Nonlinear viscoelasticity and stress‐softening behavior of chloroprene rubber reinforced by multiwalled carbon nanotubes

The viscoelasticity and stress‐softening behavior of chloroprene rubber (CR) filled with multiwalled carbon nanotubes (MWCNT) and carboxylated multiwalled carbon nanotubes (MWCNT‐COOH) were studied using a Rubber Process Analyzer 2000 (RPA2000). In the strain sweep measurements, it is found that CR/MWCNT and CR/MWCNT‐COOH compounds have different behavior on storage modulus (G′). With increasing strain, G′ of CR/MWCNT (100/8) compound decreases at strain less than 2°, while G′ of CR/MWCNT‐COOH (100/8) compound stays at constant, indicating that MWCNT‐COOH has stronger filler–filler network and filler–rubber interactions as compared to MWCNT in CR matrix. CR/MWCNT (MWCNT‐COOH) vulcanizates have higher G′ but lower loss modulus (G″) than the corresponding uncured compounds. Repeated strain sweep scans were carried out to study the stress‐softening behavior of CR compounds. A stress‐softening effect of the filled CR compounds is observed and becomes more pronounced with increasing loading of MWCNT or MWCNT‐COOH. The correlation between the Payne effect and stress‐softening effect of CR/MWCNT (MWCNT‐COOH) vulcanizates is also studied. It is found that the difference of the storage moduli at 0.1° and 10° strain amplitudes and the difference of storage moduli of first and second strain sweeps at 0.1° strain amplitude show a positive linear correlation. POLYM. COMPOS., 35:2194–2202, 2014. © 2014 Society of Plastics Engineers     

Effect of fillers and additives on the properties of SBR vulcanizates

Methacrylic acid (MAA) and methyl methacrylate (MMA) were used as additives for peroxide‐cured styrene–butadiene rubber (SBR) filled with three inorganic fillers with different particle sizes and surface activity, for example, MgO, Mg(OH)₂, and BaSO₄. The experimental results show that the introduction of MAA can improve the mechanical properties of SBR vulcanizates filled with MgO, Mg(OH)₂, or BaSO₄. A small amount of MAA leads to significant increases in the modulus, tensile strength, and tear strength. MMA has little effect on the mechanical properties of the SBR vulcanizates. The SEM micrographs show that MAA can improve the interfacial bonding between SBR and the three kinds of fillers. The SBR–filler interaction was studied by Kraus plots. The relationship between the SBR–filler interaction and the mechanical properties was explored. m, a characteristic constant of a filler–SBR matrix, represents the interfacial bonding between fillers and SBR and the accumulated structure of the fillers. At a given ?, a high value of m means a strong interaction between SBR and the filler and, therefore, strong mechanical properties. The Payne effect of the SBR vulcanizates was observed, and the vulcanizates have low storage moduli at high strains and high storage moduli at low strains, and the moduli are nonlinear and increase the nonlinearity as the filler content increases. The loss moduli and loss factor reach their maximums at moderate and high strain amplitudes, respectively. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 775–782, 2003     

A simple theory of filler reinforcement in elastomers subjected to shear

The effects of a filler in an elastomer can be described by means of a theory based on a simple model in which the filler particles are assumed to be of uniform size, of cubic shape, and dispersed in such a manner as to occupy the points of a cubic space lattice. For the case of shear deformation, simple relations can be derived for the increase in the storage modulus G' and the loss modulus, G″ of the bulk material with an increase in filler content. Furthermore, the theory predicts the temperature shift of two points which can be easily determined experimentally: the inflection point of G' and the maximum of G″.     

Dynamic mechanical properties of SBR and EPDM vulcanisates filled with cryogenically pulverized flexible polyurethane foam particles

The dynamic mechanical properties of rubber vulcanisates filled with cryogenically pulverized polyurethane foam particles, used as a reinforcing filler, were investigated with respect to storage modulus (E′), loss modulus, and the variation of glass transition temperature. Two rubbers were using styrene–butadiene rubber (SBR) and ethylene–propylene copolymer (EPDM). The effects of filler concentration and filler characteristics (such as particle size and moisture content) were also monitored. It was found that the optimum dynamic mechanical properties of the compounds were obtained when introducing the PU particles of 40–50 parts per hundred (pph) rubber in the SBR and 30 pph in the EPDM, the properties being affected by the size of PU particles and moisture content. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1129–1139, 1999     

Fly ash particles and precipitated silica as fillers in rubbers. I. Untreated fillers in natural rubber and styrene–butadiene rubber compounds

In this study, we investigated the effects of untreated precipitated silica (PSi) and fly ash silica (FASi) as fillers on the properties of natural rubber (NR) and styrene–butadiene rubber (SBR) compounds. The cure characteristics and the final properties of the NR and SBR compounds were considered separately and comparatively with regard to the effect of the loading of the fillers, which ranged from 0 to 80 phr. In the NR system, the cure time and minimum and maximum torques of the NR compounds progressively increased at PSi loadings of 30–75 phr. A relatively low cure time and low viscosity of the NR compounds were achieved throughout the FASi loadings used. The vulcanizate properties of the FASi‐filled vulcanizates appeared to be very similar to those of the PSi‐filled vulcanizates at silica contents of 0–30 phr. Above these concentrations, the properties of the PSi‐filled vulcanizates improved, whereas those of the FASi‐filled compounds remained the same. In the SBR system, the changing trends of all of the properties of the filled SBR vulcanizates were very similar to those of the filled NR vulcanizates, except for the tensile and tear strengths. For a given rubber matrix and silica content, the discrepancies in the results between PSi and FASi were associated with filler–filler interactions, filler particle size, and the amount of nonrubber in the vulcanizates. With the effect of the FASi particles on the mechanical properties of the NR and SBR vulcanizates considered, we recommend fly ash particles as a filler in NR at silica concentrations of 0–30 phr but not in SBR systems, except when improvement in the tensile and tear properties is required. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2119–2130, 2004     

Effect of filler on the relaxation time spectra of filled polymers

The temperature and frequency dependences of the complex shear modulus G^* and tan δ of mechanical losses of epoxy compositions with various fillers were studied. The method of Ninomiya-Ferry applied to the reduced curves of frequency dependence of the effective part of the shear modulus was used to draw up relaxation time spectra for specimens with various concentrations of the filler. Regularities in the change of type and position of the spectral curves with increase in filler concentration were indicated. The findings make it possible to draw conclusions about the effect of the filler on the properties of the polymer matrix in the boundary layer and about changes in the conditions of the deformation of the polymer interlayers between the filler particles as compared with the deformations in bulk specimens.     

A Comparative Study on Curing Characteristics,Mechanical Properties,Swelling Behavior,Thermal Stability,and Morphology of Feldspar and Silica in SMR L Vulcanizates

Abstract

Comparison studies on effects of feldspar and silica (Vulcasil C) as a filler in (SMR L grade natural rubber) vulcanizates on curing characteristics, mechanical properties, swelling behavior, thermal analysis, and morphology were examined. The incorporation of both fillers increases the scorch time, t ₂, and cure time, t ₉₀, of SMR L vulcanizates. At a similar filler loading, feldspar exhibited longer t ₂ and t ₉₀ but lower values of maximum torque, M_HR, and torque difference, M_HR–M_L than did silica-filled SMR L vulcanizates. For mechanical properties, both fillers were found to be effective in enhancing the tensile strength (up to 10 phr), tensile modulus, and hardness of the vulcanizates. However, feldspar-filled SMR L vulcanizates showed lower values of mechanical properties than did silica-filled SMR L vulcanizates. Swelling measurement indicates that swelling percentages of both fillers-filled SMR L vulcanizates decrease with increasing filler loading whereas silica shows a lower swelling percentage than feldspar-filled SMR L vulcanizates. Scanning electron microscopy (SEM) on fracture surface of tensile samples showed poor filler–matrix adhesion for both fillers with increasing filler loading in the vulcanizates. However, feldspar-filled SMR L vulcanizates showed poorer filler–matrix adhesion than did silica-filled SMR L vulcanizates. Thermogravimetric analysis (TGA) results indicate that the feldspar-filled SMR L vulcanizates have higher thermal stability than do silica-filled SMR L vulcanizates.     

On the potential of organoclay with respect to conventional fillers (carbon black,silica) for epoxidized natural rubber compatibilized natural rubber vulcanizates

Onium modified montmorillonite (organoclay) was compounded with natural rubber (NR) in an internal mixer and cured by using a conventional sulfuric system. Epoxidized natural rubber with 50 mol % epoxidation (ENR 50) in 10 parts per hundred rubber (phr) was used as a compatibilizer in this study. For comparison purposes, two commercial fillers: carbon black (grade N330) and silica (grade vulcasil‐S) were used. Cure characteristics were carried out on a Monsanto MDR2000 Rheometer. Organoclay filled vulcanizate showed the lowest values of torque maximum, torque minimum, scorch, and cure times. The kinetics of cure reaction showed organoclay could behave as a cocuring agent. The mechanical testing of the vulcanizates involved the determination of tensile and tear properties. The improvement of tensile strength, elongation at break, and tear properties in organoclay filled vulcanizate were significantly higher compared to silica and carbon black filled vulcanizates. In terms of reinforcing efficiency (RE), organoclay exhibited the highest stiffness followed by silica and carbon black filled vulcanizates. Scanning electron microscopy revealed that incorporation of various types of fillers has transformed the failure mechanism of the resulting NR vulcanizates compared to the gum vulcanizates. Dynamic mechanical thermal analysis (DMTA) revealed that the stiffness and molecular relaxation of NR vulcanizates are strongly affected by the filler–rubber interactions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2438–2445, 2004     

Utilization of bowstring hemp fiber as a filler in natural rubber compounds

The cure characteristics and physicomechanical properties of natural rubber (standard Nigerian rubber) vulcanizates filled with the fiber of bowstring hemp (Sansevieria liberica) and carbon black were investigated. The results showed that the scorch and cure times decreased, whereas the maximum torques increased, with increasing filler loadings for both bowstring hemp fiber and carbon black filled vulcanizates. The tensile strength of both bowstring hemp fiber and carbon black filled vulcanizates increased to a maximum at a 40 phr filler concentration before decreasing. The elongation at break and rebound resilience decreased, whereas the modulus, specific gravity, abrasion resistance, and hardness increased, with increasing filler contents. The carbon black/natural rubber vulcanizates had higher tensile strength, which was about 1.5 times that of bowstring hemp fiber/natural rubber vulcanizates. This superiority in the tensile strength was probably due to the higher moisture content and larger particle size of the bowstring hemp fiber. However, the bowstring hemp fiber/natural rubber vulcanizates showed superior hardness. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of oxidized carbon black on the mechanical properties and molecular motions of natural rubber studied by pulse NMR

The mechanical properties such as elastic modulus and stress-relaxation and spin-spin relaxation time T₂ from pulse NMR were measured for surface-oxidized carbon-black-filled natural rubber. The extent of reinforcement increased with CB volume percent in the range of 0–30%. At a given CB percent, this quantity increased by surface oxidation of fillers and decreasing filler size. From pulse NMR experiment, it was found that there were three components in rubber molecules which have different values for T₂. Stress-relaxation time and elastic moduli fitted one master curve against effective volume, fraction which is the sum of filler and bound rubber fraction. It was found that the distance between particle surfaces is the most important factor influencing reinforcing properties of filled polymers.     

Viscoelastic properties of suspensions with weakly interacting particles

Rheological characterization of a model suspension containing hydroxyl-terminated polybutadiene and glass beads with filler concentration up to 30% by volume was performed by using a Haake parallel disk rheometer. The rheological tests conducted were the measurement of the storage modulus, G′, loss modulus, G′, and complex viscosity, η*, as functions of the frequency and the steady shear viscosity as a function of the shear rate. The linear viscoelastic region was determined to extend up to 50% strain by measuring G′, G′, and η* as functions of strain amplitude. By using multiple gap separations between the disks, it was found that the suspension did not exhibit slip at the walls of the rheometer. G′ and G′ were used to determine the relaxation times distribution, G_i(λ_i, ⊘) as functions of the relaxation time, λ_i, and the filler content, ⊘. The relaxation moduli, G_i(λ_i, ⊘), decreased with the relaxation time, but increased with the filler content. The Cox–Merz rule was also observed to be valid for these suspensions. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 507–514, 1998     

Mechanical properties of polypropylene filled with calcium carbonate

The tensile behavior of polypropylene (PP) filled with calcium carbonate particles has been studied using a tensile test. In particular, the effect of strain rate, filler content, and filler size upon the elastic modulus, yield stress, and strain of surface-modified and unmodified particles-filled PP were investigated. The results indicated that the elastic modulus and yield stress of an unmodified system were increased with an increase of strain rate and filler content, and with a decrease of filler size. The yield strain was decreased with an increase of filler content, and with a decrease of filler size, but did not depend on the strain rate. Although the dependence of elastic modulus on the filler size was maintained even by the surface-modified fillers, that dependence on the strain rate and filler content was decreased by such fillers. This may be because the modifier is present at the interface of filler and polymer matrix.     

Curing Characteristics,Fatigue and Hysteresis Behaviour of Feldspar Filled Natural Rubber Vulcanizates

Curing characteristics, fatigue, and hysteresis behaviour of feldspar filled SMR L vulcanizates and feldspar filled ENR 50 vulcanizates were studied. Two different types of natural rubber, SMR L and ENR 50 having 0 and 50 mol% of epoxide groups were used. The feldspar filled natural rubber vulcanizates were compared at similar filler loading which were used at 0, 10, 20, and 30 phr of filler loading. The curing characteristics such as scorch time (t ₂) and cure time (t ₉₀) slightly increased with increasing feldspar loading for both rubber vulcanizates. Besides t ₂ and t ₉₀, maximum torque (M _HR) significantly increased for both rubbers with increasing feldspar loading. The fatigue test showed that fatigue life decreased with increasing extension ratio, strain energy and filler loading. As the filler loading increased, the poor wetting of the feldspar by the rubber matrix gave rise to poor interfacial adhesion between filler and rubber matrix. Results also indicate that the vulcanizates with the highest feldspar loading exhibited the highest hysteresis. The feldspar filled SMR L vulcanizates showed higher fatigue life and lower hysteresis compare to feldspar filled ENR 50 vulcanizates.     

Rheological behavior and network dynamics of silica filled vinyl‐terminated polydimethylsiloxane suspensions

Present article reports the rheological properties and network dynamics of fumed silica filled vinyl‐terminated polydimethylsiloxane suspensions. The results reveal that as filler loading increases, the span of the linear viscoelastic region with constant dynamic storage modulus is narrowed with increase in strain amplitude while the relaxation time of the compounds get shifted to longer time scales. The dynamics of filler‐network indicated significant Payne effect due to fumed silica incorporation into the PDMS matrix. Further, strain‐induced agglomeration of fumed silica particles, characterized by a peak in the dynamic loss modulus curve could also be observed. High loss‐tangent was observed for lower contents of filler in the suspension, an effect with an apparent relationship to the loosely formed filler‐network. The formation of a saturated network structure of fumed silica particles was evident from the dynamic modulus and complex viscosity data, that remained unaffected with frequency till a critical amount of fumed silica loading. Han plots (storage modulus versus loss modulus) revealed the microstructural changes for various filled systems that was attributed to build‐up of the filler‐network causing an apparent evolution of yielding phenomenon. Van Gurp‐Palmen plots (complex modulus versus phase lag) showed that flow behavior of the filled PDMS suspensions resembled to that of typical viscous fluids. POLYM. ENG. SCI., 57:973–981, 2017. © 2016 Society of Plastics Engineers     

A comparative study of aging characteristics and thermal stability of oil palm ash,silica, and carbon black filled natural rubber vulcanizates

Filler‐filled natural rubber (NR) vulcanizates were prepared by conventional laboratory‐sized two roll mills and cured using sulfuric system. The effect of thermal aging on physical properties and thermogravimetric analysis (TGA) of oil palm ash (OPA) and commercial fillers (i.e., silica vulkasil C and carbon black N330)‐filled NR vulcanizates at respective optimum loading and equal loading were studied. Before aging, the OPA‐filled vulcanizates showed comparable optimum strength as carbon black‐filled vulcanizates. The hardening of aged filler‐filled NR vulcanizates happened after aging, thereby tensile strength and elongation at break reduced while the modulus increased. Fifty phr carbon black‐filled vulcanizates showed better retention in tensile properties as compared to silica (10 phr) and OPA (1 phr). This was attributed to the addition of different filler loading and this finding was further explained when equal loading of filler‐filled vulcanizates was studied. Fourier transform infra‐red analysis showed chemical structure had changed and tensile fractured surface exhibited smooth appearance due to the deterioration in tensile properties after aging. TGA also denoted the thermal stability was depending on the amount of filler loading. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4474–4481, 2013     

Evaluation of dynamic elastic properties of wood‐filled polypropylene composites

Dynamic modulus of elasticity (MoE) and shear modulus of wood‐filled polypropylene composite at various filler contents ranging from 10% to 50% was determined from the vibration frequencies of disc‐shaped specimens. Wood filler was used in both fiber form (pulp) and powder form (wood flour). A novel compatibilizer, m‐isopropenyl‐α,α‐dimethylbenzyl‐isocyanate(m‐TMI) grafted polypropylene with isocyanate functional group was used to prepare the composites. A linear increase in dynamic MoE, shear modulus, and density of the composite was observed with the increasing filler content. Between the two fillers, wood fiber filled composites exhibited slightly better properties. At 50% filler loading, dynamic MoE of the wood fiber filled composite was 97% higher than that of unfilled polypropylene. Halpin‐Tsai model equation was used to describe the changes in the composite modulus with the increasing filler content. The continuous improvement in elastic properties of the composites with the increasing wood filler is attributed to the effective reinforcement of low‐modulus polypropylene matrix with the high‐modulus wood filler. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1706–1711, 2006     

Toughening of isotactic polypropylene with CaCO3 particles

The mechanisms of deformation and fracture of isotactic polypropylene filled with CaCO₃ particles were studied. Three types of particles with average diameters of 0.07, 0.7, and 3.5 μm were used at filler volume fraction from 0.05 to 0.30. The experiments included slow tensile tests, notched Izod impact tests with varying notch depths, and fracture resistance tests using double-cantilever-beam sample configurations. In slow tension, addition of fillers increased the modulus and decreased the yield stress independently of filler type. The strain at break increased with initial incorporation of fillers but decreased at higher loadings. The 0.7 μm diameter particles improved Izod impact energy up to four times that of the unfilled matrix. The other particles had either adverse or no effect on the impact toughness. The toughening mechanisms at work were plastic deformation of interparticle ligaments following particle-matrix debonding with additional contribution coming from crack deflection toughening. The failure of the 0.07 and 3.5 μm diameter particles to toughen the matrix was attributed to poor dispersion.     

Structure,morphology, and properties of HNBR filled with N550, SiO2, ZDMA,and two of three kinds of fillers

The vulcanization properties, mechanical properties of hydrogenated nitrile rubber (HNBR) filled with carbon black (N550), zinc dimethacrylate (ZDMA), SiO₂ independently and two of three kinds of fillers together were investigated, respectively. The filler‐dispersion was characterized by the transmission electron microscopy (TEM) and dynamic mechanical properties. The results showed that HNBR composite filled with SiO₂ or ZDMA displayed high tensile strength, elongation at break and compression set. The HNBR composite filled with N550 displayed low compression set, tensile strength and elongation at break. The dispersion of SiO₂ in HNBR compound was better than that in HNBR vulcanizates because of SiO₂ particles self‐aggregation in vulcanizing processing. ZDMA particles with micron rod‐like and silky shape in HNBR compounds changed into near‐spherical poly‐ZDMA particles with nano size in HNBR vulcanizates by in situ polymerization reaction. The N550 particles morphology exhibited no much change between HNBR compounds and vulcanizates. N550/ZDMA have the most effective reinforcement to HNBR and the appropriate amount of ZDMA is about 25% of total filler amount by weights. The theory prediction for Payne effect (dispersion of the filler) shown by the dynamic properties is identical with actual state observed by TEM. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Torrefied agro-industrial residue as filler in natural rubber compounds

This study explored the feasibility of using torrefied biomass as a reinforcing filler in natural rubber compounds. Carbon black was then replaced with the torrefied biomass in elastomer formulations for concentrations varying from 0% to 100% (60 parts per hundred rubber or phr total). Their influence on the curing process, dynamic properties, and mechanical properties was investigated. Results were compared with the properties of vulcanizates containing solely carbon black fillers. Time to cure (t₉₀) for compounds with torrefied biomass fillers increased, while filler-filler interactions (ΔG') decreased, compared to carbon black controls. At low strains, the tan δ values of the torrefied fillers vulcanizates were similar to the controls. Incorporation of torrefied biomass into natural rubber decreased compound tensile strength and modulus but increased elongation. Replacement with torrefied fillers resulted in a weaker filler network in the matrix. Still, results showed that moderate substitution concentrations (~20 phr) could be feasible for some natural rubber applications.     

Guayule natural rubber composites: impact of fillers on their cure characteristics,dynamic and mechanical behavior

Guayule natural rubber (GNR) is an alternative resource of Hevea natural rubber (HNR) with 99.9% cis content in its 1,4-polyisoprene chemical backbone. In this study, compounds were formulated independently with four different reinforcing fillers such as carbon black (HAF), precipitated silica (VN3), fume silica (FUM) and nanofly ash (NFA) for the advancement of GNR based products. The cure characteristic, dynamic-mechanical performance and mechanical properties of GNR composite were studied with the reinforcing effect of different fillers on GNR. The cure characteristic results demonstrated that HAF and FUM silica filled compounds had more processing safety than VN3 and NFA filled compounds. Viscoelastic parameters of the vulcanizates were studied by dynamic mechanical analysis to estimate the glass transition characteristics and dynamic behavior. The higher storage modulus of FUM silica vulcanizate was an indication of superior filler reinforcing nature and improved rolling resistance than other filled systems. Additionally, HRTEM analysis also proved the better filler dispersion ability of FUM silica in GNR matrix. The mechanical properties were studied with a variation of each filler loading of 8, 16, and 32 phr in GNR vulcanizates. The tensile strength of each filled system increased with an increase of filler content from 8 to 32 phr. In comparison, FUM silica GNR vulcanizates exhibited better mechanical properties, therefore, it was considered as a better structure-performance composite than those of HAF, VN3 and NFA filled composites.