| Recently,novel biochemical materials prepared from cellulose have received much attention in academic research for their unique advantages of low-cost,abundances,sustainability and bio-compatibility.In this paper,preparation of high strength cellulose hydrogel,formation mechanism of cellulose bead and production of sulfonated cellulose bead was explored.The results will definitely promote functionalization and industrial application of cellulose.The following work has been conducted in the paper.Firstly,high strength cellulose hydrogel was formed by gradient displacement method.The results showed that strength of cellulose hydrogel(with concentration was 5%)regenerated by gradient displacement method(414 KPa)was much higher than that of hydrogel regenerated by other solvent,including water(180.1 KPa)DMAc(256.18 KPa),DMSO(206.81 KPa),DMF(213.39 KPa)and acetone(270.81).Also,the matrix of hydrogel using gradient displacement method was much homogeneous and its skeleton of the cellulose hydrogel was compactly packed,in addition the cellulose of hydrogel with lower crystallinity(34.2%).Specially,the influence for stages of gradient displacement method also should be considered,and results showed the highest strength of cellulose hydrogel(536.61 KPa)was obtained by six-stages gradient replacement.While effects of dissolution conditions and organic solvents on the strength of hydrogel were explored.The strength of hydrogel regenerated by water could reach 524.83 KPa by increased cellulose concentration to11% and the strength and toughness of hydrogel was influence by different DP of cellulose.However,the strength of gel decreased with solvents molecular weight increase,the strength decreased to 358.19 KPa(n-butanol)from 552.88 KPa(methanol).And the strength of gel increased from 57.89 KPa to 327.89 KPa with ethanol concentration increased,which was mainly due to the hydrogen bond density changed.In addition,the zero-emission industrialized production of high-strength hydrogel achieved by four-stage countercurrent exchange scheme.Secondly,preparation cellulose bead by dropping was studied.The effects of dissolution conditions,nozzle diameter,dropping height and regenerated baths on the regularity of cellulose bead were investigated.The regular cellulose bead could be obtained at optimal cellulose solution viscosity of 280-380 mPa·S,which could berealized by decreasing cellulose concentration(<4%)or increasing solution temperature to 130-160?.Meanwhile,the viscosity of cellulose solution(5%)reached 3.3*104 mPa·S at room temperature and co-solvents could effectively reduce to the optimum viscosity range.When solution viscosity was at 380-1000 mPa·S,regular cellulose bead could be obtained by nozzle diameter of 1 mm,dropping height of 5-8 cm and non-polar solvent aqueous solution.The effects of drying(natural drying,freeze-drying and supercritical drying)on the pore of cellulose aerogel were analyzed.The aerogel was characterized by micro-CT and scanning electron microscopy(SEM),the results showed naturally dried aerogel completely collapsed and lost porous structure.The pores of aerogel with freeze-dried were homogeneous.However,it was much more uniform pore structure of the aerogel dried by supercritical method,the specific surface area was as high as 300-320 m2/g.In addition,the crystallinity of regenerated cellulose by natural drying(36.7%),freeze-drying(24.39%)and supercritical-drying(22.16%)were much lower than that of original cellulose(63.2%).Finally,preparation of sulfonated cellulose bead under homogeneous reaction conditions was studied.Fourier transform infrared spectroscopy(FTIR),elemental analysis and X-ray diffraction(XRD)were used to characterize cellulose samples,the results showed sulfonate groups were successfully grafted with cellulose molecular chains.The sulfonate degree of cellulose could be significantly increased by raising sulfur trioxide-pyridine complex,while the regularity reduced.The crystallinity of sulfonated cellulose(18.95%)was lower than that of regenerated cellulose(24.39%)due to the sulfonic groups hinder recrystallization of cellulose. |
PDF Full Text Request