Organocatalytic aqueous formulations: green organocatalytic hydrophobization of heterogeneous polysaccharide-based materials in water through “on-water” mechanisms†

Abstract

A concept for developing stable, water-based colloids for simple, effective, green, and organocatalytic hydrophobization of heterogeneous polysaccharide-based materials (e.g., cellulose, wood, and paper) in water is disclosed. The addition of a surfactant, an organocatalyst, and a hydrophobic agent (e.g., alkyl trialkoxysilane) to water results in organocatalytic polymerization and the formation of a water-based suspension, which, upon homogenization, forms a stable colloid. The mechanism for the generation of this organocatalytic aqueous formulation (OAF) is elucidated by microscopy and spectroscopy. It is initiated by organocatalytic alkyl alkoxysilane polymerization within the nanomicelles formed by the surfactant in water through an “on-water” Type IIa mechanism. Next, these micelles expand to a microsize upon further polymerization, eventually leading to aggregation and the formation of a suspension through an “on-water” Type III mechanism. Homogenizing this suspension yields a stable colloid with water as the medium. The OAFs were then applied to various cellulosic substrates (e.g., cellulose paper, paper sheets, cotton, and wood) by spraying, roll-coating, or dipping. Organocatalytic colloidal particle modification of a wide range of cellulosic substrates (e.g. paper, cotton, and wood) in water through an “on-water” mechanism, which we here classify as Type IV, results in hydrophobic (contact angles of >145°) or superhydrophobic (contact angles of >150°) cellulosic surfaces. Thus, the OAFs can be utilized for modifying a wide range of industrially relevant cellulose-based materials under eco-friendly conditions. The dual role of the organocatalyst in mediating colloidal particle formation and green hydrophobic modification of heterogeneous polysaccharides exemplifies a novel approach for harnessing the catalytic potential of small molecules for organic reactions in water.