Preparation And Structure Characterisation Of Liquid Crystalline Solutions Of Cellulose In Phosphoric Acid/Polyphosphoric Acid

Cellulose is most abundant nature polymer material, which is a renewable natural resource, reproducing itself through natural cycle by using sunlight, in one word, it is an infinite, free and clean source of energy. In the recent years, oil price increases and its exhausting year by year both are accelerating the development of new biodegradable products emerging from the biomaterials. Cellulose, being as the most effective and the most promising oil substitute, attracts more and more interests from all over the world.A new cellulose dissolution system is investigated in this study. By dissolving cellulose in phosphoric acid/polyphosphoric acid, it is found that a larger cellulose solid content could be dissolved quickly in a hypothermic situation. Therefore, this work is divided into the following aspects:First of all, the equilibration of the phosphoric acid/polyphosphoric acid solvent system is studied by the means of Ultraviolet spectrophotometer and the equilibration time at 72-76% P2O5 concentrations is identified. Besides of this, the stability of the complex acid solvent system is investigated by observing the change of apparent viscosity with the time going.Secondly, the dissolution behavior of the cellulose in phosphoric acid/polyphosphoric acid solvent system is presented with respect to the influence of initial dissolving temperature, cellulose solid content and P2O5 concentration. It is found that the initial dissolving temperature would not influence the system too much while 0℃seems to be a optimum choice. The cellulose solid content enlarger the temperature rising rate of the system evidently, meanwhile, cut down the dissolution time. The increasing of the P2O5 concentration would destroy the dissolving capacity of the solvent system. In the end, the studying of mechanism of cellulose dissolving in complex acid systems show that the dissolution of cellulose is due to the protonation reaction with the acid solvent, the generated ionic group H4PO4+ can infiltration into the cellulose molecular, destroy the intra/inter-molecular hydrogen-bond and dissolve the cellulose ultimately.The following part researches the change of cellulose crystalline structure and morphology after regenerating. The employed WAXD and FTIR reveals a structure transition from cellulose-Ⅰto cellulose-Ⅱwith a decrease of crystallinity. Moreover, the study on the coagulation bath show us the altering of the coagulation category would neither not change the cellulose morphology nor participate in regeneration, it is a true physical process without another side reaction.Finally, the cellulose liquid crystallinity and its formation mechanism are studied. To some extent, the shearing force is necessary to inducing an anisotropic cellulose solution, which can be considered as a rearranging process of the cellulose molecular chain. Due to the application of shear load, the random distributed cellulose macromolecules move along the direction of the load, during which the adjacent macromolecules assemble together to form a more orderly crystal structure.