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Dissolution of Cellulose in Alkali Complex Solvent and Its Spinning Properties

Author: YuanBinLan
Tutor: YuJianYong；LiFaXue
School: Donghua University
Course: Textile Material and Textiles Design
Keywords: Cellulose Alkali compound solvent Rheology Spinnability Solidification mechanism
CLC: TQ340.1
Type: Master's thesis
Year: 2009
Downloads: 105
Quote: 0
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Abstract

Cellulose is a renewable resource and environmentally friendly materials, but intermolecular and intramolecular hydrogen bonds exist in a very strong and can not be melted and dissolved, greatly limits the development and application of cellulose. The wet spinning cellulose solution has a long history, but viscose, cupro and Lyocell fibers such preparation there is environmental pollution or production cost too high. Based on this, we use lower-cost NaOH / thiourea / urea / water co-solvent for dissolving cellulose and wet spinning, learn more about the cellulose in the solvent system in the dissolution process, discusses the solution flow Variable properties of the regenerated cellulose fibers prepared by spinning conditions and the relationship between performance, and explore the process of wet spinning mechanism of coagulation precipitation. The main research contents and results are summarized as follows: through an optical microscope at different temperatures of cellulose pulp solvent dissolution process, the results show that when the composite solvent temperature is 0 ℃, cellulose begins to dissolve, as the temperature decreases dissolve better, -8 ℃ when the cellulose is completely dissolved; NMR spectra showed that the direct dissolution of cellulose composite solvents and no derivative formation. Rheological experiments showed that different concentrations of cellulose solution are shear thinning non-Newtonian fluid; same concentration of cellulose solution, the shear stress and viscosity index structures are decreased with increasing temperature; non-Newtonian index with the rise of temperature increase; flow activation energy calculation results show that, at a shear rate of 200 s ^{-1 , the cellulose solution with increasing concentration of the basic solution flow activation energy unchanged. Optimized by uniform design method cellulose solution wet spinning process of solidification conditions and stretching conditions. When the coagulation bath was 10 wt% H ₂ SO ₄ / 12.5 wt% Na ₂ SO ₄, the solidification temperature Loss of 15 ℃ and nozzle draft was -30%, the strength of the spun fiber 1.29 cN / dtex. X-ray diffraction results show that cellulose fiber has prepared cellulose Ⅱ type crystal structure, crystallinity higher than native pulp and viscose fibers; optical microscope and scanning electron micrograph photos show that the spun fiber has a circular cross-section and a smooth surface, unlike the jagged viscose fiber cross section, which is mainly caused due to the two different solidification process. With the spinning draw ratio increases, the cellulose fiber breaking strength increases, and the elongation at break decreases. The results show that regeneration of regenerated cellulose fiber coagulation mechanism is a two-phase separation, the rich phase is solidified layer of cellulose and cellulose lean phase uncured layer. Wet-spun cellulose gel solidification model of the solidification rate (ε / t ^{1/2 ) and Mass ratio (△ k) test results show that solidification of the cellulose solution and the cellulose concentration coagulation bath type, the concentration of the coagulation bath, the coagulation time and the molecular volume of the coagulant. ε / t ^{1/2 reaction of the wet-spinning a solution of cellulose during the solidification speed, size, and its value is affected by the concentration of the coagulation bath and the coagulating agent of molecular volume changes; cellulose solution and the coagulation bath, the mass transfer between rate △ k coagulation bath temperature and solidification with the increase of time; cellulose concentration from 4 wt% to 6 wt%, the cellulose solution solidification rate (ε / t ^{1/2 ) to increase the mass transfer rate (△ k) has been reduced; with the coagulation bath temperature solidification speed, △ k increases rapidly. Negative spinneret during spinning the spinning line drawing and stretch ratio of the prepared fiber structure and performance impact. Wet spinning trickle extruded outlet expansion might cause the actual draw ratio is higher than the apparent negative draft, the destruction of the spinning process, the fiber tensile properties decrease. As the swell ratio increases, the cellulose solution at a spinning speed v _Lmax down, spinnability was poor. By changing the free flow velocity (v _f), the spinning line relaxation time (τ), Young's modulus (Xe) and breaking strength (S ^{* ) and other physical parameters, can effectively improve the spinning speed and increasing the stability of the spinning process.}}}}}

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