Academic literature on the topic 'Silica-natural rubber nanocomposite'

The solution behavior of polymer/silica hybrid nanocomposites was investigated using a Brookfield viscometer. The nanocomposites were prepared using the sol-gel technique with tetraethoxysilane (TEOS) as the precursor for silica. The sol-gel reaction was carried out in the pH range of 1.0-2.0, which was maintained by the addition of concentrated HCl. Poly (vinyl alcohol) (PVA)/silica nanocomposites demonstrated a bigger rise in solution viscosity after continuous measurement for five days than either- acrylic rubber (ACM)/silica or epoxidised natural rubber (ENR)/silica nanocomposites. Detailed investigation of the PVA/silica system indicated that it exhibited Newtonian behaviour when the solutions contained (5 or 7.5 wt% of PVA,) even when increasing the TEOS concentration to 50 wt%, although at one particular TEOS concentration (10 wt%), the nanocomposite was pseudoplastic when the concentration of PVA was increased to 10 wt%. The reinforcement factor [Formula: see text] for those PVA/silica hybrid nanocomposites containing 5 wt% of PVA deviated strongly from the Guth-Smallwood prediction. Instead they obeyed a relationship of the type ηmax = η0(1 + aϕb), where a = 4.45 and b = 0.38, calculated for this system. The viscosity decreased with increasing temperature for both PVA and the representative nanocomposite with 30 wt% TEOS (PVA30), although the activation energy for flow of the nanocomposite did not vary to a great extent.

ABSTRACT Tire rolling resistance (RR) is a key performance index in the tire industry that addresses environmental concerns. Reduction of tire rolling resistance is a critical part of lowering fuel consumption, which could be achieved by changing both design and compound formulation. The major challenge is availability of a suitable software code to evaluate RR of tires using nonlinear viscoelastic properties of rubber. We developed a rolling resistance code and used it to predict rolling resistance of truck bus radial tires with nanocomposite based tread compounds. The energy dissipation in the tire is evaluated using the product of elastic strain energy and loss tangent of materials through post-processing using the rolling resistance code developed in this work. The elastic strain energy is obtained through steady state rolling simulation of tires using commercial software. The loss tangent versus strains at two reference temperatures is measured in the laboratory using a dynamic mechanical thermal analyzer. A temperature equation is developed to incorporate the effect of temperature on loss energy. Good correlation of rolling resistance is observed between simulation and experimental results. Nanocomposites used in this study are prepared based on natural rubber and polybutadiene rubber blends with either organoclay and carbon black or organoclay and silica dual filler system. Carboxylated nitrile rubber, a polar rubber, is used as a compatibilizer to facilitate the clay dispersion in the rubber matrix. Compared with general carbon black or silica tread compounds, substantial improvement of rolling resistance is predicted by finite element simulation with nanocomposite based tread compounds containing dual fillers.

Organosulfonic acid-functionalized mesoporous silica is a class of heterogeneous acid catalysts used in esterification processes due to its high surface area, shape-selective properties, and strongly acidic sites. Since water is generated as a by-product of esterification, the surface of mesostructured silica is modified to enhance hydrophobicity and catalytic performance. In this study, a series of propylsulfonic acid-functionalized nanocomposites based on natural rubber and hexagonal mesoporous silica (NRHMS-SO3H) with different acidities were prepared via an in situ sol-gel process using tetraethyl orthosilicate as the silica source, dodecylamine as the nonionic templating agent, and (3-mercaptopropyl)trimethoxysilane as the acid-functional group precursor. Compared with conventional propylsulfonic acid-functionalized hexagonal mesoporous silica (HMS-SO3H), NRHMS-SO3H provided higher hydrophobicity, while retaining mesoporosity and high surface area. The catalytic activity of synthesized solid acids was then evaluated via batch esterification of levulinic acid (LA) with alcohols (ethanol, n-propanol, and n-butanol) to produce alkyl levulinate esters. NRHMS-SO3H exhibited higher catalytic activity than HMS-SO3H and ultra-stable Y (HUSY) zeolite owing to the synergistic effect between the strongly acidic-functional group and surface hydrophobicity. The activation energy of the reaction over the NRHMS-SO3H surface was lower than that of HUSY and HMS-SO3H, suggesting that tuning the hydrophobicity and acidity on a nanocomposite surface is a compelling strategy for energy reduction to promote catalysis.

A highly performing natural rubber/silica (NR/SiO2) nanocomposite with a SiO2loading of 2 wt% was prepared by combining similar dissolve mutually theory with latex compounding techniques. Before polymerization, double bonds were introduced onto the surface of the SiO2particles with the silane-coupling agent. The core-shell structure silica-poly(methyl methacrylate), SiO2-PMMA, nanoparticles were formed by grafting polymerization of MMA on the surface of the modified SiO2particles via in situ emulsion, and then NR/SiO2nanocomposite was prepared by blending SiO2-PMMA and PMMA-modified NR (NR-PMMA). The Fourier transform infrared spectroscopy results show that PMMA has been successfully introduced onto the surface of SiO2, which can be well dispersed in NR matrix and present good interfacial adhesion with NR phase. Compared with those of pure NR, the thermal resistance and tensile properties of NR/SiO2nanocomposite are significantly improved.

The rheological behavior of an epoxidized natural rubber (ENR) nanocomposite containing 10 wt.% of silica particles was examined by time-resolved mechanical spectroscopy (TRMS), exploiting the unique capability of this technique for monitoring the time-dependent characteristics of unstable polymer melts. The resulting storage modulus curve has revealed a progressive evolution of the elastic component of the composite, associated with slower relaxations of the ENR macromolecular chains. Two major events were identified and quantified: one is associated with the absorption of the epoxidized rubber macromolecules onto the silica surface, which imposes further restrictions on the motions of the chains within the polymer phase; the second is related to gelation and the subsequent changes in rheological behavior resulting from the simultaneous occurrence cross-linking and chain scission reactions within the ENR matrix. These were quantified using two parameters related to changes in the storage and loss modulus components.

This study is the first report on the synthesis, characterization and application of amine-functionalized mesoporous nanocomposites based on natural rubber (NR) and wormhole-like mesostructured silica (WMS). In comparison with amine-functionalized WMS (WMS-NH2), a series of NR/WMS-NH2 composites were synthesized via an in situ sol-gel method in which the organo-amine group was grafted onto the nanocomposite surface via co-condensation with 3-aminopropyltrimethoxysilane (APS) as the amine-functional group precursor. The NR/WMS-NH2 materials had a high specific surface area (115–492 m2 g−1) and total pore volume (0.14–1.34 cm3 g−1) with uniform wormhole-like mesoporous frameworks. The amine concentration of NR/WMS-NH2 (0.43–1.84 mmol g−1) was increased with an increase in the APS concentration, corresponding to high levels of functionalization with the amine groups of 53–84%. The H2O adsorption–desorption measurement revealed that NR/WMS-NH2 possessed higher hydrophobicity than WMS-NH2. The removal of clofibric acid (CFA), a xenobiotic metabolite of the lipid-lowering drug clofibrate, from the aqueous solution using WMS-NH2 and NR/WMS-NH2 materials was investigated using a batch adsorption experiment. The adsorption was a chemical process in which the pseudo-second order kinetic model expressed the sorption kinetic data better than the pseudo first-order and Ritchie-second kinetic order model. In addition, the CFA adsorption sorption equilibrium data of the NR/WMS-NH2 materials were fitted to the Langmuir isotherm model. The NR/WMS-NH2 with 5% amine loading had the highest CFA adsorption capacity (6.29 mg g−1).

5-Hydroxymethylfurfural (HMF) is one of the most important lignocellulosic biomass-derived platform molecules for production of renewable fuel additives, liquid hydrocarbon fuels, and value-added chemicals. The present work developed niobium oxides (Nb2O5) supported on mesoporous carbon/silica nanocomposite (MCS), as novel solid base catalyst for synthesis of HMF via one-pot glucose conversion in a biphasic solvent. The MCS material was prepared via carbonization using natural rubber dispersed in hexagonal mesoporous silica (HMS) as a precursor. The Nb2O5 supported on MCS (Nb/MCS) catalyst with an niobium (Nb) loading amount of 10 wt.% (10-Nb/MCS) was characterized by high dispersion, and so tiny crystallites of Nb2O5, on the MCS surface, good textural properties, and the presence of Bronsted and Lewis acid sites with weak-to-medium strength. By varying the Nb loading amount, the crystallite size of Nb2O5 and molar ratio of Bronsted/Lewis acidity could be tuned. When compared to the pure silica HMS-supported Nb catalyst, the Nb/MCS material showed a superior glucose conversion and HMF yield. The highest HMF yield of 57.5% was achieved at 93.2% glucose conversion when using 10-Nb/MCS as catalyst (5 wt.% loading with respect to the mass of glucose) at 190 °C for 1 h. Furthermore, 10-Nb/MCS had excellent catalytic stability, being reused in the reaction for five consecutive cycles during which both the glucose conversion and HMF yield were insignificantly changed. Its superior performance was ascribed to the suitable ratio of Brønsted/Lewis acid sites, and the hydrophobic properties generated from the carbon moieties dispersed in the MCS nanocomposite.

Quaternized polyvinyl alcohol (QPVA) was synthesized and used as an intermedium to improve dispersion of silica (SiO2) in natural rubber (NR). QPVA/SiO2 nanoclusters reinforced NR nanocomposite was prepared by latex compounding via electrostatic interaction. TEM micrographs demonstrated QPVA/SiO2 nanoclusters were distributed around NR particles, forming shell-core structure. The mechanical properties and thermal ageing resistance of NR-QPVA/SiO2 were significantly improved compared with that of neat NR. The tensile strength of NR-QPVA/SiO2 film was improved by 60%, when the SiO2 content is 3%. SEM pictures indicated SiO2 was homogenous dispersed throughout NR matrix in the presence of QPVA. It also demonstrated that SiO2 could enhance thermal stability of NR, as NR-QPVA/SiO2 had best surface morphology after 72 hours thermal ageing at 100 °C. The thermal decomposition temperature and glass transition temperature of NR-QPVA/SiO2 film increased to a higher temperature due to strong polymer–filler interaction, which also indicated that all the ingredients were compatible and homogenous.

Great interest was recently devoted to the use of inorganic particles as a reinforcing filler in tires for the automotive industry. In fact,the reinforcing of elastomers by the addition of these fillers affects the stiffness, strength, elongation at break, fracture toughness, energy dissipation (rolling resistance), friction to ice or wet grip, wear (abrasion resistance)and on the material processability. Therefore, the technology improvement of tires currently has to satisfy the requirements of sustainable development in order to reduce fuel consumption, environmental pollution and acoustic noise. Carbon black has been the only additive used for this purpose for a long time but silica is now becoming the alternative reinforcing filler; as it offers a lot of advantages, such as better rolling resistance and reduction of the heat buildup; moreover, it can be suitably employed in all cases where the black color is not required. Natural rubber-silica (NR-SiO2) composites are usually prepared by mechanical mixing. Unfortunately, silica particles have a strong tendency to interact with each other within the elastomeric matrix, favoring the inhomogeneous dispersion due to particle tendency to agglomerate and in principle to reduce the filler-rubber interaction. Significant contributions to overcome the disadvantages derived from filler-filler interaction of the silica particles; they are obtainable by enhancing the filler-rubber interaction, which causes additional cross-linking in the rubber structure. The enhancement of filler-rubber interaction is obtained by the use of coupling agents which interact with both the polymer (hydrophobic) and the silica(hydrophilic) surface groups,due to the presence of different functionalities at the ends of the molecules. An alternative approach and object of the present Ph.D thesis,is to prepare composites by in situ formation of the silica filler particles by sol-gel hydrolysis and condensation of tetraethoxysilane(TEOS. Therefore,the aim of this work is to prepare silica-natural rubber (NR-SiO2) composites, with the intention of improving the properties which normally the compound, prepared by mechanical blending possesses. Several factors like nature of the solvent, nature of the catalyst, medium pH, molar ratio between alkoxysilane and water or solvent, gelling and drying temperatures are fundamental sol-gel parameters which can modify the process of the nanocomposite preparation in order to optimize the better homogeneity of the filler distribution inside the rubber matrix. Therefore, considering the filler particle growth in situ in the polymeric matrix, it is possible to distinguish two possible preparation techniques which differ in some of the factors affecting the sol-gel process: aqueous and non-aqueous in situ sol-gel methods. In addition to these factors that influence the preparation of the composite, the amount of the filler present in the silica-rubber composite affects the final performance. In fact, the enhancement in mechanical properties can be achieved when the composite contains the optimal amount of the filler required to form a continuous filler network within the rubber matrix; filler amounts less of this percolation threshold show mostly constant and poor mechanical properties. The presence of a continuous filler network and its homogeneity depends on the filler characteristics, such as size and shape of the particles and on the in situ composite preparation method used. The formation of a convenient filler network is in turn relatable to the physical and chemical interactions among the particles and among their aggregates (filler-filler interaction) and to the chemical and physical interactions between the particles and the matrix (filler-rubber interaction). The presence of functional groups on the particle surface can significantly influence the interface between the filler particles and the rubber matrix; consequently, modifying the filler-filler and filler-rubber interaction leads to the variation of the reinforcement level of the composites. With the intention to investigate and to rationalize the effects induced by surface functionalization of the filler on the properties of rubber composites, during the aqueous sol-gel synthesis of the silica the surface was functionalized by using trialkoxysilane having different functional groups. These functionalities were selected among those which are suitable for promoting the formation of differently shaped silica particles or for modulating the filler-filler and the filler-rubber interactions. Silica particles were modified by molecules containing alkylthiol, thiocarboxylate, alkyldisulfide, alkyltetrasulfide (silica functionalized with containing S groups); vinyl, propyl, octyl chains, alkylamine, alkylcyanate and alkylisocyanate groups (silica functionalized with containing N groups). For this purpose a mixture of TEOS and TMSPM ((3-mercaptopropy)trimethoxysilane) or TESPD (bis(3-triethoxysilylpropyl)disulfide) or TESPT (bis(3-triethoxysilylpropyl) tetrasulfide) or NXT (3-octanoylthio-1propyltriethoxy) or VTEOS (vinyltriethoxysilane) or PTEOS (triethoxy(propyl)silane) or OCTEOS (triethoxy(octyl)silane) or APTEOS ((3-aminopropyl)triethoxysilane) or CPTEOS (3-cyanopropyltriethoxysilane) or ICPTEOS (3-(triethoxysilyl)propylisocyanate) were introduced in NR latex (containing 60 % dry rubber, 39.3 % of water and 0.7% of NH3) during the aqueous sol-gel process. The functionalized molecules were selected with the aim of promoting the formation of different shapes on silica particles (anisotropic or spherical), moreover of modifying the filler-filler and filler-rubber interaction through the chemical functionalities of substituents. In the aqueous in situ sol-gel method, the presence of large amounts of water helps the silica precursors to react quickly in the early stage of the synthesis in rubber matrix, allowing thus to increase the hydroxyl group numbers on particle surfaces, making them less compatible with the rubber and in this way favoring particle aggregation. Through the non aqueous in situ sol gel method, the oxygen present in silica nanoparticles is provided by a suitable reaction and not, as in the aqueous in situ sol gel method, by the water solvent. During this method, the addition of two simple solvents on the metal oxide precursor can generate water in situ that can start sol-gel hydrolysis and condensation reactions. In order to work in an environment without the presence of the water as initial reactant, the silica-rubber composite by the non-aqueous in situ sol-gel method was prepared starting from a solution of dry NR with toluene (inert solvent) and TEOS, which was added to formic acid and alcohol (ethanol of benzylalcohol). Therefore, well defined amounts of water were formed through the esterification reaction produced by formic acid and alcohol, which control the formation of metal oxide growth within the rubber matrix. Moreover, in order to understand better the morphology of the silica particle growth in NR through the in situ sol-gel method, bare silica and functionalized silica powders were prepared by using the same method without the rubber. These powders were morphologically characterized with the intention of more easily evaluating the shape, the size, the surface area, the effect of the metal oxide precursor and the modification of the silica surface. Regarding the composites, the amount of silica was determined by thermogravimetric analysis(TGA) in air. The stability and the reactivity of the functional groups and the hydrolysis rate of the alkoxy groups of the trialkoxysilanes in the early stage of the sol-gel reaction were evaluated by ATR-FTIR. The homogeneity of the particle dispersion, the dimension and shape of silica aggregates were investigated by SEM and TEM, to draw appropriate relations between the filler morphology and the reinforcement of the elastomeric network. The efficacy of the filler network in reinforcing the rubber matrix was assessed by swelling measurements. The Electron Spin Resonance(ESR) behavior of nitroxide radical, introduced as spin probe in order to check the rigidity of the rubber chains, was also investigated. The static and dynamic-mechanical properties of the nanocomposites, both uncured and vulcanized, were investigated and discussed referring to the network morphology, allowing to suggest a connection between the silica precursors used and the functional properties and the amount of the filler. The vulcanization kinetics was also studied, as well as the homogeneity of the dispersion of the filler and the rubber networks. Hardness, abrasion resistance, tensile analysis and compression set results of vulcanized composites were discussed taking into account the structural, morphological and mechanical characteristics determined before. Silica-natural rubber composites for tire applications with a controlled composition and morphology was obtained by in situ sol-gel method and compared with conventional mechanical blending prepared by using silica Rhodia and dried NR. Regarding the in situ sol-gel method of nanocomposite preparation, two different synthetic approaches were carried out by starting from the same silica precursor: aqueous and non aqueous methods. Deep investigation on the relationship between composition, size and morphology of the silica particles, dispersion network degree and dynamic mechanical behavior of uncured composites allowed to rationalize the final performance of the cured composites. In fact, the efficacy of silica filler to improve the mechanical properties of the tires for the automotive industry is related both to the interaction among the silica particles and aggregates (filler-filler interaction) and to their capability to interact with the rubber matrix (filler-rubber interaction). Therefore, the characteristics of the silica such as shape, size, surface area, nature of the surface (OH group, functional molecules and amount), degree of aggregation lead to modify the nature of the interface with the rubber and also the homogenous distribution of the filler network. The obtained results for aqueous in situ sol-gel silica-natural rubber preparation led to the following conclusions: - The aqueous sol-gel method is a promising procedure to prepare nanocomposites from silica precursor TEOS mixed to trialkoxisilanes having different functional groups when the filler precursor doesn’t react quickly through hydrolysis and condensation reactions in water environment and allow to control the filler-filler and filler-rubber interactions. - The functional groups from different substituted silicon alkoxide precursors promote during the sol-gel process the formation of different silica particle shapes and modify the filler-filler and filler-rubber interaction.In particular,the precursor functionalities induced the formation of anisotropic shaped silica particles, unlike the spherical ones derived from TEOS. - Different precursors give rise to particle networks with different degrees of continuity, depending on physical and chemical properties of particles they originate. Spherical or slightly anisotropic particles with homogeneous size show the best self assembling behavior and form continuous networks. When particles contain surface groups able to interact with each other (e.g. hydroxyl, amino and thiol groups), the formation of chemical bonds makes the filler-filler interaction stronger along the network. - The network continuity within the composite is the main prerequisite to obtain strong rubber reinforcement. Not homogeneous distribution of the filler and irregular segregation of particles induce large voids in the network, lowering the dynamic-mechanical properties. However, it appears that a strong chemical interaction among particles can balance the absence of a fully continuous network, preserving high storage modulus. This is the case of the network in NR-TMSPM, where the thiol functionality assists the bonding interaction. On the contrary, the large voids observed in the network of NR-OCTEOS are not compensated by bonding interactions among particles, which are absent or very weak due to the presence of the surface alkyl groups. - The different filler-rubber interaction due to substituents able to chemically interact with the polymer, promotes the homogeneous distribution of the filler particles even if its contribution to the reinforcement properties is less effective than that to the filler-filler interaction. Thus filler-filler interaction governs the dynamic-mechanical properties of silica rubber composites either through the shape induced physical interactions responsible for the network formation, or by the chemical interaction among particle surface groups. - To sum up when a choice among different functionalized silica is required, the suggestion is to look for well assembled and continuous filler networks, eventually assisted by chemical interaction among particles. The second condition seems very important, in fact in the case of NXT network, the homogeneous particle distribution is not sufficient to guarantee strength; instead the dynamic-mechanic behavior of NR-NXT is enhanced after thermal treatment which allows the sulphur-rubber interaction. - Regarding the properties of the vulcanized composites, it is evident that the preparation of the silica in situ improve the rigidity, the hardness, the tensile strength and reduce the dissipation of the energy, which means an improvement in rolling resistance. The obtained results for non-aqueous in situ sol-gel silica-natural rubber preparation led the following conclusions: -The non-aqueous in situ sol-gel synthesis is a procedure to prepare nanocomposites allowing the in situ growth of small particles in rubber matrix in the absence of large amount of water. In addition, due to the slow hydrolysis and condensation reaction rate of the precursors it possible to control at molecular level the growth of the metal oxide particles and therefore the filler-filler interaction and the dispersion in rubber matrix. - Non-aqueous in situ sol-gel silica-natural rubber nanocomposites were prepared by in situ esterification reaction between formic acid and ethylalcohol or benzylalcohol which produce controlled amount of water for the hydrolysis and condensation reaction. Therefore inside the dried NR it is possible to growth high amount of silica particles well distributed in a network were the particles are less aggregated and show lower filler-filler interaction in comparison with the composite prepared by conventional blending route. - Silica-natural rubber composites were obtained containing large amount of well dispersed silica (75 phr or 43% wt) without using coupling agents. -The nature of the alcohol involved in the esterification reaction influences the shape and the size of the silica prepared in swollen natural rubber. Silica particles produced in ethanol environment are bigger than those produced in presence of benzylalcohol, and create an effective reinforcement of the rubber when their amount is higher than 60 phr (37% wt). In spite of the different particle dimensions, silica produced from the two different routes are equally highly dispersed in the rubber matrix, due to the lower hydrophilicity of the surface, and a large amount of filler is required to form an efficient silica network able to reinforce the composite. -This behavior, peculiar of silica particles prepared by non aqueous in situ method, confirm that even if a homogeneous distribution of the particles in the matrix is required to obtain an efficient and strong reinforcement of the rubber, highly separated particles with low filler-filler interaction hinder an efficient filler network. On the other side the non aqueous synthesis allows to load a large amount of silica in the rubber, which could not be loaded with the traditional blending method without using a compatibilizer or disperdent agent.

Natural rubber (NR) is representative biomass polymer and the effective uses are strongly contributed to sustainable society. This chapter presents the innovative and advanced rubber nanocomposites with polystyrene-encapsulated silica nanohybrids (PS-nSiO2) subsequently used as a nanofiller for NR and NR/styrene butadiene rubber (NR/SBR). The PS-nSiO2 were prepared via ‘in situ' differential microemulsion polymerization. The core-shell nanohybrids of PS-nSiO2 were achieved with an average diameter of 40 nm using a smaller amount of surfactant, compared to microemulsion polymerization method. Moreover, the effects of the NR and NR/SBR filled with PS-nSiO2 nanohybrids on the mechanical properties, thermal stability, flammability and morphology are also discussed. The results indicated that the encapsulation of nSiO2 with PS can provide not only the well-dispersion of nanoparticles in the rubber matrix but also the synergistic properties of two components from the polymer and the inorganic nanoparticles by improving mechanical properties, thermal stability and flammability of rubber nanocomposites.

This paper presents the obtaining and characterization of new elastomeric nanocomposites based on natural rubber reinforced with plasticized starch, precipitated silica and layered clay, for obtaining consumer goods for the food industry. Obtaining nanocomposites was carried out by the technique of mixing and melt interleaving. The mixtures were vulcanized in the press, at high temperatures, using peroxides as vulcanizing agents, and triallyl cyanurate as vulcanizing coagent. In order to obtain products with improved characteristics, the influence of the amount of modified organic montmorillonite layered clay (OMMT) Nanomer I31PS and the adhesion promoter between mineral filler and polymer - bis-[3-(triethoxysilyl)-propyl]-tetrasulfane (TEPS) on the characteristics of the mixtures, was analysed. The rheological characteristics of the samples show an increase of the minimum torque at the increase in the amount of OMMT type nanofiller and a decrease in the optimal vulcanization time by adding the adhesion promoter between the rubber and the filler. An improvement of the mechanical characteristics of the samples was observed at the introduction of both OMMT and TEPS. These changes may be due to both the nanofiller reinforcement effect and the changes in the morphology of the mixture. The samples showed a good behaviour after immersion in different environments specific to the food industry (water, ethyl alcohol, 10% glucose solution, 0.9% sodium chloride solution and sunflower oil). SEM analyses indicate that the starch particles, together with the other ingredients of the mixture, are quasi uniform distributed in the elastomer matrix. Several superficial microcracks are observed, on the surface of the analysed material, without structural discontinuities or other defects.