Rubber-filler Interaction Research Articles

Effect of Sulfur Variation on the Vulcanizate Structure of Silica-Filled Styrene-Butadiene Rubber Compounds with a Sulfide-Silane Coupling Agent.

The vulcanizate structure of filled compounds is affected by filler–rubber interactions (FRI) and the chemical crosslink density (CCD) of the matrix rubber. In particular, in filled compounds using a silica–silane system, FRIs due to silica–rubber coupling are a major influencing factor for the vulcanizate structure and physical properties. In this study, the effect of sulfur variation on the vulcanizate structure of silica-filled solution styrene–butadiene rubber compounds using a sulfide–silane coupling agent was studied. The vulcanizate structure according to sulfur variation was quantitatively analyzed using the swelling test and Flory–Rehner and Kraus equations. As the sulfur content increased, both FRI and the CCD increased, and it was confirmed that sulfur variation influenced the silica–rubber coupling efficiency through increased FRI. In addition, field emission scanning electron microscope images showed that increased FRI contributed to improvements in silica dispersion, abrasion resistance, and energy loss characteristics.

Effect of Fillers on the Recovery of Rubber Foam: From Theory to Applications.

Natural rubber foam (NRF) can be prepared from concentrated natural latex, providing specific characteristics such as density, compression strength, compression set, and so on, suitable for making shape-memory products. However, many customers require NRF products with a low compression set. This study aims to develop and prepare NRF to investigate its recoverability and other related characteristics by the addition of charcoal and silica fillers. The results showed that increasing filler loading increases physical and mechanical properties. The recoverability of NRF improves as silica increases, contrary to charcoal loading, due to the higher specific surface area of silica. Thermodynamic aspects showed that increasing filler loading increases the compression force (F) as well as the proportion of internal energy to the compression force (Fu/F). The entropy (S) also increases with increasing filler loading, which is favorable for thermodynamic systems. The activation enthalpy (∆Ha) of the NRF with silica is higher than the control NRF, which is due to rubber–filler interactions created within the NRF. A thermodynamic concept of crosslinked rubber foam with filler is proposed. From theory to application, in this study, the NRF has better recoverability with silica loading.

Detailed investigation of the reinforcing effect of halloysite nanotubes-filled epoxidized natural rubber

The properties of rubber composite depend on the compatibility between rubber and filler. This is specifically of concern when preparing composites with very different polarities of the rubber matrix and the filler. Natural rubber (NR) and halloysite nanotubes (HNT) are one of the examples of the incompatible system. Epoxidized natural rubber (ENR) was used as the main matrix, with halloysite nanotubes (HNT) as a filler, in order to obtain composites with improved performance. ENR was prepared in house using performic acid with a controlled reaction time to obtain samples with mole epoxide levels from 10 to 40 mol%. Varying the mole epoxide levels was expected to optimize the formulation for this rubber composite. The compounds obtained were then investigated for the rubber–filler interactions of the ENR and HNT. By increasing the mole percentage of epoxide, the scorch and cure times were decreased while the maximum torque and torque differences increased. The ENR at 40 mol% epoxide exhibited least filler–filler interaction as shown from the Payne effect together with the supporting result from FTIR spectrum. However, this ENR compound did not yield the optimum tensile strength due to the constraint on the rubber–filler interaction. This study revealed that the use of ENR with a suitable mole percent of epoxide can dramatically reduce the filler–filler interaction and hence enhance the dispersion of HNT, which was seen from SEM micrographs, and resulted in enhancement of the mechanical and dynamical properties of the composites.

Influences of crosslinkable crystalline copolymer on the polymer network and filler dispersion of NR/ESBR/CB nanocomposites

Considering that the short service life and frequent replacement of the off-the-road tires (OTR) have raised critical environmental problems, the development of long service life OTR with low rolling resistance, high resistance to abrasion and fatigue holds great potential in resolving both environmental and resource issues. Herein, crystalline trans-1, 4-poly (butadiene-co-isoprene) (TBIR) is introduced into the traditional formula of the OTR tire tread stocks (natural rubber (NR)/emulsion polymerized styrene-butadiene rubber (ESBR)). The effects of TBIR on polymer aggregation structures, crosslinking networks, filler-rubber interactions and filler dispersion are examined and discussed in detail. It has been revealed that the TBIR-incorporated nanocomposites present reduced heat build-up and rolling resistance, outstanding abrasion and fatigue resistance. The study is expected to propose effective strategy to develop “green” OTR tire tread stocks with excellent performances like low rolling resistance and prolonged service life.

Intrinsic properties of the matrix and interface of filler reinforced silicone rubber: An in situ Rheo-SANS and constitutive model study

The intrinsic properties of the silicone rubber matrix reinforced by filler silica have been investigated with in situ rheo-small-angle neutron scattering (SANS) and deuterated chain labeling. SANS results reveal that: (i) the average diameter of aggregates and the thickness of bound rubbers (BR) are about 81 nm and 5.6 nm, respectively. (ii) The aggregates size distribution of the filler network is statistically stable during deformation. (iii) Strain mainly causes the agglomerate breakdown/reconstruction and the rubber matrix deformation. Interestingly, the evolution of the aggregates covered with BRs has the similar tendency to the nonlinear strain-stress curve (SSC). However, the tendency of the BR evolution diverges from the SSC. Considering the hydrodynamic amplification effect of filler and the filler-rubber interaction, a modified constitutive model is established and utilized to correlate the macroscopic properties with the micro-structure evolution of silicone rubber. The results suggest that the reinforced rubber matrix might play the dominant role in sustaining the external loading with a hardening effect. While filler presents contradiction effects for reinforcing yet suffering from the agglomerate breakdown and the interface weakening.

Correlation between the Crosslink Characteristics and Mechanical Properties of Natural Rubber Compound via Accelerators and Reinforcement.

The extreme elasticity and reversible deformability of rubber, which is one of the most versatile polymers in modern society, is dependent on several factors, including the processing conditions, curing system, and types of additives used. Since the rubber’s mechanical properties are influenced by the existing structural crosslinks, their correlation with the crosslink characteristics of rubber was investigated using the equilibrium swelling theory of the Flory–Rehner equation and the rubber–filler interaction theory of the Kraus equation. Herein, we examined whether the accelerator and reinforcement agent quantitatively contributed to chemical cross-linkages and rubber–filler interaction. In conclusion, the accelerator content supported the chemically crosslinked structures of the monosulfides and the disulfides in natural rubber (NR). Additionally, these results demonstrated that the mechanical properties and the thermal resistance of NR were dependent on the crosslink characteristics. The findings of this study provide an insight into the development and application of NR products for the mechanical optimization of rubber-based products.

New insight into structure-property relationships of natural rubber and styrene-butadiene rubber nanocomposites filled with MWCNT

The outstanding properties of carbon nanotubes (CNT) have generated a lot of interest at a scientist and industrial level. CNT have attracted great attention due to their exceptional mechanical, electrical and thermal properties and also for their large aspect ratio, that is, small size and higher surface area. On this regard, CNT-rubber composites have been prepared, using natural rubber (NR) and styrene butadiene rubber (SBR) as matrices, and varying the amount of filler from 0 to 20 phr. In order to understand and optimize the properties of these materials, a fundamental and systematic study has been done with the aim of quantifying the relative contribution of the different factors that determine the reinforcing effect of these nanoparticles. The results obtained from the different characterizations of the composites (study of the electrical and mechanical properties, Payne effect, dynamical mechanical analysis, low field NMR and swelling experiments) reveal a good filler-rubber interaction, a high reinforcement effect, and an increase on the electrical conductivity of the compounds. However, all these improvements are limited by the detrimental effect of the CNT on the vulcanization process.

VULCANIZATE STRUCTURES AND MECHANICAL PROPERTIES OF RUBBER COMPOUNDS WITH SILICA AND CARBON BLACK BINARY FILLER SYSTEMS

ABSTRACTThe physical properties of rubber compounds are mainly determined by the filler dispersion within the rubber matrix, filler–rubber interaction, and chemical crosslink structure caused by sulfur. Carbon black or silica is typically used as a reinforcing filler in tire tread compounds; however, binary filler systems comprising the two types of filler are also currently being used to complement each other. This study used binary filler systems to manufacture vulcanizates and classified the vulcanizate structures as chemical crosslinks caused by sulfur, physical crosslinks caused by carbon black (carbon black–bound rubber), and silica–silane–rubber networks caused by silica and silane. The effect of each vulcanizate structure on the physical properties was also calculated. In the proposed binary filler system, silica chemically bonds with rubber molecules, unlike carbon black. Therefore, the crosslink density per unit of silica content was 19% higher than that of carbon black, in which rubber molecules were physically adsorbed on the surface. Tensile properties affected by 1 unit of crosslinking density for each filler were calculated, and silica was found to contribute more in the low-elongation range, whereas carbon black contributed more in the high-elongation range. Regarding tan δ at 60 °C and abrasion resistance per unit crosslink density of filler, carbon black made a greater contribution than silica, whereas silica had a greater contribution to wet traction and snow traction.

PHYSICOELECTRICAL PROPERTIES AND PIEZORESISTIVE SENSING OF THE EXTRUSION-BASED CONDUCTIVE RUBBER COMPOSITES: SIMULTANEOUS EFFECTS OF THE EXTRUSION PARAMETERS

ABSTRACT Flexible conductive rubber composites (CRCs) were prepared based on carbon black–filled oil-extended styrene–butadiene rubber soft matrix. Using a variety of screw designs, the simultaneous effects of the twin-screw extrusion parameters (i.e., kneading element, dispersing position, and screw speed) on the physicoelectrical properties of the CRCs were investigated statistically. The increased intenseness of the extrusion parameters significantly enhances the piezoresistive sensing via the improved filler dispersion, increased rubber–filler interaction, and weakened filler–filler networks. Nevertheless, the influence of the kneading elements on the properties of the CRCs significantly decreases with an increase in the intenseness of the dispersing position or the screw speed, referred to as a “negative interaction.” An extreme intenseness of the screw design causes the excellent piezoresistive sensing of the CRCs, but with undesirable mechanical strength. Because those properties need to be balanced, many methods of adjusting the CRCs to be more suitable for strain-sensor application, in terms of not only piezoresistive performance but also mechanical strength, were thus established.

Ultrasonic Extrusion of NR Gum and Its Effect on the Structure and Properties of Unfilled and Silica‐Filled NR

Natural rubber (NR) has been extruded without and with ultrasonic treatment at various ultrasonic amplitudes. The effect of ultrasonic treatment on structure of NR, its compounds with silica and silica/silane and their vulcanizates have been studied. Processing‐structure‐properties relationship of untreated and treated materials has been established. With the increase of ultrasonic amplitude power consumption is increased and die pressure is reduced. Size exclusion chromatography measurements show that the NR molecular weight is reduced with the ultrasonic treatment. The storage modulus and loss modulus, complex viscosity and loss tangent results also confirmed the degradation of NR chains by imposition of ultrasound, especially after treatment at high amplitude. After mixing with silica and silica/silane, it was found that degradation of NR caused a reduction in the rubber–filler interaction, an increase in the filler–filler interaction and flocculation upon heating. Physical properties of vulcanizates including M100, ultimate elongation, and stress at break are also deteriorated. POLYM. ENG. SCI., 60:925–934, 2020. © 2020 Society of Plastics Engineers

The effect of non-rubber components on mechanical properties of TESPD silane coupling agent in silica-filled rubber compounds

Silica is reinforcing filler with high polarity, leading to the difficulty to get the homogenous mixing with a natural rubber (NR) compound, which normally becomes silica agglomeration. A silane coupling agent is applied in a silica-filled NR compound in order to enhance compatibility between silica and rubber. Moreover, non-rubber components, especially proteins, are believed to have competition with silane coupling agent during a silanization [1, 2]. In this work, the interaction between the silane coupling agent and silica-filled NR materials was investigated to show the components influencing in the filler-filler and filler-rubber interaction as well as mechanical properties. The rubber types with different non-rubber components such as fresh NR, deproteinized NR (DPNR) and polyisoprene rubber (IR), absence of non-rubber constituents were mixed with bis-triethoxysilylpropyl disulfide (TESPD) and silica by using an internal mixer at high temperature. Payne effect of the unvulcanised rubber samples were characterized to study silica dispersion, respectively. A swelling test was used to determined crosslink density in the rubber samples after a vulcanisation system. In addition, the effect of non-rubber components on mechanical properties of rubbers was investigated to find the relationship between the crosslink density and filler-rubber network.

Effect of acrylonitrile butadiene rubber on the properties of silica-reinforced natural rubber

The effect of acrylonitrile butadiene rubber (NBR) as a compatibilizer in silica-reinforced natural rubber (NR) is studied. NBR, Emulcril 3380 with 32-34%, was various at 5, 10, 15, 20 and 25 part per hundred parts of rubber (phr) to be used as a compatibilizer for silica-filled NR. The use of NBR as a compatiblizer can improve cure time (T90), cure rate index (CRI), and Mooney viscosity of silica-filled NR compounds, but the re-agglomeration of filler still observes. The use of NBR does not show significantly effect on bound rubber contents. However, tensile strength, reinforcement index and tear strength are increased with increasing amount of NBR contents due to a presence of some rubber-filler interaction through acrylonitrile groups of NBR and silanol groups on the silica surface. It leads to observe more surface roughness on tensile fractured surfaces.

Strain-rate independent small-strain-sensor: Enhanced responsiveness of carbon black filled conductive rubber composites at slow deformation by using an ionic liquid

Small-strain-sensors, based on conductive carbon black (CB) filled conductive rubber composites (CRCs), have been developed. An ionic liquid (IL) was used to improve the way that the piezoresistive response is independent of strain rate at small strains. Cyclic sensing behaviour at small strains was investigated under a sequential alteration of strain rates. At small strains, the CRCs without IL respond inefficiently to slow deformation cycles, giving a strain-rate dependent sensitivity. On the contrary, the presence of IL enhances the response to slow deformations. At elongations up to 3%, the loosely packed conducting parts and the sufficient rubber-filler interaction achieved with the use of an IL/CB ratio of 1.0 make the piezoresistive responses efficiently independent of the strain rates. Also, the sensitivity is at least threefold higher, compared with CRCs without IL. So, the IL enables the construction of strain-rate independent small-strain-sensor.

Self-assembled lignin-silica hybrid material derived from rice husks as the sustainable reinforcing fillers for natural rubber

Biomass derived fillers have been developed as sustainable substitution of carbon black (CB) used in rubber industry to reduce the dependence on fossil fuels. Lignin is the abundant component of biomass, but has poor reinforcing performance due to its huge particle size. In this work, we prepared a lignin/silica (LS) hybrid material from rice husks via a facile self-assembly method. The formation of LS cut lignin macromolecules into fragments and resulted in a small average particle size of 320 nm. When LS was filled into the natural rubber to substitute 10 phr CB, both filler-filler interaction and filler-rubber interaction were enhanced compared with the single use of CB. In consequence, the obtained 10LS/40CB/NR vulcanizates showed overall improvement in tensile strength, tear strength and abrasion resistance compared with the 50CB/NR vulcanizates. For the sustainable development of rubber industry, the natural LS hybrid material with low production cost is a promising reinforcing filler for the partial replacement of CB.

Using chloroprene rubber waste in rubber blends: optimizing performance by adding fillers

In the present study, chloroprene rubber waste (CRW) was used in an attempt to extend its use and create a value-added material based on natural rubber (NR) and CRW blends. Conventional fillers including carbon black (CB), silica (SS) and calcium carbonate (CC) were used individually to optimize the performance of the rubber blends. The properties evaluated were the curing characteristics, physical and dynamic properties and thermal stability. From the results obtained, it is clear that the type and amount of filler play a crucial role in promoting the performance of the blend. A faster curing rate was observed for the blends containing CB and CC, while SS-filled NR/CRW blends showed the opposite trend. SS-filled NR/CRW blends exhibited tremendously improved tensile properties compared with CB- and CC-filled blends. This is because two types of competing interactions/reactions take place: the dipole–dipole interaction between SS and CRW and the silane coupling reactions. The tensile properties are also in good agreement with the observed dynamic properties. A higher storage modulus and a lower damping factor were found in the blends containing CB and SS, indicating more restricted molecular mobility caused by rubber–filler interactions.

Enhancement of thermal conductivity and mechanical properties of silicone rubber composites by using acrylate grafted siloxane copolymers

Thermally conductive composites have attracted much attention due to their application in the thermal management of electronics. But most of the thermally conductive composites exhibit poor filler dispersion and weak filler-polymer interfacial interaction, which would deteriorate the mechanical properties and impede the enhancement of thermal conductivity. Herein, three new copolymers were synthesized through hydrosilylation reaction of poly(dimethylsiloxane-co-methylhydrosiloxane) (PDMS-PHMS) with methyl methacrylate (MMA), glycidyl methacrylate (GMA), and 3-(trimethoxysilyl)propyl methacrylate (MPS), respectively. The copolymers were used to enhance the thermal conductivity and mechanical properties of Al2O3/silicone rubber (SR) composites. MPS grafted PDMS-PHMS and GMA grafted PDMS-PHMS could increase the bound rubber content of Al2O3/SR compounds, and increase the crosslink density and filler-rubber interaction of Al2O3/SR vulcanizates. The addition of MPS grafted PDMS-PHMS into an Al2O3/SR (500/100) composite could increase the tensile strength and elongation at break from 1.72 MPa and 33.0% to 3.69 MPa and 56.9%, respectively, and increase the thermal conductivity from 1.42 to 1.73 W/(m·K). The MPS grafted PDMS-PHMS/Al2O3/SR composite was successfully used as a thermal interface material between a LED chip and a heat sink, showing outstanding thermal management capability as a thermally conductive composite.

Effect of NR-g-cellulose coupling agent into NR-cellulose composite dispersibility and its physical properties

Natural rubber and cellulose are two materials with very different compatibility, so it is difficult to produce homogenous composite without using coupling agent. Natural rubber is nonpolar while cellulose is polar. The combination of natural rubber with cellulose is expected to produce composite with higher strength. The reinforcement concept of polymeric materials, such as natural rubber with cellulose as filler, results from increased rubber-filler interactions. This study aims to determine the effect of NR-g-Cellulose as coupling agent on the dispersibility of the composite and its physical properties. Hexamine/resorcinol and silane were used as a reference for a commercial coupling agent. Cellulose material was mixed in two-roll open mill together with natural rubber and other chemicals using three types of coupling agents, hexamine/resorcinol, silane, and NR-g-Cellulose. The FESEM result of the surface of composite indicated that composite with NR-g-Cellulose as coupling agent showed homogenously dispersed compared to two other types of coupling agent but it is lower in physical properties, especially in tensile strength, tear strength, compression set, and rebound resilience of the composite. It may be caused by the NR-g-Cellulose coupling agent not working optimally and therefore it needs a high temperature to optimize the coupling agent to react with natural rubber and cellulose.

Design of Elastomeric Bridge Bearing Pad Compound Formula Based on Hydrogenated Natural Rubber

Laminated elastomeric bearing pad which is commonly produced by natural or chloroprene rubber is functioned as isolation system in bridge or flyover structures. In the research, hydrogenated natural rubber (HNR) was evaluated its feasibility to be used as base elastomer on steel-laminated bearing pad production by designing rubber compound formula. The compounding procedures of HNR applied various vulcanization system and carbon black filler types. The physical and mechanical tests result showed that only hardness parameter could fill the standar quality requirement of commercial elastomeric bearing pad as stated in AASHTO M251 in the range of 50 "“ 70 Shore A scale. The tensile property and compression set value of the HNR vulcanizates were under the requirement. This was due to low rubber-filler interaction and rigidity of crosslink network. The low interaction was more evident with increasing carbon filler particle size. By adjusting semi efficient vulcanization system and used N220 as carbon filler in designing compound formula,HNR was regarded as alternative promosing base elastomer for elastomeric bridge bearing pad manufacture. Nevertheless, it was necessary to improve the procedure to achieve better tesile property and compression set parameter.

An innovative approach to utilize waste silica fume from zirconia industry to prepare high performance natural rubber composites for multi-functional applications

Silica fume (SF) is silica-rich amorphous waste by-product obtained during zirconium silicate electrofusion process. The key objective of the study was to determine the efficiency of SF as a reinforcing filler in Natural Rubber (NR) compounds vis a vis the conventional filler, high abrasion furnace (HAF) black. Inter-particle distance and particle size distribution analysis from Transmission Electron Microscopy exhibited homogeneous dispersion of filler in hybrid composite (NR SF20/HAF30) with Bis[3-(triethoxysilyl)propyl] tetrasulfide (TESPT). NR composite with 20 phr SF loading improved modulus by 107%, tensile strength by 12%, and tear strength by 28% over gum NR. Hybrid composite showed 111% increase in modulus than NR SF20 composite. Theoretical modelling of Young's modulus with volume fraction of filler quite fit with Guth-Gold equation. Hybrid composite with TESPT showed 72% reduction in heat build-up compared to NR HAF50 composite. Thermal stability improved by 6 °C and rolling resistance reduced by 64% for hybrid TESPT composite compared to NR HAF50 composite. Constrained region in NR composites obtained from dynamic mechanical analysis showed improved rubber-filler interaction in hybrid TESPT composite. Hence, this work not only provides a new approach to utilize industrial waste but also provides for a high performance NR composite at low cost.

INFLUENCES OF THE COMPATIBILITY OF NR/SSBR AND PHASE-SELECTIVE DISTRIBUTION OF SILICA ON ITS STATIC AND DYNAMIC PROPERTIES

ABSTRACT The compatibility between solution polymerized styrene–butadiene rubber (SSBR 2466) and natural rubber (NR) is characterized by differential scanning calorimetry and dynamic mechanical thermal analysis. The single glass transition in the entire temperature range of all NR/SSBR blends and good correlation between Tg and SSBR fraction prove the excellent compatibility between SSBR 2466 and NR. With increasing SSBR content, a reduced Payne effect, more homogeneous dispersion of silica, stronger rubber–filler interaction, and more silica selectively distributed in the SSBR phase were determined via rubber-processing analysis, transmission electron microscopy, bound rubber, and thermogravimetric analysis, respectively. The high vinyl content, low styrene content, and end-functionalized structure of SSBR play vital roles in promoting its compatibility with NR and a stronger rubber–silica linkage. The resulting increased tan δ at 0 °C and low tan δ at 60 °C indicates good wet-skid resistance and low rolling resistance by blending SSBR 2466, and 70/30 NR/SSBR is the best balance for producing a “green tire” tread.