Chrome-tanned leather shavings as a filler of butadiene-acrylonitrile rubber

The noxious wastes from the tanning industry such as chrome-tanned leather shavings were used as the only filler of rubber mixes containing carboxylated butadiene-acrylonitrile rubber (XNBR) or butadiene-acrylonitrile rubber (NBR), and a dispersing agent Limanol PEV (Schill & Seilacher). The best form addition of leather powder to the rubber mixes is mixed the waste protein with zinc oxide. The leather powder added to the rubber mixes improves the mechanical properties: tensile strength (T(s)), elongation at break (epsilon(b)) and increase the cross-linking density of carboxylated XNBR and NBR rubber mixes. Satisfactory results of these studies are presented in this work.     

Mechanical reinforcement in natural rubber/organoclay nanocomposites

Aim of this work is to get an insight into the mechanisms by which nanofillers produce mechanical reinforcement in polymers above their glass transition temperature. To this purpose, the mechanical behaviour of natural rubber/organo-modified montmorillonite vulcanisates produced by melt mixing with various filler contents was investigated. Data of the initial modulus, evaluated from stress–elongation curves obtained in tensile tests carried out at room temperature and a fixed cross-head rate, were analysed as a function of the organoclay content by applying mechanical models proposed in the literature. Such analysis provided an evaluation of the filler percolation threshold. Further, tests performed with varying temperature and rate pointed out appreciable rate and temperature dependence only for samples containing amounts of organoclay higher than the percolation limit, that is in presence of filler networking. Such a typical viscoelastic behaviour associated to the presence of the filler network contributes to support the hypothesis that in filled rubbers the mechanisms of filler networking is based on the formation of confined regions of immobilised polymer that join the filler particles of the network, as recently proposed.     

Master curve of filler localization in rubber blends at an equilibrium state

In this study, the phase-specific localization of filler in NBR/NR blends was characterized by means of the selective extraction method and wetting concept. A strong dependence of silica localization on the filler loading was found. A model based on thermodynamic data was proposed for a quantitative prediction of filler localization in rubber blends. The filler localization can be described by a master curve demonstrating a characteristic behavior in dependence on the filler surface tension data of blend components and filler. The effect of filler loading on the silica localization is sufficiently explained by this model by taking into consideration the deactivation of the silanol groups on the silica surface by adsorbed curing additives. Using the master curve, the surface tension of filler affected by curing additives and silane addition can be estimated that may be useful for evaluation and comparison of the effect of different coupling agents. Surface tension values of different fillers were estimated by means of the master curve and they lie in the same order compared to those reported in literature. A potential transfer of filler within a rubber blend can be also quantitatively predicted.     

Feasible incorporation of devulcanized rubber waste in virgin natural rubber

Devulcanized rubber waste produced from end-of-life passenger tyres by continuous shear flow stage control reaction technology was used both as filler and as part of rubber in a natural rubber matrix to develop the use of the rubber compound and lower the cost. The measurements of cure characteristics, swelling behaviour, crosslink density and dynamic and mechanical properties were carried out in our laboratory. In the present study it was found that using devulcanized rubber as part of rubber yields much better properties than using it as filler. Up to 15 phr devulcanized rubber used as filler and up to as much as 50 phr devulcanized rubber used as part of rubber can be incorporated in a new product without any noteworthy deterioration in performance arising.     

Conductive rubber composites from different blends of ethylene-propylene-diene rubber and nitrile rubber

Conductive rubber composites were derived from different blends of ethylene-propylene-diene monomer (EPDM) rubber and acrylonitrile butadiene rubber (NBR) containing acetylene black. The electrical and mechanical properties of these composites were measured. The percolation limit for achieving high conductivity of conductive filler depends on the viscosity of the blend. The higher the viscosity, the higher is the percolation limit. The conductivity rises with increasing temperature, and the activation energy of conduction increases with the decrease in the loading of conductive filler and percentage of NBR in the blend. Electrical hysteresis and an electrical resistivity difference during the heating-cooling cycle are observed for these systems, which is mainly due to some kind of irreversible change occurring in the conductive networks during heating. The mechanisms of conduction of these systems were discussed in the light of different theories. It was found that the degree of reinforcement by acetylene black in blends compares with those in the pure components NBR and EPDM. This is due to incompatibility of two elastomers in the blend. This revised version was published online in November 2006 with corrections to the Cover Date.     

Polymer-filler interactions in rubber reinforcement

The reinforcement of elastomers by finely divided fillers, particularly carbon black and silica, is fundamental to the rubber industry. Optimal reinforcement appears to involve both physical and chemical interactions. From a consideration of the effects of particle size as such, it appears that reinforcement, in the sense of tensile enhancement, will occur with any very finely divided filler. Physical factors prevent escape of the polymer from the filler surface (vacuole formation) but allow stress delocalization through interfacial slippage. Occasional stronger bonds may be introduced advantageously to facilitate dispersion, reduce particle/ particle interactions, and optimize practical properties relating to resilience and durability. Several lines of evidence suggest that only a minor amount of strong bonding is necessary or desirable, such that polymer/filler slippage can occur, under stress, over most of the interfacial area.     

Effect of the microstructure of a filled rubber on its overall mechanical properties

Mechanical behavior of filled rubber is very different from the corresponding unfilled gum rubber. To understand such difference, a multiscale material model of a filled rubber, which combines molecular mechanics, statistical mechanics and micromechanics, has been developed. The model has been used to explore how filler particles and filler–elastomer bond strength influence the overall elastic properties of a filled rubber. The model confirmed the well-established phenomena such as non-uniform strain amplification, but now, the model added much more detailed molecular information such as cross-linking density, bond strength at filler–elastomer interface, etc. to the whole phenomena. This capability enables us to investigate the influences of the factors on the overall mechanical properties of filled rubber. The results revealed that the degree of stretching is significantly amplified in elastomer chains that locate in between the filler particles along the loading direction. The degree of non-uniform stretching increases with filler volume fraction. The fully stretched elastomer chains contribute significantly greater force and stiffness than those that are stretched less. Both the Mullins effect and the Payne effect come from the non-uniform filler size and/or spatial distribution. Reducing non-uniformity of filler size and spatial distribution can decrease the degree of the Mullins effect and the Payne effect. Improving bond strength at filler–elastomer interface can delay the Mullins effect and the Payne effect but cannot eliminate them.     

Magnetic and processability studies on rubber ferrite composites based on natural rubber and mixed ferrite

Polycrystalline single phasic mixed ferrites belonging to the series Ni_1–x Zn _x Fe₂O₄ for various values of _x have been prepared by conventional ceramic techniques. Pre-characterized nickel zinc ferrites were then incorporated into a natural rubber matrix according to a specific recipe for various loadings. The processability and cure parameters were then determined. The magnetic properties of the ceramic filler as well as the ferrite loaded rubber ferrite composites (RFC) were evaluated and compared. A general equation for predicting the magnetic properties was also formulated. The validity of these equations were then checked and correlated with the experimental data. The coercivity of the RFCs almost resemble that of the ceramic component in the RFC. Percolation threshold is not reached for a maximum loading of 120 phr (parts per hundred rubber by weight) of the filler. These studies indicate that flexible magnets can be made with appropriate magnetic properties namely saturation magnetisation (M _s) and magnetic field strength (H _c) by a judicious choice of x and a corresponding loading. These studies also suggest that there is no possible interaction between the filler and the matrix at least at the macroscopic level. The formulated equation will aid in synthesizing RFCs with predetermined magnetic properties.     

Self-vulcanizable rubber blend system based on epoxidized natural rubber and chlorosulphonated polyethylene

A mill-mixed blend of epoxidized natural rubber and chlorosulphonated polyethylene becomes vulcanized during moulding in the absence of any vulcanizing agent. Such a system of self-vulcanizable rubber blend is miscible, as is evident from differential scanning calorimeter studies and dynamic mechanical analysis. The physical properties of the blend are comparable to those of conventional rubber vulcanizates and the blend can be reinforced by carbon black filler.     

The mechanical properties of rubber compounds containing soft fillers

A detailed examination of failure of properties of polybutadiene containing soft elastomeric fillers has previously been described [1]. Here the effect of filler modulus and filler-matrix adhesion on tear strength is measured. Tear behaviour depends upon the level of interfacial adhesion; when high, tear strength increases with increasing filler hardness, but if interfacial adhesion is low, incorporation of fillers may result in low tear strengths. An estimate of the edge flaw size is made from the tear strength and strain energy densities at break. It was found that compounds with low interfacial adhesion generally had edge flaw sizes of the same order as the maximum filler particle size. A correlation between tear strength and tear surface morphology is made.     

Filler dispersion evolution of acrylonitrile–butadiene rubber/graphite nanocomposites during processing

In this work, acrylonitrile–butadiene rubber/expanded graphite compounds with initial fine dispersion of nanosize graphite were prepared by latex compounding method, and then the dispersion evolution of the graphite during subsequent mixing and vulcanization was carefully investigated by using rubber process analysis, X-ray diffraction and transmission electron microscopy. The results showed that a significant filler network was already formed in the initial compounds because of the nanoscale dispersion and the high width/thickness ratio of graphite even at a content of less than 5 phr. During shearing, the graphite dispersion evolution is strongly related to the initial filler network. The filler network as well as the dispersion could also be obviously altered by changing the curing pressure and temperature during vulcanization, suggesting that the initial fine dispersion of graphite in the rubber/graphite nanocomposites could be maintained by reducing shear and by curing at a higher temperature and at a lower pressure.     

耐高温硅橡胶的配方研究

为提高硅橡胶的耐高温性能,确定最佳的实验配方,以乙烯基硅橡胶为基础胶,八氢基笼型倍半硅氧烷(T_8H_8)为交联剂,白炭黑为补强填料,纳米级氧化锡为耐热填料,制备出一种耐高温硅橡胶.该配方中T_8H_8为自行合成的耐高温硅橡胶交联剂,通过红外光谱(FTIR)、X射线衍射(XRD)、核磁共振氢谱(1HNMR)对T_8H_8结构进行表征,探究了不同配方对硅橡胶耐热性能的影响.结果表明,当乙烯基硅油用量为100 phr,T_8H_8中Si—H与乙烯基硅橡胶中Si—Vi的摩尔比为4∶1,白炭黑添加量为15 phr,氧化锡添加量为8 phr时,硅橡胶的初始分解温度达到489.77℃,拉伸强度为4.06 MPa,剪切强度1.69 MPa.     

Volume change and gas transport at uniaxial deformation of filled natural rubber

The volume dilatation of differently filled specimens of natural rubber has been measured using a deformation dilatometer. If the matrix detaches from the filler particles, hollow spaces form. The volume dilatation caused by this effect can be measured and calculated if the material is submerged in a liquid medium. The measured volume dilatation reflects the interaction between filler and matrix. If we take a measurement in a gas, only the volume dilatation of the matrix is recorded, but not that of the visible hollow spaces, because gas can diffuse from the measurement chamber into the sample. Stress-induced crystallization occurs with all samples. Its course due to deformation has been examined using a deformation calorimeter. Here an influence of the interaction between filler and matrix has been found. Filler particles which do not adhere closely to the matrix enhance the diminution of locally high tensions and deformations and thus hinder the stress-induced crystallization. The volume contraction caused by stress-induced crystallization can be recorded clearly only if one uses a liquid as the measurement medium. Due to gas exchange between the sample and its environment and the different gas solubilities in the amorphous and crystalline material no stress-induced crystallization can be detected. At the same time, a possibility opens up of determining gas solubilities in crystalline material.[/p]Dedicated to Professor Dr F. H. Müller on the occasion of his 80th birthday.     

Utilization study on red brick waste as novel reinforcing and economical filler for acrylonitrile butadiene rubber composite

Red brick waste (RBW) powder was used as a reinforcing filler for acrylonitrile butadiene rubber (NBR) for preparing eco-friendly composites. The main constituent of this waste is silica which is considered to be one of the traditional fillers used in the rubber industry. So it was worthwhile to get (RBW) in a suitable manner by using this waste as a filler for NBR. Physicomechanical properties were evaluated, including tensile strength, elongation at break, hardness shore A, and change in mechanical properties after thermal-oxidative aging for seven days at 90 °C. In addition, equilibrium swelling in toluene for prepared composites was also included. Moreover, cross-linking density was measured according to Flory Rehner's equation. From physicomechanical measurements, it is observed that the tensile strength and hardness (shore A) increased with increasing the waste filler content because of the red brick filler's stiffness. In contrast, the elongation at break and equilibrium swelling degree decreased with increasing the waste filler content. The morphology of the polymeric composites was monitored using a scanning electron microscope which reflects the uniform distribution of the filler inside the NBR matrix. The electrical and magnetic properties of NBR/RBW composites were evaluated. The electrical measurements revealed that the values of ε′ increase by increasing red brick waste while ε'' decreases by increasing filler content. The dc conductivity σ_dc values lie in the order of 10^–11 S/cm. This finding recommends that such composites could be used for insulation and antistatic applications. In addition, the magnetic measurements show superparamagnetic behavior in NBR/RBW composites. Therefore, the obtained composites be used as electromagnetic composites based on electrical and magnetic measurements.

Graphical Abstract

     

橡胶相尺度对亚微米或纳米橡胶颗粒填充环氧复合材料性能的影响

对比研究了由液体橡胶在环氧树脂中原位形成的亚微米橡胶/环氧复合材料和在环氧树脂中直接添加纳米橡胶颗粒形成的纳米橡胶/环氧复合材料的性能。研究表明：未固化混合物的黏度随着纳米橡胶相的加入逐渐增加,但随着亚微米橡胶相含量的增加而降低;橡胶/环氧复合材料的玻璃化转变温度随着纳米橡胶颗粒的加入逐渐增加,但随着亚微米橡胶相含量的增加而降低;两种橡胶相的添加均使复合材料的弹性模量降低,断裂延伸率增加;在较低含量时,纳米橡胶颗粒可以提高环氧的拉伸强度;两种橡胶填充的橡胶/环氧复合材料均显示出明显的增韧效果。微观形貌分析表明,两种橡胶均可以在应力作用下脱粘并促进裂纹尖端的塑性变形。     

Polymeric composites based on polystyrene and cement dust wastes

Due to the economical and environmental concern, polymer mortar and polymeric composites were prepared by mixing recycled polystyrene waste and cement dust waste as a filler. Virgin polystyrene and portland cement were used for comparison. Cement dust was treated by the reaction with stearic acid to increase the adhesion between the filler and the polymer matrix. The composites were prepared by mixing different concentration of treated and untreated cement dust (30, 50, 70 and 90 wt.%) with either virgin or recycled polystyrene. The suitability of the prepared polymeric composites as building materials in terms of mechanical properties, water absorption and chemical resistance was studied. After 1 week immersion in water, 10% sodium chloride (NaCl) and 10% sodium sulfate (Na₂SO₄) solutions, it was found that the chemical resistance and the mechanical properties were enhanced and the water absorption was retarded. The recycled polystyrene composites filled with treated cement dust gave the highest abrasion resistance and the lowest weight loss, also the best compressive and bending strength.     

Viscoelasticity studies for a fibrous collagen material: chrome-free leather

Chrome-free leather such as glutaraldehyde-tanned leather behaves very differently from chrome-tanned leather. Information regarding its viscoelasticity has not been previously reported. Hysteresis and stress relaxation are two essential properties associated with viscoelasticity. We have designed a cyclic tensile test to measure these properties to gain insight into the structural difference between chrome-free and chrome-tanned leather. Observations revealed that chrome-free leather tanned with glutaraldehyde has a higher hysteresis than chrome-tanned leather. Stress relaxation experiments, on the other hand showed chrome-free leather has very similar relaxation curves as chrome-tanned leather. Both leathers demonstrate a rapid decrease in stress for the first few seconds followed by a much slower decay thereafter. The chrome-free leather, however, has a greater initial stress than chrome-tanned leather, indicating a higher stiffness than chrome-tanned leather. Moreover, observations showed the viscoelasticity of leather was affected significantly by its fatliquor content. A decrease of loading energy in a cyclic stress–strain experiment resulted from higher fatliquor content in leather. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.     

Multi-phase toughened epoxy with poly(ether sulphone) and carboxyl-terminated butadiene-acrylonitrile rubber

The structure and properties of ternary blends of epoxy with poly(ether sulphone) (PES) and carboxyl-terminated butadiene-acrylonitrile rubber (CTBN) have been investigated. In these blends, the phase separation occurs in two stages: a macrophase separation during mixing and a microphase separation during curing. At low PES compositions, the PES-rich spherical domains are dispersed. With increasing PES composition, a co-continuous structure develops and, eventually, the phases are inverted. Regardless of structure change, the modulus and yield stress changes with composition just follow the simple rule of mixtures. However, the fracture toughness of these blends exhibits a synergistic effect. Among the various compositions, 55 weight ratio of CTBN to PES exhibited the maximum toughness, which was 140% larger than that calculated from the rule of mixtures. The synergism is believed to be due to the bridging by the PES-rich phase followed by a lowering of the yield stress. The lowering of the yield stress can enlarge the process zone size and the amount of plastic dilatation of the matrix.     

The effect of dispersed paint particles on the mechanical properties of rubber toughened polypropylene composites

The influence of dispersed paint particles on the mechanical properties of rubber toughened PP was investigated. The matrix was basically a hybrid of PP, rubber and talc. Model systems with spherical glass bead filled matrix were also studied to examine the effect of filler shape and size. Properties like tensile strength, strain at break, impact strength, and fracture toughness were influenced by the dispersed inclusions. Tensile strength at yield decreased linearly according to Piggott and Leinder's equation. Strain at break decreased more drastically with paint particles than glass beads, revealing that irregularly shaped particles offered greater stress concentrations. The tensile strength and strain at break were less influenced by the size of paint particles whereas a slight decrease in the modulus values was observed with decreasing particle size. Impact strength and fracture toughness also decreased with increasing filler fraction. Lack of stress transfer between filler and matrix aided in reduction of impact strength. Decrease in fracture toughness was influenced by volume replacement and constraints posed by fillers. The size of paint particles had little effect on the impact strength and fracture properties at the filler concentration levels used in this investigation.     

NR/CSM/biogenic silica rubber blend composites

Biogenic silica (BSi) was added at different ratios to some polymer blends of polyisoprene rubber (NR) and chlorosulphonated polyethylene rubber (CSM) cured by conventional sulfur system. The reinforcing performance of the filler was investigated using rheometric, mechanical and swelling measurements, differential scanning calorimetry (DSC), thermogravimetric (TGA) and scanning electron microscopy (SEM) analysis. There was a remarkable decrease in the optimum cure time (t_c90) and the scorch time (t_s2), which was associated with an increase in the cure rate index (CRI), with filler loading up to 30 phr in the different blend ratios. The tensile strength and hardness was 4–5 Sh-A higher in the case for the different blend compositions, while the resistance to swelling in toluene became higher. SEM photographs show that the filler is located at the interface between the different polymers which induces compatibilization in the immiscible blends. DSC scans of the filled blends showed shifts in the glass transition temperatures Tg which can be attributed to the improve interfacial bonding between filler and NR/CSM matrix. A higher thermal stability of NR/CSM/BSi composites was detected.