Hardness measurements of silicone rubber and polyurethane rubber cured by ionizing radiation

This work investigates the hardness of both silicone rubber and polyurethane rubber cured by ionizing radiation. Shore A hardness is used to characterize the subject elastomers in relation to the crosslinking process. Various formulations of both materials have been investigated in order to achieve the optimum cure conditions. A small amount of a chemical curing agent has been incorporated in some formulations in order to reduce the required dose to achieve full cure conditions. Silicone rubber improved in hardness with increasing absorbed dose, whereas hardness remained constant over a broad range of absorbed doses for polyurethane rubber.     

Influence of reversion on adhesion in the rubber-to-metal vulcanization-bonding process

The vulcanization bonding process is used in a growing number of industrial applications where rubber-to-metal bonded assemblies are needed. The complexity of this process lies in the fact that the vulcanization of the rubber and curing of an adhesive previously coated on the metallic surface have to take place simultaneously during a single molding step.In the present work, we present an instrumented molding device allowing the production of adhesion peeling test samples under well controlled curing temperature cycles. Tests performed on a model natural rubber compound with a commercial adhesive system show that, for high cure temperatures, the quality of the rubber-to-metal bonding obtained is significantly reduced. The decrease of the peeling energy appears to be inversely proportional to the reversion undergone by the rubber during cure. Such a result points out the necessity of taking into account this phenomenon for optimization of the vulcanization bonding process.     

三元乙丙橡胶/蒙脱土纳米复合材料制备中硫化体系的比较

采用了熔融插层和两种硫化体系硫磺 促进剂和过氧化物体系制备了三元乙丙橡胶 蒙脱土纳米复合材料 ,并将这两种体系形成的纳米复合材料进行了形态、力学性能和光学性能的比较 ,同时采用Flory Rehner方程对它们的硫化行为进行了评价 .X射线衍射 (XRD)、透射电镜 (TEM)、力学性能和光学性能的测试结果表明 ,由硫磺硫化体系制备的纳米复合材料为不透明和剥离型 .其原有的d0 0 1 衍射峰消失 ,有序层被剥离成 10 0～ 2 0 0nm的片层均匀分散在EPDM基体中 ,其力学性能有了极大的提高 ;而过氧化物体系制备的纳米复合材料为半透明和插层型 .对两种体系的硫化行为的评价结果表明 ,随着有机蒙脱土加入量的增加 ,硫磺 促进剂硫化体系的t90 延长 ,交联密度减小 ,最大 最小转矩也变小 ;而过氧化物硫化体系的相应值却变化不大     

Effect of Ground Rubber Powder on Properties of Natural Rubber

Ground rubber powder (GRP) with three different sizes was incorporated into nature rubber matrix with different loading. Cure characteristics, swelling behaviour, crosslink density, tensile fractured surface, and mechanical properties have been studied. Based on the cure characteristics, it is evident that the processability of the rubber compounds has not changed obviously with the different GRP loading. The introduction of GRP in virgin rubber leads to the increase in swelling degree and the decrease in crosslink density. Tensile strength, hardness and abrasion resistant deteriorate with the increase of GRP loading, but the tear resistance gets better. If the ground rubber particles are smaller, the properties are more similar to the virgin rubber. Because of the phase separation of the GRP and matrix, the properties get worse with the bigger ground rubber powder.     

The effect of grass fiber filler on curing characteristics and mechanical properties of natural rubber

Natural rubber is reinforced with a novel type of grass fiber (Cyperus Tegetum Rox b). The effects of fiber loading of different mesh sizes on curing characteristics and mechanical properties of grass fiber filled natural rubber composite are studied. Since 400 mesh grass fiber loaded natural rubber composite shows superior mechanical properties, therefore the effect of silane coupling agent was studied for this particular composite. Here composites were prepared by using water leached grass fiber. Optimum cure time increases with the increase in fiber loading but the change in scorch time is less. The same trend of increase in optimum cure time is observed in the presence of Si69. But the value is higher compared to that of rubber composite without Si69. With increase in the fiber loading, modulus and hardness of the composite increases but tensile strength decreases. The mechanical properties of the composite, namely moduli at 200 and 300% elongation and hardness increase in the presence of Si69 but tensile strength is less compared to that of the composite without Si69. Elongation at break is not much affected due to the presence of Si69. Copyright © 2004 John Wiley & Sons, Ltd.     

The effect of mercapto- and thioacetate-modified EPDM on the curing parameters and mechanical properties of natural rubber/EPDM blends

The vulcanization characteristics of natural rubber (NR)/ethylene-propylene-ethylidenenorbornene (EPDM) rubber blends were studied in the presence of thioacetate-(EPDMTA) or mercapto-modified EPDM (EPDMSH), using oscillating disk rheometer. The effect of both functionalized EPDMs was investigated in unaccelerated-sulfur curing system and accelerated-sulfur curing systems containing 0.4 and 0.8 phr of MBTS. Both EPDMTA and EPDMSH act as accelerator agent in the curing process, as indicated by the higher values of cure rate index and lower values of activation energy of vulcanization. A substantial increase of the crosslink density has been also observed in EPDMSH-modified blends. Both EPDMTA and EPDMSH resulted in an increase in tensile strength, but the best performance has been achieved with EPDMSH, probably because of the increase of crosslink density associated to the reactive compatibilization promoted by the reaction between mercapto groups and rubber matrix. The best ageing resistance has been observed in EPDMTA-modified blends.     

Incorporation of Pigments in TEOS Derived Matrices

Small organic pigments were incorporated in TEOS derived sol-gel layers on glass. The layers were characterised on transparency, lightfastness and pencil hardness. It was found that transparent layers can be made. Pigment loaded layers have a better lightfastness than layers into which dyes are incorporated. As only moderate curing temperatures (160°C) were applied, the organic fraction originating from the organic stabilizer present in the pigment dispersion remains to a large extent in the layer. Therefore the pencil hardness decreases with the amount of stabilizer used to disperse the pigment particles. The type of pigment has no influence on the pencil hardness.     

Interpreting the signal from a localized fluorescence sensor: a study by angle-resolved XPS and dynamic SIMS

Angle-resolved X-ray photoelectron spectroscopy (XPS) and dynamic secondary ion mass spectroscopy (DSIMS) experiments were conducted to assess the interactions between a diamine curing agent and a glycidoxysilane-modified glass substrate. This effort was motivated by earlier work, in which a fluorescent probe localized in dilute quantities in the silane layer was used to track the penetration of the resin into the silane layer, as well as the resin cure. XPS and DSIMS experiments were performed on the silane layers immersed only in the resin hardener, providing more detailed information about the concentration profile and structural reorganization within the silane layer due specifically to hardener penetration. Dynamic SIMS spectra reveal the presence of hardener in the layer, as indicated by the strong CN- signal throughout the silane layer thickness. The XPS results indicate the presence of an amine gradient within the top 10 nm of the silane coating, with less amine penetration deeper into the silane layer. The XPS data also suggest some level of anisotropy in the molecular structure of the diamine/glycidoxysilane coating, as revealed by the differences in the relative atomic concentrations and peak positions of the C1s components at two different take-off angles.     

硅橡胶新硫化体系的研究

本文介绍一种硅橡胶新硫化体系,即利用Diels-Alder反应使聚硅氧烷进行交联。所用生胶为含乙烯基的高分子量聚甲基硅氧烷,所用交联剂(硫化剂),即双烯体,系含有环戊二烯基的有机硅化合物。所得弹性体的物理机械性能达到高强度硅橡胶水平。     

Interdiffusion at the interface between poly(vinylpyrrolidone) and epoxy

Electron microprobe analysis (EMP) was used to study interdiffusion in bilayer films of thermoplastic poly(vinylpyrrolidone) (PVP) and a thermoset epoxy. The bilayer films were prepared by casting a stoichiometric mixture of the uncured diglycidyl ether of bisphenol A epoxy (DGEBA) and 4,4′-diaminodiphenylsulfone (DDS) on the PVP film and then curing the system in a two-step process under a nitrogen atmosphere. For the EMP studies, the sulfur signal was used as a probe for DDS, while the nitrogen signal served as a probe for both DDS and PVP. The addition of brominated DGEBA to the conventional DGEBA in a 1: 1 weight ratio allowed the bromine signal to be used as a probe for the epoxy phase. It was found that the interfacial thickness was much larger for the film prepared from low molecular weight PVP than that from high molecular weight PVP. Interdiffusion was suppressed when the initial cure temperature in the two-step cure cycle was 130°C compared to 170°C, in which the first stage of the cure reaction dominated the interdiffusion process. More importantly, it was demonstrated that the diffusion front of the curing agent was located closer to the thermoplastic polymer phase as compared to that of the thermoset polymer in the interface region. This tendency was more significant in the system with the larger interfacial thickness. These results have important consequences on interphase structures and properties. They suggest that crosslinking of the epoxy in the interphase may be suppressed because of an insufficient amount of curing agent and that the not-fully-reacted curing agent in the PVP phase may act to plasticize this phase. © 1997 John Wiley & Sons, Inc.     

Effect of Non-Woven Carbon Nanofiber Mat Presence on Cure Kinetics of Epoxy Nanocomposites

Summary : An investigation was carried out into the cure kinetics of carbon nanofiber (CNF) mat-epoxy nanocomposites, composed of bisphenol-A based epoxy resin and diethylene triamine as a curing agent. It was observed that the rate of cure reaction for CNF mat-epoxy nanocomposites was higher than that for neat epoxy resin at low curing temperatures and the presence of the CNF mat produced the maximum influence at a certain curing temperature and time. At high curing temperature and long curing times, the effect of CNF mat on the cure rate was insignificant. The CNF mat-epoxy composite exhibited somewhat lower value of activation energy than that of the neat epoxy system at the beginning of the curing stage. The weight fraction of CNF mat also affected the cure reaction of epoxy nanocomposites at the same curing temperature. As the amount of CNF mat increased, the cure rate was higher at the same cure time. However, at high CNF mat loading, the cure reaction was retarded since the amount of epoxy and hardener decreased dramatically at high CNF contents together with the hindering effect of the CNF mat on the diffusion of epoxy resin and the curing agent, leading to lower crosslinking efficiency. Although the curing efficiency of epoxy nanocomposites dropped at high CNF mat content, the glass transition temperature (T_g) was still high due to the ultra-high strength of the CNF mat. The cure kinetics of CNF mat-epoxy nanocomposites was in good agreement with Kamal's model.     

The effects of a silane coupling agent on curing characteristics and mechanical properties of bamboo fibre filled natural rubber composites

The effects of a silane coupling agent on curing characteristics and mechanical properties of bamboo fibre filled natural rubber composites were studied. Scorch time, t₂ and cure time, t₉₀ of the composites decrease with increasing filler loading and with the presence of a silane coupling agent, Si69. Mooney viscosity also increases with increasing filler loading but at a similar filler loading shows lower value with the presence of Si69. The mechanical properties of composites viz tensile strength, tear strength, hardness and tensile modulus were also improved with the addition of Si69.     

Alteration of matrix curing characteristics and its role in extension of hydrodynamic equation for predicting viscoelastic properties of nitrile rubber/silica nanocomposites

Neglecting the alteration of matrix curing characteristics in a filled rubber nanocomposite, as a result of possible interactions between the nano filler and curing agent ingredients, leads to inaccurate properties prediction using conventional hydrodynamic equations. In the current work, we present a new empirical extended version of hydrodynamic equation and examine its capability in predicting the viscoelastic properties of NBR/nanosilica system in which the negative influence of the filler on the curing process of the NBR matrix was confirmed through various analyses such as tensile test, rheometry, swelling experiments, and dynamic mechanical analysis. The results showed that the proposed empirical extended model is able to account the contribution of alteration of matrix curing characteristics in changing the composite properties below the filler percolation threshold. It was demonstrated that the extended model provides more accurate prediction of viscoelastic properties of silica‐filled cured NBR nanocomposites above glass transition temperature.     

The nature of the structural gradient in epoxy curing at a glass fiber/epoxy matrix interface using FTIR imaging

The curing process of an epoxide system was studied at the interface formed between a silane-coated glass fiber and an epoxy matrix. The gradient in the structure of the epoxy resin as a result of the cure process at the fiber/matrix interfacial region was monitored by FTIR imaging. For comparison, the epoxy curing at the interface formed between the epoxy resin and (a) an uncoated glass fiber and (b) a polyorganosiloxane (obtained from the silane used for the glass-fiber coating) were also monitored. Chemically specific images of the OH and the H-N-H groups near the interface region were obtained. These images suggest that there is a chemical gradient in the structure of the matrix from the fiber surface to the polymer bulk due to different conversions. The basis of the different kinetics of the curing reactions is a result of amino group inactivation at the interface. This deactivation translates into an off-stoichiometry of the reaction mixture, which is a function of the distance from the surface of the glass fiber.     

Liquid sorption by rubber sheets and evaporation; models and experiments

The sorption of liquid by rubber sheets has been considered as a diffusion process controlled by a constant diffusivity. In spite of the swelling, the thickness of the sheet may be assumed to remain constant for integrating Fick's law as diffusion proceeds. The evaporation of liquid from the rubber is diffusion controlled. No analytical solution can be obtained in general cases. A model is described, based on an explicit method with finite differences, taking into account the diffusivity and rate of evaporation. This model gives results for desorption in good agreement with experiments in the case of motionless air and with stirring. Results with high stirring can also be obtained by analytical solution of Fick's law integrated by taking zero for the concentration of liquid on the rubber faces at the start of the process.     

聚氯乙烯表皮成分对加成型硅橡胶固化的影响

采用流变学方法研究了双组分加成型硅橡胶在不同聚氯乙烯(PVC)表皮上的固化动力学,并利用红外光谱、核磁共振波谱、电感耦合等离子体质谱仪等手段分析了PVC表皮成分,以确定导致双组分加成型硅橡胶不固化的具体原因。 结果表明,PVC表皮中导致硅橡胶不固化的主要元素为P元素。 在固定硅橡胶厚度为1 mm的情况下,当PVC表皮中的P元素质量分数低于3×10^-3%时,浇注在其上的双组分加成型硅橡胶依然能固化;而当PVC表皮中的P元素质量分数超过约2.4×10^-2%时,虽然浇注在其上的双组分加成型硅橡胶的中间层依然能固化,但与PVC表皮接触部分的硅橡胶不固化,且不固化层厚度随P元素质量分数增加而增加。 本文还研究了在P元素质量分数低于3×10^-3%的PVC表皮上,降低硅橡胶厚度至微米级时的固化行为,在P元素质量分数低于3×10^-3%的PVC表皮上,当硅橡胶厚度低于2 μm时,硅橡胶出现不完全固化现象。 双组分加成型硅橡胶在含有P元素的PVC表皮表面的固化行为主要是由硅橡胶样品中铂催化剂总含量及PVC表皮中的P元素含量确定的,同时也会受到双组分加成型硅橡胶反应速率以及铂催化剂、P元素在硅橡胶中的扩散速率的影响。     

The Effect of 3-aminopropyltrimethyoxysilane (AMEO) as a Coupling Agent on Curing and Mechanical Properties of Natural Rubber/Palm Kernel Shell Powder Composites

This research is conducted using palm kernel shell powder (PKS) as filler in natural rubber The effect of 3-aminopropyltrimethoxysilane as coupling agent on composites were studied at different palm kernel shell loading i.e, 0 5, 10, 15 and 20 phr The palm kernel shell was crushed and sieved to an average particle size of 5.53 μm The palm kernel shell filled natural rubber composites were prepared using laboratory size two roll mill The curing characteristics such as scorch time, cure time and maximum torque were obtained from rheometer The palm kernel shell powder filled natural rubber composites were cured at 150^oC using hot press according to their cure time Curing characteristics, tensile properties, rubber-filler interaction and morphological properties of palm kernel shell powder filled natural rubber were studied Scorch time and cure time show reduction but tensile strength, elongation at break, modulus at 100% (M100) and modulus at 300% (M300) increased with the presence of 3-aminopropyltrimethyloxysilane Rubber-filler interaction studies showed that rubber filler interaction in natural rubber filled with palm kernel shell powder improved with incorporation of 3-aminopropyltrimethyoxysilane.     

The sulfur reversion process in natural rubber in terms of crosslink density and crosslink density distribution

Unfilled natural rubber compounds composed of conventional (CV), semi-efficient (SEV), efficient (EV) and sulfur donor (SD) vulcanization systems were heat aged to promote sulfur reversion. Rheometry, hardness, strain-strain characteristics including Mooney-Rivlin analysis, equilibrium solvent swell and Double Quantum (DQ) Nuclear Magnetic Resonance (NMR) were used to monitor crosslink density changes. A loss of crosslink density was observed by rheometry, C₁, equilibrium swelling and by DQ NMR as a function of cure extent. No chain scission reactions were operating in the time/temperature conditions used. All crosslink distributions were unimodal and the network homogeneity followed the order of EV > SD > SEV > CV. The crosslink distribution narrowed during the curing process for the CV and SEV systems. Non-oxidative maturation reactions were advantageous in promoting a more random distribution of crosslinks in the polymer matrix.     

硅橡胶/氟橡胶并用胶的制备及力学性能

硅橡胶和氟橡胶作为国防、航天等重要领域的耐热材料一直被人们青睐,但其有着各自地优缺点且价格昂贵,本文尝试将这两种橡胶制成并用胶以解决氟橡胶不耐低温和加工性差的问题,以期增大其使用温度范围。采用机械共混法制备硅橡胶/氟橡胶并用胶,研究了硅橡胶和氟橡胶的混炼工艺、并用比、共硫化体系和硫化条件对并用胶力学性能的影响。结果表明,当硅橡胶/氟橡胶的质量比为10∶90,共硫化体系为3~#硫化剂/过氧化二异丙苯(DCP),一段硫化温度为170℃、硫化压力为10MPa、硫化时间为30min,二段硫化温度为200℃、硫化时间为6h时,并用胶的力学性能达到最好。     

Utilization of waste tire rubber in hybrid plywood composite panel

The aim of this work was to use waste tire rubber (WTR) in the middle layer of hybrid plywood materials. The effects of four variable parameters, namely, WTR contents (430 and 720 g), resin contents (120 and 160 g/m²), hot pressing (single‐stage and two‐stage), and arrangements of veneer layers on the mechanical, physical, and acoustical properties, were studied. Beech (Fagus orientalis) and alder (Alnus glutinosa) veneers having 1.8‐mm thickness were used in the production of hybrid plywood panels. Rubber layers of 3‐ and 5‐mm thickness were used in the middle layer of plywood samples. To produce plywood panels, single‐stage and two‐stage hot‐pressing processes were used. Bonding of wood layers was performed using 120 and 160 g/m² urea‐formaldehyde resins, and to form the rubber layers and bond them to wood layers, methylene diisocyanate resin (150 g/m²) was used. Overall trend showed that with the increase in rubber content, the physical properties (water absorption, thickness swelling, and sound absorption) of the manufactured panels were improved, while the mechanical properties (modulus of rapture, modulus of elasticity, and impact strength) of the panels were reduced. Both physical and mechanical performances of plywood panels were improved with increase in resin content. An increase in the WTR content in plywood improved the composite's acoustical property. The production process of the wood/rubber plywood did not significantly affect their properties. The order of improvement in the physical properties of the panels is rubber content > resin content > arrangement of layers > pressing process. Copyright © 2015 John Wiley & Sons, Ltd.