氢化丁腈橡胶的特殊品种及应用

为进一步提高氢化丁腈橡胶的性能,原材料开发商研制生产了包括低温氢化丁腈橡胶、耐热氢化丁腈橡胶、易加工氢化丁腈橡胶、丙烯酸盐增强氢化丁腈橡胶、氢化羧基丁腈橡胶和氢化丁腈橡胶/塑料共混胶等一系列特殊品种。     

氢化丁腈橡胶共混改性的技术进展

氢化丁腈橡胶是一种新型的综合性能优异的橡胶 ,目前已在许多特种橡胶制品上获得了应用。但其价格昂贵 ,因而开展氢化丁腈橡胶与其它聚合物的共混改性是十分重要的 ,既可降低成本 ,也可赋予共混物优异的性能。本文综述了氢化丁腈橡胶与塑料的共混、氢化丁腈橡胶的增强改性以及氢化丁腈橡胶与其它橡胶共混改性的技术进展。     

硫化氢腐蚀丁腈橡胶的机理

探讨了硫化氢气体及其饱和水溶液对丁腈橡胶性能的影响,采用吉布斯函数验证了硫化氢对丁腈橡胶中残留氧化锌腐蚀的可能性,并通过红外光谱定性和定量分析了硫化氢对丁腈橡胶大分子的腐蚀行为。结果表明,硫化氢的腐蚀会降低丁腈橡胶的物理机械性能;硫化氢气体并不能腐蚀丁腈橡胶中的氧化锌,只有在发生水解后反应才能自发进行;硫化氢气体及其饱和水溶液均能与丁腈橡胶主链中的碳碳双键及侧基氰基发生反应,在硫化氢气体中以双键腐蚀为主,在硫化氢饱和水溶液中则以氰基腐蚀为主,其中腐蚀氰基时为一次加成和二次加成反应。     

氢化丁腈橡胶的加工技术与应用进展

综述了氢化丁腈橡胶的硫化和老化体系的研究进展,并总结了氢化丁腈橡胶在复合材料中的应用进展,指出了我国氢化丁腈橡胶的发展前景。     

粉末氢化丁腈橡胶的制备及其在PVC中的应用

本文采用水和肼法对丁腈胶乳进行加氢,通过凝聚法制备了粉末氢化丁腈橡胶(PHNBR),并开展了粉末氢化丁腈橡胶与粉末丁腈橡胶对PVC的性能的影响对比研究。研究结果表明,加入粉末橡胶后,材料模量降低,随着粉末氢化丁腈橡胶份数增加,拉伸强度未发生明显变化,材料的断裂伸长率增加,韧性得到提升。由于氢化丁腈橡胶优异的耐老化性能,加入粉末氢化丁腈橡胶的PVC复合材料耐老化性能优于加入粉末丁腈橡胶的PVC复合材料。同时,加入粉末橡胶后,PVC的低温脆性也有一定程度的改善。     

氢化丁腈橡胶的开发研究

阐述了由丁腈橡胶制备氢化丁腈橡胶的研究工艺 ,给出了最佳工艺参数 ,考察了催化剂的活性及选择性 ,测试了氢化丁腈橡胶的IR谱图及分子量和分子量分布 ,评价了氢化丁腈橡胶的物理性能。     

饱和丁腈橡胶的性能及应用

1前言对不饱和的橡胶进行氢化,使橡胶分子中的双键得到饱和,从而达到改性的目的。同样,丁腈橡胶氢化之后,可以改变丁腈橡胶原有的性能特点。德国拜耳公司推出了商品名为Theban的氢化丁腈橡胶新产品。这种产品在结构上保留了丁腈橡胶氰基极性的特点,但主链则是饱和碳氢结构,使氢化丁腈橡胶显示出非常优异的耐油性、耐候性和高温下的耐磨性。从伸长保持50%和耐用的时间关系来看,它的耐热性比丁腈橡胶提高20~30℃。2氢化丁腈橡胶的配合技术氢化丁腈橡胶可用丁腈橡胶的设备进行加工,但是胶料的粘度高,粘性差,容易引起混炼脱辊、起泡、采用减少…     

开发新型的氢化丁腈橡胶

氢化丁腈橡胶(HNBR)是在丁腈橡胶(NBR)的碳一碳双键中加氢产生氢化作用而得氢化丁腈橡胶(HNBR)的各项物理机械性能均要优于丁腈橡胶该文通过对新开发的HNBR进行系统研究和开发．阐述了HNBR的基本特性和与传统的NBR物理机械性能的对比优点。     

开发新型的氢化丁腈橡胶

氢化丁腈橡胶 (HNBR)是在丁腈橡胶 (NBR)的碳 -碳双键中加氢产生氢化作用而得。氢化丁腈橡胶 (HNBR)的各项物理机械性能均要优于丁腈橡胶。该文通过对新开发的HNBR进行系统研究和开发 .阐述了HNBR的基本特性和与传统的NBR物理机械性能的对比优点。     

氢化丁腈橡胶膜片的研制

通过结构设计、主体胶料选择、配方设计和骨架材料选择等研制出了氢化丁腈橡胶膜片。结果表明,与现有丁腈橡胶膜片相比,氢化丁腈橡胶膜片的耐油性和耐高温老化性明显提高,使用寿命明显延长。     

Study of the hydration of CaO powder by gas–solid reaction

Hydration of CaO powders by reaction with water vapor has been studied in isothermal and isobaric conditions. Experimental tests were performed within the temperature range of 70 °C–420 °C and with a water vapor pressure from 5 to 160 hPa by means of a thermogravimetric device. Two powders, exhibiting slight differences in their physical properties, were studied. However, for one of the powders and under some temperature and pressure conditions, the reaction is not complete. The difference of behavior between both CaO powders was interpreted by considering the effect of the morphological properties on the mechanism of growth of Ca(OH)₂.     

The influence of water removal techniques on the composition and microstructure of hardened cement pastes

The removal of water from hardened cement paste for analysis or to arrest ongoing hydration has been reported to affect the composition of hydrated phases and microstructure. The effect that arresting the hydration of hardened cement paste by replacing the pore water with acetone before drying, and by removing the water by freeze, vacuum and oven drying has on the hardened cement paste has been investigated. Two pastes were studied, a cemented iron hydroxide floc where a high proportion of ordinary Portland cement (OPC) had been replaced by pulverised fuel ash, and a pure hydrated OPC. The results showed that none of the water removal techniques caused any major deterioration in the composition and microstructure of the hardened cement pastes studied, but the pores appeared better preserved after arresting hydration using acetone quenching. Freeze drying appeared to cause more cracking of the microstructure than the other water removal techniques.     

Quantification of Phospholipids Classes in Human Milk

Phospholipids are integral constituents of the milk fat globule membranes and they play a central role in infants’ immune and inflammatory responses. A methodology employing liquid chromatography coupled with evaporative light scattering detector has been optimized and validated to quantify the major phospholipids classes in human milk. Phospholipids were extracted using chloroform and methanol and separated on C18 column. Repeatability, intermediate reproducibility, and recovery values were calculated and a large sample set of human milk analyzed. In human milk, phospholipid classes were quantified at concentrations of 0.6 mg/100 g for phosphatidylinositol; 4.2 mg/100 g for phosphatidylethanolamine, 0.4 mg/100 g for phosphatidylserine, 2.8 mg/100 g for phosphatidylcholine, and 4.6 mg/100 g for sphingomyelin. Their relative standard deviation of repeatability and intermediate reproducibility values ranging between 0.8 and 13.4 % and between 2.4 and 25.7 %, respectively. The recovery values ranged between 67 and 112 %. Finally, the validated method was used to quantify phospholipid classes in human milk collected from 50 volunteers 4 weeks postpartum providing absolute content of these lipids in a relatively large cohort. The average content of total phospholipids was 23.8 mg/100 g that corresponds to an estimated mean intake of 140 mg phospholipids/day in a 4-week old infant when exclusively breast-fed.     

Effect of plasma treatment of polymeric tape carriers on wetting behaviour of aqueous ceramic tape casting slurry

Due to environmental and health aspects, aqueous ceramic slurries are preferred to traditional organic solvent systems in tape casting. An important obstacle associated with the high surface energy of water is poor wetting of aqueous ceramic slurries on polymeric tape carriers. Therefore, we measured the contact angles of an aqueous epoxy-based ceramic slurry on polyethylene terephtalate (PET), polypropylene (PP), polymethyl methacrylate (PMMA), and aluminium-coated polyethylene terephtalate (PET-Al) films and investigated approaches to improving their wetting. We evaluated the effect of plasma treatment of the tape carrier surface on the wetting behaviour and compared it with the effect of adding non-ionic amphiphilic surfactants to the ceramic slurry. The treatment of the tape carrier surface by low-temperature plasma substantially improved the wetting behaviour of aqueous ceramic slurry. The lowest contact angle of 31° was obtained on the PET film. Although the addition of non-ionic surfactants improved both the wetting behaviour of the slurry and the detachment of the polymeric carrier from the ceramic tape even better than the plasma treatment of the carrier surface did, the plasma-treated carriers still present a useful alternative to the surfactants. In the case of the plasma-treated PET carrier the surfactants could be fully eliminated and potential drawbacks related to the use of surfactants could be prevented.     

The hydration of reactive cement-in-polymer dispersions studied by nuclear magnetic resonance

The behaviour of two novel cement-in-polymer (c/p) dispersions, namely cement-in-poly(vinyl acetate) and cement-in-poly(vinyl alcohol) upon exposure to water at room temperature was investigated by a combination of various NMR methods. The swelling, cracking, and the water ingress were monitored non-destructively using ¹H single point imaging. The hydration of the cement matrix was investigated using ²⁹Si NMR whilst ¹³C CPMAS NMR spectra allowed the quantification of the kinetics of the hydrolysis reaction of poly(vinyl acetate) into poly(vinyl alcohol). The polymer controls the rate of water ingress and swelling which in turn determines the behaviour of the c/p dispersions upon exposure to water. For the cement-in-poly(vinyl alcohol), the rates of water ingress and swelling are much faster than the hydration of the clinker whilst for the cement-in-poly(vinyl acetate) the slow rates of the two processes allow the formation of a cementious matrix which assures the stability of the sample.     

Effect of carbonation on the hydro-mechanical properties of Portland cements

We evaluate experimentally the effect of carbonation on the hydro-mechanical properties of Portland cement. Samples were carbonated at 90 °C and 28 MPa under wet supercritical CO₂. Two types of carbonation features were achieved, either the samples were homogeneously carbonated or they displayed sharp carbonation fronts. Using a tri-axial apparatus, the static elastic moduli and the mechanical strength were measured at in-situ pressure conditions (28 MPa) and showed a degradation of the mechanical properties of the samples where a carbonation front prevailed. Water and gas permeabilities were measured and showed that the samples with a carbonation front exhibit a stress sensitive permeability. P and S elastic wave velocities were measured to evaluate dynamic (ultrasonic range, 1 MHz) elastic moduli. The use of an effective medium theory approach enabled us to characterize the density and distribution of cracks within the samples. This approach outlines that the samples which developed a carbonation front were damaged.     

Assessment of the long-term stability of cementitious barriers of radioactive waste repositories by using digital-image-based microstructure generation and reactive transport modelling

Cement-based grout plays a significant role in the design and performance of nuclear waste repositories: used correctly, it can enhance their safety. However, the high water-to-binder ratios, which are required to meet the desired workability and injection ability at early age, lead to high porosity that may affect the durability of this material and undermine its long-term geochemical performance.In this paper, a new methodology is presented in order to help the process of mix design which best meets the compromise between these two conflicting requirements. It involves the combined use of the computer programs CEMHYD3D for the generation of digital-image-based microstructures and CrunchFlow, for the reactive transport calculations affecting the materials so simulated. This approach is exemplified with two grout types, namely, the so-called Standard mix 5/5, used in the upper parts of the structure, and the “low-pH” P308B, to be injected at higher depths.The results of the digital reconstruction of the mineralogical composition of the hardened paste are entirely logical, as the microstructures display high degrees of hydration, large porosities and low or nil contents of aluminium compounds.Diffusion of solutes in the pore solution was considered to be the dominant transport process. A single scenario was studied for both mix designs and their performances were compared. The reactive transport model adequately reproduces the process of decalcification of the C-S-H and the precipitation of calcite, which is corroborated by empirical observations. It was found that the evolution of the deterioration process is sensitive to the chemical composition of groundwater, its effects being more severe when grout is set under continuous exposure to poorly mineralized groundwater. Results obtained appear to indicate that a correct conceptualization of the problem was accomplished and support the assumption that, in absence of more reliable empirical data, it might constitute a useful tool to estimate the durability of cement-based structures.     

Experimental determination of the effective anionic charge density of polycarboxylate superplasticizers in cement pore solution

The specific anionic charge density of polycarboxylate superplasticizers can be determined experimentally by titration with a cationic polyelectrolyte. In this study, the anionic charge densities of several polycarboxylates based on methacrylate ester chemistry were measured in aqueous solution at pH 7 and 12.6, resp., and in cement pore solution. The anionic charge of the polycarboxylates increases with increasing pH value as a result of deprotonation of the carboxylate groups in the polymer backbone. Addition of Ca²⁺ ions generally causes a decrease of the anionic charge density. The reduction in anionic charge varies and depends on the architecture of the polycarboxylate. The effect results from the binding of calcium ions by the carboxylate groups, both through complexation and counter-ion condensation. Consequently, the effective anionic charge density of polycarboxylates in cement pore solution can differ significantly from the charge density which is calculated based on the chemical composition. Generally the -COO⁻ functionality may coordinate Ca²⁺ as a monodentate or bidentate ligand. The type of coordination depends on the steric accessibility of the carboxyl group. In PC molecules possessing high side chain density, the -COO⁻ group is shielded by the side chains and coordinates as bidentate ligand, producing a neutral Ca²⁺-PC complex. Accordingly, this type of PC shows almost no anionic charge anymore in cement pore solution. In PCs possessing high amount of -COO⁻, Ca²⁺ is coordinated monodentate, resulting in an anionic complex. Consequently, this type of PC shows significant anionic character in pore solution. Its adsorption behaviour is determined by a gain in enthalpy which derives from the electrostatic attraction between the PC and the surface of cement. This way, by utilizing the relatively simple method of charge titration, it is possible to assess the electrostatic attraction which, besides entropy gains, is the driving force behind the adsorption of polycarboxylates on the cement surface and thus determines their effectiveness as dispersing agent. The findings are generally applicable to other anionic admixtures used in cement.     

Influence of bleed water reabsorption on cement paste autogenous deformation

The effects of bleed water reabsorption and subsequent early age expansion on observed autogenous deformation are investigated in this research. Bleeding was induced by varying superplasticizer and shrinkage-reducing admixture dosages and by increasing the water-to-cement ratio. This research revealed that significant early age expansion occurs with increasing chemical admixture dosages and higher water-to-cement ratios, as expected, due to increasing bleeding of those samples. When samples were rotated, negligible early age expansion was observed. Thus, bleed water reabsorption is shown to be the primary mechanism causing initial expansion in sealed autogenous deformation samples. Thermal dilation and ettringite growth appear to have a minimal influence on the observed expansion. Rotating the samples during setting eliminates the potential for bleed water reabsorption and is recommended for all autogenous deformation testing.