Influence of hygrothermally degraded polyester-urethane on physical and mechanical properties of chloroprene rubber

The influence of hygrothermally-degraded polyester urethane (HD-PUR) waste on chloroprene rubber (CR) has been studied giving special attention to curing behaviour, mechanical properties and dynamic mechanical behaviour. The presence of primary and secondary amines in HD-PUR, did not increase the cure rate of CR. The mechanical properties of chloroprene vulcanizates were improved upon HD-PUR addition. The strain-induced crystallisation of CR did not show any deviation upon the addition of HD-PUR. Crosslink densities calculated from swelling studies, stress-strain behaviour, and modulus measurements are found to increase upon HD-PUR addition and showed similar trend. The glass transition temperature (T_g) did not show any significant change, with the addition of HD-PUR. Scanning electron microscopic studies have been done in order to have an insight into fracture behaviour of the samples and to analyse the microstructure of the blends.     

Dielectric properties of thermally degraded chloroprene rubber

We performed dielectric measurements on thermally aged carbon-black-filled chloroprene rubber (CR). Primary and secondary processes were observed in unaged and thermally aged CR. The primary process is due to the cooperative motion of chloroprene chains in CR, and the secondary process is due to the local motion of chloroprene chains. For the primary process, the relaxation time slightly increases and symmetric shape parameter of the loss spectrum decreases with increasing aging time. For the secondary process, the relaxation strength decreases with increasing aging time, and reaches zero after 50 h. These changes in the dielectric relaxation parameters are due to the progress of the dehydrochlorination reaction at the chloroprene chains.     

An elastomeric conducting composite based on polyaniline coated nylon fiber and chloroprene rubber

Chloroprene rubber-polyaniline (PANI) coated nylon fiber composites containing PANI powder were prepared by mechanical mixing on a two-roll mill. PANI was synthesized by chemical polymerization of aniline in presence of hydrochloric acid. PANI coated nylon fiber was prepared by in situ polymerization of aniline on nylon fiber. The cure parameters cure kinetics, filler dispersion, mechanical properties, DC electrical conductivity and thermal degradation parameters of the composites were evaluated. Cure rate index and cure reaction constants indicated that the rate of cure reaction changes on filler addition. Filler addition at higher loadings led to agglomeration. The tensile strength and modulus values increased suggesting a reinforcement effect. The conductivity, thermal characteristics and thermal degradation kinetic parameters are also presented.     

Gas permeation properties of ethylene vinyl acetate–silica nanocomposite membranes

The effect of silica nanoparticles on the gas separation properties of ethylene vinyl acetate (EVA) copolymer containing 28% vinyl acetate has been investigated. The EVA and hybrid EVA–silica membranes were prepared via thermal phase inversion method. Silica nanoparticles prepared by hydrolysis of tetraethylorthosilicate (TEOS), through the sol–gel mechanism. The prepared membranes were characterized using FT-IR, SEM, DSC and XRD methods. FT-IR and SEM results indicated the nanoscale dispersion of silica particles in polymer matrix. As confirmed by XRD and DSC analyses, increasing the silica content enhances the amorphous regions significantly. Gas permeation of EVA–silica nanocomposite membranes with silica contents of 5, 6 and 10 wt.% was studied for N₂, O₂, CO₂ and CH₄ single gases at pressures of 4, 6 and 8 bar. The obtained results suggest a significant increase in permeability of all gases and an increase in CO₂/N₂ and CO₂/CH₄ gases selectivities upon increasing the silica content. The possible reasons for such behavior were stated and discussed. The pressure dependence of the gas permeabilities of the membranes was also investigated.     

Ageing mechanism and mechanical degradation behaviour of polychloroprene rubber in a marine environment: Comparison of accelerated ageing and long term exposure

Polymers are widely used in marine environments due to their excellent properties and good weathering resistance. Despite this extensive use, their long term behaviour in such an aggressive environment is still not well known. To assess the polymer durability within reasonable durations, it is essential to perform accelerated ageing tests to accelerate the degradation kinetics but without any modification of the degradation process. This study therefore proposes and validates accelerated ageing tests to study marine ageing of a silica-filled chloroprene rubber (CR) used for offshore applications. Several accelerated ageing protocols are investigated for temperatures ranging from 20 to 80 °C in renewed natural seawater. The ageing consequences are characterized using physical measurements (FTIR, solid state NMR) and mechanical testing based on monotonic tension tests. Instrumented micro-indentation tests are also employed, in order to describe accurately the ageing gradients through sample thickness. The measurements obtained on the samples cut from accelerated specimens are compared to those obtained from the topcoat of an offshore flowline aged under service conditions for 23 years. For both kinds of specimens, polychloroprene develops rapid material changes most clearly represented by a considerable increase in stiffness, which allows the accelerated ageing protocols to be validated.     

Investigation of influence of constant magnetic fields on the structure and properties of chloroprene latex based films

The influence of constant magnetic fields with induction up to 0.6 T on the supermolecular structure and properties of chloroprene latex based films was investigated. The method used were X-ray analysis, volume resistivity measurement, light microscopy and photocurrent measurement in polarized light, mechanical properties of films and density measurements. It was found that the changes in magnetic field induction have significant effects on the film structure and all properties investigated. The observed dependences may be connected to different ratios between magnetic field induction, which acts as an orientating force, and the material's elastic forces, which act in a disorientating manner.     

Correlation between mechanical and electrical properties for assessing the degradation of ethylene propylene rubber cables used in nuclear power plants

The correlation among the indenter modulus, the elongation-at-break, and the breakdown-voltage strength for the ethylene propylene rubber (EPR) cables subjected to long-term thermal aging and high-temperature water submerging conditions were investigated in this work. The mechanical and electrical limits of EPR insulation material were evaluated by using an indenter modulus, with non-destructive advantage, to monitor the cable condition and to assess its remaining life. Results show that it is plausible to use indenter modulus to monitor the EPR cables for the condition approaching the end of cable service life. Testing parameters on indenter modulus, including indenter diameter, penetration speed, and penetration depth, were studied for monitoring cable degradation condition. Finally, this paper discusses the cable acceptance criteria under thermal and moisture-related aging environments. Results show that the breakdown-voltage strength is a better acceptance criterion for assessing the cable aging condition in a wet environment. While, if the cable is located in a high temperature environment, the elongation-at-break is a better criterion.     

消解乳化-火焰原子光谱法测定氯丁橡胶中的钠钾镁锌

用消解乳化技术处理氯丁橡胶样品,即先用浓硝酸消解样品,再用乙醇 甲基异丁基酮混合溶剂溶解消解产物并用乳化剂TritonX 100或OP乳化成乳浊液。以原子吸收法测定镁、锌,以原子发射法测定钠、钾,建立了快速测定氯丁橡胶中钠、钾、镁、锌的火焰原子光谱法(FAS)法。分别以硝酸钾、Ba2 作为钠、钾的消电离剂。对样品处理方法、溶剂及乳化剂的选择、试液与空白溶液粘度的一致性、各种干扰及检出限进行了考察。测定结果的相对标准偏差<1.5%,加标回收率99.5%～103 0%。     

Fourier-transform rheology of unvulcanized styrene butadiene rubber filled with increasingly silanized silica

ABSTRACT

Silica as one the most important fillers for rubber material is routinely modified by silane to improve its compatibility with the rubber matrix. Silanization of the silica particle affects both the linear and nonlinear rheological behaviors of the compounds. Their rheological nonlinearity, however, is mostly analyzed in an indirect way from linear rheological parameters, e.g. G′(ω₁, γ₀) and G″(ω₁, γ₀), which lose their physical meaning in the nonlinear viscoelastic regime. In the present work, the nonlinearity is directly quantified by the Fourier-transform rheology (FT-Rheology) technique in terms of I_3/1(ω₁, γ₀), the third relative higher harmonic, for unvulcanized styrene butadiene rubber compounds filled with a fixed amount of silica, but varying dosages of silane. With the proposed model for I_3/1(γ₀), the contributions toward nonlinearity from the filler networks at a low strain amplitude and the one from the polymer networks at high strain amplitude can be successfully separated for filled systems. The utmost nonlinearity contribution from the filler networks decreases with the silane content, which is assigned to the weakening interparticle interaction of the filler. With increasing silanization of silica, the utmost nonlinearity contribution from the polymer networks is found to increase. This nonlinear mechanical response is attributed to the enhanced interfacial interaction between the filler and polymer.     

Structure-property relationship of highly crosslinked rubber-iron oxide composite based on chloroprene rubber (CR) as well as on nitrile rubber (NBR); a comparative study using different models

Abstract

Highly crosslinked elastomer-iron oxide composite for grinding as well as for polishing application. With the recent introduction of organic acid-based coolants in polishing applications, the designed composites should have good resistance to oils. This investigation reports the preparation and properties of high crosslinked elastomer-iron oxide composites based on Chloroprene Rubber (CR) as well as on Nitrile Rubber (NBR) as main elastomer matrix and their comparative study. In NBR system, a small amount of natural rubber (NR) was used to improve the abrasion resistance. The crosslink density (CLD) was determined from the plateau modulus in DMA using Nielsen’s model. CLD was also determined based on the equilibrium-swelling ratio by using Flory-Rehner model. The CLD at lower cure time estimated by both methods was substantially different. Nevertheless, it converges to a common value at highly crosslinked state. Highly crosslinked CR shows 500% higher modulus at high temperature when compared to the NBR system.

Highly crosslinked elastomeric composites based on Chloroprene Rubber (CR) as well as Nitrile Rubber (NBR) with high iron oxide content were prepared. This investigation gives insights into the fabrication of composites and evaluates the network structure of highly crosslinked composites. Different models were used to characterize the elastomeric network structures in the composites.     

The influence of non-rubber constituents on performance of silica reinforced natural rubber compounds

An in-rubber study of the interaction of silica with proteins present in natural rubber show that the latter compete with the silane coupling agent during the silanisation reaction; the presence of proteins makes the silane less efficient for improving dispersion and filler–polymer coupling, and thus influences the final properties of the rubber negatively. Furthermore, the protein content influences the rheological properties as well as filler–filler and filler–polymer interactions. Stress strain properties also vary with protein content, as do dynamic properties. With high amounts of proteins present in natural rubber, the interactions between proteins and silica are able to disrupt the silica–silica network and improve silica dispersion. High amounts of proteins reduce the thermal sensitivity of the filler–polymer network formation. The effect of proteins is most pronounced when no silane is used, but they are not able to replace a coupling agent.     

Effects of rubber type on the curing and physical properties of silica filled rubber compounds

As environmental regulations are getting stricter, tire industries for automobiles have shown much interest in substituting silica for conventional carbon black partially or entirely. To take full advantage of silica as fillers for rubbers, it is essential to find a reasonable rubber system that shows an excellent performance with silica reinforcement. Therefore, in this study, several different rubber compounds comprising the same amount of silica were prepared with several different rubber systems, respectively. The processability, curing characteristics, and mechanical and viscoelastic properties of the rubber compounds were investigated to analyze the performance of the rubber compounds as tire tread materials. Among the rubber compounds studied, SBR1721 compound comprising natural rubber (NR) and styrene butadiene rubber (SBR) with high styrene content was considered the most appropriate for application to tire tread materials. Copyright © 2008 John Wiley & Sons, Ltd.     

共混硫化丁腈橡胶-氯丁橡胶的物理性能

将丁腈橡胶(NBR)和氯丁橡胶(CR)按不同质量分数共混并硫化,研究了硫化橡胶在自然环境、热空气老化、热油老化等条件下的物理性能,并测定了硫化橡胶与镀铜钢丝的粘合性能.结果表明,随着CR质量分数的增大,混炼胶的焦烧时间逐渐缩短.经热空气老化后,NBR的硬度增加幅度比CR的硬度增加幅度大,拉断强度降低幅度则比CR的小得多.此外,NBR的耐油性能优于CR.就物理性能以及与镀铜钢丝的粘合性能而言,单一NBR和单一CR优于共混NBR/CR.     

Influence of silica on shape memory effect and mechanical properties of polyurethane-silica hybrids

Polyurethane block copolymer (PU) was synthesized and was followed by a sol-gel reaction with tetraethoxysilane (TEOS) to prepare high performance polyurethane-silica hybrids with shape memory function. Their tensile and shape memory properties were compared as a function of TEOS content and PU hard segment content. A tensile test showed that the mechanical properties were largely influenced by TEOS content, and the maximum elongation-at-break as well as maximum breaking stress and modulus were obtained when TEOS at 10 wt% was used. Shape memory of hybrids was also obtained from a thermomechanical test, and showed good shape retention and shape recovery of more than 80% for all samples. Consequently, by silica hybridization, an improvement in the mechanical properties and shape recovery force of PU could be achieved without any decrease in their shape recovery effect.     

Morphology and mechanical and viscoelastic properties of natural rubber and styrene butadiene rubber latex blends

The morphology and mechanical and viscoelastic properties of a series of blends of natural rubber (NR) and styrene butadiene rubber (SBR) latex blends were studied in the uncrosslinked and crosslinked state. The morphology of the NR/SBR blends was analyzed using a scanning electron microscope. The morphology of the blends indicated a two phase structure in which SBR is dispersed as domains in the continuous NR matrix when its content is less than 50%. A cocontinuous morphology was obtained at a 50/50 NR/SBR ratio and phase inversion was seen beyond 50% SBR when NR formed the dispersed phase. The mechanical properties of the blends were studied with special reference to the effect of the blend ratio, surface active agents, vulcanizing system, and time for prevulcanization. As the NR content and time of prevulcanization increased, the mechanical properties such as the tensile strength, modulus, elongation at break, and hardness increased. This was due to the increased degree of crosslinking that leads to the strengthening of the 3‐dimensional network. In most cases the tear strength values increased as the prevulcanization time increased. The mechanical data were compared with theoretical predictions. The effects of the blend ratio and prevulcanization on the dynamic mechanical properties of the blends were investigated at different temperatures and frequencies. All the blends showed two distinct glass‐transition temperatures, indicating that the system is immiscible. It was also found that the glass‐transition temperatures of vulcanized blends are higher than those of unvulcanized blends. The time–temperature superposition and Cole–Cole analysis were made to understand the phase behavior of the blends. The tensile and tear fracture surfaces were examined by a scanning electron microscope to gain an insight into the failure mechanism. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2189–2211, 2000     

Influence of surfactant surface coverage and aging time on physical properties of silica nanoparticles

The experimental results on the influence of surfactant surface coverage and aging time on physical properties of silica nanoparticles were reported. The spherical silica nanoparticles have been synthesized using polyethylene glycol (PEG) as the surfactant and oil shale ash (OSA) as a new silica source. In order to identify the optimal condition for producing the best quality silica nanoparticles with the good dispersion and uniformity, the effects of surfactant surface coverage and aging time were investigated. It was found that the particle size and distribution of silica nanoparticles depend on the concentration of PEG in dispersion. At relatively low concentration, 0–2 wt.%, the existing PEG is not sufficient to prevent further growth of the initially formed silica nanoparticles, leading to large aggregates of silica particles. When the PEG concentration increases to 3 wt.%, self-assembled PEG layer on the surface stabilizes the initially formed silica nanoparticles and the silica particles with average diameter of 10 nm are uniformly distributed. With further increasing the concentration of PEG, the number of PEG aggregates increases and silica nanoparticles are mainly formed inside the entangled PEG chains, resulting in an observation of clusters of silica nanoparticles. Moreover, it was found that as the aging time increased, the shape of silica nanoparticles becomes regular and the particle size distribution becomes narrow.     

Characterization of effects of thermal-oxidative aging on styrene-butadiene rubber/silica composites with vitamin C-lanthanum complex

A novel rubber antioxidant, vitamin C-lanthanum complex, was prepared and applied in styrene-butadiene rubber (SBR)/silica composites. The anti-aging behavior of SBR/silica composites with vitamin C-lanthanum complex was systematically investigated by mechanical property retention after aging, oxidation induction time, exothermic enthalpies of thermal oxidation, and thermo-oxidative degradation kinetics. The highlight of this work lies in the fact that several thermal analysis techniques were successfully applied to fully evaluate the thermal-oxidative aging of SBR/silica composites and the vitamin C-lanthanum complex was found to endow SBR/silica composites with better protection against aging than commercial antioxidants, which may be beneficial for better characterization of rubber aging and fruitful for the preparation of highly aging-resistant rubber composites, respectively.     

Effect of non‐rubber components on the mechanical properties of natural rubber

Effect of the nanomatrix structure on mechanical properties of natural rubber was investigated in relation to the strain‐induced crystallization. Structure of natural rubber was analyzed through Fourier transform infrared spectroscopy, wide‐angle X‐ray diffraction measurement and transmission electron microscopy. The nanomatrix of the non‐rubber components was found to be inevitably formed in natural rubber, in which natural rubber particles linking to fatty acids were dispersed in the nanomatrix of the proteins and phospholipids. The nanomatrix disappeared after deproteinization of natural rubber with urea. Tensile strength and modulus of natural rubber were reduced by removal of the fatty acids and the proteins, which resulted in disappearance of the nanomatrix structure. The effect of fatty acids on the crystallization of natural rubber in small particles as a dispersoid was proved by tensile test of blend of natural rubber and styrene butadiene rubber. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of filling mixtures of sepiolite and a surface modified fumed silica on the mechanical and swelling behavior of a styrene-butadiene rubber

A styrene-butadiene copolymer is filled with mixtures of pyrogenic silica combined with a silane coupling agent and fibers of organophilic sepiolite. The mechanical properties of the composites reveal that a mixture of double fillers impart to the elastomeric matrix a higher degree of reinforcement than that which would result from a simple addition of the two types of fillers. The swelling ratio of the composite containing the two types of fillers was found to highly decrease with regard to the pure polymer reflecting strong interactions with the matrix. The changes in the state of dispersion by adding the second filler were evaluated by transmission electron microscopy.     

Effects of methyl methacrylate grafting and in situ silica particle formation on the morphology and mechanical properties of natural rubber composite films

The effects of methyl methacrylate (MMA) grafting and in situ formation of silica particles on the morphology and mechanical properties of natural rubber latex (NRL) were investigated. MMA grafting on NRL was carried out using cumyl hydroxy peroxide/tetraethylene pentamine (CHPO/TEPA) as a redox initiator couple. The grafting efficiency of the grafted NR was determined by solvent extractions and the grafted NRL was then mixed with tetraethoxysilane (TEOS), a precursor of silica, coated by adherence to a glass surface to form a film and cured at 80°C. The resultant products were characterized by FT‐IR and transmission electron microscopy. The influence of varying the MMA monomer weight ratio on the surface morphology of the composites was investigated by scanning electron and atomic force microscopy. The PMMA (poly MMA) grafted NRL particles were obtained as a core/shell structure from which the NR particles were the core seed and PMMA was a shell layer. The silane was converted into silica particles by a sol–gel process which was induced during film drying at 80°C. The silica particles were fairly evenly distributed in the ungrafted NR matrix but were agglomerated in the grafted NR matrix. The root‐mean‐square roughness increased with an increasing weight ratio of MMA in the rubber. The in situ silica particles in the grafted NR matrix slightly increased both the modulus and the tear strength of the composite film. Copyright © 2008 John Wiley & Sons, Ltd.