Computational Studies of Cellulose-based Materials

Sammanfattning: Cellulose is a remarkable organic biopolymer and sustainable raw material existing in nature. Over the past several decades, the study of cellulose materials has attracted significant attention in chemistry, physics, biomedicine, and engineering fields. The unique properties of cellulose such as high tensile strength, biocompatibility, and renewability, enabled its applications in numerous industries, including textiles, construction, biomedicine, pulp production, energy, and even electronics. However, in-depth research on the performance of cellulose-based materials and devices is still in high demand due to the complexity of cellulose and its derivatives.  This thesis uses a theoretical modelling method to explore the cellulose-based materials structure, morphology and properties, and predict cellulose-based devices performance. The method is efficacious in understanding natural phenomena and solving practical problems through mathematical modelling, computer engineering, and data analysis.  This thesis focuses on three computational studies: (I) cellulose nanomaterials, (II) cellulose composites, and (III) cellulose-based ion exchange membranes in aqueous organic redox flow batteries (AORFBs). The first part presents theoretical insights into cellulose nanocrystal (CNC), surface modifications, and regenerated cellulose. The second part includes numerical models of light propagation in cellulose composites such as transparent wood, and the third part involves modelling and simulation of AORFBs.  In part (I), we constructed Martini 3 coarse-grained (CG) molecular dynamics (MD) models describing different crystalline structure of CNCs (including Iβ/II/IIII). Subsequently, we investigated the dispersion and aggregation properties of COO− modified CNC Iβ in NaCl aqueous solutions and found that the results are consistent with experimental observations. Also, based on topologies developed for cellulose Iβ/II, we studied the regeneration process of cellulose crystallites. The X-ray diffraction (XRD) was used to monitor structural changes and microcrystal formation during regeneration. The XRD results indicate that the regenerated cellulose crystallites are cellulose II, which are in line with the experimental measurements. In part (II), we explored light propagation in transparent wood (TW), i.e., cellulose/PMMA composite materials, using TW models developed by us. The models were built by identifying cellulose fiber structures in SEM images. We employed ray tracing, a relatively simple but proven accurate and efficient technique, and rigorous electromagnetic methods to analyze the light propagation in TW and extract the refractive index of the TW. In part (III), we constructed a model of an AORFB based on the Tertiary-Current-Distribution/Nernst-Planck equations implemented in COMSOL. Then we simulated the charge-discharge and capacity loss curves of the AORFBs. The simulation results are consistent with the experimental measurements.  We believe that the results reported in the thesis provide better understanding of cellulose-based materials and devices, advance the computational methods for modelling and simulations of cellulose, and promote the sustainable development of technology and industry.