(601a) Cellulose Silylation in Flow with Enhanced Temperature and Pressure

Silylation is the introduction of a silyl group in substitution for active hydrogen in molecules. Because it reduces the polarity of the material surfaces and considering the abundant hydroxyl group (-OH) in cellulose structure, silylation has been widely utilized to produce modified cellulosic materials include but not limited to cotton fabrics, microcrystalline cellulose, bacterial cellulose and nanocellulose. Modified cellulose with higher hydrophobicity showed improved reinforcement performance. The silylated cellulose also showed reduced inter- and intramolecular hydrogen bonding, which alters the rheological behavior of materials during processing. However, the modification yields usually are not ideal and studies reported that the silylation often only happens at the substrate surface. Alternatively, flow chemistry offers well-controlled environment and the possibility of achieving high temperature and pressure in a very small reaction zone. This benefits the contact of reactants in the solution or suspension and uniformity of the reaction condition, compared to reactions in beakers or flasks with continuous stirring.

In this study, we conducted silylation reaction on cellulosic particles derived from different resources using amino silanes in a flow-chemistry set up. Silanes with different chemical structures, include 3-(2-aminoethylamino) propyltrimethoxysilane (AEAPTMS) and (3-Aminopropyl) trimethoxysilane (APTMS) were used as the reagent. We tested the flow reaction design with two scenarios: 1) passing reagent and cellulosic particles to the designated temperature region with defined volume, with or without increased pressure; and 2) fix the cellulosic particles in a region with designated temperature and pass reagent through a defined volume. The temperature was increased to above 100 ℃, which is usually the limit of silylation temperature in literature. The surface chemistry of modified cellulosic substrates was characterized by Fourier Transform Infrared Spectroscopy (FTIR) and the nitrogen content was quantified via X-ray photoelectron spectroscopy (XPS). X-Ray Diffraction (XRD) was used to indicate changes of crystal structure and overall crystallinity of cellulosic substrates. Atomic Force Microscopy (AFM) was used to evaluate the morphology and mechanical properties of the unmodified and modified samples when nanocellulose were used as the substrates. The results suggested that the flow chemistry facilitate the silylation in bulk thus yielding a higher degree of substitution. In addition, the flow-reactor reduces the required time to achieve the substitution compared to reaction in batch. Therefore, flow chemistry offers the potential of large-scale modification of cellulosic materials, as well as providing novel molecular architectures in functional material innovation.