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Rubber-Based Pressure-Sensitive Adhesives
Published in István Benedek, Mikhail M. Feldstein, Technology of Pressure-Sensitive Adhesives and Products, 2008
Precipitated Silicas (SiO2). Precipitated silicas are common fillers used to impart thixotropy to NR- and SBR-based formulations. Precipitated silica is produced by the reaction of sodium silicate (3SiO2·Na2O) with sulfuric or hydrochloric acid. The concentration of reactants, rates of addition, temperature, and drying are process variables determining the properties of the precipitated silica, such as oil absorption, specific surface area, porosity, primary particle, and agglomerate size and shape. The moisture content in precipitated silicas is high (3–7%) and three types of water are available: free water (easily removed by heating at 105°C), adsorbed water (removed by heating at 200°C), and constitutional water (removed at 700–900°C).
Pyrogenic Silica—Rheological Properties in Reactive Resin Systems
Published in Michel Nardin, Eugène Papirer, Powders and Fibers, 2006
Herbert Barthel, Torsten Gottschalk-Gaudig, Michael Dreyer
Finely divided silicas may be classified according to their manufacturing process—there are natural products, byproducts, and synthetic products. The product origin implies distinct differences of the properties of these silicas. Natural products as quartz powders or diatomaceous earth, and by-products that include fused silica, silica fume, or fly ashes from metallurgy and power plants are mostly crystalline silica products of micron size particles with surface areas up to 1 m2/g. In contrast, synthetic silicas from wet processes or thermal pyrogenic reactions are typically amorphous silica products with a high surface area of > 100 m2/g. Wet processes that are based on the reaction of soluble silicates with aqueous acids lead to silica gels or precipitated silica.1 By far, the most important thermal pyrogenic path is the flame hydrolysis of silanes, which gives access to pyrogenic silica, silica.
Foaming Chemistry and Physics
Published in Leslie R. Rudnick, Lubricant Additives, 2017
Kalman Koczo, Mark D. Leatherman, Kevin Hughes, Don Knobloch
The silica used in antifoams is amorphous and of high purity, typically either fumed or precipitated [145], and has to consist of fine particles, typically less than a micrometer in size. Fumed silica is typically made by burning silicon tetrachloride (SiCl4) with oxygen and hydrogen, with HCl as a by-product. Very fine, round, nonporous particles are formed with primary particle sizes as low as a few nm [146], but they agglomerate to larger aggregates. Precipitated silica is made from alkaline silicates, by precipitating them with mineral acids, such as sulfuric acid, and then can be dried and ground. The precipitated silica particles are porous and their primary size is also very small, but can also aggregate into large units.
Role of Rubber Stiffness and Surface Roughness in the Tribological Performance on Ice
Published in Tribology Transactions, 2018
Nihat A. Isitman, András Kriston, Tibor Fülöp
Carbon black was introduced in the early 1900s as a rubber-reinforcing filler with the main function being increased wear resistance (Blow and Hepburn (1)). Today, precipitated silica, used as partial or full replacement of carbon black, is the filler of preference, especially in tire tread rubber compounds (Brinke (2)). The primary motivation for using silica as a filler is that it allows a significant expansion of the wet grip–rolling resistance–wear triangle of tire performances (Mihara (3)). In fact, precipitated silica has been found to provide higher hysteresis at high frequencies, which is an indication of improved wet grip, and reduced hysteresis at low frequencies, which is an indication of lower rolling resistance (Brinke (2)).
New functional materials derived from amorphous silica
Published in Environmental Technology Reviews, 2023
Zheng Wang, Ying Wang, Jian Hua Zhu
Silica particles can be prepared through wet (using silica gel, precipitated silica) or thermal (using pyrogenic silica) methods, using various silica precursors. These particles have numerous hydroxyl groups, known as silanols, on their surface, making them hydrophilic and reactive. Moreover, these silanols can be transformed into other functional groups to enhance their usefulness. The existence of functional groups on the surface of silica particles is vital to determine their properties such as chemical binding ability and hydrophilicity or hydrophobicity. Modifying the hydrophilic surface of silica can enable it to become hydrophobic and reactive. Especially, organic functionization can alter these surface silanols of silica particles through either physical adsorption or chemical covalent bonding. However, the formal method has its weakness of thermal and solvolytic instability because two phases, the guest adsorbate and the host adsorbent, usually have a relatively weak interaction such as hydrogen bonding or van der Waals forces even though the anchoring is sometimes used for surface bonding. For this reason, the latter method adopts different organosilane coupling agents like organoalkoxysilanes or organochlorosilanes to the silylanize the hydroxyl groups on the silica through chemical modification, in which the inorganic oxide particles will be chemically reacted to generate a much stronger interaction linking the modifier and the silica [2]. Apart from the routine strategy of hydration, dehydration and re-hydration of amorphous silica to change its surface state [3], tailoring the pore size distribution, adjusting the surface morphology and curvature, changing the acid–base properties of the surface and covering and sealing along with introducing guest species can all transform the amorphous silica to functionalize the low-cost raw material to become the required material with high added-value.
Macroscopic mechanical properties of elastomer nano-composites via molecular and analytical modelling
Published in Soft Materials, 2018
In order to describe the silica data, we modify two parameters in the theory. First the activation energy is increased from kJ/mol to kJ/mol. Note that the latter value corresponds to the hydrogen bond energy. The silica used here is a precipitated silica, usually possessing a large density of hydroxyl groups on its surface (around 5 to 6 per square nanometer). It is, therefore, reasonable that hydrogen bonding between particles is present. Notice that this is different for Aerosil in Figure 2, which is a fumed silica, possessing a much reduced density of hydroxyl groups (around 2 per square nanometer). It is worth reminding the reader that in general there are several competing types of bonds between adjacent aggregates and that the general expression accounting for the number of closed bonds is proportional to (cf. above). Here we consider only one, presumably the dominant, term, i.e. . In the case of Aerosil in Figure 2 we had used kJ/mol. Even though hydrogen bonds are possible, their relative fraction compared to weaker bonds formed by polymer segments physisorbed on the particles surfaces is likely small for Aerosil (cf. the detailed discussion regarding this point in reference (16)). Therefore the smaller associated with these weaker bonds dominates. In the case of HiSil 210 this apparently is different and the change to kJ/mol by itself yields the red dashed curve. In addition, it was consistently found in computer simulations that when the bonds linking particles become stronger increases (e.g. reference (20)). We account for this by increasing to . The factor 1.5 here is a convenient fit parameter, which yields the intersection with the solid black curve at about the temperature where the experimental curves cross. In principle, however, a separate modeling calculation for this particular system is needed to obtain the correct .