Aramid fiber reinforced EPDM microcellular foams: Influence of the aramid fiber content on rheological behavior,mechanical properties,thermal properties,and cellular structure

In this paper, aramid fiber (AF)/ethylene-propylene-diene monomer (EPDM) microcellular foams added with different content of AF are prepared by the supercritical foaming method. The effect of the AF content on the rheological behavior, mechanical properties, thermal properties and cellular structure of the AF/EPDM microcellular foams has been systematically studied. The research illustrates that compared with pure EPDM, the AF/EPDM matrix has greater viscosity and modulus, which is conducive to reduce the cell size and increase its density. And the thermal stability of EPDM foams is improved with the addition of aramid fiber. Meanwhile, when the content of AF is added to 1 wt%, the AF/EPDM microcellular foam exhibits a relatively low thermal diffusion coefficient and apparent density with the thermal conductivity to 0.06 W/mK. When the AF is added to 5 wt%, the tensile strength of the AF/EPDM microcellular foam increases to 1.95 MPa, which is improved by 47% compared with that of the pure EPDM foam. Furthermore, when the compressive strain reaches to 50%, the compressive strength of the AF/EPDM microcellular foam is 0.48 MPa, improved by 296% compared with that of the pure EPDM foam.     

Generation of low‐density high‐performance poly(arylene ether sulfone) foams using a benign processing technique

In this study, a benign process was used to successfully produce low density foam from poly(arylene ether sulfone) (PAES). Both carbon dioxide (CO₂) and water as well as nitrogen and water were used as physical blowing agents in a one‐step batch process. A large amount of blowing agents (up to 7.5%) was able to diffuse into the PAES resin in a 2‐h saturation time. Utilizing water and CO₂ as the blowing agents yielded foam with better properties than nitrogen and water because both the water and CO₂ are plasticizers for the PAES resin. PAES foam produced from CO₂ and water had a large reduction in foam density (～80%) and a cell size of ～50 μm, while maintaining a primarily closed cell structure. The small cell size and closed cell structure enhanced the mechanical properties of the foam when compared with the PAES foam produced from nitrogen and water. The tensile, compressive, and notched izod impact properties of the PAES foams were examined, and the compressive properties were compared to commercially available structural foams. With reduced compression strength of 39 MPa and reduced compression modulus of 913 MPa, the PAES foam is comparable to polyetherimide and poly(vinylchloride) structural foams. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

A Novel PEEK Foam with Ultra-High Temperature-Resistant by Temperature Induced Phase Separation

Polyaryletherketone is a kind of special engineering plastics with excellent comprehensive properties, high strength, good stability, and almost insoluble in any common solvent except concentrated sulfuric acid at room temperature. However, its high processing temperature also hinders its application and development in the foam. Here, a series of polyetheretherketone (PEEK) and diphenyl polyetheretherketone (PEDEK) composite foams are prepared by temperature induced phase separation, using diphenyl sulfone as solvent. The microstructure, thermal and mechanical properties of PEEK and PEDEK foam are compared. Highly porous PEEK and PEDEK foams with densities ranging from 0.13 to 0.25 g cm⁻³, with compressive strength ranging from 0.68 to 2.6 MPa, respectively, are produced. Meanwhile, the introduction of diphenyl structure can effectively improve the performance of PEEK foams at high temperature. It is found that PEDEK foam has a higher operating temperature than PEEK, and the compressive strength of 0.24 g cm⁻³ foam is still ≈1 MPa at 200 °C.     

Preparation and characterization of magnesium aluminate (MgAl2O4) spinel ceramic foams via direct foam-gelcasting

Lightweight MgAl₂O₄ spinel ceramic foams with high mechanical strength and good dielectric properties were prepared with a direct foam-gelcasting method using MgAl₂O₄ and TiO₂ (rutile phase, as sintering aid) powders. The effects of calcination temperature and foam volume on bulk density, apparent porosity, and on the mechanical and dielectric properties of the ceramic foams were investigated. Tailored porosity (75.14–82.46%), pore size (10–200 μm), dielectric constant (1.66–2.05), and compressive strength (4.0–14.3 MPa), were obtained based on the change of the foam volume in the foamed slurries, and the calcination temperature of porous ceramics. The compressive strength and dielectric constant of the as-manufactured spinel foam with a porosity of ~75.14% was as high as 14.3 MPa and 2.05, respectively. The spinel ceramic foam which had a porosity of 81.84% was prepared with a foam volume of 350 mL and a sintering temperature of 1500 °C, and exhibited heterogeneous pore structures, whereby large and open spherical cells involved in small circular windows on the internal walls with a mean pore size of ~66.26 μm and a grain size of ~8 μm. The experimental dielectric constant matches well with that calculated by the modified Bruggeman model. The dependence of the mechanical strength on the relative density can be represented by the Gibson and Ashby model. The fitted index values of the power relationship were 3.504 and 3.533, compared to the theoretical value of 1.5. The ceramic foam can potentially become a new type of electromagnetic wave-transmitting radome material due to its low dielectric constant (1.66–2.05) and dielectric loss (0.0026–0.006) values.     

Fabrication of polyamide 12T micro-cellular foams with ultra-high compressive strength via in situ polytetrafluoroethylene fibrillation using supercritical carbon dioxide foaming

The development of micro-cellular foams with ultra-high compressive strength and high volume expansion ratio (VER) is a challenging task. Herein, polyamide 12T (PA12T) micro-cellular foams with ultra-high compressive strength were fabricated via in situ polytetrafluoroethylene (PTFE) fibrillation using supercritical CO₂ foaming technology and a chain extender. The resulting branched structure showed considerably improved viscoelasticity and foaming performance, thus improving the cell morphology of the PA12T foam and exhibiting high VER. The PTFE fibrillation network induced melt strength enhancement, crystallization nucleation, and cell nucleation. The branched PA12T foam with 1.5 wt% PTFE exhibited the smallest cell diameter (15 μm) and highest cell density (3 × 10⁹ cells/cm³). The compressive strength of the foam (0.50 MPa under 5% strain) was 70% higher than that of pure PA12T. This research offers an effective method for producing high-VER PA12T foams with adjustable micro-cellular structures and excellent mechanical properties.     

Mechanical properties of methacylic acid/acrylonitrile copolymer foam

To gain a foam plastic with excellent mechanical properties, tensile mechanical properties of methacylic acid/acrylonitrile (MAA/AN) copolymer and the corresponding foam microstructure were studied, and furthermore effects of the density, heat treatment, and crosslinking agent on foam mechanical properties were also discussed in this paper. The results reveal that the tensile strength and modulus of the copolymer after heat treatment are 64 MPa and 4.2 GPa respectively, when compared with 58 MPa and 3.8 GPa before heat treatment respectively. Foam mechanical properties are enhanced with the rise of the density, and the values tested accords with the theoretical values of pentagonal dodecahedron mechanical model basically. Foam mechanical properties are enhanced via heat treatment, and the same result can be observed after using the crosslinking agent (acrylamide) too. All these results indicate that MAA/AN copolymer foam possesses excellent mechanical properties, such as its tensile, 10% compressive and shear strength are 1.3, 0.8, and 0.8 MPa respectively when the foam density is 52 kg/m³. POLYM. ENG. SCI., 47:314–322, 2007. © 2007 Society of Plastics Engineers.     

A novel process to high-strength and controlled-shrinkage Al2O3 foams with open-cell by Al powder hollowing technology

Ceramic foams with open-cell structures have attracted extensive attention due to their unique structure and superior properties. But these materials often exhibit the weakness of high sintered shrinkage and low strength at high porosity levels. In this work, novel ceramic foams with open-cell structures have been obtained using Al powder by combining direct foaming and gelation freezing (DF–GF). The foams are assembled by hollow Al₂O₃ particles resulting from the Kirkendall effect, in which expanded particles overcome the shrinkage of sintering. The influence of sintering temperature on the microstructure and properties of foams are investigated. The Al₂O₃ foams show near-zero-shrinkage at 1773 K after undergoing the process of first expansion and then shrinkage. Compared to other conventional open-cell foam, this foam displays relatively high compressive strength of 0.35–2.19 MPa at high porosity levels of 89.45%–94.45%, attributed to hierarchical pore structure and reaction bonding between Al and O₂. This method from pore structure design provides a novel route for the preparation of controlled shrinkage and high-compressive strength alumina foam with open-cell toward potential application.     

Mechanical Properties of Silicon Oxycarbide Ceramic Foams

The mechanical properties of ceramic foams obtained through a novel process that uses the direct foaming and pyrolysis of preceramic polymer/polyurethane solutions were investigated. The elastic modulus, flexural strength, and compressive strengths were obtained for foams in the as-pyrolyzed condition; values up to 7.1 GPa, 13 MPa, and 11 MPa, respectively, were obtained. The strength of the foam was virtually unchanged at temperatures up to 1200°C in air; however, long-term exposure at 1200°C led to a moderate degradation in strength, which was attributed to the evolution of intrastrut porosity during the oxidation of residual free carbon, as well as devitrification of the foams struts.     

An experimental and theoretical investigation of the compressive properties of multi-walled carbon nanotube/poly(methyl methacrylate) nanocomposite foams

Polymer nanocomposite foams are promising low density substitutes for nanocomposites. Carbon nanotube/polymer nanocomposite foams possess high strength, low density, and can be made conductive. Good control of foam properties is of great importance in the application of such materials. In the current study, multi-walled carbon nanotubes (MWNTs) with controlled aspect ratio were used to alter the foam morphology in MWNT/poly(methyl methacrylate) (PMMA) nanocomposite foams produced by a supercritical carbon dioxide (CO₂) foaming process. It was found that with the addition of one weight percent of MWNTs, the Young’s modulus of polymer foams increased by as much as 82%, and the collapse strength increased by as much as 104%. The influence of MWNT aspect ratio on the compressive properties of nanocomposite foams was investigated. The addition of MWNTs influenced the foam properties in two ways: improving the compressive properties of the solid matrix, and reducing the bubble size of the nanocomposite foams. A modified constitutive model for predicting the compressive properties of high density closed-cell polymer foams was developed. The influence of the bubble size on the mechanical properties of polymer foams was discussed based on the new model.     

Compressive and thermal characterization of syntactic foams containing hollow silicon carbide particles with porous shell

Silicon carbide hollow particle (SiC_HS) reinforced vinyl ester matrix syntactic foams are prepared and characterized for compressive properties and coefficient of thermal expansion (CTE). Two types of SiC_HS were utilized in 60 vol % to prepare syntactic foams. These SiC_HS had ratio of inner to outer radius of 0.91 and 0.84 for the thin and thick walled particles. The specific compressive strength values were 33.4 and 38.8 kPa/kg/m³ and the specific compressive modulus values were 0.8 MPa/kg/m³ and 0.6 MPa/kg/m³ for the thin and thick walled SiC_HS‐filled syntactic foams, respectively. The shell of the hollow particles contained microporous voids, and the porosity was estimated as 16.6% and 24.8% in the walls of the thin and thick walled particles, respectively. The shell porosity adversely affected the specific compressive strength and the modulus of the syntactic foam. However, the SiC_HS‐filled syntactic foams exhibited low CTE values (26.7 and 15.9 × 10^?6/°C). These CTE values were 65.1% and 79.3% lower than the CTE of the neat resin. Such properties can be useful for applications where syntactic foams are exposed to high temperatures and dimensional stability is important. A theoretical model is used to estimate the porosity level in the SiC shells and estimate the effective mechanical properties of the porous SiC material that forms the particle shell. Such analysis can help in using the models as predictive tools to estimate the mechanical properties of syntactic foams. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40689.     

Hierarchical cellular scaffolds fabricated via direct foam writing using gelled colloidal particle-stabilized foams as the ink

Hierarchical cellular architectures hold great potential in a vast range of applications due to their superior mechanical properties and multifunctionality. In the present work, hierarchical structures composed of porous struts patterned in the form of quadrangular and triangular honeycombs were fabricated via direct foam writing (DFW) using colloidal particle-stabilized Al₂O₃-MgO-SiO₂ foams as the ink. Hydration process of MgO and subsequent formation of colloidal Mg(OH)₂ network endowed the foam ink with viscoelasticity and high storage modulus. The resulting honeycombs with ultrahigh overall porosity (95.3%) and robust compressive strength (2.5 MPa) can be readily fabricated by DFW. The current work exhibits a significant step toward the scalable production of cellular ceramics with hierarchical architecture for various applications, including tissue scaffolds, catalyst supports, thermal insulation, and lightweight structures.     

Reinforcement of soy polyol‐based rigid polyurethane foams by cellulose microfibers and nanoclays

Water‐blown rigid polyurethane foams from soy‐based polyol were prepared and their structure–property correlations investigated. Cellulose microfibers and nanoclays were added to the formulations to investigate their effect on morphology, mechanical, and thermal properties of polyurethane foams. Physical properties of foams, including density and compressive strength, were determined. The cellular morphologies of foams were analyzed by SEM and X‐ray micro‐CT and revealed that incorporation of microfibers and nanoclays into foam altered the cellular structure of the foams. Average cell size decreased, cell size distribution narrowed and number fractions of small cells increased with the incorporation of microfibers and nanoclays into the foam, thereby altering the foam mechanical properties. The morphology and properties of nanoclay reinforced polyurethane foams were also found to be dependent on the functional groups of the organic modifiers. Results showed that the compressive strengths of rigid foams were increased by addition of cellulose microfibers or nanoclays into the foams. Thermogravimetric analysis (TGA) was used to characterize the thermal decomposition properties of the foams. The thermal decomposition behavior of all soy‐based polyurethane foams was a three‐step process and while the addition of cellulose microfibers delayed the onset of degradation, incorporation of nanoclays seemed to have no significant influence on the thermal degradation properties of the foams as compared to the foams without reinforcements. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Microcellular foaming of silicone rubber with supercritical carbon dioxide

In spite of great concern on the industrial application of microcellular silicone rubber foams, such as in electric and medical devices, only a few works can be found about the foaming of silicone rubber. In this study, microcellular silicone rubber foams with a cell size of 12 μm were successfully prepared with curing by heat and foaming by supercritical CO₂ as a green blowing agent. The microcellular silicone rubber foams exhibited a well-defined cell structure and a uniform cell size distribution. The crosslinking and foaming of silicone rubber was carried out separately. After foaming, the silicone rubber foam was cross-linked again to stabilize the foam structure and further improve its mechanical properties. Foaming process of cross-linked silicone rubber should be designed carefully based on the viscoelastic properties because of its elastic volume recovery in the atmosphere. The basic crosslinking condition for small cell size and high cell density was obtained after investigating the rheological behavior during crosslinking.     

EVA/EPDM/IR/IR共混发泡材料的研制与应用

进行了ＥＶＡ／ＥＰＤＭ／ＩＲ三元共混和ＥＶＡ／ＥＰＤＭ／ＩＲ／ＩＲ四元共混发泡材料的研制,经物性对比表明：共混发泡材料的物性较非共混发泡普遍提高。ＥＰＤＭ的混入可以增加发泡材料的拉伸强度和撕裂强度,同时降低收缩率和永久压缩变形;ＩＲ的混入除具备ＥＰＤＭ的优点外尚对提高发泡材料的柔软度有帮助;ＩＲ的混入仅改善发泡材料二次热压成型制品表面的清晰度。     

Ultrahigh compressive strength and heat resistance of polystyrene/polyphenylene oxide foams of supercritical carbon dioxide foaming

Polystyrene (PS) foam materials are lightweight, but suffer from poor compressive strength and heat resistance, among other problems, which limit their application. Herein, a method for preparing PS foam with high compressive strength and high heat resistance using supercritical CO₂ is proposed. PS/polyphenylene oxide (PPO) blends were prepared using a corotating intermeshing twin-screw extruder. The results showed that PPO exhibited excellent molecular-level compatibility with PS, which substantially improved mechanical properties and heat resistance of PS. Foam samples of PS/PPO blends with the same expansion ratio were prepared via batch foaming experiments, and the compressive strength of different foams was determined at different temperatures. At room temperature, the compressive strength of the PS/PPO-30% foam increased by 173% compared with pure PS foam. As the testing temperature increased from 30 to 120°C, the compressive strength of pure PS foams decreased rapidly. Nevertheless, PS/PPO foams maintained high compressive strength at high temperatures.     

硬质聚氨酯/二氧化硅纳米粒子复合材料泡沫形貌和性能研究

利用2种不同粒径的球形二氧化硅（SiO2）纳米粒子作为填料,制备了硬质聚氨酯（PU-R）/SiO2纳米粒子复合材料泡沫。利用扫描电子显微镜考察复合材料的形貌,通过压缩试验、尺寸稳定性测试和热导率测试表征复合材料的力学性能、尺寸稳定性和热导率。结果表明,球形SiO2纳米粒子对复合材料的泡孔结构有明显的细化作用（孔径从纯PU-R泡沫的303 μm降低到170 μm）,可以有效提高复合材料的压缩性能（与纯PU-R泡沫相比,比强度和比模量分别提高了8.3 %和12.5 %）,降低了其线膨胀系数,并使热导率略微下降,而对尺寸稳定性无明显影响。与粒径为400 nm的SiO2纳米粒子相比,粒径为700 nm的SiO2纳米粒子较易均匀分散,对PU-R泡沫力学性能的改善效果更为明显。     

Effect of organoclay on the morphology,mechanical, and thermal properties of polyimide/organoclay nanocomposite foams

A series of polyimide (PI)/organoclay nanocomposite foams containing different contents of organoclay were prepared by the monomer in situ intercalative polymerization. The effect of organoclay on the chemical structure, morphology, mechanical, and thermal properties of the nanocomposite foams was studied. Fourier transform infrared spectra showed that the hydrogen bonds between organoclay and the polymer matrix were formed. X‐ray diffraction and transmission electron microscope results indicated that the organoclay were well dispersed in the PI matrix. The compressive strength and tensile strength of the nanocomposite foams enhanced significantly, especially for the nanocomposite foam containing 4 wt% organoclay, increasing by 15% and 9%, respectively, compared with these of the neat PI foam, and the presence of the organoclay in the PI foam improved apparently the cellular structure of the nanocomposite foams. Besides, thermogravimetric analysis revealed that the addition of organoclay improved the thermal stability of the nanocomposite foams strongly, and dynamic mechanical analysis indicated that the incorporation of organoclay significantly influenced the storage modulus of the nanocomposite foams. POLYM. COMPOS., 35:2311–2317, 2014. © 2014 Society of Plastics Engineers     

Biobased Polyurethane Composite Foams Reinforced with Plum Stones and Silanized Plum Stones

In the following study, ground plum stones and silanized ground plum stones were used as natural fillers for novel polyurethane (PUR) composite foams. The impact of 1, 2, and 5 wt.% of fillers on the cellular structure, foaming parameters, and mechanical, thermomechanical, and thermal properties of produced foams were assessed. The results showed that the silanization process leads to acquiring fillers with a smoother surface compared to unmodified filler. The results also showed that the morphology of the obtained materials is affected by the type and content of filler. Moreover, the modified PUR foams showed improved properties. For example, compared with the reference foam (PUR_REF), the foam with the addition of 1 wt.% of unmodified plum filler showed better mechanical properties, such as higher compressive strength (~8% improvement) and better flexural strength (~6% improvement). The addition of silanized plum filler improved the thermal stability and hydrophobic character of PUR foams. This work shows the relationship between the mechanical, thermal, and application properties of the obtained PUR composites depending on the modification of the filler used during synthesis.     

Design and formulation of polyurethane foam used for porous alumina ceramics

The present work studied a simple direct foaming method for preparation of porous alumina ceramics by expansion of a ceramic suspension based on polyurethane (PU) foam system. The effects of polyurethane formulas including catalyst composition, blowing agent content, NCO index and solid content on the samples properties were investigated. The results showed that the homogeneity, porosity and mechanical properties are various for different formulas. The dried green bodies showed diametrical compressive strength in the range of 0.39–1.25 MPa and were amenable to machining operations such as milling, drilling and lathing. Meanwhile, PU formulas play an important role in the microstructures and mechanical properties of green bodies and sintered ceramic foams. Pyrolytic removal of polyurethane skeleton followed by sintering at 1550 °C produced alumina bodies with open cell porosity 54–75% and diametrical compressive strength 1.39–28.47 MPa. Microstructure showed both large (200–300 μm) and small (50–100 μm) pores all with various sizes of windows. Based on the optimization of polyurethane formulation, the porous alumina foam with porosity of 64% and compressive strength of 25.26 MPa was prepared. This polyurethane foam system is easily available and low-cost, which could be widely applied in preparation of other porous ceramics, such as ZrO₂, SiO₂, etc.     

Microstructural and mechanical properties of Al2O3 and ZTA foams prepared by thermo-foaming technique

Alumina and zirconia toughened alumina foams were fabricated through a thermo-foaming method using varying amounts of powder to sucrose weight ratio. All the fabricated foams were characterized for their compressive strength, bending strength, and fracture toughness under static loading conditions. The compressive strength increases with an increase in a weight ratio from 0.4 to 1.2. The maximum compressive strength values were found to be 1.9 MPa, and 1.8 MPa for alumina and zirconia toughened alumina foams, respectively. Further increase in powder to sucrose weight ratio led to a decrease in the compressive strength due to the partial collapse of the cell walls during the foaming process. The 3-point bend test results revealed an improvement of bending strength and fracture toughness values of zirconia toughened alumina foams compared to alumina foam, which can be attributed to the transformation toughening mechanism.