Rubber magnets based on NBR and lithium ferrite with the ability to absorb electromagnetic radiation

Rubber magnetic composites were prepared through the incorporation of magnetic soft lithium ferrite into acrylonitrile butadiene rubber. Standard sulfur‐based curing and peroxide curing systems were used for cross‐linking of rubber matrices. The experimental part was focused on the investigation of ferrite content and curing system composition on cross‐link density, physical‐mechanical, magnetic and shielding characteristics of composites. The results demonstrated that cross‐link density and physical‐mechanical properties of composites can be modified by both the amount of ferrite and composition of the curing system. The influence of curing systems on magnetic properties was negligible. It can be stated that the application of lithium ferrite to rubber matrix leads to the preparation of rubber composites with the ability to efficiently absorb harmful electromagnetic radiation in the tested frequency range. The shielding efficiency of composites increased with increasing content of magnetic filler.     

Magnetic composites based on natural rubber prepared by using peroxide and sulfur curing system

In this work, rubber magnetic composites were prepared by incorporation of strontium ferrite into elastomeric matrix based on natural rubber. Cross‐linking of the rubber matrix was performed by using sulfur and peroxide curing system. The study was aimed at the investigation of the type of curing system and magnetic filler content on curing process and cross‐link density of prepared materials. Then, the influence of both factors on physical–mechanical and magnetic properties was observed. The obtained results demonstrate that sulfur‐cured composites show better physical–mechanical properties, especially at lower content of strontium ferrite. With increasing amount of ferrite, the differences between the characteristics of both types of composites became less visible, while peroxide‐cured sample with maximum ferrite content showed superior tensile strength in comparison with tensile strength of maximally filled sample cured with sulfur system. The obtained results demonstrate better compatibility between the rubber and the filler when peroxide system was introduced for cross‐linking of the rubber matrix. Copyright © 2014 John Wiley & Sons, Ltd.     

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     

In vitro drug release from silicone rubber–polyacrylamide composite

Composite materials containing drugs were prepared from silicone rubber and hydrogel. Cross linked polyacrylamide (PAAm) hydrogel particles were incorporated into a silicone rubber to enhance the hydrophilicity and drug release capacity of silicone rubber as a matrix. Progesterone and Thymol Blue were used as a hydrophobic and hydrophilic drug model, respectively. Different amounts of polyacrylamide (PAAm) were mixed with the drugs and uncured silicone rubber at room temperature. The composite matrices were formed using a compression molding press and cured by thermal and γ-irradiation curing methods. In vitro drug release behavior of composites and their physical and mechanical properties were investigated. The results indicated that the hydrophilic character of silicone rubber was more pronounced with increasing the amount of PAAm. Also, a significant effect on the drug release profiles was observed. The γ-irradiation curing method improved mechanical properties of composites and affected the drug release profiles. It was found that the amounts of released progesterone from γ-irradiated samples increased in comparison with the thermally cross linked composite since released Thymol Blue was reduced.     

Analysis of the thermogenesis mechanism of natural rubber under high speed strain

This work highlights the relationship of crosslink density, entanglement points and various sulfide crosslinks with the thermogenesis properties of natural rubber (NR). The impact of cross‐link and entanglement on thermogenesis properties was evaluated by heat build‐up test, swelling behavior, statistical thermodynamic calculation, and classic viscoelastic theory. It was found that cross‐link and entanglement points have “pinning” effect to the rubber chain, thus remarkably restricting the motion of the rubber chain and reducing thermogenesis. Besides, the effects of various sulfide crosslinks and cross‐link length on thermogenesis were compared and discussed varying the sulfur vulcanization system. It was found that the semi‐effective vulcanization system using N‐cyclohexyl‐2‐benzothiazolesulfenamide (CZ) and 2‐Mercaptobenzothiazole (M) has the lowest thermogenesis (bottom temperature rise is 7.5°C, middle is 18.7°C), which on account of combined short crosslink length with high rigid rubber chain (crosslink network dominated by mono‐ and disulfides). As a result, the deformation degree of the rubber chain during curl up‐extension and the thermogenesis are further reduced. Finally, a combination of natural film coagulation and semi‐effective vulcanization system was used to prepare a low thermogenesis NR, in which bottom and middle temperature rise were only 5.0°C and 14.1°C, respectively.     

Effect of nature and extent of crosslinking on swelling and mechanical behavior of styrene–butadiene rubber membranes

The influence of crosslink type and crosslink density on the swelling and mechanical behavior of styrene–butadiene rubber (SBR) membranes were studied in four aliphatic hydrocarbons. To vary the crosslink type and crosslink density, SBR was vulcanized by four different vulcanizing systems viz conventional, efficient, peroxide and a mixture of sulfur and peroxide. SBR vulcanizates having mono or disulfidic crosslinks (efficient system) exhibited the highest solvent uptake whereas those with C–C bonds (peroxide system) showed the lowest. SBR crosslinked by the mixed system showed superior mechanical properties in the unswollen, swollen and deswollen conditions. Arrhenius and thermodynamic parameters were evaluated from the diffusion data. Finally, a comparison between theoretical and experimental diffusion results was carried out.     

Study on the Effect of Nano and Active Particles of Alumina on Natural Rubber–Alumina Composites in the Presence of Epoxidized Natural Rubber as Compatibilizer

Natural rubber composites with alumina of different particle sizes (28 nm nano particles, 200 nm active particles and > 1000 nm raw alumina) were prepared by the usual rubber processing technique. Epoxidized natural rubber (ENR) was used in the composites as compatibilizer. Cure characteristics and mechanical properties of all composites were analyzed. The values of minimum rheometric torque (M_L), maximum rheometric torque (M_H) and torque difference (M_H – M_L) increased. Maximum enhancement was observed for the nano-filled composites. It endorses the view that nano alumina reveals highest interaction with natural rubber in presence of ENR. Scorch time and optimum cure time values for nano-composites were highest among all types of composites. Vulcanization reaction for the sulfur curing system of the composites was found to follow first order rate kinetics. Specific rate constant decreased with decreasing particle size in composites. Crosslink densities of composite-vulcanizates showed increasing trend with decreasing particle size of alumina. Mechanical properties of the composite vulcanizates increased with decreasing particle size of alumina - nano composites exhibiting much higher mechanical strength. Results of oxidative resistance reveal that particle size of alumina in composite vulcanizates has a significant impact on aging behavior.     

Novel biphasic structured composite prepared by in situ silica filling in natural rubber latex

The sol‐gel reaction of tetraethoxysilane in natural rubber (NR) latex was conducted to produce in situ silica‐filled NR latex, followed by adding sulfur cross‐linking reagents to the latex in a liquid state. The latex was cast and subjected to sulfur curing to result in a unique morphology in the NR composite of a flexible film form. The contents of in situ silica filling were controlled up to 35 parts per one hundred rubber by weight. The silica was locally dispersed around rubber particles to give a filler network. This characteristic morphology brought about the composite of good dynamic mechanical properties. Synchrotron X‐ray absorption near‐edge structure spectroscopy suggested that the sulfidic linkages of the sulfur cross‐linked composites were polysulfidic, S_x (x ≥ 2), and a fraction of shorter polysulfidic linkages became larger with the increase of in situ silica. The present observations will be of use for developing a novel in situ silica‐filled NR composite prepared in NR latex via liquid‐phase soft processing. Copyright © 2011 John Wiley & Sons, Ltd.     

Preparation and properties of natural rubber composites reinforced with pretreated carbon nanotubes

In order to achieve dramatic improvements in the performance of rubber materials, the development of carbon nanotube (CNT)‐reinforced rubber composites was attempted. The CNT/natural rubber (NR) nanocomposite was prepared through solvent mixing on the basis of pretreatment of CNTs. Thermal properties, vulcanization characteristics, and physical and mechanical properties of the CNT/NR nanocomposites were characterized in contrast to the carbon black (CB)/NR composite. Through the addition of the CNTs treated using acid bath followed by ball milling with HRH (hydrated silica, resorcinol, and hexamethylene tetramine) bonding systems, the crystallization melting peak in differential scanning calorimetry (DSC) curves of NR weakened and the curing rate of NR slightly decreased. Meanwhile, the over‐curing reversion of CNT/NR nanocomposites was alleviated. The dispersion of the treated CNTs in the rubber matrix and interfacial bonding between them were rather good. The mechanical properties of the CNT‐reinforced NR showed a considerable increase compared to the neat NR and traditional CB/NR composite. At the same time, the CNT/NR nanocomposites exhibited better rebound resilience and dynamic compression properties. The storage modulus of the CNT/NR nanocomposites greatly exceeds that of neat NR and CB/NR composites under all temperature regions. The thermal stability of NR was also obviously improved with the addition of the treated CNTs. Copyright © 2008 John Wiley & Sons, Ltd.     

电子束辐射固化环氧树脂的动态力学分析——树脂化学结构、分子量及其分布的影响

应用不同化学结构、分子量及其分布的环氧树脂进行了电子束辐射固化实验 ,对固化物进行了动态力学分析 ,研究了不同样品凝胶含量、内耗tanδ及动态模量的变化规律 .分析结果表明环氧树脂辐射反应活性与其化学结构有很大关系 ,酚醛型环氧树脂的辐射反应活性高 ,固化后高温模量及玻璃化温度较高 ,而脂环族环氧树脂反应活性小 .在低辐射剂量下 ,环氧树脂的固化度随分子量增大略有下降 ,但固化物的玻璃化温度随分子量增加而升高 .增大辐射剂量 ,树脂固化度的提高受分子量大小的影响很小 ,分子量较大样品的网络均匀程度有所提高 ,在较高反应程度下 ,玻璃化温度主要受固化度影响 .树脂固化程度也是决定其模量高低的主要因素 ,而在固化程度相近的情况下 ,分子量的影响作用很大 .在同样辐射剂量下 ,分子量分布宽的树脂固化反应程度高 ,但交联网络均匀性低 .     

Synthesis of a caged bicyclic phosphates derived anhydride and its performance as a flame‐retardant curing agent for epoxy resins

A novel curing and flame‐retardant agent (PEPA‐TMAC) was successfully synthesized. The chemical structure was characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). Use of PEPA‐TMAC as part of the curing agent in combination with another anhydride for a commercial epoxy resin (EP) was studied. Results of differential scanning calorimetry (DSC) indicated that PEPA‐TMAC was an effective curing agent for EP. The dynamic mechanical analysis (DMA) results showed that the glass transition temperature (T_g) and cross‐linking density (V_e) of EP composites exhibited an increase trend with the addition of PEPA‐TMAC. The limiting oxygen index (LOI) value of EP composites reached 26.9%, and the cone calorimeter results indicated that peak heat release rate (PHRR), total heat release (THR), smoke produce rate (SPR), and total smoke produce (TSP) remarkably decreased with increasing PEPA‐TMAC content. TGA data showed that the addition of PEPA‐TMAC greatly increased the amount of residual char during combustion. The morphology of the residual char was studied by SEM and showed that the addition of PEPA‐TMAC greatly increased the stability of EP composites. The thermogravimetric analysis (TGA), energy‐dispersive X‐ray spectroscopy (EDS), and FTIR results revealed the flame‐retardant mechanism that PEPA‐TMAC can promote the formation of charred layers with the phospho‐carbonaceous complexes in the condensed phase during burning of EP composites.     

Synthesis of peroxide‐curable butyl rubber via suzuki–miyaura coupling of halogenated butyl rubber with 4‐vinylphenylboronic acid

The Suzuki–Miyaura coupling reaction of brominated butyl rubber (BIIR) and/or chlorinated butyl rubber with a mixture of 4‐vinylphenylboronic acid and phenylboronic acid was carried out in THF under various conditions using a di‐μ‐chlorobis [5‐hydroxy‐2‐[1‐(hydroxyimino‐κN)ethyl]phenylκC] palladium(II) dimer, which is a type of cyclopalladated complex, as a catalyst. When BIIR and a small amount (Pd/Br ≈ 1/1000) of complex were used as the substrate and catalyst, respectively, a 4‐vinylphenyl and phenyl group could be introduced to butyl rubber in a high yield. Isomerization of the exo carbon–carbon double bond in BIIR was observed during the coupling reaction to give a cis and trans endo structure. The peroxide curing behavior of the resulting polymer at 170 °C indicated that the polymer could be cured by dicumyl peroxide, and the maximum torque of the resulting material, which reflects the crosslink density, was controllable by the composition of the boronic acids used. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Dynamic mechanical behavior of acrylonitrile butadiene rubber/poly(ethylene‐co‐vinyl acetate) blends

The dynamic mechanical behavior of uncrosslinked (thermoplastic) and crosslinked (thermosetting) acrylonitrile butadiene rubber/poly(ethylene‐co‐vinyl acetate) (NBR/EVA) blends was studied with reference to the effect of blend ratio, crosslinking systems, frequency, and temperature. Different crosslinked systems were prepared using peroxide (DCP), sulfur, and mixed crosslink systems. The glass‐transition behavior of the blends was affected by the blend ratio, the nature of crosslinking, and frequency. sThe damping properties of the blends increased with NBR content. The variations in tan δ_max were in accordance with morphology changes in the blends. From tan δ values of peroxide‐cured NBR, EVA, and blends the crosslinking effect of DCP was more predominant in NBR. The morphology of the uncrosslinked blends was examined using scanning electron and optical microscopes. Cocontinuous morphology was observed between 40 and 60 wt % of NBR. The particle size distribution curve of the blends was also drawn. The Arrhenius relationship was used to calculate the activation energy for the glass transition of the blends, and it decreased with an increase in the NBR content. Various theoretical models were used to predict the modulus of the blends. From wide‐angle X‐ray scattering studies, the degree of crystallinity of the blends decreased with an increasing NBR content. The thermal behavior of the uncrosslinked and crosslinked systems of NBR/EVA blends was analyzed using a differential scanning calorimeter. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1556–1570, 2002     

Mechanical properties and thermal analysis of low‐density polyethylene + polypropylene blends with dialkyl peroxide

Polypropylene + low density polyethylene (PP + LDPE) blends involving 0, 25, 50, 75 and 100 wt% of PP with dialkyl peroxide (DAP) were prepared by melt blending in a single‐screw extruder. The effects of adding dialkyl peroxide on mechanical and thermal properties of PP + LDPE blends have been studied. It was found that at lower concentrations of peroxide (e.g., 0–0.08 wt% of dialkyl peroxide) LDPE component is cross‐linked and Polypropylene (PP) is degraded in all compositions of PP + LDPE blends. Mechanical properties (Tensile strength at break, at yield and elongation at break), Melt flow index (MFI), hardness, Scanning Electron Microscope (SEM) and thermal analyses (DSC) of these blends were examined. Because of serious degradation or cross‐linking the mechanical properties and the crystallinty (%) of those products were decreased as a result of increasing peroxide content. Copyright © 2009 John Wiley & Sons, Ltd.     

Dynamically vulcanized ethylene propylene diene terpolymer/nylon thermoplastic elastomers

A thermoplastic elastomer (TPE) of ethylene propylene diene terpolymer (EPDM) and nylon with excellent mechanical properties was prepared by dynamic vulcanization. The effects of the curing systems, compatibilizer, nylon content and reprocessing on the mechanical properties of EPDM/nylon TPEs were investigated in detail. Experimental results indicate that maleic anhydride (MAH) grafted EPR has a better performance in compatibilizing the EPDM/nylon blends compared with other compatibilizers containing acid group. Tensile strength and elongation at break go through a maximum value at a compatibilizer resin content (on total rubber dosage) of 20%. EPDM/nylon TPE using sulfur as curative has higher tensile strength and elongation than that of TPE using phenolic resin or peroxide as curatives. Tensile strength and elongation at break increase with increasing nylon content. Scanning electron microscopy results show that rubber particles distributed at an average size of 1 μm in dynamic vulcanized EPDM/MAH-g-EPR/nylon TPE.     

Filler-elastomer interactions: influence of silane coupling agent on crosslink density and thermal stability of silica/rubber composites

In this work, the crosslink density and thermal stability of the silica/rubber composites treated by silane coupling agents, i.e., gamma-aminopropyl triethoxysilane (APS), gamma-chloropropyl trimethoxysilane (CPS), and gamma-methacryloxypropyl trimethoxysilane (MPS), were investigated. The chemical structures of modified silicas were studied in term of solid-state 29Si NMR spectroscopy. The crosslink density of the composites was determined by swelling measurement. The development of organic functional groups on silica surfaces treated by coupling agents led to an increase in the crosslink density of the composites, resulting in increasing final thermal stability of the composites. The composites treated by MPS showed the superior crosslink density and thermal stability in these systems. The results could be explained by the fact that the organic functional groups of silica surfaces by silane surface treatments led to an increase of the adhesion at interfaces between silicas and the rubber matrix.     

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.     

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。     

A model study on effect of glucose on the basic characteristics and physical properties of natural rubber

Glucose at various concentrations was incorporated into sugar free purified natural rubber (PNR) latex to model the effect of carbohydrate on the basic characteristics and physical properties of natural rubber (NR). PNR samples treated with various concentrations of glucose were characterized for the basic properties of unvulcanized NR, i.e., gel content, molecular weight distribution and Mooney viscosity to evaluate the effect of sugar on these parameters. In addition, the effect of glucose on the physical properties of vulcanizates derived using sulfur and peroxide vulcanization was investigated. Glucose was shown to affect the viscosity of unvulcanized NR and the discoloration of vulcanized NR. Moreover, glucose was found to have a strong effect on crosslink density, as well as tensile and dynamic properties of sulfur vulcanizates, while those properties of peroxide vulcanizates was not much affected by glucose.     

Scanning electron microscopy methods for studying interfacial interaction in polymer blends

The scanning electron microscopy method in combination with the selective etching technique for polymer blends have been used to evaluate interfacial interaction in natural rubber and low density polyethylene blends. The morphology of the polymer blends, studied under externally applied strain, has been investigated to understand the role of interface adhesion between natural rubber and polyethylene phases, for two separate crosslinking systems, i.e. sulphur and peroxide.

Externally induced strain which facilitates phase separation in sulphur cured blends by initiating cracks at the interface; peroxide curing prevents separating out of the polyethylene phase from the natural rubber matrix. In the latter case, induced stress is distributed predominantly by developing fine flaw paths in the rubber matrix.

The method which has been developed for natural rubber and polyethylene blend systems may be used to evaluate the degree of interfacial adhesion between the dispersed phase and the dispersion medium for other kinds of polymer-polymer, polymer-filler as well as polymer-fibre composites.