Synthesis and characterization of elastomeric polyurea foam

Polymeric foams are ubiquitous in impact mitigation for civilian and military applications; the performance in such loading scenarios can be elucidated through quasi-static and dynamic mechanical testing. The present study reports on the complex microstructure of newly synthesized polyurea foams exhibiting a hierarchical structure consisting of large perforated semi-closed spherical cells with a mean diameter of 370 ± 162 μm surrounded by smaller closed, spherical cells with size distribution of 69 ± 18 μm. The stress–strain curves were used to calculate the basic mechanical properties and to predict the dynamic behavior of the foams. Nonlinear regression and finite element analyses were used to calibrate the Ogden hyperfoam model to explicate the hyperelastic behavior. The performance of the polyurea foam was found to outperform a benchmark foam in nearly all the elastic and energy absorbing properties. For example, one variation of the newly synthesized foam stored nearly doubled the energy of the benchmark foam while being 12% lighter. Low-density polyurea foam was found to decelerate an incoming impact mass with a minimum G-level that was nearly one third lower than the higher density polyurea and benchmark foams. In all, the behavior of the foam is dependent on the parameters of the fabrication process. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48839.     

Investigation and Development of Epoxy Foams

The development of low toxicity rigid epoxy foams as an alternative to polyurethane foams for electronics encapsulation is described. The basic foam components - epoxy resin, hardener, accelerator, blowing agent and surfactant - are blended to form a two part system which is mixed and foamed when required. Each foam component is selected for its contribution to the foaming reaction and the final foam properties. The balance of component miscibility, viscosity, reaction rate and exotherm determine foam quality. Foam properties are affected by (1) density (2) cell structure and (3) the molecular structure of the reactants. Initial foam development utilised epoxy/amine chemistry and produced two foams, Feldex F3 and F4. Subsequently, use of a more reactive polymercaptan hardener improved foam strength and process times, resulting in Feldex F5 and F6 which have been used successfully to prepare quality mouldings and encapsulated electronics. Recently, development has been extended to new areas of application, e.g. high temperature foams. The mechanical, electrical, thermal and chemical properties of the best epoxy foams have been evaluated; selected results are reported. The epoxy foams developed offer low density, high strength, low dielectric constant and loss tangent, high volume resistivity, good thermal insulation, low corrosivity and low toxicity. In addition, epoxy foams soften in acetone, an advantage over their polyurethane counterparts since encapsulated electronics may be retrieved without employing corrosive solvents. (Feldex is a registered trade mark of THORN EMI Electronics.)     

水基泡沫的稳定性评价技术及影响因素研究进展

综述了当前比较常用的和新开发的泡沫稳定性评价技术,评述了水基泡沫稳定性的影响因素,并对改变泡沫稳定性的途径进行了探讨,同时展望了有关泡沫稳定性研究的发展方向。     

夹芯板材用硬质酚醛泡沫性能的研究

对用于夹芯板材的硬质酚醛泡沫的发泡过程进行了研究。讨论了发泡温度、固化剂和发泡剂对泡沫体性能的影响。结果表明:反应温度控制在70℃～80℃,固化剂用量控制在16%～20%,得到的泡沫体均匀细腻,综合性能好。     

酚醛泡沫的制备

研究了两种酚醛泡沫的制备, 一种是用加热法制备酚醛泡沫, 另一种是尿素改性酚醛泡沫的制备。实验表明, 用加热方法制备的酚醛泡沫, 压缩强度较常温发泡提高一倍左右, 吸水率降至原来的一半, 导热系数由原来的００３３ Ｗ／ ｍ · Ｋ 降至００２８ Ｗ／ ｍ· Ｋ, 泡沫均匀、细腻。尿素改性酚醛泡沫, 其性能介于加热发泡和常温发泡两种酚醛泡沫之间, 但可降低成本。二者在管道保温领域具有广阔的应用市场。     

Fabrication and overcoating of divinylbenzene foam shells using dual initiators

Divinylbenzene (DVB) shells with a density of about 100 mg/cc were produced using a dual‐thermal initiator system. New high‐gain designs for direct‐drive ignition at the National Ignition Facility and the OMEGA laser facility at the Laboratory for Laser Energetics require low‐density foam shells such as these. Previous research using a single initiator system produced fragile DVB shells that cracked or imploded during the fabrication process. The dual‐initiator DVB system used in the present study enabled the shells to be robust enough to produce a high yield of intact shells. The two thermal initiators used were azobisisobutyronitrile (AIBN) and another azo‐type initiator, V‐70. The DVB shells were 800–3500 μm in diameter, with shell wall thickness 7%–10% of the diameter. Because the foam shells were porous, a full‐density permeation barrier of poly(vinyl phenol) was developed and deposited on the shells using two techniques to enable the shells to retain gas. The initial results show that the permeation barrier was pinhole free and could hold the gas in a gas‐filled shell. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2523–2529, 2006     

HCFC-141b发泡剂制备的半硬质聚氨酯整皮泡沫

采用氢氟氯烃1，1－二氯－1－一氟乙烷（简称HCFC－141b)代替一氟三氯甲烷（简称CFC－11）作发泡剂帛得具有臻密表皮层的半硬质聚氨酯整皮泡沫塑料，采用扫描电子显微镜观察了两种发泡剂帛得材料的内部泡孔结构，比较了两者的力学性能，结果表明；采用HCFC－141b代替CFC－11可以帛得性能良好的半硬质聚氨酯整皮泡沫塑料。     

Nanoporous Ag and Pd foam: Redox induced fabrication using electrochemically deposited nanoporous Cu foam with no need to any additive

A simple, rapid and green method for fabrication of nanoporous metal (Ag and Pd) foams using electrochemically deposited nanoporous copper foam is presented. Ideally direct electrochemical formation of Ag and Pd foam structures without any additive reagent does not lead to a desired result; however, indirect fabrication starting from electrochemically fabricated Cu foam seems promising. Highly porous copper foam is fabricated electrochemically at a copper sheet and in turn serves as a hard template and a redox inducer for the deposition of Ag or Pd. The redox induced replacement of copper foam with Ag or Pd is done via simple immersion of as-fabricated nanoporous copper foam in cation aqueous solutions of Ag or Pd. The surface morphology of the as-fabricated foam is characterized by scanning electron microscopy (SEM), EDX and X-ray diffraction. The hydrogen evolution reaction is investigated as an example to demonstrate the electrocatalytic ability of as-fabricated foams.     

硬质泡沫橡胶浮子的试制

针对泡沫浮子的使用要求，筛选出了用于制备泡沫橡胶浮子的配方体系，通过实验确定出了3种不同发泡剂的泡沫橡胶浮子的配方，比较了垂直自由发泡法、垂直加压发泡法和水平加压发泡法的优缺点。     

Simple and generally applicable method of determination and evaluation of foam properties

A new, simple foam test, in which a well-controlled volume of gas is introduced into a definite volume of solution, is presented along with the method of analysis. Aqueous solutions of sodium dodecyl sulfate (SDS), n-octyl-β-d-glucopyranoside, hexadecyltrimethylammonium bromide (CTAB), and n-hexanol, i.e., four systems forming metastable and transient foams, were studied. The parameter R5, defined as the ratio of the height of the foam at 5 min after formation to the initial height, is proposed for the evaluation of foam stability. Foams having R5 values higher than 50% can be considered as metastable. Lower R5 values indicate low-stability foams. Changes of R5 values with concentration are similar to those of foam half-life with concentration. Thus, instead of measurements lasting hours for the foam half-life, one can obtain similar information from tests lasting only a few minutes. With this test also one can obtain information about the solution contents in foams. This parameter can be used as an additional criterion for the evaluation of foam stability. In the case of metastable foams formed by SDS, CTAB, and n-octyl-β-d-glucopyranoside, the initial foam volume was almost equal to the volumes of the dispersed gas and the solution carried into the foam by the bubbles. This shows that there was practically no rupture of foam films at the stage of the foam formation.     

Performance characteristics of novel mechanical foam breakers in a stirred tank reactor

Unlimited foam formation and insufficient foam collapse can have serious effects in an aerated system such as a fermentation process. Mechanical foam breakers are used in foam control to avoid the drawbacks associated with the use of chemical antifoams and defoaming agents. In this paper, two new foam breakers consisting of a two‐blade paddle with three slits, and a two‐blade paddle with 168 thin needles have been tested. They gave significantly reduced critical speeds and power consumption for foam control in a stirred vessel, compared with some conventional foam breakers. The effects of various parameters, namely the physical properties of the foaming solution, type of gas sparger, surfactant concentration, and foam‐breaker clearance above liquid level, have been investigated. The degree of difficulty of controlling dynamic foams generated continuously in a stirred vessel is found to be a function of the nature of the foam, ie its bubble size, its liquid holdup, and the degree of foamability of the system. © 1999 Society of Chemical Industry     

泡沫塑料保温材料的研究进展

简述了国内外泡沫塑料保温材料的发展现状;介绍了聚氨酯泡沫塑料、聚苯乙烯泡沫塑料和酚醛泡沫塑料的研究进展;展望了泡沫塑料保温材料的应用前景和发展趋势。     

酚醛泡沫在高温热处理过程中结构与性能的变化

以甲阶酚醛树脂为原料制备了酚醛泡沫,经高温热处理进而得到酚醛树脂基碳泡沫。通过FTIR、TGA、SEM、压缩强度及热导率检测等手段,分析研究了酚醛泡沫在高温热处理后结构与性能的变化情况。结果表明:氮气保护下,酚醛泡沫经高温处理后形成了以碳元素为主的碳泡沫;与酚醛泡沫相比,碳泡沫的表观密度、泡孔孔径较小,泡孔虽仍以闭孔结构为主,但是开孔结构明显增多;酚醛泡沫及碳泡沫的压缩强度和热导率都随着泡沫密度的增加而增大,另外同酚醛泡沫相比,碳泡沫的压缩强度和热导率均相对较高。     

聚乙烯挤出发泡的研究

采用自由发泡工艺研究了聚乙烯低发泡成型的配方及工艺条件，讨论了偶氮二碳酰胺(AC)、乙烯／醋酸乙烯共聚物(EVA)、过氧化二乙丙苯(DCP)用量、螺杆转数对制品性能的影响。结果发现，每100份聚乙烯中AC用量3份、EVA用量为5份、DCP用量为0．02份、螺杆转速为30r／min时，制得制品泡孔结构分布均匀，机械性能较好。     

Revisiting flexible polyurethane foam flammability in furniture and bedding in the United States

The flammability of flexible polyurethane foam has been well studied to date, via smoldering and flaming ignition. Its contribution to fire loss in the United States has also been well documented, as the flammability of this material will contribute to large fire events when not protected from ignition and heat sources. Despite this known fire risk, fire protection approaches for polyurethane foam are being questioned in regards to fire protection performance, as well as proven and hypothesized concerns over health impacts before and after fire events. The flammability of flexible polyurethane foam in furniture and bedding is a clear and present danger that must be addressed, and this article discusses the current available technologies for fire protection, with pros and cons of these approaches. Known physical and chemical behavior of these foams in fires is discussed, as well as how this behavior contributes to large fire events. Finally, issues that still need further research and information to definitively address the polyurethane foam flammability in the United States is discussed.     

混凝土发泡剂及泡沫稳定性的研究

介绍了混凝土发泡剂的发展概况 ,分析了发泡剂泡沫的稳定性 ,阐述了发泡剂的性能优劣是影响发泡混凝土生产的关键 ,而其自身性质和掺入方式都对混凝土性能产生较大影响。     

水泥企业自备电厂油罐区消防系统设计

结合6000t/d熟料生产线自备电厂的工程设计实例，详细介绍了自备电厂燃料油储油罐区的消防系统设计。包括泡沫灭火系统的选择、系统组成、消防冷却水系统的设计，泡沫消防泵站及消防水池及泵站的设计。     

A flame‐retardant composite foam: foaming polyurethane in melamine formaldehyde foam skeleton

A composite foam, polyurethane–melamine formaldehyde (PU/MF) foam, was prepared through foaming PU resins in the three‐dimensional netlike skeleton of MF foam. The chemical structure, morphology, cell size and distribution, flame retardancy, thermal properties and mechanical properties of such composite foam were systematically investigated. It was found that the PU/MF foam possessed better fire retardancy than pristine PU foam and achieved self‐extinguishment. Moreover, no melt dripping occurred due to the contribution of the carbonized MF skeleton network. In order to further improve the flame retardancy of the composite foam, a small amount of a phosphorus flame retardant (ammonium polyphosphate) and a char‐forming agent (pentaerythritol) were incorporated into the foam, together with the nitrogen‐rich MF, thus constituting an intumescent flame‐retardant (IFR) system. Owing to the IFR system, the flame‐retardant PU/MF foam can generate a large bulk of expanded char acting as an efficient shielding layer to hold back the diffusion of heat and oxygen. As a result, the flame‐retardant PU/MF foam achieved a higher limiting oxygen index of 31.2% and exhibited immediate self‐extinguishment. It exhibited significantly reduced peak heat release rate and total heat release, as well as higher char residual ratio compared to PU foam. Furthermore, the composite foam also showed obviously improved mechanical performance in comparison with PU foam. Overall, the present investigation provided a new approach for fabricating a polymer composite foam with satisfactory flame retardancy and good comprehensive properties. © 2018 Society of Chemical Industry     

Stabilization of natural gas foams using different surfactants at high pressure and high temperature conditions

Natural gas foam can be used for mobility control and channel blocking during natural gas injection for enhanced oil recovery, in which stable foams need to be used at high reservoir temperature, high pressure and high water salinity conditions in field applications. In this study, the performance of methane (CH₄) foams stabilized by different types of surfactants was tested using a high pressure and high temperature foam meter for surfactant screening and selection, including anionic surfactant (sodium dodecyl sulfate), non-anionic surfactant (alkyl polyglycoside), zwitterionic surfactant (dodecyl dimethyl betaine) and cationic surfactant (dodecyl trimethyl ammonium chloride), and the results show that CH₄-SDS foam has much better performance than that of the other three surfactants. The influences of gas types (CH₄, N₂, and CO₂), surfactant concentration, temperature (up to 110°C), pressure (up to 12.0 MPa), and the presence of polymers as foam stabilizer on foam performance was also evaluated using SDS surfactant. The experimental results show that the stability of CH₄ foam is better than that of CO₂ foam, while N₂ foam is the most stable, and CO₂ foam has the largest foam volume, which can be attributed to the strong interactions between CO₂ molecules with H₂O. The foaming ability and foam stability increase with the increase of the SDS concentration up to 1.0 wt% (0.035 mol/L), but a further increase of the surfactant concentration has a negative effect. The high temperature can greatly reduce the stability of CH₄-SDS foam, while the foaming ability and foam stability can be significantly enhanced at high pressure. The addition of a small amount of polyacrylamide as a foam stabilizer can significantly increase the viscosity of the bulk solution and improve the foam stability, and the higher the molecular weight of the polymer, the higher viscosity of the foam liquid film, the better foam performance.     

机械搅拌式发酵罐中的消泡技术研究与探讨

分析了好氧性微生物发酵过程中由于搅拌、气体引入和微生物代谢等产生泡沫的原因和泡沫对发酵生产过程的危害。介绍了工业生产中所采用的化学消泡和机械消泡方法、常用的几种化学消泡剂和机械消泡结构形式,以及它们在使用过程中的优点和不足之处,并提出了一种新型机械消泡装置——变径孔式消泡器,这种消泡器是依靠泡沫通过变径孔通道时所产生的压力变化和转动时所产生的剪切力来实现消泡目的的,消泡效果良好。