Prevention of Hydrosilation Cure Inhibition in a Polysiloxane Adhesive by Surface Oxidation

For a variety of reasons epichlorohydrin-ethylene oxide (ECO)-based compounds, in the form of rain erosion boots or sleeves, are bonded to aircraft radomes using a hydrosilation-cured RTV polysiloxane adhesive. Unfortunately, cure of the adhesive can be completely inhibited by unreacted vulcanizing agent and/or ECO cure by-products. We have earlier shown that this inhibition can be prevented by treating the ECO surface with hydrogen peroxide to oxidize the hydrosilation catalyst poisons to a harmless state. In this study we have used spectroscopic techniques to monitor the hydrosilation reaction kinetics and in turn to identify the poison, define the poisoning level and monitor the poison removal by hydrogen peroxide treatment. The degree of poison removal is also correlated with adhesive bond strength using a 180°; peel test. The critical poison in the system was excess ECO vulcanizing agent which can be completely removed from the surface using a 30 vol. % H₂O₂ treatment for 30 minutes as long as the initial vulcanizing agent concentration is 1 p.p.h. or less.     

Silicone acrylates through the hydrosilation of polyacryloyloxy functional monomers with copolymers of dimethyl and hydrogen methylsiloxanes

Silicone acrylates, as possible electron beam (EB) curable release coatings for paper, were prepared by the platinum-catalyzed hydrosilation of polyacryloyloxy functional monomers with copolymers of dimethylsiloxane and hydrogen methylsiloxane (PDMHMS). The hydrosilation of either 1,6-hexanediol diacrylate (HDDA) or trimethylolpropane triacrylate (TMPTA) with PDMHMS occurs to only one of the 2 or 3 available olefinic groups, respectively, as long as excess monomer is present. The amount of excess monomer needed to prevent gelation during hydrosilation or subsequent storage in excess of 1 month appears to be dependent on the hydrogen methylsiloxane content of the PDMHMS. A release coating having excellent cohesive and adhesive strength on paper was obtained by the EB curing of the product of hydrosilation of TMPTA with a PDMHMS containing 4 mol % hydrogen methylsiloxane at a dose-to-cure of 2 Mrad, but the aged release force was excessively high. The poor aged-release performance was likely due to dilution of the dimethylsiloxane content of the coating with excess monomer required to stabilize the silicone acrylate. © 1993 John Wiley & Sons, Inc.     

助硫化剂对过氧化物共硫化NBR／CM的影响

研究了不同助硫化剂对过氧化物共硫化NBR／CM的影响。实验结果表明,助硫化剂S、PDM和Zn（MMA）。均能有效地提高共混物的拉伸强度和撕裂强度;助硫化剂S和TCY均能降低共混物的DIN磨耗体积。     

Investigation of polysiloxanes containing phenylethynyl groups as cross‐linkers of heat‐curable silicone rubber

Hydrosilation‐curing vulcanizates (HCV) and peroxide‐curing vulcanizates (PCV) were prepared respectively by using polysiloxanes containing phenylethynyl groups (PE‐PDMS) as cross‐linkers. The mechanical properties and average molecular weights of effective units (M̄_c) of HCV and PCV were measured. The experimental results show that PE‐PDMS can be used as cross‐linkers of heat‐curable silicone rubber instead of C gum, and when adding suitable amounts of PE‐PDMS, the vulcanizates exhibited good mechanical properties. The tear strength of some vulcanizates reached 30.0 kN/m, the tensile strength 11.7 MPa, the modulus at 100% extension 3.3 MPa, and the permanent deformation is low. PE‐PDMS also has cure retardation to hydrosilation‐cure silicone rubber and thus can prolong the shelf time of stocks. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1554–1557, 2000     

Chemical cleaning of Turkish lignites by leaching with aqueous hydrogen peroxide

Two Turkish lignites (Beypazari and Tunçbilek) were leached with the solutions of hydrogen peroxide in water or in 0.1 N H₂SO₄. The effects of some process parameters, such as concentration, time and temperature, on the removal of ash and sulphur have been investigated. The rate of ash and sulphur removal are relatively high in the first 30 min, but slow after 60 min of the reaction time. Depending on the type of lignite, the maximum reductions ranged from 30 to 70% in ash, from 70 to 95% in pyritic sulphur, and from 42 to 58% in total sulphur. A relatively small reduction (a maximum of 25%) was estimated for organic sulphur. The optimum process conditions were established as a hydrogen peroxide concentration of 15 wt.%, a temperature of 30 °C and a leaching time of 60 min. High peroxide concentration or high temperature did not result in an appreciable further reduction in ash and sulphur. Due to partial dissolution or oxidation of the lignites, some organic material losses occurred but no heating value loss was estimated. An overall kinetic approach was also applied for pyritic sulphur removal, and the conversion data were analyzed by using both homogenous and heterogeneous reaction models.     

冷法H_2O_2氧化制备马铃薯淀粉粘合剂及改性研究

在室温下,以马铃薯淀粉为原料,双氧水为氧化剂,制备出了马铃薯淀粉粘合剂.探讨了氧化剂用量、催化剂用量、糊化剂用量、氧化时间、糊化时间、粉水比、络合剂用量对粘合剂性能的影响,以粘度和初粘力为评价指标,通过L18(37)正交试验确定制备淀粉粘合剂的最佳条件为:m(水)∶m(马铃薯淀粉)=5∶1,双氧水1.3 mL,硫酸亚铁0.2 g,NaOH为3.0 g,氧化时间90 min,糊化时间30 min,硼砂0.3 g.并以添加聚乙烯醇进行接枝改性,提高其干燥时间和初粘力,实验得到添加量为5%时效果最好.     

Hydrogen‐containing silicone resin as the crosslinking agent of heat‐curable silicone rubber

The hydrosilation‐cured vulcanizates (HCV) of silicone rubber were prepared by using hydrogen‐containing silicone resin (HSR) as the crosslinking agent. The influences of both the amount and structure of HSR on hydrosilation‐curing silicone rubber (HCSR) were discussed. The results indicate that HSR is a good crosslinking agent for HCSR. The tensile strength, tearing strength, elongation at break, and hardness of the vulcanizates can reach 9.6 MPa, 37.8 kN/m, 870% and 56 SHA, respectively. The aging stability of the vulcanizates can be improved greatly. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3066–3069, 2003     

Removal Characteristics of Organic Pollutants in Sewage Treatment by a Pre-Coagulation,Ozonation and Ozone/Hydrogen Peroxide Process

The applicability of a sequential process of ozonation and ozone/hydrogen peroxide process for the removal of soluble organic compounds from a pre-coagulated municipal sewage was examined. 6–25% of initial T-COD_Cr was removed at the early stage of ozonation before the ratio of consumed ozone to removed T-COD_Cr dramatically increased. Until dissolved ozone was detected, 0.3 mgO₃/mgTOC₀ (Initial TOC) of ozone was consumed. When an ozone/hydrogen peroxide process was applied, additional COD_Cr was removed. And we elucidated that two following findings are important for the better performance of ozone/hydrogen peroxide process; those are to remove readily reactive organic compounds with ozone before the application of ozone/hydrogen peroxide process and to avoid the excess addition of hydrogen peroxide. Based on these two findings, we proposed a sequential process of ozonation and multi-stage ozone/hydrogen peroxide process and the appropriate addition of hydrogen peroxide. T-COD_Cr, TOC and ATU-BOD₅ were reduced to less than 7 mg/L, 6 mgC/L and 5 mg/L, respectively after total treatment time of 79 min. Furthermore, we discussed the transformation of organic compounds and the removal of organic compounds. The removal amount of COD_Cr and UV₂₅₄ had good linear relationship until the removal amounts of COD_Cr and UV₂₅₄ were 30 mg/L and 0.11 cm^?1, respectively. Therefore UV₂₅₄ would be useful for an indicator for COD_Cr removal at the beginning of the treatment. The accumulation of carboxylic acids (formic acid, acetic acid and oxalic acid) was observed. The ratio of carbon concentration of carboxylic acids to TOC remaining was getting higher and reached around 0.5 finally. Removal of TOC was observed with the accumulation of carboxylic acids. When unknown organic compounds (organic compounds except for carboxylic acids) were oxidized, 70% was apparently removed as carbon dioxide and 30% was accumulated as carboxylic acids. A portion of biodegradable organic compounds to whole organic compounds was enhanced as shown by the increase ratio of BOD/COD_Cr.     

Electrochemical oxidation of Crystal Violet in the presence of hydrogen peroxide

BACKGROUND: The combination of electrochemical oxidation using a Ti/RuO₂? IrO₂ anode with hydrogen peroxide has been used for the degradation of Crystal Violet. The effect of major parameters such as initial pH, hydrogen peroxide concentration, current density, electrolyte concentration and hydroxyl radical scavenger on the decolorisation was investigated. RESULTS: The decolorisation rate increased with initial pH and hydrogen peroxide concentration, but decreased with electrolyte and radical scavenger concentration. The decolorisation rate increased with current density, but the increase became insignificant after current density exceeded 47.6 mA cm^?2. On the other hand, hydrogen peroxide decomposition rate increased with initial pH and current density, but decreased with electrolyte and radical scavenger concentration. The amount of hydrogen peroxide decomposed during 30 min reaction increased linearly with hydrogen peroxide dosage. The main intermediates were separated and identified by gas chromatography–mass spectrometry (GC–MS) technique and a plausible degradation pathway of Crystal Violet was proposed. At neutral pH, the electrochemical process in the presence of hydrogen peroxide was more efficient than that in the presence of Fenton's reagent (electro‐Fenton process). CONCLUSION: The anodic oxidation process could decolorise Crystal Violet effectively when hydrogen peroxide was present. Almost complete decolorisation was achieved after 30 min reaction under the conditions 2.43 mmol L^?1 hydrogen peroxide, 47.6 mA cm^?2 current density and pH₀ 7, while 62% COD removal efficiency was obtained when the reaction time was prolonged to 90 min. Copyright © 2010 Society of Chemical Industry     

Surface modification of UHMWPE fibers

Ultrahigh molecular weight polyethylene (UHMWPE) fibers have a high specific strength, high specific modulus, and outstanding toughness, but their poor adhesive properties has limited their use for composite material applications. In this research, the effects of chemical etching on the surface chemistry and topography have been explored using chromic acid, potassium permanganate, and hydrogen peroxide etching. The smooth surface observed on the as-received fiber was rich in ether and/or hydroxyl oxygen. This smooth surface resulted from the presence of an outer layer, a weak boundary layer, that was removed by all the etchants. A fibrillar structural hierarchy was revealed beneath this outer layer and the fiber was relatively unchanged by further etching. Chromic acid, the strongest etchant studied, produced a rough and oxidized UHMWPE surface with both ether and carbonyl oxygen. The combination of outer layer removal, roughness, and changes in oxygen bonding helps explain the improved adhesion on chromic acid etching in spite of the reduction in surface oxygen. Neither hydrogen peroxide nor potassium permanganate etching roughened or oxidized the surface to a great extent and neither yielded improved adhesion. © 1994 John Wiley & Sons, Inc.     

混炼硅橡胶的配合技术(九)

介绍了用2，4-二氯过氧化苯甲酰作硫化剂的挤出成形用混炼硅橡胶（包括低硬度混炼硅橡胶、不粘连芯线的混炼硅橡胶、高电气强度电线用混炼硅橡胶）的配制方法及改进其加工和表面性能的方法；同时，还介绍了用甲基苯甲酰类过氧化物作硫化剂时改进混炼硅橡胶表面性能的方法（包括添加含氢硅油、硅藻土、二烷基过氧化物或过氧化苯甲酰以及细化硫化剂粒子）。     

过氧化物硫化体系对AEM/三元尼龙TPV性能的影响

采用过氧化物F40和DCP两种类型的硫化体系,同比改变过氧化物硫化体系中助硫化剂和硫化剂的用量,探究硫化剂添加量对AEM/PAM15动态硫化体系的影响。结果表明,随硫化剂添加量的增加,硫化程度先增加后减小;F40与DCP相比,对材料的性能影响相似,但DCP硫化过程中伴有刺激性气味且速率过快;动态硫化后的TPV[1]与硫化前相比,多了一个界面玻璃化温度,显示了两种基料良好的结合性能。     

Reactive bonding of natural rubber to metal by a nitrile–phenolic adhesive

The mechanism of adhesive bonding of rubber to metal using an interlayer of bonding agent (adhesive) is discussed with respect to various physical and chemical events such as adsorption at the metal surface, chemical crosslinking within the adhesive, interdiffusion, and formation of interpenetrating networks at the rubber–adhesive interface. An investigation on the peel strength of a natural rubber (NR)–adhesive–metal joint, made by vulcanization bonding using nitrile–phenolic adhesive containing various concentrations of toluene diisocyanate–nitrosophenol (TDI–NOP) adduct, is presented. A single‐coat adhesive, consisting of a p‐cresol phenol formaldehyde resin, nitrile rubber (NBR), and vulcanizing agents in methyl ethyl ketone solvent, was selected for the study. Considerable improvement in the peel strength was obtained by the incorporation of TDI–NOP adduct into the nitrile–phenolic adhesive. The peel strength increases as the concentration of TDI–NOP adduct in the adhesive composition increases, then levels off with a transition from interfacial failure to cohesive tearing of rubber. The peel strength improvement is believed to be attributed to the interfacial reactions between the bonding agent and natural rubber, when TDI–NOP adduct is incorporated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2597–2608, 2001     

相转移催化氧化体系在燃料油脱硫中的应用

介绍了以过氧化氢为氧化荆的相转移催化氧化脱硫研究现状.对过氧化氢/有机酸/季铵盐体系、过氧化氢/杂多酸/季铵盐体系和过氧化氢/合成相转移催化剂体系在脱除燃料油中噻吩、苯并噻吩、二苯并噻吩等方面的应用作了综述.指出了过氧化氢/合成相转移催化剂体系是燃料油深度脱硫的一个重要研究方向.     

The role of activated carbon as a catalyst in GAC/iron oxide/H2O2 oxidation process

The catalytic properties of granular activated carbon (GAC) in GAC/iron oxide/hydrogen peroxide (H₂O₂) system was investigated in this research. Batch experiments were carried out in de-ionized water at the desired concentrations of ethylene glycol and phenol. Rate constants for the degradation of hydrogen peroxide and the formation rate of iron species were determined and correlated with mineralization of ethylene glycol at various GAC concentrations. The observed first order degradation rate of hydrogen peroxide in the absence of iron oxide and organic matter increases linearity with the increasing of the GAC concentration. The decomposition rate of hydrogen peroxide was suppressed significantly as the solution pH became acidic or by reducing the surface area of the GAC. The reduction of the surface area was obtained by loading an organic compound (such as phenol) on the GAC or by using the oxidizing agent (H₂O₂). The addition of both chemicals, phenol and H₂O₂, affects mainly the surface area of the small pores, resulting in reducing the catalytic activity inside the micropores.The catalytic properties of the GAC were used to accelerate the formation rate of the ferrous ions, which is known in the literature to be the limiting rate reaction in the classic Fenton like reagent. It was shown that the ethylene glycol mineralization rate was increased by more than 50%.Finally, optimization of the GAC consumption leading to the fastest mineralization of the ethylene glycol, resulting in decreasing of the decomposition rate of H₂O₂ while enhancing the generation rate of ferrous ions.     

Properties of natural rubber/recycled ethylene–propylene–diene rubber blends prepared using various vulcanizing systems

The role of various vulcanizing systems on the curing characteristics, mechanical properties, morphology and dynamic mechanical analysis of natural rubber and recycled ethylene–propylene–diene rubber blends was investigated. Accelerated sulfur-vulcanizing systems (semi-EV and EV), peroxide, and mixed sulfur/peroxide-vulcanizing systems (semi-EV/peroxide and EV/peroxide) were observed and compared. The blends were processed on a two-roll mill, and a fixed amount of carbon black was also incorporated. Amongst the blends, accelerated sulfur-vulcanizing systems exhibited higher torques, state of cure, tensile strength and elongation-at-break, in comparison with the peroxide-vulcanizing system, whereas the tensile modulus, hardness and cross-link density showed lower trend. In the mixed sulfur/peroxide-vulcanizing systems, it showed intermediate behavior to the individual sulfur- or peroxide-vulcanizing systems. This was associated to the interference of peroxide during the cross-linking formation. SEM micrographs of semi-EV-vulcanizing system exhibited more roughness and cracking path indicating that higher energy was required towards the fractured surface. The high cross-link density observed from the swelling study could be verified from the storage modulus (E′) where peroxide vulcanized blends provided a predominant degree of cross-linking followed by semi-EV, semi-EV/peroxide, EV and EV/peroxide-vulcanizing systems, respectively. The glass transition temperature (T _g) depicted at maximum peak of mechanical loss factor (tanδ _max), indicating that semi-EV-vulcanizing system showed highest T _g value. The T _g values can be ordered as semi-EV > peroxide > semi-EV/peroxide > EV > EV/peroxide-vulcanizing systems. The T _g of rubber vulcanizates can be increased due to the restriction of molecular movement such as cross-link density.     

Phenol photodegradation with oxygen and hydrogen peroxide over TiO2 and Fe-doped TiO2

Photodegradation of phenol was investigated with two types of oxidant agents in water, oxygen and hydrogen peroxide, at two different reaction pH with a series of nanosized iron-doped anatase TiO₂ catalysts with different iron contents. The catalysts have been prepared by a sol–gel/microemulsion method. Firstly, iron-doped titania catalysts were studied with respect to their activity behavior when oxygen was used as oxidant agent in the photocatalytic degradation of aqueous phenol in comparison with un-doped reference catalysts. Secondly, two catalysts (TiO₂ and 0.7 wt.% Fe-doped TiO₂) were selected to extend the study for the employment of hydrogen peroxide as oxidant at different concentrations and two initial reaction pHs. An enhancement of the photocatalytic activity is observed only for relatively low doping level (ca. 0.7 wt.%) in catalyst calcined at 450 °C preferably using hydrogen peroxide as oxidant agent which is attributable to the partial introduction of Fe³⁺ cations into the anatase structure. Nevertheless, it has been demonstrated that catalyst surface properties can play an important role during phenol photodegradation process on the basis of the analysis of differences found in the photoactivity as a function of reaction pH.     

Modelisation Of Micropollutant Removal In Drinking Water Treatment By Ozonation Or Advanced Oxidation Processes (O3/H2O2)

A simulation program is described, tested and used, to predict micropollutant removal in an ozonation bubble tower with or without hydrogen peroxide addition. To compute the removal efficiency, we need to know the chemical reactivity between organic compounds and oxidant species (molecular ozone and hydroxyl radicals), the ozone mass transfer from the gaseous phase to the liquid phase (k_La) and the hydrodynamic model describing the reactor. In this case, we divide the reactor into three parts (water arrival, air arrival and intermediate zones). Each part is modelled using completely stirred tank reactors in series (CSTR).

In each CSTR, the calculation of oxidant concentrations (O₃, H₂O₂) is made through mass balance equations and a semi-empirical formula which gives hydroxyl radical concentrations as a function both of ozone concentration and the main characteristics of the water to be treated (pH, TOC, alkalinity). Another semi-empirical formula links ozone consumption to the same characteristics.     

The electrocatalytic influence of underpotential lead adsorbates on the reduction of oxygen at glassy carbon electrodes in acid solution

The electrochemical reduction of oxygen and hydrogen peroxide has been investigated on a glassy carbon rotating disk electrode in 0.5 M HClO₄ at various concentrations of Pb²⁺. An overall 2-electron reduction of O₂ to H₂O₂ is found on glassy carbon which, in the presence of Pb²⁺, is positively catalyzed. The electrocatalytic effect can be correlated to an underpotential deposition (UPD) of lead at a limited number of active sites on the glassy carbon surface. The hydrogen peroxide reduction is nearly completely inhibited by the UPD of lead. The observed concentration dependence with respect to Pb²⁺ is in accordance with the Nernstian behaviour of the UPD process.     

A型铸造粘合剂的研究

以聚乙烯醇为主要原料,采用化学改性的方法成功制备了A型铸造粘合剂。研究了甲醛、双氧水和交联剂对铸件性能的影响。结果表明,该粘合剂完全能满足铸造生产,其性能优于合脂油,是节能环保型产品。该粘合剂最大特点是能回用旧砂,回用的比例可达50%。