Surface modification of silica nanoparticles by a polyoxyethylene sorbitan and silane coupling agent to prepare high-performance rubber composites

The interfacial interaction between nano-silica and rubber matrix is very important for the preparation of high-performance rubber composites. In this paper, we first proposed the use of TWEEN-20 as a new silica modifier, it has four long arms consisting of three polyether chains with terminal hydroxyl group and a fatty chain. The oxygen on the polyether can form a hydrogen bond with the silanol groups on silica surface, and the terminal hydroxyl groups can chemically react with the silanol groups without any VOCs. Moreover, the long fatty chain can weaken silica polarity to obtain a better compatibility with rubber, so that silica modified by TWEEN-20 with chemical reaction and physical absorption can homogeneously disperses in rubber matrix. Nextly, we prepared high-performance natural rubber (NR) composites by adjusting the ratio of TWEEN-20 to TESPT to adjust the physical and chemical interaction between nano-silica and rubber molecular chains. The results indicated that the performances, including the filler dispersion, static mechanical properties, and dynamic heating (viscoelastic self-heating), were optimal when the ratio of TESPT to TWEEN-20 was 2:1. In addition, one-third of TESPT was replaced by TWEEN-20 to prepare silica/rubber composites, which can reduce one-third of VOCs, improve “scorchy”, and achieve high dispersion of silica.     

Locating a silane coupling agent in silica-filled rubber composites by EFTEM

A silane coupling agent (SA) was added to silica/rubber composites at different mixing temperatures and the formation of a coupling layer at the silica/rubber interface was investigated by energy-filtering transmission electron microscopy. Bis(triethoxysilypropyl)tetrasulfane (TESPT), which was used as the SA, reacted with the silanol groups on the silica surface and with styrene-butadiene rubber to form an interfacial coupling layer. The silicon and sulfur elemental distributions were analyzed by electron energy loss spectroscopy (EELS) and elemental mapping. The amount of TESPT trapped in the rubber matrix could be qualitatively estimated by EELS, and the in situ formed coupling layer could be characterized by elemental mapping. The result indicated that the formation of the coupling layer was affected by the mixing temperature. The technique described here will contribute to the study of interface-property relationships and the evaluation of the role of SAs in polymeric composites.     

Effect of fly ash silica and precipitated silica fillers on the viscosity,cure, and viscoelastic properties of natural rubber

The viscosity, cure properties, storage, and loss moduli and tan δ of natural rubber (NR) filled with the same amounts of precipitated silica (PSi) and fly ash silica (FASi) fillers were measured. The fillers were treated with bis[3‐triethoxysilylpropyl‐]tetrasulfide (TESPT), or, used in the rubber untreated. TESPT is a sulfur‐containing bi‐functional organosilane that chemically adheres silica to rubber and also prevents silica from interfering with the reaction mechanism of sulfur cure. The dispersion of PSi and FASi in the rubber was investigated using scanning electron microscope (SEM). The effects of silica type and loading and surface treatment on the aforementioned properties were of interest. The SEM results showed that the FASi particles were larger in size and had a wider particle size distribution when compared with the PSi particles. The viscosity of the compounds decreased progressively with mixing time, and the compounds with FASi had a lower viscosity than those filled with PSi. The treatment with Si69 had no beneficial effect on the dispersion of the fillers in the rubber matrix. At low temperatures, the type and loading of the filler had no effect on the storage and loss moduli of the compounds, but the effect was more pronounced at high temperatures. There was also evidence from the tan δ and glass transition temperature (T_g) measurements that some limited interaction between the filler particles and rubber had occurred because of TESPT. Copyright © 2008 John Wiley & Sons, Ltd.     

A new method for crosslinking and reinforcing acrylonitrile–butadiene rubber using a silanized silica nanofiller

Using a high loading of synthetic precipitated amorphous white silica nanofiller, an acrylonitrile–butadiene rubber containing 26% by weight acrylonitrile was crosslinked and its mechanical properties were measured. The silica surfaces were pre‐treated with bis(3‐triethoxysilylpropyl)tetrasulfide (TESPT) to chemically adhere silica to the rubber. To optimize the reaction between the tetrasulfane groups of TESPT and the rubber, accelerator and activator were added. The rubber was fully crosslinked and the hardness, tensile strength, stored energy density at break, elongation at break, tearing energy, and modulus increased substantially because of the filler. The bound rubber, crosslink density, tan δ, and glass transition temperature measurements indicated a strong interaction between the filler and rubber. This new method helped to substantially reduce the use of the curing chemicals and produce a safer and more cost‐effective rubber compound without compromising the good mechanical properties of the rubber, which are essential for long service life. Copyright © 2009 John Wiley & Sons, Ltd.     

Potentialities of silane-modified silicas to regulate palladium nanoparticles sizes

A promising approach to control palladium nanoparticle sizes by application of silane modified silicas was suggested. The combination of reductive properties of silicon hydride groups and hydrophobic properties of alkylsilyl groups which act as agglomeration limiters for metal nanoparticles gives an opportunity to synthesize uniformly distributed particles with a specified size. Silicas modified with triethoxysilane (TES) and diisopropylchlorosilane (DIPCS), as well as, the combination of hexamethyldisilazane (HMDS) and triethoxysilane were applied for formation of such bifunctional matrices. Properties of the silane-modified silica samples and changes occurred during the formation of palladium nanoparticles were studied by IR spectroscopy. Thermal stability of surface chemical compounds was investigated by thermogravimetric analysis (TGA); low-temperature nitrogen adsorption was used to study structural properties of the applied materials. With the use of transmission electron microscopy (TEM) the dependence of palladium nanoparticle size on the nature of support surface layer was found.     

Viscoelastic behaviour of silica filled natural rubber composites – Correlation of shear with elongational testing

Dynamic mechanical behaviour of natural rubber-silica composites was studied by a frequency sweep method at different temperatures (40 °C,70 °C and 100 °C) using a dynamic mechanical analyzer and a rotorless rheometer, RPA, in an attempt to establish a correlation between the two. The composites with silica content up to 40 phr were studied. It was found that the dependence of dynamic modulus on the frequency as obtained from both the instruments followed a similar trend. This suggests that the dynamic mechanical properties of rubber compounds can be determined even during curing. A correlation could be arrived at between the two sets of data, making it possible to predict one set knowing the other. The impact of silane coupling agent, bis (3-triethoxysilylpropyl tetrasulphide), TESPT, on viscoelasticity was also investigated. The mechanical properties were improved in the presence of TESPT. Additionally, an increase in thermal stability was also observed in the presence of TESPT. Scanning electron micrographs showed the better filler dispersion in the case of silane-coupled silica composites.     

Microstructure and properties of styrene‐butadiene rubber based nanocomposites prepared from an aminosilane modified synthetic lamellar nanofiller

In this work, a novel nanocomposite series based on styrene‐butadiene rubber (SBR latex) and alpha‐zirconium phosphate(α‐ZrP) lamellar nanofillers is successfully prepared. The α‐ZrP lamellar filler is modified at the cation exchange capacity by γ‐aminopropyltrimethoxysilane and the filler surface modification is first discussed. A significant improvement of the mechanical properties is obtained by using the surface modified nanofillers. However, no modification of the gas barrier properties is observed. The impact of addition of bis(triethoxysilylpropyl)tetrasulfide (TESPT) as coupling agent in the system is discussed on the nanofiller dispersion state and on the filler–matrix interfacial bonding. Simultaneous use of modified nanofillers and TESPT coupling agent is found out with extraordinary reinforcing effects on both mechanical and gas barrier properties and the key factors at the origin of the improvement of these properties are identified. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1051–1059     

Optical properties of a polyethylene dispersion with a luminescent silica prepared by surface grafting of a perylene derivative

A micrometric silica modified with perylene derivative (SiO₂–TES) has been prepared by hydrolysis–condensation reactions between silica and N,N’-bis-(3-triethoxysilylpropyl)-perylene-tetracarboxyldiimide (P-TES) and utilized as filler in LLDPE films together with a compatibilizer. Spectroscopic analyses on SiO₂–TES confirmed the grafting of P-TES on silica, while its amount was determined by thermogravimetric analysis. Solid state NMR provided information about the structure of silicon atoms involved in the condensation of SiO₂ and P-TES that resulted mainly in silicon atoms grafted with bi-dentate anchorages.UV–Vis and fluorescence analyses carried out on P-TES showed the ability of the dye to generate J-type aggregates in apolar solvents. The same analyses on SiO₂–TES revealed the presence of both isolated and aggregated dye molecules grafted on silica surface, while on polymeric dispersions of SiO₂–TES, they have shown only the presence of P-TES aggregates grafted to silica.Thanks to the direct correlation between optical properties (obtained both by UV–Vis and by fluorescence analyses) and the chemical environment of composites, the luminescent silica SiO₂–TES could be used to estimate the filler dispersion extent in different microcomposite polymer materials.     

Improvement of properties of silica‐filled styrene‐butadiene rubber composites through plasma surface modification of silica

The performance of plasma surface modified silica filler in styrene‐butadiene rubber (SBR) matrix has been analyzed. The conditions of plasma modification have been optimized by taking secant modulus as a standard parameter and the occurrence of the modification has been confirmed by surface area determination and Fourier transform infrared spectroscopy. The plasma‐modified surface of silica has been found to be composed of carbon–carbon double bonds and carbon–hydrogen bonds. Silane treatment also has been carried out on silica filler surface for a comparative assessment of its influence in the curing behavior and filler–rubber interaction. The cure reactions of all the rubber compounds have been found to be proceeded according to first‐order kinetics. A reduction in the cure reaction rate constant has been observed with the loading of unmodified and surface modified silica, emphasizing the cure deactivation of the matrix rubber by the silica filler. The filler dispersion, as revealed by scanning electron microscopy, has been found to be greatly improved by the plasma as well as silane treatment. The filler–rubber interaction has been found to be greatly improved by both surface treatments, but the best balance of mechanical properties has been observed with plasma surface modification only. Copyright © 2004 John Wiley & Sons, Ltd.     

Characterization of the reactivity of a silica derived from acid activation of sepiolite with silane by 29Si and 13C solid-state NMR

The mechanism of the reaction between a silica sample coming from acid treatment of sepiolite (denominated Silsep) and an organosilane, namely bis(triethoxysilylpropyl)tetrasulfane (TESPT), has been evaluated by solid state NMR spectroscopy, being compared with the silanization reaction of a commercial silica. The effect of the silane concentration and temperature on the course of the reaction was considered. Experimental results indicate that the silanization reaction is more effective in the case of Silsep, favoring both the reaction of silane molecules with the filler surface and the reaction between neighboring silane molecules. This different behavior is attributed to structural factors, moisture, and number of acid centers on silica surface. Environmental scanning electron microscopy (ESEM) was used to deposit micrometric water drops on the surface of these samples and to evaluate the proportion and distribution of the organophylization process.     

Preliminary Study on the Dynamic Properties of PMVS Filled with Surface-treated Silica

Dynamic properties of polymethylvinylsiloxane (PMVS) filled with surface-treatedsilica (SiO2) were studied using an advanced rheometric expansion system (ARES). The results revealed that the coupling agent, bis (3-triethoxysilylpropyl) tetrasulfane (TESPT) exerted a pronounced effect on the storage modulus (G‘), and the effect of TESPT involved a frequency-dependent relation.     

Preparation of boehmite—silica colloids: Rods, spheres, needles and gels

A method is presented for the synthesis of amorphous silica rods with a boehmite core. The addition of boehmite needles to a mixture of tetraethoxysilane (TES), ethanol and aqueous tetramethylammonium hydroxide solution produces gels or aggregates. However, when boehmite needles are previously coated with silica in an aqueous sodium silicate solution, they serve in the TES solution as nuclei for the polymerisation of part of the hydrolysed TES into discrete, amorphous silica rods. The rods tend to stick together probably because of the increase in ionic strength caused by the TES hydrolysis. In the absence of boehmite nuclei, silica only forms discrete, non-aggregated spheres, which demonstrates that the Stöber silica sphere synthesis can be performed with a base other than ammonia.     

Filler-elastomer interactions: influence of silane coupling agent on crosslink density and thermal stability of silica/rubber composites

In this work, the crosslink density and thermal stability of the silica/rubber composites treated by silane coupling agents, i.e., gamma-aminopropyl triethoxysilane (APS), gamma-chloropropyl trimethoxysilane (CPS), and gamma-methacryloxypropyl trimethoxysilane (MPS), were investigated. The chemical structures of modified silicas were studied in term of solid-state 29Si NMR spectroscopy. The crosslink density of the composites was determined by swelling measurement. The development of organic functional groups on silica surfaces treated by coupling agents led to an increase in the crosslink density of the composites, resulting in increasing final thermal stability of the composites. The composites treated by MPS showed the superior crosslink density and thermal stability in these systems. The results could be explained by the fact that the organic functional groups of silica surfaces by silane surface treatments led to an increase of the adhesion at interfaces between silicas and the rubber matrix.     

Preparation of purified spent coffee ground and its reinforcement in natural rubber composite

Spent coffee ground (SCG) contains a variety of organic compounds such as fatty acids, amino acids, polyphenols, polysaccharides, etc. In this study, purification of SCG was carried out by alkalization and bleaching treatment and the purified SCG (PSCG) was characterized by various techniques, i.e., FTIR, XRD, BET, SEM and TGA. PSCG was later treated with Bis-triethoxysilylpropyl tetrasulfide (TESPT). Both PSCG and TESPT-treated PSCG were then incorporated into natural rubber (NR) to investigate their reinforcement magnitude in the bio-composite. Results revealed the eradication of lignin and other non-polysaccharide components after the purification leading to the significant increases in specific surface area and cellulose content of PSCG. Although the addition of PSCG into NR showed cure time reduction in association with the increased modulus and hardness, its reinforcement was not very high due to the large particle size and the abundance of hydroxyl groups in PSCG. The TESPT treatment significantly improved the reinforcement of PSCG due to the increases in rubber-filler interaction and crosslink density. However, the reinforcement of both PSCG and TESPT-treated PSCG is still relatively low compared to the commercial nanofillers and, thus, they can be considered as a cheap and eco-friendly filler in NR.     

Preparation and enhanced properties of poly(propylene)/ silica‐grafted‐hyperbranched polyester nanocomposites

A series of poly(propylene) silica‐grafted‐hyperbranched polyester nanocomposites by grafting the modified hyperbranched polyester (Boltorn? H20), possessing theoretically 50% end carboxylic groups and 50% end hydroxyl groups, which endcapped with octadecyl isocyanate (C19), onto the surface of SiO₂ particles (30 nm) through 3‐glycidoxy‐propyltrimethoxysilane (GPTS) was prepared. The effect of silica‐grafted‐modified Boltorn? H20 on the mechanical properties of polypropylene (PP) was investigated by tensile and impact tests. The morphological structure of impact fracture surface and thermal behavior of the composites were determined by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC), respectively. The melt viscosity of composites was investigated by melt flow index (MFI). The obtained results showed that: (1) the modified Boltorn? H20 was successfully grafted onto the SiO₂ surface confirmed by FT‐IR and X‐ray photoelectron spectroscopy (XPS) analysis; (2) the incorporation of silica‐grafted‐modified Boltorn? H20 (3–5 wt% SiO₂) greatly enhanced the notched impact strength as well the tensile strength of the composites; (3) the incorporation of silica‐grafted‐modified Boltorn? H20 had no influence on the melting temperature and crystallinity of PP phase; (4) the MFI of PP composites increased when the silica‐grafted‐modified Boltorn? H20 particles were added compared with PP/SiO₂ or PP/SiO₂‐GPTS composites. Copyright © 2004 John Wiley & Sons, Ltd.     

Plasma polymerization of acetylene onto silica: an approach to control the distribution of silica in single elastomers and immiscible blends

Surface modification of silica by acetylene plasma polymerization is applied in order to improve the dispersion in and compatibility with single rubbers and their blends. Silica, used as a reinforcing filler for elastomers, is coated with a polyacetylene (PA) film under vacuum conditions. Water penetration measurements show a change in surface energy due to the PA‐film deposition. The weight loss measured by thermo‐gravimetric analysis (TGA) is higher for the PA‐coated silica compared to the untreated filler, confirming the deposition of the PA film on the silica surface. Time of flight‐secondary ion mass spectrometry (ToF‐SIMS) shows the well‐defined PA cluster peaks in the high mass region. Scanning electron microscopy (SEM) measurements show silica aggregates, coalesced by the coating with smooth and uniform surfaces, but without significant change in specific surface area. Elemental analysis by energy dispersive X‐ray spectroscopy (EDX) measurements also confirms the deposition of the polymeric film on the silica surface, as the carbon content is increased. The performance of single polymers and their incompatible blends based on S‐SBR and EPDM, filled with untreated, PA‐ and silane‐treated silica, is investigated by measurements of the bound rubber content, weight loss related to bound rubber, cure kinetics, reinforcement parameter, Payne effect, and mechanical properties. The PA‐ and silane‐modified silica‐filled pure S‐SBR and EPDM samples show a lower filler–filler networking compared to the unmodified silica‐filled elastomers. Decrease in the reinforcement parameter (α_F) for the plasma‐polymerized silica‐filled samples also proves a better dispersion compared to silane‐modified and untreated silica‐filled samples. On the other hand, the PA‐silica‐filled samples show a higher bound rubber content due to stronger filler–polymer interactions. Finally, the PA‐silica‐filled pure EPDM and S‐SBR/EPDM blends show high tensile strength and elongation at break values, considered to be the result of best dispersion and compatibilization with EPDM. Copyright © 2008 John Wiley & Sons, Ltd.     

Effects of methyl methacrylate grafting and in situ silica particle formation on the morphology and mechanical properties of natural rubber composite films

The effects of methyl methacrylate (MMA) grafting and in situ formation of silica particles on the morphology and mechanical properties of natural rubber latex (NRL) were investigated. MMA grafting on NRL was carried out using cumyl hydroxy peroxide/tetraethylene pentamine (CHPO/TEPA) as a redox initiator couple. The grafting efficiency of the grafted NR was determined by solvent extractions and the grafted NRL was then mixed with tetraethoxysilane (TEOS), a precursor of silica, coated by adherence to a glass surface to form a film and cured at 80°C. The resultant products were characterized by FT‐IR and transmission electron microscopy. The influence of varying the MMA monomer weight ratio on the surface morphology of the composites was investigated by scanning electron and atomic force microscopy. The PMMA (poly MMA) grafted NRL particles were obtained as a core/shell structure from which the NR particles were the core seed and PMMA was a shell layer. The silane was converted into silica particles by a sol–gel process which was induced during film drying at 80°C. The silica particles were fairly evenly distributed in the ungrafted NR matrix but were agglomerated in the grafted NR matrix. The root‐mean‐square roughness increased with an increasing weight ratio of MMA in the rubber. The in situ silica particles in the grafted NR matrix slightly increased both the modulus and the tear strength of the composite film. Copyright © 2008 John Wiley & Sons, Ltd.     

Preparation of thermosensitive PNIPAM microcontainers and a versatile method to fabricate PNIPAM shell on particles with silica surface

Thermosensitive PNIPAM microcontainers were prepared by using silica particles as template. Silica particles were prepared by the St?ber method and surface modified with linear P(NIPAM-co-MPS) chains. PNIPAM shell was then fabricated on the P(NIPAM-co-MPS)-modified silica particles through precipitation polymerization of NIPAM and MBA. Finally, PNIPAM microcontainers were obtained by removing the silica cores with NaOH. The materials were characterized by TEM, FTIR, GPC, and DLS. The PNIPAM microcontainers exhibit good thermosensitivity. The method to fabricate thermosensitive PNIPAM shell can be generalized to a versatile method for preparing PNIPAM shell on particles with silica surface, which includes surface modification with P(NIPAM-co-MPS) and precipitation polymerization of NIPAM and MBA using the modified particles as seed. Through this method, PNIPAM shell was successfully fabricated on iron oxide/silica nanostructures with a wormlike shape and relatively large size, which demonstrates the versatility of the method.     

Rubber products prepared from silica modified by radiation-induced admicellar polymerization

Unmodified silica, silica modified with Si69, silica modified by thermal admicellar polymerization and silica modified by radiation-induced admicellar polymerization were applied as rubber reinforcement. Mechanical properties of these different rubber formulae were subsequently tested. The results revealed that the mechanical properties of rubber reinforced with silica modified by admicellar polymerization were superior to those reinforced with unmodified silica or silica modified with Si69. As for the silica modified by admicellar polymerization, cetyltrimethyl ammonium bromide (CTAB) proved to be the most effective surfactant, compared to dodecyltrimethyl ammonium bromide (DTAB) and tetradecyltrimethyl ammonium bromide (TTAB).     

The interaction at the solid/liquid interface of 2,4-dichlorophenoxyacetic acid with silica modified by reaction with ammonia gas

A method for the attachment of ammonia to modified silica gel has been developed. In the first step, tetraethylorthosilicate and (3-glycidoxypropyl)trimethoxysilane were co-condensed in the presence of n-dodecylamine, a neutral surfactant template, to produce a modified mesoporous silica. The epoxy group incorporated into the mesoporous silica was opened by ammonia gas thus introducing amine chelate groups covalently bound to the inorganic surface. The modified material contained 1.13+/-0.06 mmol of amine per gram of silica, exhibited a surface area of 831+/-29 m(2)g(-1) and a porous diameter of 1.95 nm. Infrared, 29Si and 13C NMR spectra were in agreement with the proposed structure of the modified mesoporous silica in the solid state. This ordered organic-inorganic hybrid presented a high capacity for the removal of the agrochemical 2,4-dichlorophenoxyacetic acid from water: the DeltaH and DeltaG values for the interaction were determined to be -110.61 and -9.37 kJ mol(-1), respectively.