Carbon foam derived from various precursors

A series of carbon foams was developed by using low-cost precursors, such as coal, coal tar pitch and petroleum pitch. The properties of the resultant carbon foams cover a wide range, e.g., bulk density, 0.32-0.67 g/cm³, compressive strength, 2.5-18.7 MPa, isotropic and anisotropic microstructure, etc. The investigation of foaming mechanism and the relationship between properties and structure indicate that the fluidity and dilatation of the foaming precursors significantly affect the foaming performance and foam structure. Raw coal samples were foamed directly without pretreatment in this work. However, for the pitch based foaming precursor, a thermal pretreatment is necessary to adjust its thermoplastic properties to meet the foaming requirement. The mechanical strength of carbon foam is found to be related to not only the foam cell structure, but also the fluidity and anisotropic domain size of the foaming precursors. In addition, the micro and mesopore structure in carbon foam matrix was investigated by gas adsorption and it was found that it also affects the strength of carbon foam and is related to the fluidity of foaming precursor.     

化学发泡法制备聚氨酯泡棉压敏胶

以聚醚多元醇(N-220、330N)和六亚甲基二异氰酸酯(HDI)为主要原料、一缩二乙二醇(DEG)为小分子扩链剂,合成了—OH封端的PU(聚氨酯)预聚体;然后加入适量的HDI三聚体、催化剂和发泡剂,在一定温度条件下制成了PU泡棉PSA(压敏胶)。研究结果表明:当R=n(—NCO)/n(—OH)=3.0、固化温度为120℃、w(HDI三聚体)=15%和w(发泡剂)=4%(均相对于—OH封端PU树脂质量而言)时,制得的PU泡棉PSA具有良好的剥离强度和力学性能,并且其可应用于汽车领域,而且满足汽车低VOC(有机挥发物)排放的环保要求。     

Controlling the drying process in vacuum foam drying under low vacuum conditions by inducing foaming by needle stimulation of the solution

Abstract

Vacuum foam drying is a promising drying technique but an extremely high vacuum is needed to achieve “foaming.” The findings reported herein show that, when a solution is partially vacuum-dried to 0.05–2?g-solvent/g-dry matter (initial drying) and the solution is then punctured with a steel needle (needle stimulation), vacuum drying resumes as a result of the solution foaming, even under conditions of an insufficient vacuum (ca. 1,000?Pa) where foaming is minimal. Methanol, ethanol, and isopropanol were used as solvents, and sugar and different molecular weight polyvinylpyrrolidone were employed as solutes. The results indicate that needle puncturing introduces minute bubbles, which then triggers foaming.     

Prediction of flow patterns in the polyurethane foaming process by numerical simulation considering foam expansion

We present a foam flow model for flow pattern prediction in the polyurethane foaming process that considers the flow caused by foam expansion due to bubble generation. The flow pattern in the cavity is calculated by taking into account the initial volume shape and the rate of foam expansion of a poured reaction mixture. The validity of the model is investigated by applying it to the Hele‐Shaw formulation, which assumes that the cavity is very thin compared to its width. The predicted flow patterns generally agree closely with experimental results measured in panel‐type molds. A three‐dimensional simulation is further developed based on the Stokes flow. The numerical formulation is performed by the control volume based‐finite element method with an equal‐order velocity‐pressure formulation that does not exhibit spurious pressure modes. The flow patterns predicted by the three‐dimensional simulation agree very closely with the experimental results. In particular, it clearly expresses the edge effect, in which the flow slows down at the edge, which is ignored in the Hele‐Shaw formulation. This numerical simulation is suitable for rapid determination of the pouring position, volume of the mixture, and the air vent position.     

可连续生产的物理发泡法可熔接PVC泡沫的研制

以PVC树脂为主料,添加表面活性剂、阻燃剂、稳定剂等助剂,用R 22作为物理发泡剂,研制了可连续生产的物理发泡法PVC泡沫,探讨了发泡剂用量、表面活性剂用量、射频仪电压对泡沫性能的影响。结果表明:表面活性剂用量增加,泡沫密度减小,拉伸强度降低;微波箱中电压变化,对PVC泡沫的影响没规律性,但有最佳值(6.0 kV);同时,电压增加,泡沫明显变黄;发泡剂R 22用量增加,泡沫密度减小,拉伸强度降低。     

有机硅泡沫材料用有机硅改性丙烯酸酯压敏胶的研究

以MMA(甲基丙烯酸甲酯)作为硬单体、BA(丙烯酸丁酯)作为软单体和KH-570(硅烷偶联剂)作为有机硅单体,采用自由基溶液聚合法制备出一种硅丙-PSA(有机硅改性丙烯酸酯压敏胶),并着重探讨了该PSA对粘接低表面能SF(有机硅泡沫材料)的可行性。研究结果表明:硅丙-PSA对SF基材具有良好的粘接性能,并且对SF基材的压缩性能、耐热性能无显著影响;有机硅单体含量及PSA胶层厚度对180°剥离强度影响较大,当PSA胶层厚度为100μm、w(KH-570)=0.5%(相对于总单体质量而言)时,PSA的剥离强度(1.53 N/25 mm)相对最大;当w(KH-570)=1.0%时,PSA的综合粘接性能(如初粘力、持粘力和剥离强度等)相对最好。     

Toughened and hydrophobically modified polyamide 11 copolymers with dimer acids derived from waste vegetable oil

A series of dimer acid (DA)-modified polyamide 11 copolymers is synthesized via melt polycondensation from 11-aminoundecanoic acid, hexamethylene diamine (HMDA), and DA, prepared by the hydrolysis of waste vegetable oil and a subsequent Diels–Alder reaction. The molecular structures and the polymers' molar masses are characterized by nuclear magnetic resonance, Fourier-transform infrared spectroscopy, size exclusion chromatography. The thermal and mechanical properties are modified with increasing the composition of DA in PA copolymers by increasing the chain irregularity of the PA, thereby reducing the hydrogen bonding strength of the amide groups. Finally, water contact angle and water absorption experiments show that the hydrophobicity of DA-modified PA copolymers is increased as compared to neat PA11. As a result, these thermoplastic materials could offer improved sustainability and performances by the addition of renewable DA monomer in PA copolymers. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47174.     

Separation of hematopoietic stem and progenitor cells from human peripheral blood through polyurethane foaming membranes modified with several amino acids

The separation of hematopoietic stem and progenitor cells (CD34⁺ cells) from peripheral blood was investigated using foamed polyurethane (PU) membranes modified with several amino acids. CD34⁺ cells were collected by first allowing the blood to permeate through the membranes, and then passing the recovered solution through the membranes. Optimal conditions for the separation of CD34⁺ cells were investigated. The highest recovery ratio of CD34⁺ cells was obtained using three sheets of PU membranes having carboxylic acid groups (PU? COOH) modified with glycine, the membranes having been pretreated by immersion in phosphate buffer solution prior to permeation of blood. A high recovery ratio of CD34⁺ cells was achieved in a recovery process using 0.5 wt % human serum albumin (HSA) or 20% dextran solution passed through PU? COOH membranes. The recovery ratios of CD34⁺ cells using platelet‐poor plasma and platelet‐rich plasma were approximately 20% and 30%, respectively, significantly less than the ratio found using 0.5 wt % HSA solution. Surface‐modified membranes having carboxylic acid groups showed a higher recovery ratio of CD34⁺ cells than membranes having zwitterionic groups. The effect of carboxylic acid groups on the surface‐modified PU membranes was to generate weak interactions by electrostatic repulsion between CD34⁺ cells and the membranes because of the negatively charged surfaces of the cells, allowing them to be detached from the membranes and collected in the recovered solution. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Porous mullite ceramics with low thermal conductivity prepared by foaming and starch consolidation

Porous mullite ceramics were prepared from an industrial grade mullite powder by foaming and starch consolidation. The viscosities of the original suspensions and the foamed ones with solid loading of 62.5 and 67.5 wt% were measured. After the steps of forming and drying, the green bodies were sintered under different temperatures from 1,200 to 1,600 °C for 2 h. The influence of solid loading of suspension and sintering temperature on the porosity and compressive strength was evaluated. The sintered mullite ceramics, with porosity from 86 to 73 vol% and corresponding compressive strength from 1 to 22 MPa, contained a multi-modal microstructure with large spherical pores and small pores on internal walls. Thermal conductivity measurement carried out by the transient plane source technique at room temperature resulted in values as low as 0.09 W/mK. In addition, the relationship between thermal conductivity and porosity was discussed in detail.     

Modeling the process of shock-wave attenuation by a foam screen

In a one-dimensional formulation, we consider the problem of decay of the discontinuity in a vertical shock tube when a gaseous suspension of water droplets is present in the channel. Such an approach is used for numerical modeling of the conditions of the physical experiment in a shock tube containing a foam screen. We discuss the dynamics of the wave processes involved in passage of the shock wave through the screen, the damping properties of the screen, and the mechanism for attenuation of the shock wave in the foam. We compare the calculated pressure diagram with the measurement results.Volgograd State University, 420062 Volgograd. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 3, pp. 135–142, May–June 1994.     

改良型A~2/O工艺对低碳源城市污水的脱氮除磷效果

以城市污水为原水,考察了一种分点进水的改良型A2/O工艺的脱氮除磷效果。试验结果表明,原水按照6∶4的体积比分别进入厌氧池和缺氧池后,增加了缺氧池的碳源浓度,提高了该系统的脱氮效果。当进水中碳氮质量比平均为6.84、硝化液回流比为200%,CODCr、TN、NH3-N和TP的平均质量浓度分别为237.02、36.39、22.99和4.98mg/L时,出水CODCr、TN、NH3-N和TP的平均质量浓度分别为34.29、10.70、0.18和0.46mg/L,去除率分别为85.53%、70.60%、99.22%和90.76%。     

Dephosphorization of a sphene concentrate with dilute mineral acids

The reaction of sphene and fluorapatite concentrates with dilute mineral acids is studied using crystal-optical analysis, X-ray powder diffraction, IR spectroscopy, and chemical analysis. The dephosphorization parameters for sphene concentrates are determined. The dephosphorization efficiency decreases in the following order: HCl > H₂SO₄ > HNO₃.     

The electrical properties of graphene modified by bromophenyl groups derived from a diazonium compound

Graphene field-effect transistors were fabricated with mechanically exfoliated single-layer graphene (SLG) and bilayer graphene (BLG) sheets and the functionalization effects of bromophenyl groups derived from a diazonium compound on its transfer properties were explored. Spectroscopic and electrical studies reveal that the bromophenyl grafting imposes p-doping to both SLG and BLG. The modification of SLG by bromophenyl groups significantly reduces the hole carrier mobility and the saturation current in SLG transistors, suggesting an increase in both long-range impurity and short-range defect scattering. Unexpectedly, the bromophenyl group functionalization on BLG does not obviously increase both types of scattering, indicating that the BLG is relatively more resistant to charge- or defect-induced scattering. The results indicate that chemical modification is a simple approach to tailor the electrical properties of graphene sheets with different numbers of layers.     

Evaluation of superplastic-foamed zirconia-based ceramics using foaming agent and a superplasticity facilitator derived from rice husk

Journal of Porous Materials - The applicability of rice husks to solid phase foaming ceramics was assessed. Through an atmospheric heat treatment on silicon carbide based mixture produced by the...     

用硫化与发泡分步法制备均孔三元乙丙橡胶泡沫

采用辐射硫化技术制备了三元乙丙橡胶泡沫,使硫化与发泡分步进行,避免了传统发泡过程中硫化速率与发泡速率难以匹配的问题。研究了发泡条件对三元乙丙橡胶泡沫密度的影响,探讨了吸收剂量和发泡剂用量对制品结构与性能的影响规律,并用扫描电镜观察了泡孔形态。结果表明,发泡温度为175℃、发泡时间为4 min、吸收剂量为20 kGy及发泡剂用量为6份(质量)时三元乙丙橡胶泡沫的泡孔比较均匀,力学性能良好。     

Cellular glass obtained from non-powder preforms by foaming with steam

Cellular glass, or foamed glass, has been obtained as a result of the heating (to 700–800 °C) of heavy and strong preforms formed due to the binding properties of the silicate additives. Durability of the preforms reached 6 MPa at the density of 1.8 g/cm³. The main expanding agent in the composition is steam, which can also be a carbon oxidizer and increase the amount of the evolved gases and decrease the density of the foamed glass obtained. As a result of changing the initial composition structure, the density of the obtained foamed glass varied from 0.14 to 0.6 g/cm³, its breaking strength - from 0.6 to 5.0 MPa. and heat conductivity – from 0.045 to 0.15 W/(m·К), respectively. The speed of expansion of the preforms had an extreme character with the induction period typical for topochemical reactions. The obtained cellular materials possessed a distinct crystalline structure. The experiments showed the possibility of obtaining cellular materials with acceptable properties from different types of glass for the solution of environmental tasks. Various technological methods of obtaining cellular material blocks from preforms of various forms were tested to use them for thermal insulation and facing materials.     

酸性化学镀法制备泡沫铝用Ni/TiH2包覆粉末发泡剂的工艺及性能研究

酸性条件下,对常用发泡剂TiH2粉末的表面进行均匀、质量比可控的Ni层包覆,提高其释氢温度并延缓释氢速率。结果表明,以硫酸镍为主盐,NaH2PO2.H2O为还原剂,制备Ni/TiH2复合粉体的最佳工艺条件为:硫酸镍质量浓度30 g/L,NaH2PO2.H2O质量浓度30 g/L,pH值4.5～4.8,缓冲剂浓度为20 g/L,稳定剂浓度为0.8 mg/L,络合剂A浓度为8 mL/L,络合剂B浓度为18 g/L,温度为80℃。Ni含量为30%Ni/TiH2复合粉体镀镍后,开始释氢温度比镀镍前提高300℃,同时释氢速率也得到明显减缓。