Dissolution, Regeneration And Graft Modification Of Cellulose

Cellulose is the most abundant nature macromolecule in the world, known as the mostpromising resources to replace fossil fuel. However, the complexity of cellulose morphologyand aggregation structure and high crystallinity, make it very difficult to react with reagents,which confine the application of cellulose. Dissolution is able to destroy the hydrogen bondsof cellulose effectively. Regenerated cellulose from dissolution had a low degree ofcrystallinity, high accessibility and high chemical activity, therefore expanding the scope ofapplication of cellulose. This project aimed at preparing cellulose which has low crystallinity,high accessibility and high chemical activity by dissolving and regenerating process, and thensubjected to graft copolymerization to synthesis functionalized cellulose graft copolymers.The main content of my research and results are listed as follows:(1) Pretreatment of cellulose. Using NaClO degradation method and high energyelectron irradiation method to process cellulose respectively. Determined the molecularweight of cellulose by viscosity method. XRD, FTIR, TG and SEM were used to characterizecellulose before and after treatment. The results showed that the degree of polymerizationwhich obtained by NaClO method is180. After NaClO treatment, the degree of crystallinityof cellulose increased, thermal stability decreased and particle size decreased. For high energyelectron irradiation method (1~100kGy), degree of polymerization was controlled by theirradiation dose. Not only irradiation could decrease the degree of polymerization, but alsonarrow the molecular weight distribution, without changing the morphology, crystal structureand thermal stability of cellulose.(2) Dissolution and regeneration of the pretreated cellulose.3kinds of cellulose(Microcrystalline cellulose, cotton linters and10kGy irradiated pulp) were dissolved bycryogenic NaOH aqueous solution, freeze-thaw treatment of NaOH aqueous solution andcryogenic urea/NaOH aqueous solution. Then cellulose was regenerated by several types ofsolvent. Polarizing microscope was used to observe the cellulose solution and to compare thedissolution ability of the three dissolution methods. FTIR, XRD, SEM and TG were used tocharacterize the regenerated cellulose. The results manifested that cellulose with low degree of polymerization and narrow molecular weight distribution enjoyed a higher solubility. Thesolubility order of the3kinds of cellulose is: Microcrystalline cellulose>10kGy irradiatedpulp> cotton linters. Freeze-thaw treatment enable cellulose of low DP fully dissolved inNaOH aqueous solution (DP about200), but cannot dissolved cellulose of higher DP. Forcellulose of higher DP, freeze-thaw treatment could only intensify swelling. Cryogenic NaOHaqueous solution and cryogenic urea/NaOH aqueous solution methods enjoyed a highersolubility for cellulose of high DP than freeze-thaw treatment. High energy irradiationimproved solubility of cellulose in NaOH aqueous solution effectively. Morphology ofcellulose was completely destroyed by dissolution and regeneration process. Degree ofcrystallinity of regenerated cellulose is significantly reduced.(3) Used regenerated cellulose as the raw material to graft acrylamide, acrylic acid, vinylacetate and styrene. FTIR, XRD, TG, DSC and SEM were used to characterize the cellulosegraft copolymers. The results proved that four kinds of monomers were successfully graftedto cellulose backbone. Among the4kinds of copolymers, the reaction of cellulose graftstyrene significantly reduced the degree of crystallinity of cellulose. The lowest degree ofcrystallinity of cellulose-g-PS can be obtained when potassium served as the initiator of aconcentration of5mmol/L. SEM photos shown than no phase separation was observed,which proved the homogeneity of the cellulose graft copolymers. Glass transition behaviorwas found during DSC tests of cellulose-g-PVAc and cellulose-g-PS, and those two sampleswent soften and sticky with temperature increase, but none of the four samples exhibitedmelting process. Cellulose-g-PS powder was able to bonded together into a transparent flatslice by compression molding, which indicated cellulose-g-PS copolymers had certain degreeof thermoplasticity.