Study On The Fabrication Of Cellulose (or Its Derivatives)/Biominerals Composites

The thesis is focusing on how to fabricate high-performance organic-inorganic polymer composites. Since widely used synthetic polymers (eg:plastics) might cause serious environmental problems, we chose natural cellulose or its derivatives as the polymer components in this thesis. Inspired by the biomineral materials (eg:shells) that widely existed in the nature, we chose carbonate biominerals (CaCO3, BaCO3) and magnetic biominerals (Fe2O3) as the inorganic components in the consideration of the abundance and potential applications as well. Thus, in this thesis, we have fabricated two kinds of cellulose (or its derivatives)/biominerals composites:1) inorganic materials (carbonate biominerals) were served as the main material and polymer additives (carboxymethyl cellulose (CMC) or other additives containing carboxyl functional groups) were served as reinforcing materials to modify the inorganic materials;2) organic polymer (cellulose) was served as the main material and inorganic biomineral (Fe2O3) was served as the reinforcing material to modify the polymer material. In the former study, we concerned about the change of the growing process of the biomineral crystals, which was caused by the change of experimental conditions, and the crystallization mechanism as well as the effect of added organic component on crystallization. While in the later study, the crystallization mechanism obtained from the former study was used as the guidance to fabricate cellulose/Fe2O3composites and both the preparations and the varying structures that was caused by altering experimental parameters became the most concerned things.The main works can be divided into following aspects:Firstly, we chose one of the most common soluble cellulose derivatives (CMC) to modulate the crystallization of BaCO3biomineral and dendritic BaCO3/CMC composite particles with bundles in the middle and branches in both ends were fabricated. Additionally, we found out that the fine structures of obtained BaCO3/CMC composite particles changed a lot if we changed the concentration of added CMC, i.e. when the content of the CMC component among the composite particles increased, the length of the particles (including the overall length of the particle and the length of the bundle in the middle part) decreased and the diameter of the rod-like units as well as the open-angles between rods increased. Based on the aforementioned information and the information of crystals’dissolving process as well as the results generated from the molecular dynamic simulation, we induced a synergistic effect of "direct-skeleton" and "oriented aggregation" that CMC chains had served during BaCO3crystallization. Moreover, the reason that CMC was considered as the effective crystal modifier was because CMC chains would selectively attach onto specific crystal face of BaCO3unit, i.e.(222) face, which lies in the edge of the rod-like unit. Beside of the length and flexibility of the polymer chains, we speculated that the carboxyl functional groups might act an important role on selective attachment.In order to verify the aforementioned speculation, we studied two new systems where additives with rich carboxyl functional groups were adopted:1) graphene oxide (GO) which contains many oxygen-containing groups (carboxyl, hydroxyl, etc.);2) polyethylene terephthalate derivative fibers which were modified with carboxyl groups (PET-COOH) and polyacrylic acid (PAA) which maintained many carboxyl groups on the surfaces of PAA chains. In order to assemble the natural biominerals’ growing patterns, in this study, we changed model biomineral from BaCO3to CaCO3and changed experimental method from compressed CO2way to gas-diffusion way. After careful investigations, we found out that the addition of GO and PET-COOH/PAA would alter the growing process of CaCO3crystals, inducing the changed structures and morphologies of CaCO3composites (CaCO3/GO composite particles and CaCO3/PET composite fibers). This discovery was mainly due to the existence of additives containing carboxyl functional groups, and this further confirmed the speculation drawn from CMC system.Since the aforementioned studies were all based on inorganic materials as the main material to obtain composites, the strength of those composites is far from satisfaction compared with the natural biomineral materials (eg:shell), leading to their limited applications. Therefore, we also studied another new kind of composites in this thesis, in which cellulose was used as the main material and Fe2O3was used as inorganic reinforcing materials. During the fabrication of cellulose/Fe2O3composites, we utilized two methods:supercritical CO2assisted method and ionic liquid assisted one-pot method. We have successfully fabricated functional cellulose/Fe2O3composites via these two methods and the composites can be in any form:through supercritical CO2assisted method, the form of the final composites depended on the initial cellulose source (eg:fiber, sheet, textile, etc.); while for ionic liquid assisted one-pot method, the form of the final composites was decided by the shape of the mould in which the sol-gel transition happened. The outstanding properties of cellulose/Fe2O3composites involved magnetic responsive property, hydrophobic property, absorption property on waste-water treatment and so on. In addition, these two environmental friendly and feasible methods have the potential applications industrially.