Guar gum improved electrolyte compatibility. These changes in properties result in increased use in different fields, like textile printing, explosives, and oil-water fracturing applications. Guar molecules have a tendency to aggregate during the hydraulic fracturing process, mainly due to intermolecular hydrogen bonding. These aggregates are detrimental to oil recovery because they clog the fractures, restricting the flow of oil. Cross-linking guar polymer chains prevents aggregation by forming metal – hydroxyl complexes. The first crosslinked guar gels were developed in the late ‘60’s. Several metal additives have been used for crosslinking, among them are chromium, aluminum, antimony, zirconium, and the more commonly used,
Sol–gel process requires an excess of water and/or the use of a hydrolysis catalyst such as acetic acid or hydrochloric acid. Intermediate species including [(OR)−Si−(OH)] or [(OR)−Si−(OH)] may result as products of partial hydrolysis reactions. Early intermediates result from two partially hydrolyzed monomers linked with a siloxane [Si−O−Si] bond: or Thus, polymerization is associated with the formation of a 1-, 2-, or 3-dimensional network of siloxane [Si−O−Si] bonds accompanied by the production of H−O−H and R−O−H species. By definition, condensation liberates a small molecule, such as water or alcohol. This type of reaction can continue to build larger and larger silicon-containing molecules