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 carbon nanofibers on mechanical and electrical behaviors of acrylonitrile‐butadiene rubber composites

Recently, carbon nanofibers have become an innovative reinforcing filler that has drawn increased attention from researchers. In this work, the reinforcement of acrylonitrile butadiene rubber (NBR) with carbon nanofibers (CNFs) was studied to determine the potential of carbon nanofibers as reinforcing filler in rubber technology. Furthermore, the performance of NBR compounds filled with carbon nanofibers was compared with the composites containing carbon black characterized by spherical particle type. Filler dispersion in elastomer matrix plays an essential role in polymer reinforcement, so we also analyzed the influence of dispersing agents on the performance of NBR composites. We applied several types of dispersing agents: anionic, cationic, nonionic, and ionic liquids. The fillers were characterized by dibutylphtalate absorption analysis, aggregate size, and rheological properties of filler suspensions. The vulcanization kinetics of rubber compounds, crosslink density, mechanical properties, hysteresis, and conductive properties of vulcanizates were also investigated. Moreover, scanning electron microscopy images were used to determine the filler dispersion in the elastomer matrix. The incorporation of the carbon nanofibers has a superior influence on the tensile strength of NBR compared with the samples containing carbon black. It was observed that addition of studied dispersing agents affected the performance of NBR/CNF and NBR/carbon black materials. Especially, the application of nonylphenyl poly(ethylene glycol) ether and 1‐butyl‐3‐methylimidazolium tetrafluoroborate contributed to enhanced mechanical properties and electrical conductivity of NBR/CNF composites.     

Thermal stability and flammability of styrene–butadiene rubber (SBR) composites

The article presents the effect of attapulgite (ATT) and its synergic action with carbon or silica on the thermal properties and flammability of cross-linked styrene–butadiene rubber. It has been shown that ATT is active filler improving the thermal and mechanical properties of composites containing this aluminosilicate. The decreased flammability of vulcanizates containing ATT compared to that of unfilled vulcanizates results from good insulating properties of the ATT used. The considerable reduction in the flammability of composites containing ATT and carbon nanofiber or silica is connected, first of all, with the formation of a homogeneous boundary layer.     

Formation of Network by Carbon Black，Silica and Their Mixing Fillers in Isoprene Rubber北大核心CSCD

The network formed by fillers has great influence on the mechanical properties of rubber materials. To understand the formation of network by carbon black,silica,and carbon black/silica mixing fillers in rubber and its influence on the properties of rubber,isoprene rubber/filler composites with different filler loadings are prepared and their micromorphology,rheological and tensile properties are investigated. It is found that the dispersion of fillers is better in rubber after cure than that in rubber before cure for all three rubber systems,and the filler size of silica is smaller than that of carbon black,but the aggregation is more severe in silica filled rubber system. In mixed filler system,the two fillers tend to aggregate separately, leading to the low modulus at small strain than that in single filler system. With the increase of the filler loading,the tensile strength increases first and then decreases,the elongation at break decreases,and the temperature rise in compression flexometer tests increases. Moreover,the temperature rise in mixed filler system is higher than that in single filler system at high filler loading. © 2022, Science Press (China). All rights reserved.     

Scanning electron microscopy studies on nitric acid corrosion of natural rubber vulcanizates

Natural rubber vulcanizates undergo severe corrosion when exposed to nitric acid. The nature and extent of damage with increasing degree of corrosion has been assessed by studies on the fall in mechanical properties, such as tensile strength and tear strength, and examination of scanning electron microscopy photomicrographs of the fracture surfaces of tensile and tear samples, both before and after acid treatment. It has been observed that, in the case of inert fillers, which simply dilute the rubber matrix, the filled vulcanizates disintegrate, on acid treatment, more quickly than the unfilled vulcanizates but that, when the filler is reinforcing, this effect is largely overshadowed by polymer-filler interaction which restricts acid corrosion.     

Reinforcement of compatibilized NR/NBR blends by fly ash particles and precipitated silica

Effects of precipitated silica (PSi) and silica from fly ash (FA) particles (FASi) on the cure and mechanical properties before and after thermal and oil aging of natural rubber (NR) and acrylonitrile–butadiene rubber (NBR) blends with and without chloroprene rubber (CR) or epoxidized NR (ENR) as a compatibilizer have been reported in this paper. The experimental results suggested that the scorch and cure times decreased with the addition of silica and the compound viscosity increased on increasing the silica content. The mechanical properties for PSi filled NR/NBR vulcanizates were greater than those for FASi filled NR/NBR vulcanizates in all cases. The PSi could be used for reinforcing the NR/NBR vulcanizates while the silica from FA was regarded as a semi‐reinforcing and/or extending filler. The incorporation of CR or ENR enhanced the mechanical properties of the NR/NBR vulcanizates, the ENR being more effective and compatible with the blend. The mechanical properties of the NR/NBR vulcanizates were improved by post‐curing effect from thermal aging but deteriorated by the oil aging. Copyright © 2008 John Wiley & Sons, Ltd.     

Visual research filler network structure in polymer composites and its structure-activity relationship by fluorescent labeling and LSCM

For organic-inorganic composite materials, the spatial dispersion of inorganic fillers in the organic matrix is of great significance for designing and manufacturing high-performance composite materials. To improve the understanding of the micro-physical mechanism of the filler-reinforced polymer matrix, we studied the relationship between filler network structure and macro-mechanical properties of silicone rubber by using fluorescent labeling technology and three-dimensional (3D) visualization imaging. The experimental results showed that a good filler network structure in the polymer matrix can more effectively dissipate external mechanical energy, which generate a visible mechanical strengthening effect. Additionally, this visualization method truly reflects the macrodispersion of the filler and the evolution of the filler network structure under dynamic stress due to its non-invasive and intuitive characteristics, which provides new theoretical guidance for the design of high-performance composites.     

The effect of crosslinking on mechanical properties of ldpe filled with organic fillers

Mechanical properties of low density polyethylene filled with various organic fillers were investigated. Different effect of different fillers on the properties was observed and the effect of crosslinking of these materials is also different. Fine anisotropic fillers behave similarly as inorganic fillers. The effect of crosslinking is the highest for composites containing large particulate fillers like beech wood flour. The effects are discussed in terms of mechanical behaviour and crosslinking degree determined from extraction or equilibrium swelling data. A formation of covalent bonds between the filler surface and polymeric matrix is proposed as a result of crosslinking.     

Thermal and mechanical properties of particulate fillers filled epoxy composites for electronic packaging application

Epoxy composites containing particulate fillers‐fused silica, glass powder, and mineral silica were investigated to be used as substrate materials in electronic packaging application. The content of fillers were varied between 0 and 40 vol%. The effects of the fillers on the thermal properties—thermal stability, thermal expansion and dynamic mechanical properties of the epoxy composites were studied, and it was found that fused silica, glass powder, and mineral silica increase the thermal stability and dynamic thermal mechanical properties and reduce the coefficient of thermal expansion (CTE). The lowest CTE value was observed at a fused silica content of 40 vol% for the epoxy composites, which was traced to the effect of its nature of low intrinsic CTE value of the fillers. The mechanical properties of the epoxy composites were determined in both flexural and single‐edge notch (SEN‐T) fracture toughness properties. Highest flexural strength, stiffness, and toughness values were observed at fillers content of 40 vol% for all the filled epoxy composites. Scanning electron microscopy (SEM) micrograph showed poor filler–matrix interaction in glass powder filled epoxy composites at 40 vol%. Copyright © 2007 John Wiley & Sons, Ltd.     

Understanding the effect of filler shape induced immobilized rubber on the interfacial and mechanical strength of rubber composites

Styrene butadiene rubber (SBR) composites with silica, halloysite nanotubes (HNTs) and montmorillonite (MMT) were prepared and the interfacial and mechanical properties were compared to understand the reinforcing behaviours of these fillers based on the results of SEM, DSC, DMA, etc. Due to the formation of interparticle domain, HNTs immobilized more rubber approaching their surface than silica and MMT. Interestingly, only tightly immobilized rubber chains made contribution to the enhancement of interfacial and mechanical strength of SBR composites. This was because the tightly immobilized rubber acted as a bridge in the filler-rubber interface and induced the formation of stretched rubber chains linked filler network when the composites were loaded in tension, while loosely immobilized rubber were easy to slip off from filler surface, causing the separation between filler and bulk rubber. Therefore, silica with more tightly immobilized rubber approaching its surface showed better reinforcing effect on rubber than HNTs and MMT.     

Comparison of reinforcing efficiency between Si-69 and Si-264 in a conventional vulcanization system

Silica has long been recognized as a reinforcing filler, especially for light colored products. The degree of reinforcement is noticeably increased when silica is used in combination with silane coupling agent. Therefore, various types of silane coupling agents are now commercially available. In the present study, two types of silane coupling agents, e.g., bis-(3-triethoxysilylpropyl) tetrasulfane (Si-69) and 3-thiocyanatopropyl triethoxy silane (Si-264) were selected for comparison of their reinforcing efficiency in a conventional vulcanization (CV) system. The results reveal that the addition of silane coupling agent not only improves compound processability, but also enhances the mechanical properties of the rubber vulcanizates. Compared with Si-69, Si-264 gives rubber compounds with better processability due to its greater ability to promote filler dis-agglomeration during mixing. In addition, Si-264 also imparts a greater degree of reinforcement. This might be attributed to the combined effects of better rubber–filler interaction, better filler dispersion and higher state of cure which are obtained when Si-69 is replaced with Si-264. The dynamic properties of the rubber vulcanizates are also improved with the presence of silane coupling agent. In this aspect, Si-69 performs better than Si-264 as it provides rubber vulcanizates with lower heat build-up.     

Calculation of the thermodynamic and adhesive properties of components of dynamically vulcanized thermoplastic elastomers

The solubility, polarity, compatibility of the components of dynamically vulcanized thermoplastic elastomers: natural rubber, polypropylene, and layered filler, which determine the composition and properties of composites were computed. On the basis of calculations components for dynamic thermoplastic composites were selected and composite materials with improved physical and mechanical properties were developed.     

Manipulation of mechanical properties of short pineapple leaf fiber reinforced natural rubber composites through variations in cross-link density and carbon black loading

The aim of this paper is to demonstrate that the stress–strain behavior of natural rubber reinforced with short pineapple leaf fiber (PALF) can easily be manipulated by changing the cross-link density and the amount of carbon black (CB) primary filler. This gives more manageable control of mechanical properties than is possible with conventional particulate fillers alone. This type of hybrid rubber composite displays a very sharp rise in stress at very low strains, and then the stress levels off at medium strains before turning up again at the highest strains. The composites studied here contain a fixed amount of PALF at 10 part (by weight) per hundred rubber (phr) and varying carbon black contents from 0 to 30 phr. To change the cross-link density, the amount of sulfur was varied from 2 to 4 phr. Swelling ratio results indicate that composites prepared with greater amounts of sulfur and carbon black have greater cross-link densities. Consequently, this affects the stress–strain behavior of the composites. The greater the cross-link density, the less is the strain at which the stress upturn occurs. Variations in the rate of stress increase (although not the stress itself) in the very low strain region, while dependent on fillers, are not dependent on the crosslink density. The effect of changes in crosslinking is most obvious in the high strain region. Here, the rate of stress increase becomes larger with increasing cross-link density. Hence, we demonstrate that the use of PALF filler, along with the usual carbon primary filler, provides a convenient method for the manipulation of the stress–strain relationships of the reinforced rubber. Such composites can be prepared with a controllable, wide range of mechanical behavior for specific high performance engineering applications.     

Sol–gel derived nano zinc oxide for the reduction of zinc oxide level in natural rubber compounds

Zinc oxide (ZnO) nanoparticles are synthesized by polymeric sol–gel method and characterized by X-ray diffraction, field-emission scanning electron microscopy. The cure characteristics, mechanical properties and thermal behaviour of natural rubber (NR) systems containing nano ZnO are investigated and compared to those of NR with micro-sized (conventional) ZnO. The NR vulcanizate with 0.5 phr (parts per hundred parts of rubber) sol–gel derived nano ZnO shows improvement in the curing and mechanical properties in comparison to the NR vulcanizate with 5 phr conventional ZnO. Thermogravimetric analysis reveals that nano ZnO impose better thermal stability than conventional ZnO in the NR vulcanizates. Thus, nano ZnO not only acts as a curing activator but also nano filler to improve the resulting properties of the NR vulcanizates. More essentially nano ZnO leads to the reduction of ZnO level in the NR compounds. Therefore, sol–gel derived nano ZnO diminishes the pollution of aquatic environment due to higher amount of conventional ZnO in rubber compounds.     

Development of Natural Rubber-Fibrous Nano Clay Attapulgite Composites: The Effect of Chemical Treatment of Filler on Mechanical and Dynamic Mechanical Properties of Composites

Common nano clay fillers have layered structure. Some nano clays like Attapulgite (AT), Sepiolite have rod like fibrous structure. Compared to layered structured clay fibrous clay AT can undergo better dispersion in polymer matrix leading to better improvement in composite properties. Chemical modifications of AT are done through amine treatment as well as by amine+silane treatment to get chemically modified fillers AAT and SAT respectively. In the present investigation, nano composites are prepared using natural rubber (NR) filled with AT, AAT and SAT. Three different loadings of each filler are used namely 2.5, 5, and 10 phr (parts per hundred of rubber). Mechanical properties like tensile strength, elongation at break increase with the increase in filler loading up to 5 phr there after these properties marginally fall when loading is increased to 10 phr due to problem of filler dispersion at higher loading. However, modulus at 300% elongation and tear strength increases with the increase in filler loading up to 10 phr. Very similar trend can also be observed for composites with chemically modified fillers, AAT and SAT. But the degree of reinforcement is higher in the case of AAT and SAT compared to that of unmodified filler AT for the same filler loading. This difference is mainly due to better polymer-filler interaction and filler dispersion in the case of chemically modified clays AAT and SAT compared to unmodified AT. Tear strength of composites increases remarkably with the addition of AT and which is further enhanced when chemically modified clays AAT and SAT are added. Dynamic-mechanical analyses of different clay composites give idea about the difference in the degree of polymer–filler interaction due to chemical treatment of filler.     

The addition of functionalized graphene oxide to polyetherimide to improve its thermal conductivity and mechanical properties

The thermal and electrical conductivity and mechanical properties of polyetherimide (PEI) containing either alkyl‐aminated (enGO) or phenyl‐aminated graphene (pnGO) oxides were studied. A solution casting method was used to prepare functionalized graphene oxide/PEI composites with different filler contents. The introduction of functionalized graphene oxide to the PEI matrix improved the thermal conductivity, electrical conductivity, and mechanical properties. The thermal conductivities of the enGO 3 wt%/PEI and pnGO 3 wt%/PEI composites were 0.324 W/mK and 0.329 W/mK, respectively, due to the high thermal conductivity of the graphene‐based materials and the strong interface adhesion due to the filler surface treatment between the fillers and the matrix. The electrical conductivities of the functionalized graphene oxide/PEI composites were larger than that of PEI, but the electrical conductivity values were generally low, which is consistent with the magnitude of the insulator. The strong interfacial adhesion between the fillers and the matrix led to improved mechanical properties. Copyright © 2014 John Wiley & Sons, Ltd.     

Properties of ethylene propylene diene rubber/white and black filler composites cured by gamma radiation in presence of sorbic acid

The effect of incorporating sorbic acid (SA), an echo-friendly curing agent, and silica or carbon black (CB) filler, as well as gamma irradiation on the physico-chemical, mechanical and thermal properties of ethylene propylene diene monomer rubber (EPDM) was investigated. The results indicated that the developed composites revealed improvement in the studied parameters over the untreated samples. Filler incorporation into rubber matrix has been proven a key factor in enhancing the swelling resistance, tensile strength and thermal properties of the fabricated composites. The improvement in tensile strength and modulus was attributed to better interfacial bonding via SA. Alternatively, a comparison was established between the performance of the white and black fillers. The utmost mechanical performance was reported for the incorporated ratios 10 phr SA and 40 phr white filler into a 50 kGy irradiated composite. Meanwhile, the incorporation of CB yielded better thermally stable composites than those filled with silica at similar conditions.     

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.     

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.     

New Inorganic Components for Dental Filling Composites

Dental composite filling materials are improved by incorporating nanofillers. They impart increased hardness and wear resistance to composites. In addition, they produce better polishing results than macrofillers. If the particles are sufficiently small, transparent composite pastes are obtainable, independent of the refractive index of the polymerisable monomers. In this context, organosols, non-agglomerated nanoparticles in organic liquid media, are especially interesting. Some of our own results on organosols are presented in this paper. Their relatively low viscosity enables the preparation of composites with a high filler load, thus reducing the shrinkage of the dental composite during polymerisation and improving the mechanical properties. Inorganic–organic hybrids are an attractive class of materials for dental fillings. The synthesis of different polymerisable ormocers for dental composites is reviewed in the second part. Ormocers can be applied as a polymerisable matrix, improving biocompatibility and wear resistance. Their use as inorganic fillers improves the thermodynamic compatibility of the filler with the matrix and enhances the polishability. Functionalised inorganic clusters used as new additives combine the properties of very small nanoparticulate fillers and well-designed highly functional monomers with high crosslinking capabilities. Xerogel colour pigments are advantageous alternative additives to conventional pigments. 3-D structural colour pigments, which are obtained by the self-assembly of monodisperse spherical particles, produce an opalescent effect resembling that of the natural enamel in highly aesthetic composites.