Preparation And Regeneration Of Cellulose/Alkaline Urea Aqueous Solution And Its Rheological Properties Characteristics

Cellulose is a green and renewable biological resource.It not only can be obtained from a variety of natural resources,but also has good chemical stability and biocompatibility.The dissertation mainly studied the dissolution,regeneration and rheological properties of cellulose,which provide a theoretical basis for the application of cellulose in three dimensional printing.In this paper,the hardwood bleached pulp,bleached bamboo pulp,bleached hemp pulp,softwood bleached pulp and softwood dissolving pulp were taken as the main research object.The solubility of cellulose was investigated by changing the amount of NaOH,the amount of urea,the stirring rate.The results showed that the solubility of the pulp increased first and then decreased with the increase of the content of sodium hydroxide.With the increase of the amount of urea,the solubility first increased gradually and then the solubility reached a certain value.With the increase of stirring rate,the solubility of cellulose increased firstly and then tended to be stable gradually as the stirring rate surpassed 6000r/min.The physical and chemical properties of regenerated cellulose(RC)were studied.Compared with the raw materials,the degree of polymerization and crystallinity of RC decreased in differently extent.XRD analysis showed that the cellulose crystals changed from cellulose I to cellulose Ⅱ after dissolution and regeneration.FTIR analysis showed that there were no new functional groups in the regenerated cellulose.The fiber quality analysis showed that the length of the cellulose decreased after the regeneration,the content of the fine fibers and the fiber width increased.The SEM showed that the surface of fibers become rougher because the number of fines on the surface of fibers increased.Cellulose hydrogel,cellulose/guar hydrogel and cellulose/PVA hydrogel were prepared with hemp cellulose solution,guar gum and PVA as raw materials and epichlorohydrin as cross-linking agent.The study found that the cellulose hydrogels of these three systems are easily compressed,while the cellulose/PVA hydrogels had a compressive strain of up to 90%,which was not crushed.The results showed that above 3 types of cellulose hydrogels are easily compressed.The compressive strain of Cellulose/PVA hydrogel could reach up to 90%.And in this case it was not crushed.FTIR,TG and SEM analysis showed cross-linking reaction occured between epichlorohydrin and raw materials.The adding of PVA or guar gum had no influence on the thermal stability of cellulose hydrogel.Cellulose hydrogel had a three-dimensional network structure,which provide a strong support skeleton for the swelling properties of hydrogels.The rheological properties of cellulose solutions in different systems(polyvinyl alcohol(PVA),guar gum,and gelatin as three types of rheological additives)were investigated.Steady state flow studies showed that four cellulose systems are pseudoplastic fluids.Strain sweep and dynamic frequency sweep showed that the storage modulus of the cellulose solution increased with the adding of PVA and gelatin,while the viscous modulus decreased.After the adding of guar gum,the storage modulus and the viscous modulus of the cellulose solution decreased.But the fluid is still a kind of the viscoelastic solid material.The linear viscoelastic zones of the cellulose system vary in magnitude.The overall trend is narrowing of the linear viscoelastic zone.