carbon dioxide and ammonia gases dispersed in the epoxy emulsion. The expanding gases induced flocculation and partial coalescence of the epoxy droplets; sequentially water molecules were entrapped within them. Finally, a curing process was carried out to stabilise the foam morphology and structure. Two types of pore morphologies were observed: a large foam-pore generated from blowing-agent gases and a cell-wall pore formed from the vapourisation of entrapped water (as the void template). Porosity and pore morphologies depended on blowing-agent content, and the viscoelasticity was affected by the epoxy/polyamide ratio. The obtained viscoelastic foams showed a large number of interconnected cells and exhibited high compression set values.

Effect of blowing agent concentration on rigid polyurethane foam and the properties of foam-core particleboard

ABSTRACT In this research, a sandwich panel with particleboard as surface layers and rigid polyurethane (PU) foam as core layers (foam-core particleboard) was produced with a one-step in situ foaming process. The effects of hydrofluorocarbon concentration as the blowing agent (BA) on the foam features and physical and mechanical properties of the produced panels were investigated. Typical micrograph of the rigid PU foam showed well-defined closed cells of spherical and polyhedral shapes. It was shown that the number of fractured cells in the foam structure was increased with the addition of BA in the amount of more than 4.5%. The results showed that the bending strength and internal bond values significantly raised with increasing BA concentration up to 6%. Screw withdrawal resistance from the face and thickness swelling were not significantly changed while the BA concentration varied. Edge screw withdrawal resistance and water absorption were drastically decreased when the blowing agent concentration was raised in the whole studied range. ABBREVIATIONS: PU: polyurethane; OH: hydroxyl; PO: polyol; ISO: isocyanate; BA: blowing agent; PMDI: polymeric methylene diphenyl diisocyanate; BS: bending strength; IB: internal bond; SWR: screw withdrawal resistance; TS: thickness swelling; WA: water absorption

Thermoplastic foam injection moulding of sandwich structures with short fibre-reinforced skin layers

Sandwich structures, consisting of a short glass fibre–reinforced polypropylene film as skin layer and chemically blown polypropylene as the core material, were produced via injection moulding. The skin layers of the sandwich structures, which contain polypropylene as well as 30 wt% and 50 wt% of glass fibres namely polypropylene–glass fibres 30 and polypropylene–glass fibres 50 respectively, were produced by film extrusion using a coat hanger die. The properties of the films were investigated by dynamic mechanical analysis. Furthermore, the influence of different glass fibre contents in the skin layers and chemical blowing agent contents in the core material of sandwich structures was studied to compare them with the compact polypropylene and the polypropylene foams. The sandwich structures were characterized with regard to density, microstructure, weight reduction, surface roughness and bending properties. In general, distinctive reinforcement effect was achieved by use of the short glass fibre with the strong influence of processing direction of the film. For the sandwich structures, it was found that a good adhesion between the skin layers and the core material can be achieved during injection moulding. The microstructure and the bending properties of the sandwich structures depend on the glass fibre–reinforced film and the chemically blown core. It was found that the use of the skin layers led to lower cell intensity in the foam core. Nevertheless, a high modulus and strength to weight ratio could be accomplished by a high stiffness of the glass fibre–reinforced film and a low density of the chemically blown core. Additionally, it was found that the surface roughness of the films could be reduced due to processing in injection moulding.

Effect of free foaming and pre-curing on the thermal, morphological and physical properties of reclaimed tyre rubber foam composites

Foaming of rubber is a well-known technique and foamed rubber products have found application in various industries including cushioning, heat insulation and sound absorption. In the current study, the foaming of reclaimed tyre rubber (RTR), as an alternative to virgin rubber, is explored. The effect of varying the amounts of waste ethylene vinyl acetate (filler), sodium bicarbonate (blowing agent) and dicumyl peroxide (co-curative) on the RTR properties was studied. Composites formulations were obtained by use of the simplex-lattice mixture design and the samples were prepared by following two foaming techniques namely, prepressing and free foaming. Hardness of free foamed samples was found to be lower than that of prepressed samples, owing to effective foaming and the formation of multiple microcells in the former. An increase in blowing agent content resulted in decreased density and thermal stability of the foamed composites. Dicumyl peroxide caused an increase in density but had no effect on thermal stability. The incorporation of a filler in formulations effected an increase in the gel content and thermal stability of the foams. Free foamed samples exhibited higher shrinkage with an increase in both waste ethylene vinyl acetate and sodium bicarbonate. However, dicumyl peroxide significantly increased the shrinkage of prepressed samples, whereas sodium bicarbonate decreased the gel content and thermal stability of both free foamed and prepressed samples. It is demonstrated in the current work that both foaming processes are applicable for RTR and the choice of the processing method is dependent on the desired properties of the composites.

Influence of talc in polypropylene foam cores of sandwich structures with skins made of thermoplastic prepregs

Properties of sandwich structures with a core of thermoplastic foam depends on cell size and cell density (cell number). Nucleating agents have a benefit to generate cell nucleation, which affects an increase in the cell density. In this study, sandwich structures composed of a polypropylene (PP) foam core and organic sheet skins in-situ produced by injection moulding process. A chemical blowing agent was employed to generate cellular structure in the core. The influence of the varying nucleating agent content with the same chemical blowing agent content on density, cellular structure and mechanical properties of the sandwich structures were investigated. The talc contents had a slight influence on the density of the sandwich structures. Moreover, flexural modulus and flexural strength of the sandwich structures consisting of the foam core with 4 wt% of talc were higher than the foam core without talc. However, the utilization of these talc contents with PP and the chemical blowing agent had no significant effect on the reduction of the cell size and the increase of the cell density.

Density graded polyethylene foams: Effect of processing conditions on mechanical properties

Uniform foams (UF) and density graded foams (DGF) were produced by using similar or different temperatures on both sides of a compression molding system. The samples were produced using linear low density polyethylene as the matrix and activated azodicarbonamide as the chemical blowing agent. Morphological properties of the produced samples were analyzed via scanning electron microscopy to relate them to their mechanical properties. In particular, flexural and impact properties are reported for samples produced under a range of temperatures (140–200°C) and blowing agent concentration (0.7–1.0 wt%). The experimental results showed that a significant difference can be obtained in flexural modulus (up to 17%) and impact strength (up to 48%) depending on the side the stress is applied on. In all cases, the DGF showed better mechanical responses than UF of similar relative density for the range of conditions tested.