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.     

Microstructure and Properties of Microcellular Poly (phenylene sulfide) Foams by Mucell Injection Molding

A series of microcellular poly (phenylene sulfide) (PPS) foams were prepared by Mucell injection molding. The cell structure, mechanical properties, crystallization behavior and dielectric property of microcellular PPS foams were systemically investigated. The results showed that the longer the length of flow passage of injection mold, the larger cell size of microcellular PPS foams. The injection parameter of shot size played an important role in relative density of microcellular PPS foams. When the relative density of microcellular PPS foam reached to 0.658, the tensile strength, flexural strength and impact strength of PPS foam materials achieved 10.82 MPa, 52.99 MPa and 0.305 J/cm², respectively. Meanwhile, with the relative density decreasing, the dielectric constant of PPS foam materials reduced, while the volume resistivity of its uprated.     

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.     

Poly(vinyl alcohol) foams reinforced with carbon nanotubes for stapedial annular ligament applications

This study aims to develop carbon nanotubes (CNTs) reinforced poly(vinyl alcohol) (PVA) foams as a possible material for stapedial annular ligament (SAL) application. As-grown (AG) and purified CNTs are used as reinforcing fillers for PVA foams. Uniaxial and cyclic compression tests reveal that specific modulus and energy dissipation behavior improve after reinforcing foam with CNTs. A relatively higher improvement in specific modulus is recorded for purified CNTs as they tend to produce stiffer cell walls. Thermogravimetric analysis shows thermal stability improves after addition of CNTs in PVA foams. The 50 wt % degradation temperature is higher for PVA_AG foam in comparison to neat PVA foam. Under dynamic loading storage, modulus is found to be higher for CNT doped foams with higher relative improvement with purified CNTs than AG CNTs. It is shown that reinforcing PVA foams with purified CNTs is a feasible strategy to improve their average mechanical properties and microstructure for SAL application. While the specific elastic modulus of neat PVA foam found to be in range of 0.05–0.06 MPa gcc⁻¹ with almost zero porosity. The addition of CNTs provides a wide range of specific elastic modulus 0.1–1.3 MPa gcc⁻¹ with an average pores size of about 300 μm. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48736.     

Thermal,mechanical and acoustic damping properties of flexible open‐cell polyurethane/multi‐walled carbon nanotube foams: effect of surface functionality of nanotubes

This article demonstrates the properties of open‐cell flexible polyurethane foams incorporating multi‐walled carbon nanotubes. Three different types of highly functionalized nanotubes having carboxyl, hydroxyl and amide functional groups were synthesized. Neat polyurethane foam and three nanocomposite foams filled with 0.1 wt% of treated nanotubes were prepared. It was found that thermal stability, mechanical properties and acoustic damping were improved significantly by incorporation of small amounts of nanotubes. The nanotubes modified with carboxyl groups were found to have much more influence compared to the other two functional groups, possibly due to better interfacial interaction and improved dispersion. Scanning electron microscopy revealed micro‐cells with average diameters less than 5 µm in the skeleton of foams filled with nanotubes modified with hydroxyl and carboxyl, the formation of which was attributed to the generation of gaseous materials through the reaction with isocyanate. Such micro‐cells were found to be influential in improving mechanical and acoustic damping. Copyright © 2010 Society of Chemical Industry     

Mechanical and acoustic performance of compression‐molded open‐cell polypropylene foams

Open‐cell materials are lightweight and multifunctional capable of absorbing acoustic energy and supporting mechanical load. The acoustic and mechanical performance of open‐cell materials can be optimized through processing. In this article, the relationships between processing parameters and acoustic and mechanical performance are shown for polypropylene (PP) foams. PP foam samples are fabricated using a combined compression molding and particulate leaching process. The results from a parametric study showed that both salt size and salt to polymer ratio affect the acoustic and mechanical performance of open‐cell PP foams. As salt size increases, cell size increased and cell density decreased. The salt to polymer ratio had opposite affect on cell density, and increasing the salt to polymer mass ratio increased the open‐cell content. The airflow resistivity decreased significantly by increasing the cell size, which means that foam samples with smaller cell size have better sound absorption. When foam samples were thin, smaller cell sizes produced better sound absorption; however, as thickness of the sample increases, medium cell size offered the best acoustic performance. The compressive strength of the foams was increased by increasing the relative density. Acoustic performance results from the parametric study were compared to the Johnson‐Allard model with good agreement. Finally, optimal cellular morphologies for acoustic absorption and mechanical performance were identified. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Processing,properties and microstructure of SiC foam derived from epoxy-modified polycarbosilane

SiC foams having controlled porosity were fabricated using epoxy modified polycarbosilane (EMPCS). The EMPCS was synthesized by refluxing adequate amount of epoxy and polycarbosilane (PCS) in THF solution at 150 °C. The EMPCS having epoxy content of 0%, 10% and 20% by weight were termed as PCS, 10EMPCS and 20EMPCS respectively. Thermal foaming of the EMPCS was carried out at 1000 °C under inert atmosphere followed by ceramization at 1200, 1400 and 1600 °C under vacuum. The cell size of the ceramized SiC foam was found to be varying between 100 and 700 µm. The ceramized SiC foams were characterized for their density, porosity and compressive strength. Total porosity was found to be 81.8 ± 3.9, 87 ± 4.1 and 90.6 ± 4.6% for the PCS, 10EMPCS and 20EMPCS based SiC foams while their bulk densities were found to be 0.6 ± 0.03, 0.4 ± 0.02 and 0.3 ± 0.01 g/cc respectively. Compressive strength was found to be the highest for the SiC foams ceramized at 1600 °C for all the types of EMPCS. The compressive strength of the 10EMPCS is found to be 2.2 ± 0.2 MPa, 2.5 ± 0.2 MPa and 3.8 ± 0.3 MPa for the foams pyrolyzed at 1200 °C, 1400 °C and 1600 °C respectively while the strength was 1.9 ± 0.1 MPa, 2.1 ± 0.2 MPa and 2.9 ± 0.2 MPa for the 20EMPCS based SiC. The 20EMPCS based SiC foam of thickness 10 mm was exposed to oxy-acetylene flame for 120 s, back face temperature was found to be around 300 °C. Microstructure and phase analysis was carried out to understand the effect of epoxy content and ceramization temperature on physical, mechanical and thermal properties of different types of the SiC foams.     

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。     

Relationship between microstructure and mechanical properties of polyether block amide foams

The mechanical behaviors of five polyether block amide foams, obtained by mold-opening foam injection process, were investigated with regard to their microstructures. The materials vary in mass ratios of hard versus soft segments, and/or in process packing time. The resulting microstructures have been characterized in terms of cavity size and shape ratios, by analyzing scanning electron microscope images after careful sample preparation. The foam mechanical responses have been characterized in compression at small and large strain. At small strain, the initial linear part of the stress–strain curve is enhanced firstly by the hard segment mass ratio and secondly by the fineness of the microstructure. Similar results have been obtained at large strain. The foam viscoelasticity at large strain has been characterized by stress relaxation and strain recovery tests, relevant for foam applications. Reduced packing time and pressure have been shown to lead to the presence of undesired large cavities. The morphological defects appear to have a negligible impact on the macroscopic mechanical behavior of the foams at infinitesimal strain, but lead to critical inconsistency at large strain. Furthermore, the mechanical behavior of the tested polyether block amide foams is controlled first by hard versus soft segments ratio, and second by the microstructure fineness.     

Biocomposite foams from poly(lactic acid) and rubber wood sawdust: Mechanical properties,cytotoxicity, and in vitro degradation

The objectives of this work were to seek a simple method for preparation of poly(lactic acid) (PLA) foams and evaluate properties of these foams for scaffold application. Using a typical blowing agent and compression molding, biocomposite foams were successfully prepared from a PLA/rubber wood sawdust (PLA/RWS) blend. Selection of RWS for the biocomposites was based on particle size. RWS particles in two size ranges were used: 212–600 μm and ≤75 μm. Alkaline and silane treatments were applied to the RWS before blending with PLA. The tensile properties, Izod impact strength, foam morphology, and thermal degradation of the biocomposite foams were evaluated. Cytotoxicity and in vitro degradation were tested to determine the potential of the biocomposite foam for use as a scaffold in tissue engineering. Silane treatment improved mechanical properties by increasing the interfacial adhesion between PLA and RWS. The density and void fraction of the foam samples had a greater effect on mechanical properties than pore size. Proliferation of MG-63 cells increased with culture time, indicating that the foam samples were not cytotoxic. Promising samples were tested for degradation in a lysozyme/phosphate-buffered saline and showed a slow rate of in vitro degradation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48259.     

Effects of liquid‐type silane additives and organoclay on the morphology and thermal conductivity of rigid polyisocyanurate‐polyurethane foams

This article investigates the effects of liquid‐type silane additives and organoclay as a solid‐type additive on the morphological, mechanical and thermal insulating properties of polyisocyanurate‐polyurethane (PIR‐PUR) foams. The organoclay likely acted as nucleating agents during the formation of PIR‐PUR foams. When the liquid silane additives and organoclay were added, the cell size and thermal conductivity of the PIR‐PUR foams appeared to be decreased. However, organoclay did not contribute to reduce the cell size distribution of the foam. PIR‐PUR foams synthesized with tetramethylsilane as a liquid‐type additive showed a smaller average cell size and lower thermal conductivity than that of PIR‐PUR foams synthesized with the other silane additives or with organoclay as a solid‐type additive. For the PIR‐PUR foam with organoclay/TEMS (1.5/1.5 php) mixture, cell size and thermal conductivity of the foam showed similar to the foam with TEMS. These results suggest that smaller cell size appears to be one of the major factors in the improvement of thermal insulation properties of the PIR‐PUR foams. Silane additives did not seem to have a strong effect on the flammability of the PIR‐PUR foams. However, heat resistance was more dominant for the foam with the organoclay at the higher temperature. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

PF泡沫塑料对PF/EPS复合泡沫塑料性能的影响

研究出一种具有较好稳定性、保温性能、力学性能和阻燃性能的酚醛树脂(PF)/可发性聚苯乙烯(EPS)复合泡沫塑料。在PF泡沫塑料颗粒基体中加入EPS发泡颗粒,充分混合固化,使PF泡沫塑料颗粒与EPS发泡颗粒紧密结合,EPS发泡颗粒被PF泡沫塑料颗粒包围并相互隔离,再用模具发泡成型得到该复合泡沫塑料。实验结果表明,PF的含量越高,稳定性、力学性能和阻燃性能越好,保温性能呈现先升高后下降的趋势,当PF的含量为80%时,PF/EPS复合泡沫塑料的表观密度为38.4 kg/m3,热导率为0.024 W/(m·K),弯曲强度为0.134 k Pa,压缩强度为323 k Pa,极限氧指数为47.9%,烟密度等级小于15,热释放速率峰值小于250 k W/m2,综合性能最好。     

Injection Molded Strong Polypropylene Composite Foam Reinforced with Rubber and Talc

Lightweight plastic foams are of great significance for saving resources and reducing energy consumption. Foam injection molding (FIM) shows a promising future to provide lightweight and shape‐complex plastic components. However, it is still challenging to produce lightweight and strong polypropylene (PP) foams by FIM due to PP's poor foaming ability. Herein, rubber and talc are employed to improve PP's foaming ability, and hence to enhance PP foam's mechanical properties. Due to the significantly enhanced rheological properties, injection molded PP composite foam exhibits greatly refined and homogenized cellular structure compared with pure PP foam. Thanks to rubber toughening effect and improved cellular morphology, PP/rubber foam shows much higher ductility than pure PP foam. Moreover, talc particles lead to remarkably enhanced rigidity of PP/rubber foams. Thus, lightweight and strong PP/rubber/talc composite foam is achieved with tensile toughness increased by 82.58% and impact strength increased by 106.21%, and they show broad industrial application prospects.     

Enhanced foamability of isotactic polypropylene composites by polypropylene‐graft‐carbon nanotube

In this article, utilizing a nucleophilic substitution reaction between epoxy group in polypropylene‐graft‐glycidyl methacrylate (PP‐g‐GMA) and carboxyl groups in oxidized carbon nanotubes (O‐CNTs), PP‐g‐CNT was fabricated for reinforcing the interfacial adhesion between CNTs and polypropylene (PP) matrix, favoring the enhancement of melt strength and elastic modulus, i.e., enhancing the foaming ability of PP composites. Cellular structure and thermo‐mechanical properties of PP foams were characterized by scanning electron microscopy and dynamic mechanical analysis, respectively. The average cell diameter of PP foams decreased from 289.2 (PP‐g‐GMA) to 96.7 μm (PP‐g‐CNT foams with 2.0 wt % O‐CNT) and the distribution of cell size also became more uniform. The storage modulus of PP‐g‐CNT foams increased by nearly 62.5% at ?40°C, compared with that of PP‐g‐GMA foams. This work also provided a new procedure for improving the foam ability and thermo‐mechanical property of PP composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 961‐968, 2013     

Microstructure and properties of epoxy foams prepared by microwave

In this article, epoxy foams comprised of diglycidyl ether of bisphenol‐A (DGEBA) based epoxy resin E₃₁ and E₅₁, polyamide resin, and water were prepared by microwave irradiation method. The structure and properties of epoxy foams were analyzed by FTIR, TGA, SEM, and DMA methods. The density and compressive performance of epoxy foams was also determined. The results indicated that the epoxy foams had excellent compressive performance and the preparation of epoxy foam by microwave irradiation was high efficiency and convenient. The composition has great effect on density, foam structure, dynamical mechanic performance, and thermal degradation behavior of epoxy foams. The epoxy foam with density from 0.08 g cm^?3 to 1.05 g cm^?3 can be obtained by varying ratio of E₅₁ and E₃₁ to control the viscosity of mixtures. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Lightweight and High Impact Polypropylene Foam Fabricated via Ultra-Low Gas Pressure Injection Molding

Foamed materials play an important role in a lightweight design. Foam injection molding (FIM) is an advanced and convenient way to fabricate lightweight structural materials. Recently, a new foam injection molding machine is developed, which only needs ultra-low gas pressure to fabricate microcellular foam. As a universal plastic, polypropylene (PP) is widely used due to its good mechanical properties. But after foaming, the toughness of the PP tends to decrease. Herein, a lightweight and high-impact polypropylene foam is fabricated via the new FIM technology with an ultra-low nitrogen pressure of 6.5 MPa. PP/polyolefin elastomer (POE) foam with a tiny cell size of 4.13 µm and high cell density of 2.7 × 10⁹  cm⁻³ is successfully obtained. Owing to the superior cellular structure, compared with the pure PP foam, after adding the POE component, the maximum impact performance is increased by 465%. In this work, an easy-to-industrialized method for preparing lightweight and high-impact injection-molded PP foams are presented.     

原位生成纳米SiO2填料对RPU性能的影响

通过控制水解温度和乳化剂的加入量,采用油包水微乳液法在聚醚多元醇中原位合成了纳米SiO2,聚醚多元醇进一步与TDI反应制备聚氨酯硬质泡沫塑料。TEM照片显示原位合成的SiO2微粒呈球状且分散,粒径范围在50～70nm。该聚氨酯硬质泡沫塑料的吸水率随着SiO2添加量的增加,先升高随后又降低。因为原位生成纳米SiO2的加入,聚氨酯硬质泡沫塑料的拉伸强度得到显著提高,冲击强度缓慢增大,而对于压缩强度则先轻微降低,一直到SiO2质量分数为1.1％时才开始急剧增大。     

Bulk and bubble-scale experimental studies of influence of nanoparticles on foam stability

Influence of silicon oxide(SiO_2) and aluminum oxide(Al_2O_3) nanoparticles on the stability of nanoparticles and sodium dodecyl sulfate(SDS) mixed solution foams was studied at bulk and bubble-scale. Foam apparent viscosity was also determined in Hele-Shaw cell In order to investigate the foam performance at static and dynamic conditions. Results show that the maximum adsorption of surfactant on the nanoparticles occurs at 3 wt% surfactant concentration. Foam stability increases while the foamability decreases with the increasing nanoparticle concentration. However, optimum nanoparticle concentration corresponding to maximum foam stability was obtained at 1.0 wt% nanoparticle concentration for the hydrophilic SiO_2/SDS and Al_2O_3/SDS foams. Foam performance was enhanced with increasing nanoparticles hydrophobicity. Air-foams were generally more stable than CO_2 foams.Foam apparent viscosity increased in the presence of nanoparticles from 20.34 mPa·s to 84.84 mPa·s while the film thickness increased from 27.5 μm to 136 μm. This study suggests that the static and dynamic stability of conventional foams could be improved with addition of appropriate concentration of nanoparticles into the surfactant solution. The nanoparticles improve foam stability by their adsorption and aggregation at the foam lamellae to increase film thickness and dilational viscoelasticity. This prevents liquid drainage and film thinning and improves foam stability both at the bulk and bubble scale.     

Effect of high temperature on the mechanical properties of hierarchical porous cenosphere/geopolymer composite foams

A hierarchical porous cenosphere/geopolymer composite foam (FHCs/KGP) was fabricated by the simultaneous incorporation of O₂ pore from hydrogen peroxide and cenosphere filler addition. Effects of both H₂O₂ content and high-temperature treatment on the microstructure, porosity and strength of porous FHCs/KGP foams were investigated systematically. The obtained FHCs/KGP foams showed typical amorphous structure and desirable porosity from 65 to 82%. The composites could crystallize in situ to FHCs/leucite foams above 1000℃. Compression strength of the FHCs/leucite foams showed a maximum value of 5 ± 0.3 MPa when treated at 1000°C. The improvement of mechanical properties for the composite foams was attributed to crack deflection, fractured microspheres and the good bond between the FHCs and matrix. This study could open opportunities to employ cellular foams as alternatives in structure and filtration applications.     

原位生成纳米SiO2及其作为填料对聚氨酯硬质泡沫塑料性能的影响

通过选择适当的乳化剂和水解温度以及控制水对于乳化剂的摩尔比,采用油包水微乳液法在聚醚多元醇中原位合成了纳米SiO2,该聚醚多元醇进一步与TDI反应制备出聚氨酯硬质泡沫塑料.TEM显示原位合成的SiO2微粒呈球状且分散,粒径为50～70nm.随着SiO2填加量的增加,该聚氨酯硬质泡沫塑料的吸水率先升后降.因为原位生成纳米SiO2的加入,聚氨酯硬质泡沫塑料的拉伸强度得到显著提高,冲击强度缓慢增大,而压缩强度则先轻微降低,一直到SiO2的含量为0.9wt%时才开始急剧增大.