过硫酸铵溶胀氧化棉花制备纤维素纳米晶体及手性膜

【作者】 王红；

【导师】 贾庆明；

【作者基本信息】 昆明理工大学 ， 化学工艺， 2020， 硕士

【摘要】 纤维素纳米晶体（NCC）悬浮液干燥成膜后具有手性。以NCC悬浮液为手性模板,加入水溶性的物质或可反应生成可溶性的物质,可以复制NCC的手性,构建手性复合材料,这已成为化学和医药等领域的研究热点。NCC的形貌和长径比对手性复合物的制备有重要意义,它的产率对实现NCC和其他手性材料的工业化有着至关重要的作用。本文以提高NCC的产率和减少反应时间为目的,棉花为原料,采用过硫酸铵（APS）溶胀氧化法和水热过硫酸铵（APS）溶胀氧化法制备NCC,考察了不同制备条件下对NCC粒子的产率、结晶度、形貌和大小等的影响,得到制备NCC的最优条件;两种方法最优条件下制备的NCC悬浮液自然干燥成膜,并证明NCC薄膜具有手性。（1）在相同氧化时间12.0h和氧化温度60°C的条件下,采用APS溶胀氧化法制备NCC,考察了不同溶胀温度、不同溶胀时间和不同固液比（棉花质量与过硫酸铵溶液体积之比）对棉花的溶胀效果、NCC的产率、粒径、结晶度、平均聚合度和Zeta电位等的影响,并采用光学显微镜、X射线粉末衍射仪（XRD）、原子力显微镜（AFM）、Zeta电位仪、傅里叶红外光谱仪（FT-IR）等对NCC的性质进行了表征。XRD、FT-IR表征表明通过APS溶胀氧化法制备的NCC中的纤维素的结构没有被破坏,结晶度与原料棉花相比增加较大,C6的C-OH被氧化为-COO^-;Zeta电位表征证明NCC间存在同种电荷相互排斥,维持了NCC悬浮液的稳定性;AFM表征可知,NCC的形貌为纺锤状,长径比在1～100范围内。APS溶胀氧化法制备NCC的最优条件为:溶胀温度25°C、溶胀时间3.0h和固液比1:50,NCC的产率、结晶度、长度分布和宽度分布、Zeta电位分别是95.75%、93.51%、136±90nm、10±5nm和-30.5m V。（2）以减少溶胀时间和反应时间为目的,在相同氧化温度60°C和固液比1:50的条件下,采用水热APS溶胀氧化法制备NCC,考察了不同溶胀温度、不同溶胀时间和不同反应时间对NCC的产率、粒径、结晶度、平均聚合度和Zeta电位等的影响,并采用光学显微镜、X射线粉末衍射仪、原子力显微镜、Zeta电位仪、傅里叶红外光谱仪等对NCC的性质进行了表征。结果表明,水热APS溶胀氧化法制备得到的NCC的形貌为纺锤状,纤维素的结构没有被破坏,结晶度与原料棉花相比增加较大,C6的-OH被氧化为-COO-,NCC悬浮液可以稳定存在。水热APS溶胀氧化法制备NCC的最优条件为:溶胀温度25°C、溶胀时间2.0h和反应时间8.0h,NCC的产率、结晶度、长度分布、Zeta电位分别是92.21%、92.98%、117±61nm和-29.7m V。与APS溶胀氧化法最优条件下制备的NCC相比,形貌、产率、结晶度等都相差不大,颗粒长度分布变窄。将原料棉花置于水热反应釜中,通过APS分解产生的气体和过硫酸根(S₂O₈^2-)水解产生的过氧化氢（H₂O₂）,受热分解产生氧气,加强反应体系的压强,减少了溶胀时间和反应时间。本文提出了APS溶胀氧化棉花制备NCC的机理:首先是APS溶液对纤维素分子链的溶胀;其次是APS中的S₂O₈^2-受热分解和水解产生的硫酸根自由基（SO₄^-·）和H₂O₂对纤维素无定形区和部分结晶区的氧化;最后是NCC的表面存在羧基,带负电荷,NCC颗粒间相互排斥,维持了NCC悬浮液的稳定。（3）将APS溶胀氧化法和水热APS溶胀氧化法在最优条件下制备的NCC悬浮液置于室温下干燥成膜,采用偏光显微镜表征NCC薄膜是否具有虹膜现象和场发射扫描电镜表征NCC薄膜横截面的形貌。结果表明:NCC薄膜在干燥过程中便开始出现虹膜,到完全干燥时出现成片的虹膜现象,其横截面的形貌呈现出层层堆积的结构,表明制备的NCC薄膜具有手性。更多还原

【Abstract】 The suspension of nanocrystalline cellulose(NCC)has chirality after drying and forming films.If water-soluble substances or water-soluble substances that are soluble after reaction are added,nanocrystalline cellulose suspension as chiral template can be used to construct chiral composites,and it has become a research hotspot in chemistry,medicine and other fields.The morphology and length-to-diameter ratios of nanocrystalline cellulose are important for preparation of chiral complexes,and yield of NCC plays a crucial role in the industrialization of nanocrystalline cellulose and chiral complexes.In this paper,in order to improve the yield of nanocrystalline cellulose and reduce reaction time,nanocrystalline cellulose was prepared from the raw material of cotton linter by the method of ammonium persulfate(APS)swelling followed by oxidation and hydrothermal ammonium persulfate swelling followed by oxidation.The effects of different preparation conditions on the yield,crystallinity,morphology and size of nanocrystalline cellulose particles were investigated in details.The natural drying film formation of nanocrystalline cellulose suspension prepared under two optimal conditions is proved to be chiral by characterization.(1)At the same condition of oxdition time at 12 hours and oxidation temperature at 60°C,the one-step of ammonium persulfate swelling followed oxidation was the method to prepare nanocrystalline cellulose suspension with the series condition of different swelling temperature,swelling time and solid-liquid ratio,which represents the mass of cotton linter divided the volume of ammonium persulfate volume.The swelling effect of cotton linters and yield,particle size,crystallinity,the average degree of polymerization and Zeta potential of nanocrystalline cellulose were analyzed by optical microscope,X-ray powder diffraction(XRD),atomic force microscopy(AFM),Zeta potentiometer and Fourier infrared spectrometer(FT-IR),respectivelly.The XRD and FT-IR characterization analysis showed that the cellulose structure of nanocrystalline cellulose prepared by the method of ammonium persulfate swelling followed oxidation was not destroyed,and the crystallinity was greatly increased compared with the raw materials cotton linter.The C-OH of C6 was oxidized to-COO-.The Zeta potential characterization proved that the same negative charges repel each other among nanocrystalline cellulose,thus maintaining the stability of nanocrystall ine cellulose suspension.According to the AFM characterization showed that the morphology of nanocrystalline cellulose was spindle.The ratio of length and diameter is in the range of 1～100.The optimal preparation conditions of the nanocrystalline cellulose is swelling temperature at 25°C,swelling time at 3.0h and the solid-liquid ratio of 1:50,which have the best swelling effect on the cotton linters.The yield,the crystallinity,the distribution of length and width and Zeta potential was 95.75%,93.51%,136±90nm,10±5nm and-30.5m V,respectively.(2)To reduce the swelling time and reaction time,the hydrothermal ammonium persulfate swelling followed oxidation was the method to prepare the NCC suspension with the series condition of different swelling temperature,swelling time and reaction time at the same condition of the solid-liquid ratio at 1:50 and oxidation temperature at 60°C.The yield,particle size,crystallinity,average degree of p olymerization and Zeta potential of NCC were analyzed by optical microscope,XRD,AFM,Zeta potentiometer and FT-IR.The analysis results showed that the morphology of nanocrystalline cellulose was spindle,the cellulose structure of nanocrystalline cellulose was not destroyed,and the crystallinity was greatly increased compared with the raw materials cotton linter.The C-OH of C6 was oxidized to-COO-and the nanocrystalline cellulose suspension can still exist stably.The results show that the optimal preparation conditions of the nanocrystalline cellulose is swelling temperature at 25°C,swelling time at 2.0h and reaction time of 8.0h.The higest yield,the highes crystallinity,the minimum length distribution and Zeta potential of nanocrystalline cellulose were 92.21%,92.98%,117±61nm and-29.7m V,respectively.Compared to the optimal results of ammonium persulfate swelling followed oxidation,the morphology of spindle,yield and crystallinity of nanocrystalline cellulose were similar.The length distribution of NCC is narrow.The raw cotton is placed in the hydrothermal reactor.The gas and hydrogen peroxide were produced by the decomposition of ammonium persulfate and the hydrolysis of persulfate,respectively.Hydrogen peroxide was heated to produce oxygen.The swelling time and oxidation time was reduced by strengthening the pressure of the reaction system in a closed reacter.The mechanism of preparation of nanocrystalline cellulose by ammonium persulfate swlling followed oxidation cotton was put forward.The first process is the swelling of cellulose molecular chain in the ammonium persulfate solution.The second process is the oxidation of the amorphous and crystalline regions of cellulose by hydrogen peroxide and sulfate radical produced by the hydrolysis and thermal decomposition of persulfateradical in the ammonium persulfate solution.The last process is that the surface of nanocrystalline cellulose has the carboxyl group with the negative charge,which maintains the stablity and unagglomeration of the nanocrystalline cellulose suspension.(3)The nanocrystalline cellulose suspension prepared by the ammonium persulfate swelling followed oxidation and the hydrothermal ammonium persulfate swelling followed oxidation under the optimal conditions were drought to film at the room temperature.Polarized light microscopy and the field emission scanning electron microscopy were used to characterize whether nanocrystalline cellulose films had irsident and the cross sectional morphology,repctively.The results show that the irisident began to appear in the drying process of nanocrystalline cellulose films and the irisident appeared in the surface of it when completely dried.The morphology of cross section showed a layer by layer stacked structure,indicating that the nanocrystalline cellulose films were chiral.更多还原