纤维素/磷酸纺丝溶液的制备

相对于粘胶法溶解纤维素,以磷酸为溶剂溶解纤维素具有操作简单、价格低廉、溶解温度较低、溶解速度较快,而且对环境污染较小等优势。通过混合多聚磷酸和磷酸制备了无水的混合磷酸溶剂体系,分析了P2O5含量、温度和搅拌速率对溶剂平衡时间的影响,并对纤维素在该溶剂体系中的溶解性能进行了研究,探讨了P2O5含量、固含量和温度对纤维素溶解性能的影响。从纺丝溶液的稳定性、均一性和可纺性方面考虑,最佳的溶解条件为:混合磷酸溶剂体系中的P2O5含量为74%,纤维素固含量为18%,溶解温度为0℃。     

纤维素在多聚磷酸中的液晶性

讨论了纤维素在多聚磷酸溶液中的溶解情况和液晶性。采用适当的配比,纤维素能够溶解于多聚磷酸并形成各向异性溶液,在偏振光显微镜下可观察到彩色图片。溶液温度、纤维素聚合度、纤维素浓度对液晶性均有影响。溶液受热后,彩色图像会消失。     

以磷酸体系为溶剂的纤维素纤维生产工艺研究

采用磷酸／多聚磷酸为溶剂溶解纤维素,制备了具有液晶性能的纺丝原液,相对于粘胶法大大缩短了纤维素溶解时间;并采用液晶纺丝工艺,制得了强度为2．04cN／dtex、模量为90．72cN／dtex的纤维素纤维。     

纤维素/磷酸纺丝溶液再生性能研究

利用磷酸/多聚磷酸混合体系溶解纤维素,用铜乙二胺法测定溶解过程的不同时间阶段纤维素的聚合度,通过XRD和IR表征溶解前后纤维素性能变化情况.并初步探讨了纤维素在混酸体系中的溶解机理和降解机理.结果表明,混酸体系溶解纤维素时间较以往溶剂体系短,由于溶解温度比较低,热降解作用不明显.XRD表明经过溶解再生的纤维素品体类型已经由纤维素Ⅰ转变为纤维素Ⅱ.红外谱图中没有新峰出现,说明没有新的官能团产生,混酸溶解纤维素没有衍生物形成.     

纤维素/NMMO溶液及其薄膜的制备与性能研究

以水质量分数为13.3%的N-甲基吗啉-N-氧化物(NMMO)为溶剂溶解棉浆粕,制备质量分数为5%～11%的纤维素/NMMO溶液。将所得溶液制备纤维素薄膜,考察了纤维素/NMMO溶液的稳定性,研究了凝固浴温度和组成对纤维素薄膜的成膜性、断面形态及力学性能的影响。结果表明:纤维素/NMMO溶液随着浓度增大,其粘度先增大后减小,再急剧上升;纤维素/NMMO溶液在玻璃介质中稳定性较好,微量Cu~(2+),Fe~(3+)等杂质存在时,其稳定性显著下降;纤维素薄膜随凝固浴温度升高,其透明性、拉伸强度和断裂伸长率均下降;相对于水,含有乙醇和NMMO的凝固浴能减缓双扩散的速度,使纤维素薄膜的拉伸强度略有提高,断裂伸长率出现不同程度下降。     

离子液体/二甲基亚砜复合溶剂干喷湿纺制备再生纤维素纤维凝固工艺研究

以棉浆粕为原料,使用离子液体/二甲基亚砜复合溶剂配制纺丝溶液,采用干喷湿法纺丝工艺制备纤维素纤维。探索了气隙长度、喷头牵伸比、凝固浴浓度、凝固浴温度对纤维结构与性能的影响。结果表明当采用气隙长度2.5 cm、喷头牵伸比1.9、凝固浴浓度30%、凝固浴温度35℃时可获得力学性能最佳、取向度最高、结晶较为完善的纤维素纤维。     

纤维素在磷酸-磷酸化合物中的溶解性能

使用超声波、18%NaOH溶液及饱和CaCl_2水溶液对纤维素进行预处理,预处理前后纤维素的结构利用偏光显微镜、扫描电子显微镜、红外光谱及X-射线衍射进行表征。将不同条件预处理后的纤维素溶解在磷酸与磷酸脲的复合溶剂中,可以发现,超声波对加快纤维素溶解的效果最为明显。又分别将预处理后的纤维素溶于磷酸(H_3PO_4)-磷酸脲(H_3O_4P·CH_4N_2O)、磷酸-六偏磷酸钠(Na_6P_6O_(18))、磷酸-磷酸二氢钾(KH_2PO_4)、磷酸-磷酸氢二钾(K_2HPO_4)中,通过对比发现,纤维素在35℃下磷酸-磷酸脲中的溶解效果最好,并且聚合度降解最小。     

链长法测定多聚磷酸中磷酸的含量

链长法是利用多聚磷酸在未水解时以氢氧化钠溶液为滴定溶液,用自动电位滴定仪滴定,并记录滴定曲线,根据曲线上的两个拐点处所消耗的氢氧化钠的体积,计算多聚磷酸中磷酸的含量。该法样品处理和分析过程简单、快速、准确、成本低,能满足多聚磷酸生产和产品检验的要求。     

湿法磷酸中金属离子净化技术研究进展

基于国内外研究现状,综述分析了湿法磷酸中金属离子的成因以及其在溶液中的存在形式。介绍了沉淀法、吸附法、离子交换法等净化金属离子的净化原理、工艺及研究成果,重点论述了溶剂萃取法的工艺流程以及溶剂、萃取相比、萃取温度、萃取时间等因素对金属离子萃取净化过程的影响。希望对改进萃取工艺、精确控制萃取过程提供参考。     

湿法磷酸中金属离子净化技术研究进展

基于国内外研究现状,综述分析了湿法磷酸中金属离子的成因以及其在溶液中的存在形式。介绍了沉淀法、吸附法、离子交换法等净化金属离子的净化原理、工艺及研究成果,重点论述了溶剂萃取法的工艺流程以及溶剂、萃取相比、萃取温度、萃取时间等因素对金属离子萃取净化过程的影响。希望对改进萃取工艺、精确控制萃取过程提供参考。     

Characterization and free radical polymerization of liquid crystalline acrylic acid/cellulose diacetate and N-vinyl-2-pyrrolidinone/cellulose diacetate solutions

Polymerizations of liquid crystalline solutions of cellulose diacetate (CDA) in acrylic acid (AA) and N-vinyl-2-pyrrolidinone (NVP) were conducted in an attempt to prepare molecular composites (polymer blends) processing a rigid rod polymer with liquid crystalline orientation. CDA was found to form liquid crystalline solutions in both AA and NVP at concentrations avove 40 wt% CDA. Polymerization of anisotropic 50 wt% CDA-AA and CDA-NVP solutions occurred with considerable retention of the starting solution anisotropy and yielded homogeneous blends (1 T_g) when the rate of polymerization was fast relative to the phase separation of the free radically polymerizing AA or NVP with CDA. Slow polymerizations lead to phase separated blends (2 T_g).     

PPTA在硫酸中的溶解性能

以硫酸为溶剂溶解聚对苯二甲酰对苯二胺(PPTA),通过热台偏光显微镜观察PPTA的溶解过程,测定溶解过程中PPTA溶液的阻塞系数(k_w)来表征PPTA在硫酸中的溶解性能。结果表明:PPTA在硫酸中先溶胀后溶解,完全溶解后为液晶溶液。随着溶解时间的增加,PPTA溶液的k_w变小,3 h后趋于稳定;随着硫酸浓度的增加以及溶解温度的升高,PPTA溶液的k_w下降;随着PPTA溶液浓度的增加,PPTA溶液的k_w变大。     

凝固浴组分对纤维素纤维结构和力学性能的影响

采用新型碱复合溶剂NaOH／j琉脲／尿素水溶液对纤维素进行溶解,并采用H2S04／Na2SO4溶液作为凝固浴,对纤维素溶液进行湿法纺丝,获得纤维素纤维。通过改变凝固浴组分,研究纤维素纤维结构和性能的变化,获得更好的纺丝条件。研究表明,当H2S04质量分数为8％～10％,Na2SO4质量分数6％～12％时,纺丝过程稳定,纤维素纤维的力学性能较好且相对稳定。纤维素纤维的断裂强度最大值可达2．06cN／dtex,纤维素纤维横截面均呈近圆形结构,且无明显的皮芯结构,同时纤维素纤维具有纤维素II的结晶特征,凝固浴组分变化对纤维素纤维的结晶度和取向因子影响不大。     

X-ray studies of regenerated cellulose fibers wet spun from cotton linter pulp in NaOH/thiourea aqueous solutions

Regenerated cellulose fibers were fabricated by dissolution of cotton linter pulp in NaOH (9.5 wt%) and thiourea (4.5 wt%) aqueous solution followed by wet-spinning and multi-roller drawing. The multi-roller drawing process involved three stages: coagulation (I), coagulation (II) and post-treatment (III). The crystalline structure and morphology of regenerated cellulose fiber was investigated by synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) techniques. Results indicated that only the cellulose II crystal structure was found in regenerated cellulose fibers, proving that the cellulose crystals were completely transformed from cellulose I to II structure during spinning from NaOH/thiourea aqueous solution. The crystallinity, orientation and crystal size at each stage were determined from the WAXD analysis. Drawing of cellulose fibers in the coagulation (II) bath (H₂SO₄/H₂O) was found to generate higher orientation and crystallinity than drawing in the post-treatment (III). Although the post-treatment process also increased crystal orientation, it led to a decrease in crystallinity with notable reduction in the anisotropic fraction. Compared with commercial rayon fibers fabricated by the viscose process, the regenerated cellulose fibers exhibited higher crystallinity but lower crystal orientation. SAXS results revealed a clear scattering maximum along the meridian direction in all regenerated cellulose fibers, indicating the formation of lamellar structure during spinning.     

New class of cellulose fiber spun from the novel solution of cellulose by wet spinning method

A novel cellulose solution, prepared by dissolving an alkali-soluble cellulose, which was obtained by the steam explosion treatment on almost pure natural cellulose (soft wood pulp), into the aqueous sodium hydroxide solution with specific concentration (9.1 wt %) was employed for the first time to prepare a new class of multifilament-type cellulose fiber. For this purpose a wet spinning system with acid coagulation bath was applied. The mechanical properties and structural characteristics of the resulting cellulose fibers were compared with those of regenerated cellulose fibers such as viscose rayon and cuprammonium rayon commercially available. X-ray analysis shows that the new cellulose fiber is crystallographically cellulose II, and its crystallinity is higher but its crystalline orientation is slightly lower than those of other commercial regenerated fibers. The degree of breakdown of intramolecular hydrogen bond at C₃[X_am(C₃)] of the cellulose fiber, as determined by solid-state cross-polarization magic-angle sample spinning (CP/MAS) ¹³C NMR, is much lower than other, and the NMR spectra of its dry and wet state were significantly different from each other, indicating that cellulose molecules in the new cellulose fiber are quite mobile when wet. This phenomenon has not been reported for so-called regenerated cellulose fibers.     

Control of the Anisotropic Structure of Cellulose Hydrate Films by Variations of Coagulation Variables

Abstract

The evolution of the structures, that developed in cellulose hydrate films from a rayon after coagulation in the precipitating bath from organic solvent, water and sulfuric acid in presence of inorganic salt has been investigated. The specific features of structure formation at coagulation and cellulose hydrate film extension have been found. It was shown that there is a high diversity of supermolecular structures, whose morphology depends on the precipitation conditions and preliminary orientation. The films structure characteristics correspond to its strength properties. An increase in salt concentration resulted in a films with a more homogeneous, tensile strength structures and small sizes of spherulites. The films of high resistance is formed, in a precipitation bath of organic solvent, because of the realization of the liquid crystalline phase in the coagulation process.     

以氢氟酸协同草酸精制石英砂尾矿及其作用机理

高纯度石英砂在建筑、玻璃制造、铸造等工业领域应用广泛,将石英砂尾矿进行除Fe、Al处理,能够得到相当于高纯度石英砂的替代产品。本研究采用广东河源石英尾矿为原料,提出以氢氟酸协同草酸精制石英砂尾矿的方法,并确定最佳的条件。通过对草酸Fe³⁺溶解络合实验,确定了草酸用量与反应温度;通过HF协同草酸精制实验,确定了酸浸反应时间与物料比例。结果表明,80℃时200g粒径60目的石英砂尾矿在100mL饱和草酸溶液与HF比为25:1(体积比)的酸浸液中,浸泡4h时对石英尾矿的处理可以达到精制的目的。精制后石英砂中二氧化硅含量可以达到99.97%,白度达87.5.实验表明,通过补加草酸与HF可实现精制液的循环应用。冷却失效的精制液可回收结晶析出的草酸,剩余精制液与石英砂水洗液一起进行尾液处理。尾液处理采用饱和澄清石灰水将废液中的杂质沉淀析出,尾液与饱和澄清石灰水的体积比为1:13时处理效果最好,处理后可以达到中水的排放标准。     

Crosslinked hydroxypropyl cellulose films retaining cholesteric liquid crystalline order. I. Effects of cast conditions and heat treatment on the textures and order of films

To eliminate the shear-induced band texture and wrinkled texture observed on the free surface of cellulosic solid cast films retaining cholesteric liquid crystalline order, we proposed a storing process of the cast solutions: the solution is stored in the same solvent vapor atmosphere as the solution. The effect of cast conditions (the storing time) on those textures and the cholesteric liquid crystalline order was determined using the lyotropic liquid crystalline solution of hydroxypropyl cellulose in methanol with crosslinker. Furthermore, the effect of heat treatment on the liquid crystalline order in the cast films was determined. The resultant crosslinked films were observed with a polarized microscope and a scanning electron microscope, and were investigated with circular dichroism. Our findings showed that the proposed storing process is needed before starting the cast process. During the process the textures vanished, due to the relaxation of the residual stress in the solution, the cholesteric liquid crystalline order became stable, and the cholesteric pitch decreased with increasing storing time. The heat treatment also affected the liquid crystalline order of the films; the peak in the circular dichroism spectrum sharpened and shifted with heat treatment, and the shift in peak seemed to depend on the crosslinker concentration. Furthermore, the crosslinking proceeded with heat treatment. © 1995 John Wiley & Sons, Inc.     

Effect of several factors on peracetic acid pretreatment of sugarcane bagasse for enzymatic hydrolysis

BACKGROUND: Lignocellulose should undergo pretreatment to enhance its enzymatic digestibility before being saccharified. Peracetic acid (PAA) is a strong oxidant that can remove lignin under mild conditions. The sulfuric acid in the PAA solution also can cause degradation of hemicelluloses. The objective of the present work is to investigate the effect of several factors on peracetic acid pretreatment of sugarcane bagasse. RESULTS: It was found that PAA charge, liquid/solid (l/s) ratio, temperature, time, interactions between PAA charge and l/s ratio, temperature and time, all had a very significant effect on the enzymatic conversion ratio of cellulose. The relative optimum condition was obtained as follows: PAA charge 50%, l/s ratio 6:1, temperature 80 °C and time 2 h. More than 80% of the cellulose in bagasse treated under the above conditions was converted to glucose by cellulase of 20 FPU g^?1 cellulose. Compared with H₂SO₄ and NaOH pretreatments under the same mild conditions, PAA pretreatment was the most effective for enhancement of enzymatic digestibility. CONCLUSION: PAA pretreatment could greatly enhance the enzymatic digestibility of sugarcane bagasse by removing hemicelluloses and lignin, but removal of lignin was more helpful. This study can serve as a step to further optimization of PAA pretreatment and understanding the mechanism of enhancement of enzymatic digestibility. Copyright © 2007 Society of Chemical Industry