Effect of auxiliary blowing agents on properties of rigid polyurethane foams based on liquefied products from peanut shell

The bio‐based rigid polyurethane (PU) foams were successfully prepared based on liquefied products from peanut shell with water as the blowing agent. The influence of reaction parameters on properties of rigid PU foams was investigated. Rigid PU foams showed excellent compressive strength and low shrinkage ratio, whereas their open‐cell ratio and water absorption were higher. Therefore, rigid PU foams were synthesized with petroleum ether, diethyl ether, and acetone as auxiliary blowing agents and their inner temperature, shrinkage performance, density, compressive strength, water absorption, and open‐cell ratio were determined. The results indicated that above rigid PU foams showed lower compressive strength than the original foam but their water absorption and close‐cell ratio were improved. Compared with the original foam, the highest inner temperature of rigid PU foams with petroleum ether, diethyl ether, and acetone as auxiliary blowing agents was reduced by 11, 19, and 23 °C, respectively. Typically, foams with petroleum ether as auxiliary blowing agent displayed better water absorption and swelling ratio in water and exhibited obvious improvement in close‐cell ratio. These foams were preferable for application in thermal insulation materials because of low thermal conductivity and better corrosion resistance. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45582.     

Preparation and Characterization of Sustainable Polyurethane Foams from Soybean Oils

Polyol derived from soybean oil was made from crude soybean oil by epoxidization and hydroxylation. Soy-based polyurethane (PU) foams were prepared by the in-situ reaction of methylene diphenyl diisocyanate (MDI) polyurea prepolymer and soy-based polyol. A free-rise method was developed to prepare the sustainable PU foams for use in automotive and bedding cushions. In this study, three petroleum-based PU foams were compared with two soy-based PU foams in terms of their foam characterizations and properties. Soy-based PU foams were made with soy-based polyols with different hydroxyl values. Soy-based PU foams had higher T _g (glass transition temperature) and worse cryogenic properties than petroleum-based PU foams. Bio-foams had lower thermal degradation temperatures in the urethane degradation due to natural molecular chains with lower thermal stability than petroleum skeletons. However, these foams had good thermal degradation at a high temperature stage because of MDI polyurea prepolymer, which had superior thermal stability than toluene diisocyanate adducts in petroleum-based PU foams. In addition, soy-based polyol, with high hydroxyl value, contributed PU foam with superior tensile and higher elongation, but lower compressive strength and modulus. Nonetheless, bio-foam made with high hydroxyl valued soy-based polyol had smaller and better distributed cell size than that using low hydroxyl soy-based polyol. Soy-based polyol with high hydroxyl value also contributed the bio-foam with thinner cell walls compared to that with low hydroxyl value, whereas, petroleum-based PU foams had no variations in cell thickness and cell distributions.     

Mechanical,acoustic, and thermal performances of shear thickening fluid–filled rigid polyurethane foam composites: Effects of content of shear thickening fluid and particle size of silica

Shear thickening fluid (STF) features a rheological property, and rigid polyurethane (PU) foams feature low thermal conductivity and excellent acoustic insulation. In this study, an STF/PU rigid foam composite sandwich structure was designed using different contents (0, 0.5, 1, or 1.5 wt %) of STF that contained 14 nm, 40 nm, or 75 nm silicon dioxide (SiO₂). The effects of STF content and silica size on the cell structure, mechanical performance, acoustic absorption, and thermal performance of the STF/PU foam were explored. The test results show that STF/PU foam exhibited three characteristic acoustic absorption peaks, and the maximum acoustic absorption coefficient reached 0.841. STF addition increased compression, bending strength, and maximum acoustic coefficient, as well as initial mass loss temperature. STF-filled PU foam composites containing 14 nm and 40 nm SiO₂ had a mild rise in thermal insulation. The rigid STF/PU foam composites with a cell structure had the maximum thermal conductivity of 0.22 W m⁻¹ K⁻¹ and sound absorption coefficient of 0.841, which confirm that they are a good candidate for sound-absorbing energy conservation materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47359.     

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.     

Physicomechanical,friction, and abrasion properties of EVA/PU blend foams foamed by supercritical nitrogen

Elastomer foams based on EVA, PU, and EVA/PU blends formulated for shoe‐sole applications were prepared by a supercritical N₂ batch foaming process and characterized for physicomechanical, friction and abrasion properties. The blending of EVA with PU was aimed for improving the friction and wear characteristics of the EVA based foams. All of the foams prepared showed spherical cells with closed‐cell morphology and the cell sizes varied with varying the EVA/PU blend ratio and CaCO₃ content of the foams. The properties such as hardness and resilience, friction coefficients and abrasion resistance improved for the EVA/PU blend foams compared to the EVA foam, but their compression set, tensile strength, and tear strength were inferior to the EVA foam. The incorporation of CaCO₃ filler increased density, hardness, tensile strength, and tear strength of the EVA/PU blend foams but decreased resilience, compression set, friction coefficients, and abrasion resistance. The improvement in friction coefficients and wear resistance obtained in the EVA/PU blend foams was significant for shoe‐sole applications. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers     

Physical properties of water‐blown rigid polyurethane foams containing epoxidized soybean oil in different isocyanate indices

To explore the potential of isocyanate usage reduction, water‐blown rigid polyurethane foams were made by replacing 0, 20, and 50% of Voranoll® 490 in the B‐side of the foam formulation by epoxidized soybean oil (ESBO) with an isocyanate index ranging from 50 to 110. The compressive strength, density, and thermal conductivity of foams were measured. The foam surface temperature was monitored before and throughout the foaming reaction as an indirect indication of the foaming temperature. Increasing ESBO replacement and/or decreasing isocyanate index decreased the foam's compressive strength. The density of the foam decreased while decreasing the isocyanate index to 60. Further decrease in isocyanate index resulted in foam shrinkage causing a sharp increase in the foam density. The thermal conductivity of foams increased while decreasing the isocyanate index and increasing the ESBO replacement. Mathematical models for predicting rigid polyurethane foam density, compressive strength, and thermal conductivity were established and validated. Similar to compressive strength, the foaming temperature decreased while decreasing the isocyanate index and increasing the ESBO replacement. Because of the lower reactivity of ESBO with isocyanate, the rate of foaming temperature decrease with decreasing isocyanate index was in the order of 0% > 20% > 50% ESBO replacement. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

热塑挤出制备无机阻燃聚乙烯醇泡沫材料及其影响因素的研究

以水为增塑剂兼物理发泡剂,氢氧化铝(ATH)为无机阻燃剂兼异相成核剂,通过热塑挤出方法制备了无机阻燃聚乙烯醇/氢氧化铝(PVAL/ATH)复合泡沫材料,采用扫描电子显微镜(SEM)等研究了水和ATH含量、口模温度、螺杆转速、交联剂对复合泡沫材料泡孔结构的影响。结果表明,适当的口模温度和螺杆转速是实现体系中水的可控、连续、稳定发泡的关键因素,适量添加的阻燃剂能够起到良好异相成核剂的作用,在最佳工艺条件下,当PVAL/ATH/水为100/80/30,口模温度为125℃,螺杆转速为30 r/min时,制备得到综合性能优异的无机阻燃PVAL/ATH泡沫材料,泡沫材料的表观密度为0.32 g/cm3,膨胀倍率为10.0,泡孔密度约为1.6×105个/cm3。此外,引入硼酸作为交联剂,有效提高了熔体强度并改善了泡孔结构,交联后泡沫材料的拉伸强度和断裂伸长率分别提高到6.3 MPa和59.2%。     

Novel preparation and mechanical properties of rigid polyurethane foam/organoclay nanocomposites

A novel method for preparing rigid polyurethane (PU) foam/organoclay nanocomposites was developed through the direct incorporation of an organoclay into PU foam matrices without the addition of any physical or chemical blowing agent. The resultant foams with an appropriate content of the organoclay had a finer cell structure than the pristine PU foams because the organoclay not only acted as a nucleating agent as expected but also acted as a blowing agent of the PU foams; this could be attributed to the bound water between the interlayers of the organoclay. In addition, the incorporation of the organoclay up to 4 phr resulted in improvements in the tensile and compressive strengths, with the maximum values appearing at 2 phr (110 and 152%, respectively). The significant improvement in the mechanical properties could be attributed to the finer cell structure and the increased internal strength of the materials due to the higher degree of hydrogen bonding. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

可再生聚酯多元醇的合成及其在聚氨酯材料中的应用

采用油酸为主要原料合成了羟值为236mgKOH／g、酸值为2．8mgKOH／g的可再生聚酯多元醇,并以此聚酯多元醇为原料制备了聚氨酯硬质泡沫。研究了该聚酯多元醇用量对泡沫发泡和力学性能的影响。结果表明,随着聚酯多元醇加入量的增加,形成聚氨酯硬质泡沫的反应速度增加;与纯聚醚多元醇制备的聚氨酯硬质泡沫相比,加入20％～30％的该聚酯多元醇制备的聚氨酯泡沫的尺寸稳定性和压缩强度增加。     

Behaviour of open-cell cordierite foams under compression

Cordierite foams were produced using the polymer foam replication method. The effects of both the structure of the polymeric foam template and the slurry's solid loads on the compressive strength and the sintered structure of the ceramic foam were evaluated in order to achieve the optimal manufacturing conditions. The compressive strengths of cordierite foams were measured at room temperature. Polyurethane (PU) foams were used as templates. Aqueous ceramic suspensions were prepared with solids weight fraction ranging from 50 to 65%. The effects of both the PU density and the solids volume fraction on porosity and strength of the developed cordierite foams were evaluated. The cordierite foams produced are of semiclosed-cell type. Some impregnation difficulties were experienced with increasing of the PU density. The compressive strength of the cordierite foams increased (from 0.1 to 2 MPa) with increasing solids volume fraction. These data are in agreement with the predictions of the model developed by Gibson and Ashby. However, the exponent of the model was half of the measured one (≈3) over the range of relative densities investigated (80–90%). Such discrepancy might be related to several factors such as the morphological differences in the structural unit of the developed foams with respect to a cubic open-cell foam or to the mixture of both open and closed cells or to the presence of non-periodic cells. In addition, it was found that the compressive strengths depended on the cell size for foams of similar relative densities and generally decreased with increasing of the cell size, which deviates from the theoretical predictions. When the starting polymeric substrate contained a higher fraction of closed cell windows, however, the ceramic material present on the cellular structure was not only distributed on the struts but also filled the cell walls. This contributed to an increase of the relative density of the cordierite foams and consequently to higher compressive strengths.     

蓖麻油酸镧对聚氨酯自结皮泡沫性能的影响

采用硝酸镧、蓖麻油酸为原料, 利用复分解法制备了蓖麻油酸镧。以蓖麻油酸镧作为催化剂, 作用于全水发泡聚氨酯自结皮泡沫材料, 考察了蓖麻油酸镧对全水发泡聚氨酯自结皮泡沫材料性能的影响。采用傅里叶红外光谱仪、紫外可见分光光度计、生物显微镜、电子万能试验机等进行表征, 结果表明蓖麻油酸镧对全水发泡聚氨酯自结皮泡沫材料的影响作用明显, 稀土元素的加入使泡沫材料的体系结构发生变化。加入蓖麻油酸镧后可明显缩短泡沫的脱模时间, 改善了泡沫强度和表皮硬度, 对形成稳定良好的泡孔结构有一定的促进作用, 添加0.3份和0.6份的蓖麻油酸镧制取的泡沫泡孔形态较好。     

水发泡对煤矿加固用聚氨酯注浆材料安全性的影响

制备了纯样煤矿加固用聚氨酯注浆材料(PU)和加入1%水发泡聚氨酯注浆材料(PU-W),研究了水发泡对聚氨酯加固材料的最高反应温度、形貌结构、压缩强度、热稳定性和阻燃性等安全性的影响。结果表明,PU和PU-W的最高反应温度都随着A、B料用量的增加而逐步增大,尤其是水发泡聚氨酯PU-W的最高反应温度和温度保持时间较纯PU有明显增加。PU的形貌呈现球状或椭球状形态,PU-W的泡孔结构主要呈现为五边形构成的球体的结构,材料的泡孔尺寸随密度的降低而增大,表现为压缩强度随密度的降低而减小。热重分析结果表明,水发泡对聚氨酯注浆材料的热稳定性影响较大,在280℃之前,PU的热稳定性优于PU-W。酒精喷灯和酒精灯燃烧试验表明,纯PU的阻燃性能较好,水发泡聚氨酯PU-W的阻燃性能降低,不能满足行业标准的要求。     

Water-blown rigid and flexible polyurethane foams containing epoxidized soybean oil triglycerides

Both rigid and flexible water-blown polyurethane foams were made by replacing 0–50% of Voranol® 490 for rigid foams and Voranol® 4701 for flexible foams in the B-side of foam formulation by epoxidized soybean oil. For rigid water-blown polyurethane foams, density, compressive strength, and thermal conductivity were measured. Although there were no significant changes in density, compressive strength decreased and thermal conductivity decreased first and then increased with increasing epoxidized soybean oil. For flexible water-blown polyurethane foams, density, 50% compression force deflection, 50% constant force deflection, and resilience of foams were measured. Density decreased first and then increased, no changes in 50% compression force deflection first and then increased, increasing 50% constant force deflection, and decreasing resilience with increase in epoxidized soybean oil. It appears that up to 20% of Voranol® 490 could be replaced by epoxidized soybean oil in rigid polyurethane foams. When replacing up to 20% of Voranol® 4701 by epoxidized soybean oil in flexible polyurethane foams, density and 50% compression deflection properties were similar or better than control, but resilience and 50% constant deflection compression properties were inferior. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Mechanical Properties of Silicone Rubber Enhanced Microcellular EPDM Foams Based on Supercritical CO2 Foaming Technology

Microcellular ethylene-propylene-diene monomer (EPDM) foams derived from miniaturizing the cellular structure can improve mechanical properties of traditional EPDM foams. It is a current challenge that microcellular EPDM foams prepared by supercritical CO₂ foaming technology cannot undergo the post-crosslinking process due to the disappearance of cellular structure, which strongly restricts the development of the mechanical properties of EPDM foams. Hence, a scalable and blending route by selecting the silicone rubber (SR) with different crosslinking temperature compared to EPDM is developed to improve mechanical properties of EPDM foams. During the pre-crosslinking process of EPDM, SR forms a complete crosslinking network, which can make up for the strength of EPDM without the post-crosslinking. Meanwhile, the silica can reduce the domain size of SR and enhance the compatibility between EPDM and SR. As expected, the addition of SR improves the storage modulus, viscosity and matrix strength of EPDM, which shows enhanced mechanical properties of EPDM foams. When the foam density is basically the same, the tensile strength and compressive strength of SR/EPDM foam are increased by 461% and 283% respectively compared with that of EPDM foam. Finally, the maximum tensile strength and compressive strength (40% strain) of SR/EPDM foam achieves 3.58 MPa and 0.59 MPa, respectively.     

Processing and properties of an ethylene–vinyl acetate blend foam incorporating ethylene–vinyl acetate and polyurethane waste foams

Waste polyurethane foam (w‐PU) and waste ethylene–vinyl acetate foam (w‐EVA) were used as fillers for the production of an ethylene–vinyl acetate (EVA) blend foam. Two different foaming techniques (single‐stage and heat–chill processes) were used for this purpose. The waste foam concentration was varied up to 30 wt % of the original EVA. The physical, mechanical, and morphological properties of the filled foam were studied. The single‐stage process produced blend foams with a lower density and a greater cell size than the foams obtained by the heat–chill process. The density and compression strength of the blend foam increased as the percentage of w‐PU foam increased. However, for the w‐EVA/EVA blend foams, the addition of w‐EVA foam did not significantly affect the density or compression strength compared to the original EVA foams. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44708.     

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.     

Improvement of thermal and mechanical properties by control of formulations in rigid polyurethane foams from polyols functionalized with graphene oxide

This article addresses the optimization of water-blown rigid polyurethane (RPU) foams obtained from a polyol functionalized with graphene oxide (GO). For this purpose, a series of RPU foams are herein synthesized by varying either the isocyanate index, the contents of catalyst or the contents of surfactant, or a combination of these three components. The modifications introduced in the formulation are based on the effect of GO on the reaction kinetics. These strategies are mainly focused on the increase of both isocyanate conversion and polymerization reaction, which decrease for the foams containing GO. Density, cellular structure, thermal conductivity, and mechanical properties of the resulting foams are herein investigated. The results show how controlling PU formulation allows to improve both the thermal and the mechanical behavior in these RPU foams containing GO. The highest cell size reduction of 25% and the lowest thermal conductivity are obtained for the sample with a simultaneous increase in isocyanate index, catalyst content, and surfactant content. Moreover, the adequate combination of these components leads to a high improvement of 59% of the relative Young's modulus and of 54% of the relative collapse stress. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47474.     

Rigid polyurethane foams with halogen-free flame retardants: Thermal insulation,mechanical, and flame retardant properties

Rigid polyurethane foam (RPUF) composites with triphenyl phosphate (TPhP), aluminum trihydrate (ATH), and zinc borate (ZnB) alone, as well as their binary blends, were prepared via a one-shot process. The amount of flame retardant (FR) or FR blend was varied from 10 to 50% by polyol weight percentage, and the weight fraction of the blends was also fixed at 40%. The effects of additives on thermal insulation, mechanical, and flame retardancy properties of the composites were investigated. Thermal conductivity of the neat foam (RPUF) decreased from 22.53 to 21.04–21.58 mW m⁻¹ K⁻¹. The compressive strength of foams displayed an increase with increasing the amount of TPhP, ATH, and ZnB till 40% by weight. The limited oxygen index values of all foams increased and the flame spread rates of all foams significantly decreased. It was also observed that the flame was self-extinguished in some cases. The cone calorimeter test results indicated that the FR additives improved the flame retardancy of the RPUF. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 47611.     

Glass bubble reinforced polyurethane foams with high mechanical strength for cryogenic temperature insulation

In this study, glass bubble (GB) is added to polyurethane (PU) foams at different weight ratios—0, 0.25, 0.5, 0.75, and 1 wt% —to investigate the changes in the mechanical and thermal properties of the foam. By conducting several tests and measurements, the density, cell morphology, compressive strength, and thermal conductivity of the foam are studied. In particular, the effect of GB additives is examined by conducting compression tests at various temperatures (−163, −100, −40, and 20°C). Scanning electron microscopy and X-ray microscope reveal that the foams exhibit higher stability below 0.5 wt%, which improves the thermal performance. On the other hand, the compressive strength of the foams increases for all weight ratios of GB, and it increases sharply at 0.75 wt%. In addition, the chemical interactions and the dispersion of additives in the PU matrix are investigated through Fourier transform infrared and X-ray diffractions analysis. It is found that the synthesis of PU foams with GB nanoparticles is an efficient method for improving the mechanical properties and insulation performance of the foam for LNG insulation technology.     

Morphology,mechanical properties,and thermal stability of polyurethane–epoxide resin interpenetrating polymer network rigid foams

A series of rigid interpenetrating network foams (IPNFs) based on a rosin‐based polyurethane (PU) and a crosslinked epoxide resin (ER) were prepared by a simultaneous polymerization technique. The morphology, mechanical properties, thermal stability, and changes in the chemical structure during the thermal degradation process of the rigid IPNFs were investigated by scanning electron microscopy (SEM), compressive testing, thermogravimetric analysis (TGA), and Fourier‐transform infrared spectroscopy (FTIR). The SEM micrographs showed that the cell structure of the rigid IPNFs became less homogeneous with increasing ER content. The brittleness of the cell walls increased as the ER content and the cure time of the rigid IPNFs increased. The compressive strength of the rigid PU/ER IPNFs increased to a maximum value and then decreased with further increase in the ER content. Similar behavior was observed for the elastic modulus. This behavior was related to the nonhomogeneous cells and more brittle cell walls for the rigid IPNFs with high ER content. The TGA data showed that the thermal stability of the rigid PU foam increased with the addition of increasing levels of ER, due to the better thermal stability of the ER compared to that of the PU. With the exception of the ER alone, a two‐stage weight‐loss process was observed for all these rigid IPNFs and for the PU foam alone. The FTIR analysis suggested that the first stage of weight loss was due to the degradation of the polyol–derived blocks of the PU, and the second weight loss stage was governed by both the degradation of the ER component and that of the isocyanate‐derived blocks of the PU. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 406–416, 2000