Fly ash particles and precipitated silica as fillers in NR/CR vulcanizates under thermal and thermal‐oil ageing

The loading effect of precipitated silica (PSi) and fly ash‐based silica (FASi) on mechanical properties of natural rubber/chloroprene (NR/CR) under thermal and thermal‐oil ageing was investigated with variation in NR content in the NR/CR blends. The selected results were compared with vulcanized NR/nitrile rubber (NR/NBR) blends. The cure time of CR vulcanizate was found to decrease with increasing NR content, but increased with silica fillers. The Mooney viscosity for CR vulcanizates reduced with increasing NR content. The addition of NR had no effect on tensile modulus and tensile strength for the FASi filled NR/CR, but the opposite trend was observed for the PSi filled NR/CR. The post‐curing effect was more significant in PSi filled NR/CR than in FASi filled NR/CR. The tensile strength of the NR/CR vulcanizates was slightly reduced after thermal ageing especially at high NR content, more extreme reduction being found by thermal‐oil ageing. The elongation at break of NR/CR with both silica fillers ranged from 400 to 900%. The hardness results were similar to the tensile modulus. The addition of PSi in NR/CR considerably increased the tear strength, but less pronounced effect was found for FASi. The resilience properties of NR/CR tended to decrease with increasing silica content. The compression set became poorer when NR content was increased. The PSi showed higher improvement in compression set than the FASi. The effects of silica and ageing on the mechanical properties for NR/CR vulcanizates were similar to those for NR/NBR vulcanizates. Copyright © 2009 John Wiley & Sons, Ltd.     

Microbial desulfurization of SBR ground rubber by Sphingomonas sp. and its utilization as filler in NR compounds

Microbial desulfurization of waste tyre rubber has been investigated with great efforts since 1990s, because waste rubber has created serious ecological and environmental problems. A microbial desulfurization technique for SBR ground rubber has been developed by a novel sulfur‐oxidizing bacterium Sphingomonas sp. The adaptability of Sphingomonas sp. with SBR ground rubber was tested with the amounts of SBR ground rubber varying from 0.5 to 4% g/l. The sol fraction of desulfurized SBR ground rubber increased 70%, compared with SBR ground rubber without desulfurization. Fourier transform infrared spectroscopy‐attenuated total reflectance (FTIR‐ATR) spectrum and X‐ray photoelectron spectroscopy (XPS) analysis of the desulfurized surface of vulcanized SBR flakes revealed that not only the oxidation of crosslinked S? S and S? C bonds, but also the rupture of C?C double bonds had happened to SBR vulcanizates during microbial desulfurization. The cure characteristics, such as scorch time and optimum cure time of natural rubber (NR) vulcanizates filled, were found to decrease with increasing contents of desulfurized SBR ground rubber, due to some reactive groups on its surface. NR vulcanizates filled with desulfurized SBR ground rubber had lower crosslink density and hardness, higher tensile strength and elongation at break, compared with those filled with SBR ground rubber of the same amount. Dynamic mechanical properties indicated that there were better crosslink distribution and stronger interfacial bonding between NR matrix and desulfurized SBR ground rubber. Scanning electron microscope (SEM) photographs showed that the fracture surfaces of NR vulcanizates filled with desulfurized SBR ground rubber had more smooth morphologies. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of surface treatment with potassium permanganate on ultra-high molecular weight polyethylene fiber reinforced natural rubber composites

The effects of surface treatment using potassium permanganate on ultra-high molecular weight polyethylene (UHMWPE) fibers reinforced natural rubber (NR) composites were investigated. The results showed the surface roughness and the oxygen-containing groups on the surface of the modified fibers were effectively increased. The NR matrix composites were prepared with as-received and modified UHMWPE fibers added 0–6 wt%. The treated fibers increased the modulus and tensile stress at a given elongation. The tear strength increased with increasing fiber mass fraction, attained maximum values at 4 wt%. The hardness of composites exhibited continuous increase with increasing the fiber content. The dynamic mechanical tests showed that the storage modulus and the tangent of the loss angle were decreased in the modified UHMWPE fibers/NR composites. Several micro-fibrillations between the treated fiber and NR matrix were observed, which meant the interfacial adhesion strength was improved.     

The influence of nano silica particles on gamma-irradiation ageing of elastomers based on chlorosulphonated polyethylene and acrylonitrile butadiene rubber

The goal of this work was to study gamma irradiation ageing of rubber blends based on acrylonitrile butadiene rubber (NBR) and chlorosulphonated polyethylene rubber (CSM) reinforced by silica nano particles. The NBR/CSM compounds (50: 50, w/w) filled with different content of filler (0–100 phr) were crosslinked by sulfur. The vulcanization characteristics were assessed using the rheometer with an oscillating disk. The vulcanizates were prepared in a hydraulic press. The obtained materials were exposed to the different irradiation doses (100, 200, 300 and 400 kGy). The mechanical properties (hardness, modulus at 100% elongation, tensile strength and elongation at break) and swelling numbers were assessed before and after gamma irradiation ageing.     

炭黑结合橡胶对天然橡胶性能的影响

本文研究了天然橡胶(NR)与五种不同类型炭黑的结合橡胶对其混炼胶的应力-应变、流变性质等的影响。结果表明,NR与炭黑的结合橡胶量随炭黑结构和表面积增加而增加。结合橡胶的增加使NR在低剪切下的本体粘度、弹性恢复性和强度增加,塑性和粘着性降低;在高剪切下流动性变差,挤出物收缩则有所下降。此外,结合橡胶的增加也增加了硫化胶的交联度,因此模量、硬度和耐磨性提高,抗张强度和伸长率却有所下降。     

天然微晶纤维素晶须补强天然橡胶的研究

采用硫酸酸解天然微晶纤维素(microcrystalline cellulose,简称MCC)制备纳米微晶纤维素晶须(cellulosewhisker,简称CW),加入天然橡胶胶乳共沉后混炼硫化.结果表明,CW对天然橡胶具有明显的补强作用,经间苯二酚(R)与六亚甲基四胺(H)改性后,NR/RH-CW复合材料的模量、断裂伸长率和撕裂强度都进一步改善.热空气(100℃,72 h)老化后,NR/RH-CW复合材料的力学性能明显优于纯NR,其拉伸强度由28.54 MPa下降至21.78 MPa,变化率缩小至23.7%;断裂伸长率由594%下降至493%,变化率缩小至17.0%,而纯NR的拉伸强度由22.0 MPa下降至2.4 MPa,变化率为89.1%;断裂伸长率由579%下降至168%,变化率为71.0%.扫描电镜分析表明,RH-CW与NR基体的界面相容性较CW改善.热重分析表明,CW的加入使NR的5%失重温度降低,但残重增加,微分曲线在520℃处出现了一个小峰,RH-CW的加入,使该峰变大,残重进一步增加.     

Impacts of filler covalent and non‐covalent modification on the network structure and mechanical properties of carbon–silica dual phase filler/natural rubber

The carbon–silica dual phase filler (CSDPF) was modified by bis (3‐triethoxy‐silylpropyl) tetrasulphane (Si69) and 1‐allyl‐3‐methyl‐imidazolium chloride (AMI), respectively. The natural rubber (NR) vulcanizates filled with modified CSDPF were fabricated through mechanical mixing followed by a high‐temperature cure process. The impacts of filler surface modification on the curing characters, crosslinked junctions, network structure, and mechanical properties of NR vulcanizates were investigated. The results showed that the Si69 interacted with CSDPF through covalent bond, while the interaction between AMI and CSDPF was hydrogen bond. Both modifications increased the cure rate of CSDPF/NR compounds as well as the crosslinked degree, compared with those of pristine CSDPF/NR compound. The modifications improved the dispersion of CSDPF in NR matrix. The covalent modification by Si69 caused a limited movement of NR chains in the CSDPF surface, which contributed to a greater tensile modulus of Si69‐modified CSDPF/NR. However, the higher content of mono‐sulfidic crosslink and the poorer content of strain‐induced crystallization in the NR matrix led to a slight increase of tensile strength and tear strength of Si69‐modified CSDPF/NR, compared with those of CSDPF/NR. The tensile modulus of AMI‐modified CSDPF/NR had a lower value due to a faster polymer chain motion on the CSDPF surface. However, the tensile and tear strength of AMI‐modified CSDPF/NR increased significantly because of the increase of mono‐sulfidic crosslink, strain‐induced crystallization, and the existed hydrogen bond between CSDPF and NR. Copyright © 2015 John Wiley & Sons, Ltd.     

Elucidation of the accelerated sulfur vulcanization of bio oil-extended natural rubber compounds

The elucidation of the role of bio-oils on the accelerated sulfur vulcanization of natural rubber (NR) compounds is discussed in this study. Two types of bio-oil, palm oil and soybean oil, were studied in direct comparison with a distillate aromatic extract oil (DAE) as a reference. The scorch and cure times of the bio-oil-extended NR compounds were shorter than those containing DAE. The use of bio-oils gave a higher cure reaction rate constant along with a lower activation energy than the use of DAE. The attenuated total reflectance-Fourier transform infrared spectroscopy analysis revealed that the fatty acid segment of the bio-oils can react with zinc oxide to give zinc carboxylate, which is then involved in and promotes the vulcanization reaction. The use of bio-oils to increase the rate of vulcanization strongly influenced the crosslink density of the obtained NR vulcanizates, yielding NR vulcanizates with a lower crosslinking density. It is proposed here that the bio-oils might consume the curing agent via the reaction between their own unsaturated fatty acid and sulfur. This was supported by the increased viscosity of the oils after exposure to sulfur at a high temperature. The tensile strength and elongation at break of the bio-oil-extended NR compounds were lower and higher, respectively, than the NR extended with DAE oil due to the lower crosslink density of the bio oil-extended NR vulcanizates.     

Effect of polyvinylchloride on the properties of rubber vulcanizates

Natural rubber (NR) and styrene-butadiene rubber (SBR) were compounded with polyvinylchloride (PVC). Some physico-mechanical and dielectric properties of resulting rubber vulcanizates were measured. It was found that the addition of PVC to both NR and SBR results in slight decreases in tensile strength and elongation at break but a marked increase in oil-resistance of the vulcanizates. Moreover, the addition of PVC to NR slightly increases both dielectric constant and dielectric losses while the addition of PVC to SBR loaded with 50 phr carbon black (HAF) lowers these parameters. Both rubber blends, especially NR, show a reasonable stability with ageing.     

SBR-XNBR blends: a novel approach towards compatibilization

The role of a few ionic and non-ionic surfactants on the solubilization of polar carboxylated nitrile rubber and non-polar styrene butadiene rubber as interfacial compatibilizer has been investigated. Conspicuous changes of characteristic features of the blend vulcanizates e.g. modulus at 200% elongation, tensile strength, elongation at break, hardness, age resistance etc are observed. The cationic surfactant, tetra butyl ammonium bromide and the anionic sodium dodecyl sulfate are found to inhibit the physical properties while the non-ionics favor the phenomenon. Scanning electron microscope supports the observed behavior.     

包覆重钙粉为填充剂的橡胶加工及性能

重钙粉作为填充剂被广泛应用于橡胶加工过程,但由于其表面具有极性,分散性较差,导致与橡胶材料界面结合较差,影响了橡胶产品的抗拉强度、断裂伸长率等力学性能。 本文采用沉淀法,在CaCl₂-H₂O-NH₃-CO₂体系中生成碳酸钙直接结晶于重钙粉颗粒表面,实现对重钙粉的表面包覆,将n(CaCl₂)：n(重钙粉)=1：100、5：100、10：100的包覆重钙粉填充到天然橡胶和再生胶中,橡胶的力学性能与填充未包覆重钙粉的橡胶相比有了一定的提升。 通过比较,在填充量较大(8.5%、15%)时,包覆重钙粉橡胶产品在硬度、定伸应力等力学性能上要好于轻钙粉橡胶产品;在填充量(5%、8.5%)时,包覆重钙粉橡胶产品的抗拉强度、断裂伸长率接近于白炭黑,硬度高于白炭黑橡胶产品。     

质子辐照对有机硅树脂增强甲基硅橡胶的性能损伤及机理

硅橡胶具有优良的电绝缘性以及耐高低温、耐电晕、耐化学腐蚀、耐大气老化、耐臭氧和耐辐射等性能，近年来在航天领域得到了广泛应用．在宇宙空间的带电粒子如质子、电子等的辐照作用下，硅橡胶会发生性能退化，其质损率上升，产生析气现象，从而直接影响航天器的可靠性和寿命．自80年代以来，人们就对不同辐照源及不同粒子注量对硅橡胶材料的影响进行了研究，但直到近几年才将研究热点转向辐照场中硅橡胶的性能退化及微观结构的演变规律，其辐照环境大多集中于γ射线、Si^＋和F^＋离子、He^2＋离子等．对于空间环境下带电粒子辐照对硅橡胶材料的影响，国外由于相应的研究工作保密性强，报道甚少；国内哈尔滨工业大学则对我国自行研制的白炭黑增强空间级甲基硅橡胶质子辐照作用后的性能与微观结构的变化做了较为深入的研究。     

Comparison of the mechanical properties at similar hardness level of natural rubber filled with various reinforcing-fillers

Commercially, the alteration of a rubber formulation is usually made in such a way as to keep the hardness of the rubber product constant. This is because a specific hardness of the rubber product sets the limit to its practical applications. Therefore, in this paper, natural rubber (NR) vulcanizates containing various fillers were prepared to have the same hardness level, and their mechanical properties were compared and related to the degree of filler dispersion. The results show that higher amounts of carbon black (CB) and silica are needed for CB- and silica-filled natural rubber vulcanizates to achieve the same hardness value as a NR vulcanizate containing 6 phr of montmorillonite clay. At equal loading of fillers, clay-filled vulcanizate exhibits higher modulus, hardness, tensile strength and compression set, but lower heat build-up resistance and crack growth resistance than those of the vulcanizates containing conventional fillers. For the vulcanizate having the same hardness value, CB-filled vulcanizate gives the better overall mechanical properties followed by the clay-filled and silica-filled vulcanizates, respectively. The explanation is given as the better dispersion of carbon black, as can be seen in the SEM micrograph.     

Effect of high-temperature curing on the crosslink structures and dynamic mechanical properties of gum and N330-filled natural rubber vulcanizates

The effects of high-temperature curing and overcuring on the cure characteristics, crosslink structure, physical properties and dynamic mechanical properties (DMPs) of gum and carbon black (N330) filled natural rubber (NR) vulcanizates cured with conventional (CV), semi-efficient (SEV) and efficient (EV) cure systems, which have about the same total crosslink densities under a moderate curing temperature of 150°C, were investigated. The gum NR vulcanizates cured with CV, SEV and EV curing systems have about the same glass transition temperature (T_g) and tan δ values below the temperature of about 0°C, but showed some apparent differences in the tan δ values increasing in the order CVG′ and tan δ values above T_g higher than those of the gum NR vulcanizates.

High-temperature curing and overcuring cause decreases to various extents in the cure plateau torque, Shore A hardness, 300% modulus and tensile strength, and lead to apparent changes in the DMPs. Typically, there is an increase in T_g of all three kinds of gum and N330-filled NR vulcanizates because of changes in the total crosslink densities and crosslink types. The CV vulcanizates show the most significant change in cure characteristics, physical properties and DMPs since the highest content of polysulfidic crosslinks appears in the CV vulcanizate, causing the highest level of reversion and having a dominant effect on the properties.     

Optimisation of physical and mechanical properties of rubber compounds by response surface methodology--Two component modelling using vegetable oil and carbon black

Response surface methodology was used for predicting the optimal composition of vegetable oil and carbon black in rubber compounding. Central composite rotatable design for two variables at five levels was chosen as the experimental design. The data obtained from measurement of properties was fitted as a two variable second order equation and were plotted as contour plots using programme developed in MATLAB v.5. It is observed from the contour plots that the increase in cross-link density caused by the formation of rubber mono-layer from its multi-layer on increasing the carbon black loading upto the central point (50 phr) of experimental region increases 300% modulus and elongation at break and reduces the ultimate properties like tear strength and tensile strength. On the other-hand hardness increases with increase in solid inclusion of carbon black. From the contours it is observed that the addition of vegetable oil upto 2-3 phr, cross-link density increases due to its coupling action leading to increase in hardness and modulus and lowering of ultimate properties like tensile strength and elongation at break. Addition of further amount of vegetable oil shows less coupling and more plasticising effect leading to increase in tear strength, tensile strength and elongation at break and decrease in hardness and 300% modulus.     

Alkanolamide as an accelerator,filler-dispersant and a plasticizer in silica-filled natural rubber compounds

A feasibility study was carried out on the utilization of Alkanolamide (ALK) on silica reinforcement of natural rubber (NR) by using a semi-efficient cure system. The ALK was incorporated into the NR compound at 1.0, 3.0, 5.0, 7.0 and 9.0 phr. An investigation was carried out to examine the effect of ALK on the cure characteristics and properties of NR compounds. It was found that ALK gave shorter scorch and cure times for silica-filled NR compounds. ALK also exhibited higher torque differences, tensile modulus, tensile strength, hardness and crosslink density of up to 5.0 phr of ALK loading, and then decreased with further increases of ALK loading. The resilience increased with increased ALK loading. Scanning electron microscopy (SEM) micrographs proved that 5.0 phr of ALK in the silica-filled NR compound exhibited the greatest matrix tearing line and surface roughness due to higher reinforcement level of the silica, as well as better dispersion and cure enhancement.     

Compounding,mechanical and morphological properties of carbon-black-filled natural rubber/recycled ethylene-propylene-diene-monomer (NR/R-EPDM) blends

Blends of natural rubber/virgin ethylene-propylene-diene-monomer (NR/EPDM) and natural rubber/recycled ethylene-propylene-diene-monomer (NR/R-EPDM) were prepared. A fixed amount of carbon black (30 phr) was also incorporated. The effect of the blend ratio (90/10, 80/20, 70/30, 60/40 and 50/50 (phr/phr)) on the compounding, mechanical and morphological properties of carbon-black-filled NR/EPDM and NR/R-EPDM blends was studied. The results indicated that both the carbon-black-filled NR/EPDM and NR/R-EPDM blends exhibited a decrease in tensile strength and elongation at break for increasing weight ratio of EPDM or R-EPDM. The maximum torque (S′M_H), minimum torque (S′M_L), torque difference (S′M_H?M_L), scorch time (ts₂) and cure time (tc₉₀) of carbon-black-filled NR/EPDM or NR/R-EPDM blends increased with increasing weight ratio of virgin EPDM or R-EPDM in the blend. SEM micrographs proved that, for low weight ratios of virgin EPDM or R-EPDM, the blends exhibited high surface roughness and matrix tearing lines. The blends also showed a reduction in crack path with increasing virgin EPDM or R-EPDM content over 30 phr. This reduction in crack path could lead to less resistance to crack propagation and, therefore, low tensile strength.     

Cure characteristics and properties of NBR composites filled with co‐precipitates of black liquor and montmorillonite

Acrylonitrile‐butadiene rubber (NBR) composites filled with co‐precipitates of black liquor and montmorillonite (CLM) were prepared by mechanical mixing on a two‐roll mill. The cure characteristics, mechanical properties, thermal properties, and thermo‐oxidative aging properties of NBR/CLM composites were evaluated. Scanning electron microscopy and transmission electron microscopy showed that the filler particles were well dispersed in the NBR/CLM composites. The scorch time and optimum cure time increase with increasing filler loading. A remarkable enhancement in tensile strength, elongation at break, 300% modulus, and shore “A” hardness was also observed. When the loading of CLM was 40 parts per hundred rubbers, it showed about seven times increase in tensile strength, about 1.8 times increase in elongation at break, about three times increase in 300% modulus, and about 1.3 times increase in shore A hardness, respectively, as compared with those of pure cured NBR. Thermal properties and thermal oxidative aging properties, in general, were also improved with loading of this novel filler. Copyright © 2011 John Wiley & Sons, Ltd.     

Cut growth and abrasion behaviour,and morphology of natural rubber filled with MWCNT and MWCNT/carbon black

Various amounts of predispersed multi-wall carbon nanotubes (MWCNT) were mixed with natural rubber (NR), with and without carbon black (CB), for preparing MWCNT-filled NR (NC) and MWCNT/CB-filled NR (NH) vulcanizates. All NH vulcanizates contained 30 phr CB and the amount of MWCNT for both NC and NH was varied from 0 to 8 phr. Helium ion microscopy (HIM) and FE-SEM images showed that MWCNT in the NH was dispersed much better than in the NC. Additionally, the well dispersed CB and MWCNT in the NH functioned synergistically in promoting an increase in longitudinal crack growth, leading to enhancement of edge-cut tensile strength (CTS) with increasing MWCNT loading. In contrast, all NC specimens ruptured in a simple lateral direction relating to their lower CTS. Results also revealed that abrasion resistance of the NH was not significantly changed with increasing MWCNT, whereas that of the NC increased. Nevertheless, abrasion resistance of both vulcanizates showed good correlation with the average value of ridge spacing on their abraded surfaces. It was also found that tensile strength of the NH was almost unchanged when the MWCNT loading was increased because the reinforcement by CB predominates over the MWCNT. However, 100% modulus and hardness of both NC and NH increased with increasing MWCNT content.     

Effect of radiation dose on the properties of natural rubber nanocomposite

Effect of radiation dose and carbon nanotubes (CNT) on the mechanical properties of standard Malaysian rubber (SMR) was investigated in this study. SMR nanocomposites containing 1–7 phr CNT were prepared using the solvent casting method and the nanocomposites were radiated at doses of 50–200 kGy. The change in mechanical properties, especially, tensile strength (Ts), elongation at break (Eb), hardness and tensile modulus at 100% elongation (M₁₀₀) were studied as a function of radiation dose. The structure and morphology of reinforced natural rubber was investigated by FESEM, TEM and AFM in order to gain further evidence on the radiation-induced crosslinking. It was found that the Ts, M₁₀₀ and the hardness of the SMR/CNT nanocomposites significantly increased with radiation dose; the elongation at break exhibited an increase up to 100 kGy, and a downward trend thereafter. Results on gel fraction further confirmed the crosslinking of SMR/CNT nanocomposites upon radiation.