Multiscale Study of Functional Acetylation of Cellulose Nanomaterials by Design: Ab Initio Mechanisms and Chemical Reaction Microkinetics

Abstract

Cellulose nanomaterials, namely cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs), present a class of multipurpose, renewable, biodegradable, and nontoxic materials, paving the way into the future of biobased materials. The abundance of hydroxyl groups on the surface allows modification of the materials properties according to application; however, to fully exploit their potential, better compatibility on the molecular level with the hydrophobic matrixes has to be explored beyond lab scale. One of the main missing pieces in functionalization of nanomaterials is a lack of studies focusing on mechanisms and kinetics, which are prerequisite for further optimization of conditions leading to optimal process in terms of both sustainable processing and optimal performance. In this study, the “by design” based approach to tailor biomaterial properties has been simulated multiscale-wise, thus providing a greatly needed input for commercialization. The microkinetic parameters of the elementary reaction steps for acetylation of two distinct types of cellulose nanomaterials were determined and refined by regression analysis. Ab initio part utilizes the density functional theory (DFT) for cellotriose as a model, which suggested that products were obtained through a mechanism consisting of active intermediate formation/subsequent competing one- or two-step (through binding/decomposition of complex) reactions. Quantum chemical simulations were used to pinpoint the most probable sequence through calculated activation barriers that served as a foundation for the development of a thorough regression analysis on experimental data sets. The yield of reaction, through formed acetyl groups was determined through Fourier transform infrared spectroscopy, leading to acquisition of critical elementary characteristics.