Effect Of Foaming Temperature Research Articles

Production, stability, and properties of in-situ Al–5ZrB2 composite foams

Stabilization is an essential requirement to produce closed-cell metal foams. In the melt route of foaming, usually ceramic particles are used as foam stabilizers. For the first time, the present study introduces ZrB2 particles as foam stabilizers. We demonstrate the foaming of in-situ based Al composite containing submicron ZrB2 particles. The effect of foaming temperature and holding time on the structural and mechanical properties of the foams was studied. The composites and foams were characterized using XRD, SEM/EDS, and optical scanning techniques. The mechanical properties of the foams were determined by subjecting the foams to a quasi-static compression test. Submicron ZrB2 particles present in the cell wall and at the gas-solid interface promoted foam stability. All the foams exhibited a good cellular structure with high expansion. Among all the foams, the foams prepared at 680 °C with a holding time of 120 s exhibited the smallest cell size and the best mechanical properties. The structural and mechanical properties of the Al–5ZrB2 foams were found to be comparable to conventional foams.

Preparing Polypropylene Auxetic Foam by a One‐Pot CO2 Foaming Process

At present, the direct preparation of polymer foam with negative Poisson ratio (auxetic foam) from nonpolar polymer resins is still a challenge. Herein, a one‐pot CO2 foaming method is established to directly prepare closed‐cell auxetic foams with different cellular structures (bimodal cell structure and homogeneous cell structure) from polypropylene (PP) resin by introducing hydrophilic additives (NaCl) into PP and regulating foaming conditions. The effects of foaming temperature, saturation time, and size of added NaCl on Poisson's ratio are studied. The comparison with PP/talc composites shows that the presence of NaCl plays a crucial role in the formation of the negative Poisson ratio of foam. Furthermore, the regulation of the size of negative Poisson ratio is achieved by controlling the amount of NaCl in PP/NaCl composites. This study has important reference significance for the preparation of nonpolar polymer auxetic foams.

Analysis of the Foaming Window for Thermoplastic Polyurethane with Different Hard Segment Contents

A series of thermoplastic polyurethanes (TPUs) with different amounts of hard segments (HS) (40, 50 and 60 wt.%) are synthesized by a pre-polymer method. These synthesized TPUs are characterized by Shore hardness, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), dynamic mechanical thermal analysis (DMTA), and rheology. Then, these materials are foamed by a one-step gas dissolution foaming process and the processing window that allows producing homogeneous foams is analyzed. The effect of foaming temperature from 140 to 180 °C on the cellular structure and on density is evaluated, fixing a saturation pressure of 20 MPa and a saturation time of 1 h. Among the TPUs studied, only that with 50 wt.% HS allows obtaining a stable foam, whose better features are reached after foaming at 170 °C. Finally, the foaming of TPU with 50 wt.% HS is optimized by varying the saturation pressure from 10 to 25 MPa at 170 °C. The optimum saturation and foaming conditions are 25 MPa and 170 °C for 1 h, which gives foams with the lowest relative density of 0.74, the smallest average cell size of 4 μm, and the higher cell nucleation density of 8.0 × 109 nuclei/cm3. As a final conclusion of this investigation, the TPU with 50 wt.% HS is the only one that can be foamed under the saturation and foaming conditions used in this study. TPU foams containing 50 wt.% HS with a cell size below 15 microns and porosity of 1.4–18.6% can be obtained using foaming temperatures from 140 to 180 °C, saturation pressure of 20 MPa, and saturation time of 1 h. Varying the saturation pressure from 10 to 25 MPa and fixing the foaming temperature of 170 °C and saturation pressure of 1 h results in TPU foams with a cell size of below 37 microns and porosity of 1.7–21.2%.

Improved Cell Morphology and Surface Roughness in High-Temperature Foam Injection Molding Using a Long-Chain Branched Polypropylene.

Long-chain branched polypropylene (LCB PP) has been used extensively to improve cell morphologies in foaming applications. However, most research focuses on low melt flow rate (MFR) resins, whereas foam production methods such as mold-opening foam injection molding (MO-FIM) require high-MFR resins to improve processability. A systematic study was conducted comparing a conventional linear PP, a broad molecular weight distribution (BMWD) linear PP, and a newly developed BMWD LCB PP for use in MO-FIM. The effects of foaming temperature and molecular architecture on cell morphology, surface roughness, and mechanical properties were studied by utilizing two chemical blowing agents (CBAs) with different activation temperatures and varying packing times. At the highest foaming temperatures, BMWD LCB PP foams exhibited 887% higher cell density, 46% smaller cell sizes, and more uniform cell structures than BWMD linear PP. Linear PP was found to have a surface roughness 23% higher on average than other resins. The BMWD LCB PP was found to have increased flexural modulus (44%) at the cost of decreased toughness (−88%) compared to linear PP. The branched architecture and high molecular weight of the BMWD LCB PP contributed to improved foam morphologies and surface quality in high-temperature MO-FIM conditions.

Batch foaming of ultra-high molecular weight polyethylene with supercritical carbon dioxide: Influence of temperature and pressure

This work is aimed at studying the foaming behavior of pure ultra-high molecular weight polyethylene (UHMWPE) with supercritical carbon dioxide (scCO2). The effects of foaming temperature and saturation pressure on the final foam structure were investigated by using two different one-step batch foaming processes. An in-situ high-pressure observing system was used to record the crystal change of UHMWPE film during heating and cooling stages with/without pressurized CO2. The results showed that the cell size and the cell density were affected by the combined effects of crystal, temperature, and pressure. Experimental results with different foaming temperatures showed that higher foaming temperatures led to larger cells and lower cell densities. In the processes of foaming during the heating stage (Proc1) and cooling stage (Proc2), the expansion ratio increased first and then decreased with the increase of temperature. Before obtaining the maximum expansion ratio, compare with Proc2, the cell size and expansion ratio of foams were smaller, and the cell density was higher in Proc1. Experimental results with different saturation pressures showed that higher pressure led to lower cell density and larger average cell diameter in Proc1 due to the reduction of crystals and melt strength. While in Proc2, higher saturation pressure led to higher cell density due to the increase of solubility of CO2, and the cell density decreased as the pressure further increased due to cell coalescence.

Solid-State Foaming of Acrylonitrile-Butadiene-Styrene/Recycled Polyethylene Terephthalate Using Carbon Dioxide as a Blowing Agent.

In this study, a single paragraph of acrylonitrile-butadiene-styrene (ABS)/recycled polyethylene terephthalate (R-PET) polymeric foams is prepared using CO2 as a blowing agent. First, the sorption kinetics of subcritical and supercritical CO2 are first studied at saturation temperatures from −20 to 40 °C and a pressure of 10 MPa, in order to estimate the diffusion coefficient and the sorption amount. As the sorption temperature increases, the diffusion coefficient of CO2 increases while the sorption amount decreases. Then, a series of two-step solid-state foaming experiments are conducted. In this process, a specimen is saturated with liquid CO2 and foamed by dipping the sample in a high-temperature medium at 60 to 120 °C. The effects of foaming temperature and depressurization rate on the morphology and structure of ABS/R-PET microcellular foams are examined. The mean cell size and the variation of the cell size distribution increases as the foaming temperature and the depressurization rate increases.

Acoustically and thermally insulating epoxy foams prepared by non‐traditional expandable microspheres

Herein, the acoustically and thermally insulating epoxy foams were prepared using non‐traditional expandable microspheres. The effect of foaming temperature and microsphere content on the morphology, the mechanical strength, the thermal insulation and acoustical properties of the epoxy foams was investigated in detail. It can be found that the closed pores can be partially opened by adjusting the preparation parameters, which is also accompanied by obvious changes in acoustic and thermal insulation properties. By giving high‐content expandable microspheres above 2 wt%, the epoxy foams exhibit highly thermal insulation, and meanwhile achieving an acceptable mechanical property. The results convince us that such light‐weight epoxy foams will outshine as the promising structural, soundproof and heat‐insulated material in many multifunctional systems, such as buildings, vehicles and aircrafts. POLYM. ENG. SCI., 59:799–806, 2019. © 2018 Society of Plastics Engineers

The effect of copolymer composition, gas content, and temperature on the bubbles nucleation and growth of styrene–methyl methacrylate copolymer/n-pentane foaming process

The foaming process involves three important steps: nucleation, bubble growth, and stability. In the present work, the foaming dynamics of styrene–methyl methacrylate (St-MMA) copolymer/ n-pentane batch foaming system was studied at nonpressurized condition using rapid temperature increasing method. Synthesized copolymers with different compositions were characterized by proton nuclear magnetic resonance analysis and rheological measurements. An in situ foaming observation apparatus was designed, and the foaming dynamics (nucleation and bubble growth behavior) was studied. Dissolved n-pentane contents in all synthesized copolymer compositions at saturation temperatures, near their glass transition temperatures, were determined. The effects of foaming temperature, copolymer composition, and n-pentane content on the foaming dynamics of St-MMA copolymer/ n-pentane system were investigated. The foaming results revealed that the nucleation rate was increased with the increasing foaming temperature, while two other aforementioned parameters were kept constant. The nucleation and bubble growth rate were decreased with increasing MMA units in copolymer composition and increased with dissolved n-pentane content increment in copolymer matrix.

Unexpected foaming behavior of heterografted comb-like PS-g-(PS/PE) copolymers with high branching density at semi-solid state under CO2 batching foam

The CO2 batching foaming behavior of heterografted comb copolymers (PS-g-(PS/PE)) with high branching density, which consisted of mixed polystyrene (PS) and semicrystalline polyethylene (PE) branching chains linked to PS backbone, were explored. Especially the effect of foaming temperature on CO2 batching foaming behavior of PS-g-(PS/PE) copolymers was deeply studied. Under the same saturation pressure and time (CO2 pressure: 13.3 MPa; saturation time: 5.5 h), the state of the samples changed with the foaming temperature (50–110 °C) from solid state to semi-solid state and finally melt state, resulting in different foaming behavior. When the foaming temperature was lower than 50 °C, all the samples (solid state) did not form foamed or porous structures. At above 60 °C, the foaming behavior of the samples strongly depended on the foaming temperature. Very surprisingly, at 60 °C, PS-g-(PS/PE) copolymers with lamellar microphase structure easily formed bimodal nanoporous structure (open-cell) composed of nanofibers, while PS-g-(PS/PE) copolymers with cylindric microphase structure also formed bimodal porous structure with larger size, but the open degree of cell wall was decreased, in which the nanofibers almost disappeared and a lot of nanosized domains appeared. When the foaming temperature was higher than 70 °C, the cell size increased and the cell density decreased with increasing foaming temperature. Furthermore, the cell structure changed from opened (porous) structure to closed structure when the foaming temperature rose, which was different from the results in the previous reports. The influence of foaming temperature on the foaming behavior of PS-g-(PS/PE) copolymers was discussed.

Effect of Foaming Temperature on Bubble Size Distribution of Liquid Aluminium Foam: Modeling and Experimental Studies

The present study examines the effect of foaming temperature on the final foam expansion and the bubble size distribution of liquid aluminium foam through mathematical modeling and validation experiments. The model calculates the rate of hydrogen release from the foaming agent (TiH2) particles, super saturation of the melt, nucleation and growth of bubbles and finally, evaluates the evolving bubble size distribution using a population balance approach. The model does not consider bubble coalescence and breakage and uses only solute diffusion for bubble growth. The simulation is performed for two conditions; firstly, for pure temperature effects and secondly, for temperature and TiH2 quantity combined effects. Upon comparison of simulation results with the experiments, following important observations are made; firstly, the predicted total number of bubbles is found to be one order of magnitude higher than the experiments while the predicted average size is one order of magnitude lower. Secondly, the spread of the predicted distributions is observed to be much narrower. These discrepancies are considered to be due to bubble coalescence and coarsening which are not modeled and shown to be strongly influenced by the foaming temperature.

The Influence of Temperature on Stability of Aluminum Foam Cell Wall during Foaming Process

This study concerns about the influence of foaming temperature which is applied to foaming process of aluminum foam to improve the stability of aluminum foam cell wall. Powder metallurgical method with four major foaming temperatures of 750°C, 800°C, 850°C and 900°C have been selected. Furthermore, the porosity of the foam was determined by ImageJ Analysis Software. Microhardness testing on the cell wall of aluminium foam was conducted according to ASTM E 92 using microhardness tester LM24AT with 200 grams and 15 s for loading time. The universal testing machine was applied to characterize the effect of foaming temperature on compression strength. The aluminum foam was observed in macroscopic and microscopic level using optical microscope (OM). The result revealed that the foaming temperature of 800°C gave the lowest value of porosity, with the highest hardness and compressive strength of 55.29 HV and 1.41 MPa, respectively. In addition, the highest porosity level was acquired by foaming temperature which was set at 900 °C. The lowest hardness value of 38.50 HV was obtained by foaming temperature of 700°C and the minimum compressive strength value of 0.75 MPa was exhibited when the foaming temperature was set at 900°C.

Foaming of poly(vinylidene fluoride-co-hexafluoropropylene) using supercritical carbon dioxide

Abstract This work studied the foaming behavior of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) in supercritical carbon dioxide (scCO 2 ). The effects of foaming temperature, foaming pressure, saturation time, depressurization time on the foam structure and crystallinity of samples were investigated. The foaming ability varies with different combinations of the foaming temperature and foaming pressure. However, a lower foaming temperature and a higher foaming pressure are more favorable for obtaining uniform foam than a higher foaming temperature and a lower foaming pressure. At a given foaming temperature and saturation time, increasing the foaming pressure leads to the decreased crystallinity and an increase in the melting temperature.

Effects of foaming temperature on the preparation and microstructure of alumina foams

Alumina foams with porosity of 94.5–93.1vol% were obtained by the thermo-foaming of powder dispersions in molten sucrose at 130°C. Effects of foaming temperature on the preparation and microstructure of the alumina foams were investigated. Low foaming temperature resulting in high viscosity facilitated the stability of the bubbles generated through condensation reactions in molten sucrose. The alumina foams showed interconnected cellular microstructure and the cells had a near spherical morphology. The cell size distribution was bimodal as a whole and the window size was unimodal in various alumina to sucrose (A/S) weight ratios. The mean cell size was varied from 740 to 1640μm and the mean window size was between 89 and 137μm. Compressive strength of the obtained alumina foams was maximum when the weight ratio of A/S is 1.4, the density was 0.272g/cm3 and the compressive strength reached 1.32MPa.

Formation mechanism and tuning for bi-modal cell structure in polystyrene foams by synergistic effect of temperature rising and depressurization with supercritical CO2

Polystyrene (PS) foams are fabricated using supercritical carbon dioxide (Sc-CO2) as a physical foaming agent in a batch foaming process. It is demonstrated that a bi-modal cell structure (BMCS) is obtained by the synergistic effect of temperature rising and depressurization using a varying-temperature mode (VTM). The formation mechanism for the BMCS is revealed. Cell nucleation occurs in the supercritical CO2-saturated polymer both in temperature rising and depressurizing stages. The nuclei formed in the former stage develop into large cells, whereas the ones formed in the latter stage evolve into small cells. The effects of foaming temperature, saturation temperature, second saturation time and foaming pressure in the VTM on the cellular structure of PS foams were investigated. The results showed that no BMCS is formed when the foaming temperature is only 10°C higher than saturation temperature. By manipulating the foaming parameters, the BMCS PS foams with a wide range of mean diameters (50.0–713.7μm) and densities (2.1×103–3.6×106cells/cm3) for the large cells, and a wide range of foam density (0.09–0.73g/cm3) are obtained.

Al–TiH2 composite ‘particles’ as foaming precursors for metallic foams

This paper describes the production of metallic foam precursors in ‘particle’ form as opposed to the typical consolidated bulk compacts. Mechanical milling was used to produce coarse composite particles of aluminum and titanium di-hydride as foaming precursors. The effect of foaming temperature on the resulting products is discussed. The porosity content in the particles was found to increase with an increase in temperature. The refined TiH2 particle size due to mechanical milling leads to limited pore sizes in foamed particles.

Effect of foaming temperature on the mechanical properties of produced closed-cell A356Aluminum foams with melting method

In this study an attempt was carried out to determine the effect of production temperature on the mechanical properties and energy absorption behavior of closed-cell A356 alloy foams under uniaxial compression test. For this purpose, three different A356 alloy closed-cell foams were synthesized at three different casting temperatures, 650 °C, 675 °C and 700 °C by adding the same amounts of granulated calcium as thickening and TiH2 as blowing agent. The samples were characterized by SEM to study the pore morphology at different foaming temperatures. Compression tests of the A356 foams were carried out to assess their mechanical properties and energy absorption behavior. The results indicated that increasing the foaming temperature from 650 °C to 675 °C and 700 °C reduces the relative density of closed cell A356 alloys by 18.3% and 38% respectively and consequently affects the compressive strength and energy absorption of cellular structures by changing them from equiaxed polyhedral closed cells to distorted cells. Also at 700 °C foaming temperature, growth of micro-pores and coalescence with other surrounding pores leads to several big voids.

Designing Issues in Polymer Foaming with Supercritical Fluids

SummaryVarious foaming routes were used in order to produce poly(methyl methacrylate) porous structures. The focus was, primarily, on the temperature‐induced phase separation method and the effect of foaming temperature was, first, investigated. It was observed that the pore size decreases with increase of foaming temperature up to the glass transition region, where the softening of the polymer matrix results in the increase of the average pore diameter with further increase of the foaming temperature. Subsequently, different porous structures were obtained using identical initial and final conditions, but varying the foaming route. The role of the intermediate foaming steps (which define the foaming route) on the final porous structure is discussed.

Processing and Stability of LM25/SiCP Composite Foams

A simple method of metal foam production is to introduce a blowing agent (e.g. TiH2) into an aluminium melt containing foam stabilisers such as oxides (usually Ca-based) and/or particles (e.g. SiC, Al2O3). In this work, Al/SiC composites (in-house and commercial Duralcan) [both of them with LM25 matrix (Al–7Si–0.3Mg)] containing particles of various sizes and contents were foamed at different temperatures using TiH2. Foamability is characterised through their expansion and collapse. It is observed that high expansions and good quality foams could be obtained upon manipulating SiC particle size and content. However, irrespective of particle size/vol.% combination, significant effect of foaming temperature is noticed on the fundamental stability of the liquid foam until solidification. Both cell size and foam density varied along the ingot height. The distribution of SiCP within the cell wall is random with no preferential segregation to gas/metal interface. The evolution of foam, and the role of SiC on foam stability are discussed based on macro and cell wall microstructural results.

Structure and Properties of Radiation Cross-Linked Polypropylene Foam

Polypropylene (PP) sheets obtained through a two-step process (masterbatch method) were crosslinked by electron beam irradiation. The crosslinked PP sheets were foamed in an oven under different processing conditions. The effects of foaming temperature and time on the mechanical properties and cell structure of PP foams were studied. With the foaming temperature increasing and foaming time lengthening, both the compression modulus and compression strength dropped. Scanning electron microscope (SEM) was employed to study the morphology and cell structure of different samples and the related morphology parameters were acquired. The results showed there was an optimum temperature and time that produced the maximum expansion ratio or the minimum foam density. As foaming temperature or time increased, the cell size increased and the cell density decreased regularly. Excessively high foaming temperature and overly long foaming time caused the coalescence and even the collapse of the cells.

Extrusion Foaming of Poly (lactic acid)/Soy Protein Concentrate Blends

AbstractPoly(lactic acid) (PLA) and soy protein concentrate (SPC) were compounded using poly(2‐ethyl‐2‐oxazoline) as compatibilizer by twin‐screw extrusion, and the resulting blends were foamed by a chemical blowing agent (CBA) using the same extruder. Effects of foaming temperature and CBA content on cell density and foam density were investigated. Polymeric methylene diphenyl diisocyanate (pMDI) as a co‐compatibilizer was added prior to foaming extrusion and its effects on foam morphology and properties were also studied. The results showed that cell density and foam density were greatly influenced by foaming temperature and CBA content. Using the strong interfacial modifier pMDI in PLA/SPC blends resulted in high‐cell density and low‐foam density when CBA concentration was low. magnified image