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     

Norbornylized soybean oil as a sustainable new plasticizer for rubbers with hybrid fillers

Carbon black (CB) and precipitated silica are two major reinforcing fillers in rubbers. CB/silica hybrid filler is also widely used in rubbers to provide balanced properties. CB/silica‐hybrid‐filler‐filled styrene‐butadiene rubber (SBR) containing naphthenic oil (NO), soybean oil (SO) and norbornylized SO (NSO) was investigated. The swelling and curing behavior and rheological, mechanical, thermal, aging and dynamic properties were studied and compared with earlier reported data on CB‐ or silica‐filled SBR. NSO provides better scorch safety and faster cure than SO. Compared with NO, the addition of SO and NSO enhances the thermal stability and aging resistance of SBR vulcanizates. SBR/NSO vulcanizates with hybrid filler exhibit a higher tensile and tear strength than SBR/NO and SBR/SO vulcanizates. A synergistic effect in the abrasion resistance of vulcanizates containing the hybrid filler is observed. An increase of sulfur content in the hybrid‐filler‐filled SBR/NSO vulcanizates provides further improvement in abrasion resistance, wet traction and rolling resistance. © 2017 Society of Chemical Industry     

Physical and chemical interaction mechanisms in silicone rubbers

Silicone rubbers were prepared with graded concentrations of two different fillers—conventional silica capable of both physical and chemical interactions with the methyl vinyl siloxane polymer and magnetic ferrite powder capable of physical interaction only. The mechanical properties of the experimental rubbers (containing both these fillers at the same time) gave characteristic plots of property isolines in the two filler concentration coordinates. To obtain theoretical counterparts of these plots, physical considerations were used to define the polymer–filler contact surface area in real polymer–filler systems and to derive probable variants of its filler concentration dependence. A mathematical model of the polymer–filler interaction was developed and was explored by computing a series of model diagrams. Comparison of the experimental and computed plots indicated that, even with a chemically active filler present, physical interaction mechanisms are dominant; their contribution in determining the mechanical properties of filled silicone rubbers appears to exceed 93%.     

Recovery of monomers and fillers from high-temperature-vulcanized silicone rubbers—combined effects of solvent, base and fillers

The depolymerization of high-temperature-vulcanized (HTV) silicone rubbers containing filler silica and alumina into cyclosiloxane monomers and spontaneous recovery of fillers were studied. First, HTV silicone rubber was treated with different types of solvents in the presence of KOH to find that a triad mixture of diethylamine, methanol and hexane was appropriate not only to dissolve the silicone rubber to a suspension but also to separate fillers completely by filtration. The filtrate was distilled to remove solvent first and then give pure cyclosiloxane monomers in 76–84% yields. Second, the rubbers were treated with other types of triad mixture of solvents and bases, e.g. tetramethylammonium hydroxide, hexane and diethylamine. After filtration, residue was again treated with the amine and hexane to recover clean fillers in 83–93% yields. Cyclosiloxane monomers were also obtained from the combined filtrates in 67–78% yields.     

The curing retardation and mechanism of high temperature vulcanizing silicone rubber filled with superconductive carbon blacks

The curing retardation and mechanism of high‐temperature vulcanizing silicone rubber (HTV SR) filled with superconductive carbon black (CB) BP2000 have been studied experimentally and theoretically. The results show that both rubber matrix and CBs have influences on the peroxide curing of rubber/CBs composites. The retardation does not appear as prominent in nature rubber (NR)/BP2000 composites as in HTV SR/BP2000 composites. Quantum chemistry calculations reveal that the curing retardation of HTV SR/BP2000 composite should not be attributed to the curing reaction dynamics of HTV SR molecules. Fourier transform infrared (FTIR) and X‐ray photoelectron spectroscopy (XPS) analyses of CBs show that the effect of radical scavenging of phenol‐OH groups existing on BP2000 surface is the main reason for the retardation in the peroxide curing reaction. The effect is found to be more effective in HTV SR/BP2000 composite and thus retards its curing. The curing retardation does not appear in silicone rubber (SR)/BP2000 composites vulcanized by condensation reaction, and the resulting vulcanizates have excellent physical properties. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers.     

Failure properties of thermoplastic elastomers from polyethylene/nitrile rubber blends: Effect of blend ratio,dynamic vulcanization,and filler incorporation

Thermoplastic elastomers from blends of high‐density polyethylene and acrylonitrile butadiene rubber were prepared by a melt‐blending technique. The blends were dynamically vulcanized using sulfur, peroxide, and mixed curing systems. The peroxide concentration was varied to obtain samples of varying degrees of crosslinking. The peroxide system showed better mechanical properties. The crosslink density determination by the equilibrium swelling method revealed that the enhancement in properties can be correlated to the extent of crosslinking. It is observed that the effect of dynamic vulcanization on the property improvement is much more pronounced in rubber‐rich blends. To study the effect of filler incorporation on mechanical properties, fillers such as carbon black, silica, silane‐treated silica, and cork‐filled samples were prepared. All filled systems, except cork filled, exhibited superior mechanical properties. Scanning electron micrographs of selected fractured surfaces were analyzed to study the failure mechanism of the different compositions. Various theoretical models were applied to correlate the observed mechanical behavior with that of theoretically predicted values. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2912–2929, 2006     

New silicone rubbers, 2. Biocompatible silicone rubbers

Biokompatible silicone rubbers have been prepared using fillers based on two types of modified amorphous silica: (i) silica containing covalently bonded reactive H-Si-groups ( 1 ) obtained by reaction of silica with methyldichlorosilane, and (ii) silica with covalently immobilized antithrombogenic agent ( 5 ), prepared by reaction of 1 with divinylbenzene, graft copolymerization with acrylic acid and subsequent esterification with amylose sulfuric acid esters ( 2 ) as a heparinoid. Silicone rubbers (SR's) were obtained by hydrosilation curing of commercially available silicone components using 1 or 5 as fillers. In contrast to 5, 1 is incorporated covalently into the silicone network. Both SR types exhibited good mechanical properties as well as excellent tissue compatibility: contrary to SR's filled with nonmodified silica the cell growth of endothelian cells on the SR's with modified fillers was found to be almost identical to that on cell culture plates.     

Biogenic silica short fibers as alternative reinforcing fillers of silicone rubbers

The performance of biogenic opaline silica short fibers, natural (NF) or modified with vinyltrimethoxysilane (MF), as primary or secondary fillers in an elastomeric matrix of poly(dimethylsiloxane), PDMS, was evaluated in this work. Compounding was carried out on a two‐roll mill, and the PDMS matrix was peroxide crosslinked by compression molding. Characterization of these fibers was performed by BET surface area, X‐ray fluorescence, infrared spectrum, X‐ray diffractometry, field emission scanning electron microscopy, and Bayer's test. The obtained rubbers were characterized by thermogravimetric analysis, field emission scanning electron microscopy, swelling measurements in cyclohexane, dynamic mechanical analysis, and tensile tests. As primary filler, NF and MF increased the thermal stability of the PDMS matrix, and MF also restricted the swelling of this matrix in cyclohexane. For the rubbers containing NF or MF as secondary filler, the swelling restriction was caused by both fibers. Silica short fibers were also efficient as primary filler in PDMS with regard to Young's modulus and tensile strength, and as secondary filler, NF and MF were effective reinforcing fillers in relation to storage and Young's modulus, resulting on an increase in the stiffness of the rubbers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 290–299, 2006     

Swelling and mechanical properties of (acrylonitrile‐butadiene rubber)/(hydrogenated acrylonitrile‐butadiene rubber) blends with precipitated silica filled in gasohol fuels

This work studied the effects of hydrogenated acrylonitrile‐butadiene rubber (HNBR) and precipitated silica (PSi) loadings in acrylonitrile‐butadiene rubber (NBR) filled with 60 parts per hundred of rubber (phr) of carbon black (CB) for oil‐resistant seal applications in contact with gasohol fuel. The cure characteristics, mechanical properties, and swelling behavior of HNBR/NBR blends reinforced with PSi before and after immersion in ethanol‐based oils (E10, E20, and E85) were then monitored. This work studied the effects of PSi loading in rubber compounds on the mechanical properties of the rubber blends. The results suggested that the scorch time of CB‐filled NBR/HNBR was not affected by HNBR loading, but the cure time, Mooney viscosity, and torque difference increased with HNBR content. The swelling of the blends in E85 oil were relatively low compared with those in E10 and E20 oils. The recommended NBR/HNBR blend ratio for oil‐resistant applications was 50/50. Tensile strength and elongation at break before and after immersion in gasohol oils increased with HNBR loading, and the opposite effect was found for tensile modulus and hardness. PSi filler had no effect on scorch time, but decreased the cure time of the blends. The swelling level of the blends slightly decreased with increasing PSi content. The recommended silica content for optimum reinforcement for black‐filled NBR/HNBR blend at 50/50 was 30 phr. The results in this work suggested that NBR/HNBR blends reinforced with 60 phr of CB and 30 phr of silica could be potentially used for rubber seals in contact with gasohol fuels. J. VINYL ADDIT. TECHNOL., 22:239–246, 2016. © 2014 Society of Plastics Engineers     

Preparation and investigation of silicon rubber containing imide-siloxane copolymers

A study has been carried out on the preparation of some modified imide-siloxane copolymers. This has been accomplished by means of addition of α,ω-dihydropoly(di-methylsiloxane)s to N,N'-diallyldiimides by hydrosilylation reaction. The copolymers were characterized by IR and NMR spectroscopy methods. Molar mass, molar mass distribution, thermal and mechanical properties of copolymers were determined. These copolymers are used as additives, mixing them in different ratios with a silicone polymer and filler to obtain imide-silicone rubbers of high temperature vulcanizing (HTV) type. Mechanical properties of the vulcanized rubbers were evaluated.     

Effect of silica and rice husk ash fillers on the modulus of polysiloxane networks

The preparation of polymethylvinylsiloxane rubbers with silica (SC) and black rice husk ash (BRHA) as fillers is reported. We conducted stress–strain experiments on these vulcanized rubbers to study the reinforcement properties of the fillers. Curves showing the dependence of the stress on the reciprocal of the elongation ratio displayed, in most cases, a slow upturn starting at rather low values of the elongation ratio attributed to a rather wide distribution of chain lengths between crosslinking points. Physical crosslinks between the hydroxyl groups of SC fillers and the polymer matrix seemed to enhance the modulus. BRHA–polymer interactions were rather weak in comparison with those occurring between SC and the polymer, presumably as a consequence of the carbon coating of the surface of the former fillers. These interactions were even less important for calcined BRHA. The absence of voids in the polymer–filler interfaces was proven by the analysis of gas diffusion across the rubbers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 421–429, 2003     

Properties of thermally conductive silicone rubbers filled with admicellar polymerized polypyrrole-coated Al2O3 particles

Polypyrrole (PPy) nanolayers were introduced on the surface of alumina (Al₂O₃) particles via admicellar polymerization. The properties of silicone rubbers (SRs) filled with PPy-coated Al₂O₃ and pristine Al₂O₃ as thermally conductive fillers were studied and compared. The results demonstrate that the addition of PPy-coated Al₂O₃ leads to a better interfacial compatibility but lower cross-linking density of the composites than pristine Al₂O₃. The improvement in the compatibility and the decrease in the cross-linking density are paradoxes in affecting mechanical properties. The improvement in the compatibility shows a slight predominance on the strength at low-filler contents. Lower cross-linking density of modified-Al₂O₃/SR composites led to a better processing performance and a higher maximum filler loading amount than the pristine Al₂O₃/SR composites, which is beneficial to increasing the thermal conductivity and maintaining a relatively good strength. The PPy-coated Al₂O₃/SR composite with 83 wt% filler content has a thermal conductivity of 1.98 W/(m K) and a tensile strength of 2.9 MPa, and the elongation at break was 63%. Functionalized fillers by admicellar polymerization used in the fabrication of filler/SR composites not only improve the interfacial compatibility but also optimize and expand the functions of the composites, which has great significance for the production and application of thermally conductive SR in some branches of industry (automotive, electrical engineering, etc.) in the future.     

The effect of fillers on relaxation phenomena of vulcanized styrene–butadiene elastomers

Standard recipe mixtures, based on styrene/butadiene rubber SBR 1500 and oil-extended SBR 1712, with varying amounts of carbon black, silica, or kaoline fillers were prepared and the stress relaxation curves of vulcanized samples were determined. The measurements were restricted to slow relaxation phenomena, observed after 50% initial elongation. Three λ-processes and a fourth ?-process, existing only in filled rubbers, were observed. The relaxation times and activation energies, determined graphically, reflect the amount and activity of the fillers. All relaxation times are lower for filled vulcanizates and decrease with increasing temperature; however, the type of filler does not affect the activation energy. The higher parameters observed for the ?-processes are discussed in terms of filler particle mobilities and rearrangements and of filler/rubber contact layer phenomena. © 1994 John Wiley & Sons, Inc.     

Effect of different types of filler and filler loadings on the properties of carboxylated acrylonitrile–butadiene rubber latex films

The effects of different types of fillers and filler loadings on the properties of carboxylated nitrile rubber (XNBR) latex were identified. Silica, mica, carbon black (CB; N330), and calcium carbonate (CaCO₃) were used as fillers with filler loadings of 10, 15, and 20 parts per hundred rubber. Furnace ashing and Fourier transform infrared analysis proved that interaction existed between the fillers and XNBR latex films. The morphology of the filled XNBR films was significantly different for different types of fillers. Mica and CaCO₃ fillers showed uneven distribution within the XNBR film, whereas other fillers, such as silica and CB, showed homogeneous distribution within the films. In the observation, silica and mica fillers also illustrated some degree of agglomeration. The mechanical properties (e.g., tensile and tear strengths) showed different trends with different types of fillers used. For silica and mica fillers, the mechanical properties increased with filler loadings up to a certain loading, and decreased with higher filler loadings. For CB filler, the mechanical properties increased gradually with increasing filler loadings. CaCO₃ fillers did not increase the mechanical properties. The crosslinking density of the XNBR films increased when they were incorporated with fillers because of the presence of elastomer–filler and filler–filler interactions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Ionic thermoplastic elastomer based on the zinc salt of sulfonated maleated EPDM rubber. II. Reinforcement by fillers

Incorporation of SRF and ISAF grades of carbon black and precipitated silica improves the physical properties of the zinc stearate plasticized ionomer, namely, the zinc salt of sulfonated maleated EPDM rubber, which behaves as an ionic thermoplastic elastomer. The reinforcing ability of the fillers follows the order SRF carbon black < silica < ISAF carbon black. The activation energy of the melt flow also follows the same order. The results of infrared spectroscopic studies and dynamic mechanical studies reveal that, apart from the rubber–filler bonding, as is normally observable in diene rubbers, ion–dipole and hydrogen‐bonding interactions occur between the active sites on the filler surface and the ionic aggregates. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 326–337, 2000     

Effect of silanized silica nanofiller on tack and green strength of selected filled rubbers

BACKGROUND: Tack and green strength of filled and gum (unfilled) natural rubber (NR), poly(styrene‐co‐butadiene) rubber (SBR), polybutadiene rubber (BR) and (SBR‐BR) blend with different loadings of reinforcement agent, silanized silica nanofiller (Coupsil 8113), were studied and the results compared and discussed. RESULTS: It was found that silica was fully dispersed in rubber matrix after 13 min of mixing. In addition, with some exceptions for NR and (SBR‐BR) blend, filler loading decreased the tack strength of the studied filled rubbers. Green strength and Mooney viscosity increased with filler loading for all studied filled rubbers but with different rates and amounts. The optimum filler loadings for NR and (SBR‐BR) filled blend were 30 and 10 phr, respectively. Tacks of NR filled rubbers were much higher than those of synthetic filled rubbers. CONCLUSION: It was concluded that filler loading alters substantially the tack and green strength of the rubbers under investigation. Copyright © 2009 Society of Chemical Industry     

Contribution of hydrogen and/or covalent bonds on reinforcement of natural rubber latex films with surface modified silica

A macromolecular coupling agent containing hydrophilic and hydrophobic groups is made to react with precipitated silica. Interfacial interactions between  OH groups of silica and  COOH groups of macromolecule are found to be created through either hydrogen bonds alone or through hydrogen bonds and covalent bonds. Aqueous dispersions of unmodified and modified silica are prepared and the colloidal stability and particle size distribution of the dispersions are observed. The dispersions at neutral pH are incorporated into vulcanized/unvulcanized natural rubber latex. The formation of hydrogen bonds and/or covalent bonds is studied via FTIR spectroscopy and their contribution in encouraging filler‐rubber interactions is emphasized through mechanical and swelling properties. Uniform distribution and dispersion of modified filler particles throughout the rubber matrix is confirmed by the microstructures of the latex films cast from filler added natural rubber latex. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40380.     

Effects of fillers on mechanical properties of a water‐swellable rubber

The mechanical properties of the water‐swellable rubber prepared by blending polychloroprene with precipitated silica, crosslinked sodium polyacrylate, polyethylene oxide, and vulcanizing agents—such as stress at break, strain at break, modulus, energy at break, and hardness—were studied before and after swelling with water. The results showed that the addition of the reinforcing filler (precipitated silica) increased the mechanical properties, while adding crosslinked sodium polyacrylate decreased the mechanical properties, although it could improve water‐absorbent properties of the water‐swellable rubber. If some polyethylene oxide was included in the rubber formulation, the water‐absorbent properties and the mechanical properties of the rubber both increased; but, with the increase of more polyethylene oxide, the mechanical properties decreased. Wide‐angle X‐ray diffracting analysis was conducted to study the crystalline behavior of the rubber, which showed that the crystallinity of the vulcanized polychloroprene increased first and then decreased with an increase in the amount of polyethylene oxide. The crosslink density of the rubber was calculated by the Flory–Rehner equation. The mechanical strength of the rubber significantly decreased after swelling with water, compared with that before swelling with water. The morphology of blends was shown by scanning electron microscopy graphs. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 577–584, 1999     

Application of lime kiln dust as a filler in the natural rubber industry

Lime kiln dust (LKD) obtained from kraft chemical recovery systems by conversion of calcium carbonate (CaCO₃) back into calcium oxide (CaO) for reuse in the causticizing process, is mainly composed of CaCO₃. A two‐stage conventional mixing procedure was used to incorporate LKD into natural rubber (NR). For comparison purposes, four commercial fillers, stearic acid coated CaCO₃, ground CaCO₃, silica, and carbon black, were also used. The effect of these fillers on the curing characteristics and mechanical properties of NR materials at various loadings ranging from 0 to 60 phr were studied. The results indicate that the use of LKD filler resulted in a lower Mooney viscosity and shorter curing time in the NR materials. The incorporation of LKD into NR improved the Young's modulus and hardness but decreased the tensile strength and tear strength. However, LKD was better in processability than the commercial fillers. Scanning electron micrographs revealed that the morphology of the rubbers filled with reinforcing fillers, such as silica and carbon black, was finer and more homogeneous compared to the those of the rubbers filled with LKD and commercial CaCO₃. The dispersion of LKD and commercial CaCO₃ fillers in the rubber matrix was discontinuous, which in turn, generated a weak structure compared with the reinforcing fillers. According to these observations, LKD could be used as a cheaper filler for NR materials where improved mechanical properties are not critical. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and heat resistance of hollow glass microbead/silicone rubber composite coating

Hollow glass microbead/silicone rubber composite coatings were prepared to improve the heat-resistance and mechanical properties of silicone rubber-based composites, using CE modified SR as the matrix and HGM as the filler. The microscopic morphology and thermal stability of the composites were characterized by scanning electron microscopy (SEM) and thermogravimetric analyzer (TGA), respectively. The results showed that the thermal stability of the composites increases with the increase of filler content. For the composite sample with a HGM mass content of 16.7%, the initial decomposition temperature (T₅) is 408°C, which is 84°C higher than that of silicone rubber. The low density and high sphericity of HGM make it easier to uniformly disperse in the polymer matrix. In addition, compared to silica, which is commonly used as an inorganic filler, the lower thermal conductivity of HGM is also beneficial for achieving better thermal shielding effect. It is confirmed that the insufficient thermal stability of the polymer matrix above 400°C can be compensated for by the properly dispersed inorganic fillers. Therefore, the thermal stability of the composite is improved by the synergistic effect of modified heat-resistant matrix and inorganic filler.