纤维素性质对纤维素溶液可纺性以及纤维性能的影响?

采用热台偏光显微镜跟踪观察了不同纤维素浆粕在N-甲基吗啉-N-氧化物一水合物(NMMO·H_2O)中的溶解过程,并利用哈克旋转流变仪分析了其溶液的流变性能。研究结果发现:纤维素的聚合度越高,温度对纤维素的溶解过程影响越大;相同纤维素浓度下,随着纤维素的聚合度的增加,溶液的结构粘度指数(△_η)、粘流活化能(E_η)以及弹性增大,即溶液可纺性下降,粘度对温度更加敏感。在此基础上,进一步探讨了纤维素性质对纤维性能的影响,结果表明Lyocell纤维的力学性能随纤维素聚合度以及纺丝液浓度的提高而提高,可纺浓度随聚合度的提高而下降。     

纤维素原料/离子液体溶液体系流变性能的研究

利用NDJ-1型旋转粘度计分别对木浆/离子液体氯化1-丁基-3-甲基咪唑([BMIM]Cl)溶液体系和水洗汽爆麦草/[BMIM]Cl溶液体系的流变性能进行了研究。考察了转子转速、温度、纤维素浓度及添加剂等对溶液粘度的影响。结果表明,两种溶液体系的流动活化能均较低,分别为42 kJ/mol和47 kJ/mol,其表观粘度随温度升高而降低;纤维素浓度和浆粕聚合度的增加都可使溶液的粘度增加。进一步研究了不同添加剂对粘度的影响,发现二甲基亚砜(DMSO)、N,N-二甲基乙酰胺(DMAC)和1,4-二氧六环的加入都能降低溶液的粘度,但以DMSO的效果最佳。     

纳米炭黑添加剂对纤维素/NMMO纺丝原液流变行为及其纤维结构性能的影响

研究了纳米炭黑添加剂对纤维素/NMMO·H2O溶液流变行为及Lyocell纤维结构与性能的影响。研究结果表明:添加了纳米炭黑的纤维素/NMMO·H2O溶液属典型的切力变稀型流体。纳米炭黑的加入使溶液的流动活化能有所增大,并且少量纳米炭黑的加入使体系的黏度有明显的降低,但随着炭黑含量的进一步增加,溶液黏度又逐渐增大。添加了适量纳米炭黑的Lyocell纤维的结构致密,其强度和模量虽略有降低,但结晶结构和热稳定性不变,由此制得的碳纤维不仅得率可有效提高,且强度和模量大大改善。     

竹纤维素/NMMO·H_2O溶液流变性能的研究

采用HAAKE RS150L型旋转流变仪对竹纤维素/NMMO.H2O溶液的流变性能进行了研究。结果表明,竹纤维素/NMMO.H2O溶液为切力变稀流体;随着竹浆粕平均聚合度的增大,溶液的非牛顿指数n减小,而溶液表观黏度η、稠度系数K、黏流活化能Eη和结构黏度指数Δη增加;随着温度的升高,溶液的表观黏度下降,非牛顿指数增大;碱处理竹纤维素/NMMO.H2O溶液的流变性能受竹纤维素原料的聚合度、α-纤维素含量(或半纤维素含量)及杂质含量等因素的综合影响。     

纤维素浆粕性质对其在NMMO溶液中的溶胀性能的影响

将4种聚合度及α-纤维素含量不同的纤维素浆粕在85℃下分别溶解于质量分数为74%,78%,80%的N-甲基吗啉-N-氧化物(NMMO)溶液中,研究了纤维素浆粕性质对其在NMMO溶液中的溶胀性能的影响。结果表明:纤维素浆粕的结晶度越高、聚合度越大、α-纤维素含量越高,溶胀效果越差;在相同实验条件下,浆粕的疏松性对其溶胀效果影响很大,浆粕越疏松,其溶胀效果越好;溶胀过程不会改变纤维素的晶型,但会使纤维素结晶度有所下降;聚合度适中、结晶度较低,疏松的纤维素浆粕适宜作为Lyocell纤维的原料。     

高半纤维素浆粕制备Lyocell纤维的研究

采用半纤维素质量分数21%的高半纤维素浆粕在N-甲基吗琳-N-氧化物(NMMO)水溶液中制备Lyocell纤维,并与半纤维素质量分数为10%的高α-纤维素浆粕的可纺性进行了对比。结果表明:高半纤维素浆粕在溶剂NMMO·H_2O中更易溶解,其过滤性能和可纺性能好,可在较高浆粕浓度下纺丝,制备成Lyo- cell纤维的产率高,且能提高Lyocell纤维的力学性能。高半纤维素浆液的稳定性能略低,在溶剂回收中需要消耗较多的双氧水进行氧化回收溶剂NMMO。     

木浆纤维素/NMMO·H_2O溶液的流变性能研究

以含水率13.7%的N-甲基吗啉-N-氧化物(NMMO)为溶剂溶解木浆纤维素形成溶液,采用红外光谱分析仪对木浆纤维素的溶解过程进行表征,并采用黏度计研究了木浆纤维素/NMMO·H2O溶液的流变性能。结果表明:木浆纤维素在NMMO中先溶胀后溶解,且可完全溶解;木浆纤维素/NMMO·H2O溶液的流动呈现切力变稀的假塑性流体特征;木浆纤维素质量分数为6%时,溶液的非牛顿流动特征明显,溶液的表观黏度(ηa)随木浆纤维素浓度的增加明显增加,随剪切速率(γ)及温度的上升而下降,当γ高于一定值即logγ大于1.3时,溶液的ηa不受温度的影响,只随γ的上升而下降,且剪切应力不随γ变化而变化,为恒定值。     

NMMO工艺纤维素膜成膜性能的研究

主要研究了NMMO工艺纤维素膜的成膜特性及不同因素对该工艺纤维素膜的物理和机械性能的影响。结果表明,纤维素浓度为4%～8%(W/W)时易于成膜,且随着浆粕聚合度的增大、纤维素浓度的增加、凝固浴温度的降低,制成的膜的力学性能较好。     

超声波处理后纤维素结构的变化及在NMMO中的溶解性能

用超声波预处理纤维素,并利用电子显微镜、X射线衍射和红外光谱对纤维素预处理前后的结构变化进行表征。结果表明,用超声波处理后,纤维素的结晶结构发生了很大的变化。用N-甲基吗啉-N-氧化物水溶液(NMMO·H2O)溶解预处理前后的纤维素,溶解过程及结果说明,超声波预处理可以加快纤维素的溶解速度,降低纤维素的分解。     

纤维素/[BMIM]Cl体系表观黏度影响因素

以1-丁基3-甲基咪唑氯盐([BMIM]Cl)离子液体为溶剂,研究了高聚合度的针叶木浆(DP=1460)在[BMIM]Cl溶剂体系中的活化能,考察了溶解温度、浆粕浓度和介孔硅添加量对纤维素/[BMIM]Cl体系表观黏度的影响.研究表明:纤维素/[BMIM]Cl体系黏流活化能AE=50.8 kJ/mol,针叶浆粕含量对体...     

羟丙基纤维素溶液的流变性能

采用ARES-RFS流变仪测定了羟丙基纤维素溶液的流变性能,考察了温度、溶液浓度、醚化剂量对溶液流变行为的影响,并得到了溶液的非牛顿指数、黏流活化能及结构黏度指数。结果表明:羟丙基纤维素溶液属于假塑性流体,随温度升高、浓度降低、醚化剂用量的增加,该溶液的表观黏度降低,非牛顿指数增大。     

Rheological characterization of concentrated cellulose solutions in 1‐allyl‐3‐methylimidazolium chloride

The rheological properties of high concentrated wood pulp cellulose 1‐allyl‐3‐methy‐limidazolium Chloride ([Amim]Cl) solutions were investigated by using steady shear and dynamic viscoelastic measurement in a large range of concentrations (10–25 wt %). The measurement reveals that cellulose may slightly degrade at 110°C in [Amim]Cl and the Cox–Merz rule is valid for 10 wt % cellulose solution. All of the cellulose solutions showed a shear thinning behavior over the shear rate at temperature from 80 to 120°C. The zero shear viscosity (η_o) was obtained by using the simplified Cross model to fit experimental data. The η_o values were used for detailed viscosity‐concentration and activation energy analysis. The exponent in the viscosity‐concentration power law was found to be 3.63 at 80°C, which is comparable with cellulose dissolved in other solvents, and to be 5.14 at 120°C. The activation energy of the cellulose solution dropped from 70.41 to 30.54 kJ/mol with an increase of concentration from 10 to 25 wt %. The effects of temperature and concentration on the storage modulus (G′), the loss modulus (G″) and the first normal stress difference (N₁) were also analyzed in this study. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Flow birefringence and viscosity of cellulose solutions in semi-dilute regime

An attempt was made to study the flow birefringence and the viscosity of the systems of cellulose in aqueous sodium hydroxide and cadoxen solutions. For this purpose alkali-soluble cellulose samples with crystal form I (simply denoted as cellulose I sample), prepared from conifer wood pulp by the steam-explosion method, and alkali-soluble cellulose samples with crystal form of cellulose II (cellulose II sample), regenerated from cuprammonium cellulose solution under specific conditions, were used. The extinction angle χ of aqueous alkali solutions of the cellulose I sample is significantly less shear rate (γ) dependent as compared with that of the cellulose II sample. In the latter system the χ versus γ relations for a given cellulose sample shifted to the higher γ side with decrease in the average molecular weight. The viscosity of the cellulose II sample in aqueous sodium hydroxide solutions is approximately twice that of the cellulose I sample in the same solvent if compared at the same molecular weight, same concentration, and same temperature. The latter solution showed a non-Newtonian property at relatively smaller γ than the former solution did. Spin-lattice relaxation time T₁ (by ¹³C-NMR) of cellulose in cadoxen solution was smaller in cellulose I, suggesting the existence of intra- and intermolecular hydrogen bondings at the C₆ position of cellulose molecules in cellulose I solution. A dynamic light scattering study on cellulose in cadoxen showed that in a 5 wt % solution of cellulose I cellulose particles are dispersed with time into smaller particles and the larger particles could be excluded by ultracentrifuge and in cellulose II solutions the cellulose particles had almost the same size during storage. The above findings indicate that in 5 wt% cellulose I solutions in aqueous alkali or in cadoxen, cellulose I is not dissolved molecularly, but a supra-molecular structure of the solid is at least partly reserved in the above solutions.     

The effect of solution variables on the solution of cellulose in dimethyl sulfoxide

Through the study of the effects of concentration, temperature, and molar ration (of paraformaldehyde to cellulose) on solution viscosity and per cent transmittance (at 530 nm), it has been demonstrated that cellulose solutions in dimethyl sulfoxide (DMSO) are readily produced. By heating 1, 2, and 50 to 100 parts by weight of cellulose, paraformaldehyde, and DMSO, respectively, extremely viscose cellulose solutions and gels were prepared. Solutions with concentrations as high as 10% were prepared. However, the optimum conditions to effect complete cellulose solution in DMSO at 75°C were found to be 0.5% cellulose and 0.8 and 1.0% paraformaldehyde. This corresponds to a paraformaldehyde-to-cellulose molar ratio of about 10:1.     

二醋酸纤维素丙酮溶液的流变性质研究

用TR - 1型气动式毛细管流变仪研究了二醋酸纤维素 (CA)丙酮溶液的流变性质 ,用X -射线衍射研究了CA的结晶结构 ,并探讨它们与流变性的关系。结果表明CA丙酮浓溶液为切力变稀的假塑性流体 ,随着溶液浓度和温度提高 ,流动曲线渐趋复杂 ;CA结晶度大小及取代均一性对流变行为有较大影响     

纤维素在离子液体中的溶解特性研究

测定了纤维素在不同结构的离子液体——1-烯丙基-3-甲基咪唑氯化物([AMIM]Cl)和1-丁基-3-甲基咪唑氯化物([BMIM]Cl)中的溶解度和溶解速率。结果发现:相同条件下,纤维素在[AMIM]Cl中具有较大的溶解度和较快的溶解速率;随着纤维素聚合度的增大,相同条件下,纤维素在离子液体中的溶解度降低。进一步通过WXRD、FT-IR、13C NMR和黏度法分析了溶解前后纤维素的化学结构、结晶结构和聚合度,结果表明:纤维素在离子液体中的溶解属于直接溶解,纤维素经离子液体溶解和再生后,晶型由纤维素I转变为纤维素II;溶解时间和温度对再生纤维素的聚合度有较大的影响,随着溶解时间的延长和溶解温度的提高,再生纤维素聚合度降低。     

Viscometric behavior of ternary concentrated solutions of hydroxypropyl cellulose and ethyl cellulose in m-cresol

The shear viscosity of blend solutions of hydroxypropyl cellulose (HPC) and ethyl cellulose (EC) in m-cresol (both HPC/m-cresol and EC/m-cresol systems form lyotropic liquid crystals) was determined by cone-plate-type and capillary-type viscometers. The textures for the same systems at rest and undergoing shear were also observed with a polarized microscope. At shear rate of 1 s^?1, viscosity exhibited a maximum and a minimum with respect to temperature, and this suggested that the phase of the matrix dominated the viscometric behavior of the ternary systems; the blend composition dependence of the viscosity was not additive, and this suggested that HPC and EC were immiscible. At relatively high shear stress, the blend composition dependence of the viscosity greatly depended on the total polymer concentration of the solutions and was quite different from that at low shear rate; the texture of the anisotropic solutions was also different from that at low shear rate. Our findings suggested that the dependence of viscosity on shear and concentration for pure HPC solution was different from that for pure EC solution.     

Shear rheology of diluted solutions of high molecular weight cellulose

A steady-state and dynamical rheological study was performed with dilute solutions (1–4%) of high molecular weight cellulose (M_w = 350,000). The solutions are strongly viscoelastic. The steady-state viscosity and the first normal stress difference have a power law dependence on the shear rate. The power law indices have the same dependence on temperature and concentration. These results as well as the correlation between the steady-state viscosity and the real part of the complex viscosity are in good agreement with the Spriggs model. The 4% concentrated solution shows the beginning of a rubber-like storage modulus plateau, suggesting the existence of an entanglement network.     

纤维素铜氨溶液的溶解性能及流变性能

研究了纤维素在铜氨溶液中不同溶解条件下的溶解特性,以及纤维素铜氨溶液的流变性能。结果表明:当溶解温度为-10℃,Cu2+浓度为1.4 mol/L,溶解时间1 h时,纤维素在铜氨溶液中有较大的溶解度;纤维素铜氨溶液为假塑性流体,其黏度随温度的升高而降低,随纤维素含量的升高而增大,当纤维素含量较高时,其黏度随温度的变化幅度较大。