Effect of the Rubber Components on the Mechanical Properties and Braking Performance of Organic Friction Materials

Vegetable oil modified phenolic resin (PF) mixed with four kinds of rubber modifiers, i.e., styrene butadiene rubber, styrene butadiene 2-vinyl pyridine rubber, nitrile butadiene rubber, and carboxyl nitrile butadiene rubber (CNBR), were used as matrices for organic friction materials. The mechanical and thermal degradation properties of all of the blends were investigated. Friction and braking tests of the organic friction materials based on the different matrices and reinforced with hybrid fibers were carried out. The results showed that the resin was most compatible with CNBR; the CNBR/PF blend possessed much higher impact and toughness, and the friction material based on this blend as a matrix exhibited better friction and braking performance. It was concluded that CNBR, the rubber with the most reactive groups, resulted in better mechanical properties of the friction material, and hence optimized the friction, wear and braking performances.     

Effect of chemical treatment on dynamic mechanical properties of sisal fiber-reinforced polyester composites fabricated by resin transfer molding

The dynamic mechanical properties of treated sisal fiber-reinforced polyester composites fabricated by resin transfer molding (RTM) have been studied with reference to fiber surface modifications, frequency and temperature. The sisal fibers have been subjected to various chemical and physical treatments like mercerization, heating at 100°C, permanganate, benzoylation and vinyl tris(2-ethoxymethoxy) silane to improve the interfacial bonding with isophthalic polyester resin. Results indicated that treatment changed the storage modulus (E′), loss modulus (E″) and damping factor (tan δ) drastically at a wide range of temperature. The E′ value increased for every treatment, and is maximum for the composites fabricated by benzoylated-treated fibers. The T _g value obtained from the E″value showed an increase as compared to untreated fiber-reinforced composites. The alkali-treated fiber-reinforced composites showed lower tan δ value. Using Arrhenius' equation the activation energy was calculated and found maximum for the composites fabricated by alkali-treated fiber, which shows good fiber/matrix interactions.     

Effects of Chemical Structure of Phenolic Resin on Damping Properties of Acrylate Rubber-Based Blends

Two types of acrylate rubber (AR)-based damping blends were prepared by using two types of phenolic resins (PF), a resole resin (RR) and a novolac resin (NR), as organic fillers. The structure and damping properties of the AR/RR and AR/NR blends obtained by hot-pressing were characterized and compared by Fourier transform infrared spectrum, scanning electron microscopy, differential scanning calorimetry, and dynamic mechanical analysis. The results showed that the chemical structures of PF and the hot-pressing process had a significant effect on the damping properties of the AR-based composites. The loss peak of AR/RR shifted to a lower temperature accompanied with a gradually reduced peak intensity with the increase of RR content. In contrast, hot-pressed AR/NR showed great improvement in damping properties, which can broaden the effective damping temperature region and an increase in the temperature of the loss peak. It was thus concluded that NR with linear structure and abundant phenolic hydroxyl groups, which can create effective hydrogen bonds with an AR matrix, even after hot-pressing, makes it a promising NR to choose as an organic additive in ARs to prepare advanced damping blends.     

Insights into the Reinforcement of Butyl Rubber by Carbon Black and Silica with the Aid of Their Dynamic Properties

Carbon black (N234) and silica (Vulksail N) with a silane coupling agent Si-69 were chosen as reinforcing fillers in butyl rubber (IIR). The rheological behavior of the IIR compounds and the dynamic mechanical properties of IIR vulcanizates were investigated with a rubber processing analyzer and dynamic mechanical analysis (DMA) to examine the filler dispersion in the rubber matrix and the interaction between filler and matrix. The data indicated that the N234 filled IIR compounds had more filler networks than those filled with silica. Filler networks first appeared at 30 phr N234 and 45 phr silica with silane coupling agent Si-69. The interaction between N234 and IIR was far stronger than that between silica and IIR. However, the silica Vulksail N filled IIR had better wet-grip and lower rolling resistance compared to the carbon black-filled IIR should IIR be chosen as a substitute of styrene-butadiene rubber (SBR) in tire tread. The reinforcing factor, R, R (related to the difference in tan d peak height at T_g for the filled and nonfilled rubbers), also demonstrated that the N234-IIR interaction was stronger than for the silica. IIR with 30 phr N234 exhibited the largest tensile strength, 20.1 MPa, for those vulcanizates examined. The tensile and tear strengths of N234 filled IIR were higher than those of IIR with similar amounts of silica. Thus, it was concluded that N234 is a more active reinforcing filler in IIR than silica (Vulksail N) even with a silane coupling agent (Si-69).     

Effect of curing temperature,fibre loading and bonding agent on the equilibrium swelling of isora-natural rubber composites

Isora fibre-reinforced natural rubber (NR) composites were cured at 80, 100, 120 and 150°C using a low temperature curing accelerator system. Composites were also prepared using a conventional accelerator system and cured at 150°C. The swelling behavior of these composites at varying fibre loadings was studied in toluene and hexane. Results show that the uptake of solvent and volume fraction of rubber due to swelling was lower for the low temperature cured vulcanizates which is an indication of the better fibre/rubber adhesion. The uptake of aromatic solvent was higher than that of aliphatic solvent, for all the composites. As the fibre content increased, the solvent uptake decreased, due to the superior solvent resistance of the fibre and good fibre–rubber interactions. The bonding agent improved the swelling resistance of the composites due to the strong interfacial adhesion. Due to the improved adhesion between the fibre and rubber, the ratio of the change in volume fraction of rubber due to swelling to the volume fraction of rubber in the dry sample (V_τ ) was found to decrease in the presence of bonding agent. At a fixed fibre loading, the alkali treated fibre composite showed a lower percentage swelling than untreated one for both systems showing superior rubber–fibre interactions.     

Solid-state NMR investigation on mica-filled rubber composites

Rubber composites filled with carbon black and mica flakes were investigated by solid-state NMR and dynamic mechanical measurements. The results show that in rubber (butyl, EPDM, and chloroprene) and rubber composites filled with mica flakes there exists an interphase of considerable fraction with a different T₁ρ value from the matrix. The hindered segmental motion in this interphase appears in the dynamic mechanical measurement with a high and broad tan δ and a high loss modulus E". The value of E" increases with increasing percentage of mica.     

Effect of Silanes on Mechanical and Thermal Properties of Silicone Rubber/EPDM Blends

The effect of four types of silane coupling agents on the mechanical and thermal properties of silicone rubber and ethylene–propylene–diene monomer (M-class) rubber (EPDM) blends is studied, namely, isobutyltriethoxysilane (BUS), acryloxypropyltriethoxysilane (ACS), aminopropyltriethoxysilane (AMS), and vinyltriethoxysilane (VIS). ACS and VIS increase the crosslink density of the blends, which results in higher tensile strength, modulus, and thermal stability, but lower elongation at break compared with the other silanes. However, the blend containing BUS shows highest tanδ in the temperature range of 45°C to 200°C. Thermogravimetric analysis shows two steps of degradation for all the samples, but little difference with the varied silanes.     

Crosslinking-Dependent Relaxation Dynamics in Ethylene–Propylene–Diene (EPDM) Terpolymer above the Glass Transition Temperature

Dynamic mechanical experiments performed on ethylene–propylene–diene (EPDM) terpolymer, cross linked to different extents, evidenced three relaxation processes. Besides the glass transition (T_g) and the melting of the ethylene crystals formed in the ethylene-based EPDM, a new transition appeared at a temperature higher than the glass transition temperature (so-called tan δ_gh) and decreased dramatically in amplitude with increase in the degree of cure. The new transition (tan δ_gh) was also above the melting point. The viscoelastic properties of the rubber with various crosslinking degrees are described. Based on the behavior of tan δ_gh and the curing properties of EPDM, the tan δ_gh peak is primarily attributed to the motion of non-elastic network chains loosely attached to the three-dimensional network, including free chains.     

Temperature and frequency dependent electrical properties of 50 MeV Li3+ ion irradiated polymeric blends

The polymeric blends of polyvinyl chloride (PVC) and polyethylene terephthalate (PET) with equal composition by weight have been irradiated with 50 MeV Li³⁺ ions at different fluences. The AC electrical properties of polymeric blends were measured in the frequency range 0.05–100 kHz, and at temperature range 40–150 ^°C using LCR meter. There is an exponential increase in conductivity with log of frequency and effect is significant at higher fluences. The value of tan δ and dielectric constant are observed to change appreciably due to irradiation. The loss factor (tan δ) versus frequency plot suggests that the capacitors of polymeric blend of PVC and PET may be useful below 10 kHz. No change in dielectric constant was observed over a wide temperature range up to 150 ^°C. Thermal stability was studied by thermogravimetric analysis. Thermal analysis revealed that chain scission is the dominant phenomena in the polymeric blends resulting in the reduction of its thermal stability. It appears from differential scanning calorimetry studies that the melting temperature decreases as fluence increases. FTIR spectra measurements also revealed that the material suffered severe degradation through bond breaking beyond the fluence of 2.3×10¹³ ions/cm².     

Studies on the Dielectric Behavior of Silica-Filled Butyl Rubber Vulcanizates After Cyclic Deformation

Abstract

The broadband dielectric spectroscopy (10^?3–10⁶ Hz) is used to study the effect of stress-strain cycles on the dielectric properties of butyl rubber vulcanizates filled with silica. The influence of chemical modification of the surface of the silica by silane coupling agent (Si69) also was investigated. In addition Transmission Electron Microscopy (TEM) and Differential Scanning Calorimetry (DSC) were carried out. Dielectric investigations of the samples were done after stress-strain cycles with maximum elongation 26%, 40%, 60%, and 80% from elongation at break, respectively. It was found that the dielectric properties recovered after storage at room temperature for about one year.     

The Effect of Reclaim Softener on Properties of Reclaimed Rubber

The reclaiming process of full tire rubber powder with no treatment was carried out with a torque rheometer. The effect of reclaim softener types and loads on reclaiming and the properties of the revulcanized reclaimed rubber were investigated. The sol fraction significantly increased and the crosslink density gradually decreased with the increase of reclaim softener loads, but the reclaimed rubber with wood tar reclaim softener had the lowest sol fraction and highest crosslink density at the same loads as other reclaim softeners. The types of reclaim softener had almost no influence on the types of scission, but the proportion of main-chain scission increased with the increase of reclaim softener loads. An improvement of processability was observed with the increase of reclaim softener, but it was accompanied by a decrease in tensile strength. Dynamic mechanical properties of the reclaimed rubber were also investigated. The uncured reclaimed rubbers loaded with reclaim softener showed much lower G′values and slightly higher tan δ values than the reclaimed rubber without reclaim softener and the cured reclaimed rubbers showed much lower G′values and slightly lower tan δ values than the blank.     

Thermal,flexural, and impact strength studies on phenolic novolac resin/acrylonitrile–butadine rubber blends

Phenolic novolac resin was modified with nitrile rubber (NBR) using resol as compatibilizer. These systems were characterized by differential scanning calorimetry, flexural and impact strength. The resin was prepared by varying percentage of NBR. The curing behavior of unmodified and NBR-modified phenolic resin has been studied. The results reveal that the exothermic heat of cure for NBR-modified system increases due to the participation of the double bond of butadiene. In addition, the impact strength and flexural strain increase with increasing percentage of NBR in the phenolic resin matrix.     

橡胶硫化促进剂二硫化四苄基秋兰姆制备及光谱分析

以双氧水为氧化剂,采用二步法合成出了二硫化四苄基秋兰姆(TBzDT),通过FTIR,XRD,TG-DTA对其进行检测,揭示了TBzDT的微观结构。FTIR从化学键角度解析了TBzDT元素之间键型,XRD从晶胞参数、晶面指数等晶体学数据,揭示出TBzDT晶体微观结构,完成了TBzDT物相组成和结构的定性鉴定。TG-DTA检测出了TBzDT的质量变化与热效应两种信息,TBzDT的相变和分解温度分别为142.5,200.9 ℃,TBzDT的分解温度偏高,为采用硫化仪研究TBzDT的橡胶硫化性能提供参考。FTIR和TG-DTA从不同侧面揭示出样品TBzDT 中蕴含少量的SC₂。     

高压下制备的累托石/酚醛树脂复合材料微结构和热性能研究

 采用物理方法在高压下制备了酚醛树脂（PF）/累托石（REC）纳米复合材料,用X射线衍射（XRD）、透射电子显微镜（TEM）及热分析（DSC/TGA）等方法,研究了复合材料的物相、显微结构以及热学性能。结果表明,不通过层间高分子聚合反应,不预先对累托石进行有机化处理,在高压下,由聚合物分子插入粘土层间,可以形成剥离型树脂/粘土纳米复合材料,并且其热学性能发生了较大的改变。     

Analysis of t-butylphenol acetylene condensed resin with methyl-methine linkages in vulcanized rubber by pyrolysis-gas chromatography/mass spectrometry

Methyl-methine linkages of Novolac, a commercially available t-butylphenol acetylene condensed (TBPA) resin, have been identified by recognition of pyrolysis pathways using pyrolysis-gas chromatography/mass spectrometry (Py-GC/mS) in vulcanized rubber. The diagnostic mass spectrum of t-butylphenol with methyl-methine linkages between phenolic rings was observed at m/z 192, corresponding to 4-t-butyl-2-ethyl-6-methylphenol. Other molecular ions were observed at m/z 178, 164, and 150 in the characteristic pyrolyzates. The ion at m/z 192 in the TBPA resin was observed to be characteristic for methyl-methine linkages between the phenolic groups, and the analytical pyrolysis-GC/mS method was thus able to identify the resin at low levels in vulcanized rubber. Copyright 1999 John Wiley & Sons, Ltd.     

Damping Properties of Ethylene-Vinyl Acetate Rubber/Nitrile Butadiene Rubber Blends

The damping and mechanical properties of ethylene-vinyl acetate rubber (EVM)/nitrile butadiene rubber (NBR) blends, with BIPB (bis (tert-butyl peroxy isopropyl) benzene) as curing agent, were investigated by DMA. It was proved by mechanical performance, DMA and crosslink density data that a chemical crosslinking reaction occurred between EVM and NBR. A new tan δ peak appeared between 40°C and 60°C in EVM/NBR = 80/20, which we suggest was due to a new molecular chain generated between EVM and NBR. Thus, the effective damping temperature range (EDTR) of EVM/NBR = 80/20 was widened from 31.6°C of EVM and 31.7°C of NBR to 40.7°C. The addition of sulfur, as a curing agent for NBR, greatly raised the height of the damping peak of EVM/NBR blend, but only slightly widened the EDTR at a cost of deterioration of mechanical performance. Zinc diacrylate (Zn (Ac)₂), as a possible graft addition to the blends, enlarged the damping peak of EVM/NBR, especially widening the EDTR of EVM/NBR = 80/20 to 50.9°C, but with a decline of mechanical properties. PVC was partially miscible with EVM/NBR blends and dramatically widened the EVM/NBR = 80/20 EDTR to 62.4°C.     

Probing the properties of particle-matrix interphase in reactive rubber-grafted polybenzoxazine resins by atomic force microscopy

Atomic force microscopy (AFM) is employed to study the amine-terminated poly (butadiene-co-acrylonitrile) (ATBN) rubber-modified polybenzoxazine resin. Topographic mapping of the fracture surface is performed in conjunction with lateral force microscopy (LFM) and force–distance curve measurements (F–d). Matrix T _g reduction is attributed to the dissolved rubber and the increased mechanical damping (tan δ) is derived from the phase-separated rubber. Saturation of the rubber in the matrix is defined at 6 wt% above which the matrix T _g is not influenced upon rubber loading. The solubility limit of the reactive rubber in the matrix phase is determined from the fractured surface using LFM. The torsional force analyzed in the matrix phase increases upon the addition of rubber and levels off at 6 wt%. The results provide a direct correlation between bulk properties acquired by DMA and fractured surface probed by AFM. The presence of interphase between the separated rubbery domain and the continuous matrix phase is confirmed and its thickness is quantified from F–d curves. Moreover, it is found that interphase properties exhibit a strong rubber-concentration dependence.     

Combining pressurized liquids with ultrasound to improve the extraction of phenolic compounds from pomegranate peel (Punica granatum L.)

The combination of ultrasound and pressurized liquid extraction (UAPLE) was evaluated for the extraction of phenolic compounds from pomegranate peels (Punica granatum L.). The influence of several variables of the process on extraction yield, including solvent type (water, ethanol + water 30, 50 and 70% v:v), temperature (50–100 °C), ultrasound power (0–800 W at the generator, or 0–38.5 W at the tip of the probe), mean particle size (0.68 and 1.05 mm), and number of cycles (1–5), were analyzed according to the yield of 20 different phenolic compounds. The most suitable temperatures for the extraction of phenolic compounds using water were from 70 to 80 °C. In general, 100 °C was not adequate since the lowest extraction yields were observed. Results suggested that ultrasound had a greater impact on extraction yields using large particles and that intermediate ultrasound power (480–640 W at the generator, or 23.1–30.8 W at the tip of the probe) produced the best results. Using small particles (0.68 mm) or large particles (1.05 mm), extraction with ultrasound was 1 cycle faster. Ultrasound may have offset the negative effect of the use of large particles, however, did not increase the yield of phenolic compounds in any of the cases studied after five cycles. Additionally, the continuous clogging problems observed with small particles were avoided with the use of large particles, which combined with ultrasound allowed consistent operation with good intra and inter-day reproducibility (>95%). Using samples with large particle size, the best extraction conditions were achieved with water extraction solvent, 70 °C extraction temperature, ultrasound power at 480 W, and 3 cycles, yielding 61.72 ± 7.70 mg/g. UAPLE demonstrated to be a clean, efficient and a green alternative for the extraction of phenolic compounds from pomegranate peels. These findings indicate that UAPLE has a great potential to improve the extraction of bioactive compounds from natural products.     

Interface effect in the silicone rubber/mineral powder composites

Silicone rubber/mineral powder composites have been prepared by surface modification and ultrafinecrashing of mineral powder, mixing and vulcanizing with silicone rubber resin. The surface and interface energy for mineral filler and silicone rubber matrix were investigated. It was found that there is a correlation between W _a/σ_SL (interfacial adhesive work/interfacial tension) and the tensile strength of the corresponding composite, especially for unmodified ultrafine mineral filler. On the other hand, the chemical modification of the surface changes the surface group on the mineral filler and results in improvement of the interfacial interaction between silicone rubber matrix and mineral filler, consequently, altering the reinforcing effect of the mineral filler.     

橡胶硫化促进剂3-甲基-2-噻唑硫酮制备及光谱分析

采用一步法合成出了3-甲基-2-噻唑硫酮(MTT),通过FTIR,XRD,TG-DSC对其进行检测和表征,揭示了MTT的微观结构和内在规律性。FTIR揭示了MTT分子内部的各元素之间的化学键键型,XRD从晶胞参数、晶面指数等晶体学数据,变换出MTT晶体微观结构,完成了MTT物相组成和结构的定性鉴定。TG-DSC检测出了MTT的质量变化与热效应两种信息,MTT的相变和分解温度分别为76.3和306.9 ℃,MTT的分解温度偏高,为采用硫化仪研究MTT的橡胶硫化性能提供参考。本研究为企业选定工作标准品,对MTT工业化生产进行跟踪检测,评判MTT的产品性能指标,提供基础实验数据。