硝化纤维素溶液冰冻过程中的粘度行为

用乌式毛细管粘度计对硝化纤维素稀溶液的粘度行为进行了研究，测定了原溶液、冰冻后溶液、冰冻后经过加热的溶液以及加热后继续冰冻溶液相对粘度的变化规律。结果表明：冰冻过程中硝化纤维素溶液粘度的降低是由于分子链内发生链内凝聚（缠结）造成的。并且发现，不同浓度的高分子溶液冰冻过程中相对粘度变化的规律不相同，浓度较高的硝化纤维素溶液在冰冻过程的初期可能同时伴随有链内凝聚和链间凝聚。文中还讨论了一种快速形成链内凝聚的方法，并对冰冻过程中硝化纤维素分子形成链内交联点的倍数进行了估计。     

名词浅解

临界凝固浓度C_c 在湿纺纺丝原液的几元体系内,逐渐加入凝固液,体系内溶液浓度降低到某一临界值,使原溶解的聚合物开始沉淀,体系发生相分离,该临界值称之为凝固临界浓度C_c。不同组成的共聚物凝固时的C_c值不同,所以通过C_c值的测定,可以判别纺丝原液的凝固性能。例如在PAN—NaSCN—H_2O的三元体系内,逐渐加入稀NaSCN水溶液,使NaSCN在NaSCN—H_2O二元体系内的重量百分浓度降低到某一临界值时,该浓度即PAN共聚物的凝固临界浓度。     

基于硝化泥炭对含铬废水的正交实验研究

采用稀硝酸处理天然泥炭,考察硝化泥炭的投加量、溶液中铬的初始浓度、溶液的初始pH和吸附接触时间对硝化泥炭的去除效果的影响。实验结果表明:实验因素影响顺序是:含铬废水的初始浓度>pH>硝化泥炭投加量>吸附时间。最佳的实验组合是:硝化泥炭投加量0.5 g、含铬废水的初始浓度20 mg/L、吸附时间80 min、pH 6。在最佳的实验条件下,溶液中的铬离子的去除率达到91.49%。     

三元体系相分离制备硝化纤维素凝胶及其动态流变性的研究

通过溶剂蒸发引发相分离从硝化纤维素/丙酮/乙醇三元体系中制备出硝化纤维素凝胶,采用线性流变学方法考察凝胶对外界刺激(如应变、频率、温度)的响应程度,研究了凝胶的动态流变性能。结果表明,溶剂/非溶剂(丙酮/乙醇)质量比或硝化纤维素含量影响最终硝化纤维素凝胶的形貌,改变溶剂比例与硝化纤维素含量对硝化纤维素凝胶的动态流变性能的影响不同,增加丙酮含量,制备出的硝化纤维素凝胶体积减小,凝胶中硝化纤维素的含量增加,储能模量G′和损耗模量G″增加,临界应变(γc)随凝胶中硝化纤维素含量的增加而减小;当丙酮/乙醇的质量比为2∶3时,增加硝化纤维素含量,G′和G″值会随着凝胶中硝化纤维素含量的增加先增大后减小。所有硝化纤维素凝胶的储能模量G′和损耗模量G″在整个温度扫描中基本不变,表明硝化纤维素分子链间和硝化纤维素/溶剂间的相互作用不会被升温破坏。     

秸秆纳米纤维素和纳米木质素的环保高效提取

以蒸爆小麦秸秆为原料,通过稀碱辅助球磨实现了纤维素组份的纳米化和木质素组份的充分溶解,实现了秸秆纳米纤维素的分离提取。分别通过胶束法和反溶剂法将溶于稀碱中的木质素再生获得球形纳米木质素及纳米木质素胶囊。在稀碱辅助球磨过程中系统研究了氢氧化钠溶液浓度、蒸爆秸秆含量、球磨珠配比和时间对纤维素纳米化及组份分离效率的影响。结果表明：在0.5 mol/L NaOH水溶液、秸秆浓度2.0%(wt)、每10 mL溶液配置球磨珠20 g、球磨时间10 h的条件下秸秆纤维素纳米化的程度最高,木质素分离效率可达99.7%。通过胶束法和反溶剂沉淀法对经离心分离的木质素碱溶液酸析和透析后冷冻干燥,分别制得了尺度为数百纳米的木质素纳米颗粒与木质素纳米胶囊。     

水合肼还原硝化棉动力学模型研究

为了处理过期的废药以达到资源回收再利用的目的,安全、环保的水合肼还原法成为废药处理的发展方向之一.通过化学动力学定律结合紫外光谱分析,研究了水合肼还原过期废药硝化纤维素(硝化棉)的动力学,为今后处理废弃发射药提供理论模型.实验采用的水合肼浓度为10、8、6、4g·L-1,温度选择30～90℃,通过硝化纤维素在水合肼溶液...     

氧浓度对硝化纤维素燃烧特性的影响

为了探讨氧浓度对硝化纤维素材料燃烧特性的影响,采用自行设计的小尺度燃烧室,通N_2稀释降低燃烧室内的氧浓度,电加热方式点燃尺寸为200×10×0.7 mm的硝化纤维素样条,并通过相机记录燃烧图像、热电偶测温、电子天平测质量和烟气分析仪测CO浓度四种方法研究了常压下水平放置、竖直放置和不同点火位置时,硝化纤维素燃烧的火焰形态、火蔓延速度、质量燃烧速率及燃烧释放出的CO浓度峰值随氧浓度降低的变化情况。结果表明:硝化纤维素燃烧特性受氧浓度影响显著,而且氧浓度对其燃烧特性影响还与放置位置和点火位置有关。     

微米级硝化纤维素的制备及性能研究

为了使硝化反应在近似均相的条件下进行,采用对精制棉进行水解处理,用稀酸水解法制得结晶度较为一致的微晶纤维素,再用硝硫混酸进行硝化得到微米级硝化纤维素。用扫描电镜和红外光谱对其微观形貌和结构进行了表征。用DSC分析了其热性能,并测试了其撞击感度和黏度。结果表明,制备微米级硝化纤维素的最佳条件为:硝硫混酸体积比为1∶3,硝化时间30min,硝化温度为35℃。制得的微米级硝化纤维素样品粒度均匀,其特性落高为57.466cm,黏度为478mPa·s,分解峰温达到211.20℃,硝化均匀,含氮量可达12.8%。     

美耐皿餐具中三聚氰胺残余单体的迁移行为研究

美耐皿餐具中残余三聚氰胺单体向食品中的迁移行为越来越受到社会关注。合成了三聚氰胺甲醛树脂,并与不同浓度的纤维素混合,配制成的模塑料,在不同工艺条件下模压成美耐皿制件,研究了纤维素含量、模压温度、模压时间、浸泡介质和浸泡时间对美耐皿制件中残余三聚氰胺单体向介质迁移行为的影响,观察了浸泡前、后制件的表面形貌变化。结果表明,美耐皿制件中残余三聚氰胺单体向乙酸稀溶液中的迁移量最大,众多因素中纤维素含量对残余单体迁移量的影响最为显著,在浸泡300 h后达到迁移平衡,乙酸稀溶液对美耐皿制件表面存在溶解性腐蚀。     

十六烷基三甲基水杨酸铵水溶液的电导和流变性能研究

研究了十六烷基三甲基水杨酸铵水溶液在稀溶液和亚浓溶液范围的电导和流变行为。体系的电导率-浓度曲线显示2个转折点:第一个转折点对应临界胶束浓度(cmc),第二个对应体系开始形成棒状胶束的浓度。计算了胶束化的热力学函数变化,证实胶束化过程主要来自于焓驱动。流变实验表明:所有体系均显示剪切稀化行为;溶液质量摩尔浓度高于119 mmol·kg-1时,体系符合Maxwell流体行为,具有单一结构弛豫时间;体系的高黏度来自于短棒状胶束之间的链接而不是缠结的蠕虫状胶束。     

Hydrophobically modified poly(sodium 2‐acrylamido‐2‐methylpropanesulfonate): synthesis and viscosity of aqueous solution

BACKGROUND: Hydrophobically modified polyelectrolytes are widely used polymers due to their good water solubility, stretched configuration in water and strong hydrophobic association. The study reported here aimed at researching the double action of hydrophobic association and electrostatic effect of novel hydrophobically modified polyelectrolytes in solution. RESULTS: A series of novel hydrophobically modified polyelectrolytes were synthesized by micellar copolymerization with various feed ratios of sodium 2‐acrylamido‐2‐methylpropanesulfonate, N‐n‐dodecylamine and sodium dodecylsulfonate. Their structure was characterized using Fourier transform infrared spectroscopy, nuclear magnetic resonance and gel permeation chromatography, and the viscosities of their aqueous and salt solutions were studied. CONCLUSION: The results show that the addition of the hydrophobic comonomer results in a decrease in molecular weight (M_w). The smaller the initial number of hydrophobes in one micelle, the higher is M_w of the resulting copolymer. The viscosity of PAD‐1.73 polyelectrolyte is less sensitive to salt than those of the others. According to the zero shear viscosity and corresponding concentration, the critical cluster‐forming concentration, critical overlap concentration and critical entanglement concentration of these polymer solutions were determined. Moreover, in the dilute regime the viscosity decreases with increasing salinity, while in the semi‐dilute regime the viscosity decreases first and then increases. It is suggested that in dilute and semi‐dilute regimes, hydrophobic intramolecular association and intermolecular association dominate, respectively. Copyright © 2009 Society of Chemical Industry     

Viscometric Study of Segmented Poly(ester-urethane) Solutions in Dilute and Extremely Dilute Concentration Domains

ABSTRACT

Synthesis and viscometric behavior of segmented poly(ester-urethane)s in N,N-dimethyl-formamide solution ranged from semidilute to extremely dilute concentration were investigated. The data reflected the conformation changes in the 17–45°C range, and the results are discussed in relation to the behavior of the poly(ethylene glycol)adipate in the same solvent. The intrinsic viscosities and critical concentration that separate the dilute–extremely dilute regimes are also studied. A scanning law between the reduced viscosity η_sp/c and the concentration for the extremely dilute regime is found and the deviations from Huggins dependence at different temperatures are discussed.     

RHEOLOGICAL AND MIST IGNITION PROPERTIES OF DILUTE POLYMER SOLUTIONS

A spinning disc atomizer has been used to characterize the mist flammability of Jet A and diesel fuels that contain high molecular weight polymers. The critical disc velocity required to produce significant flame propagation was shown to depend on polymer concentration, molecular weight, solvent viscosity, and polymer degradation.

The viscoelastic properties of these same polymer solutions have been characterized by a maximum Darcy viscosity measured from flow in packed tubes. For the polymers discussed in this paper, the maximum Darcy viscosity was independent of the bead size or tube length; however, it was strongly affected by the same variables that affected mist flammability; i.e., polymer concentration, molecular weight, solvent viscosity, and polymer degradation.

The critical ignition velocity of dilute polymer solutions is shown to depend on the Darcy viscosity in a similar manner as observed for viscous oils. At low viscosities, the ignition velocity is only slightly affected, but the dependence grows stronger as the viscosity (both shear and Darcy) increases. A close correspondence was also shown to exist between the ignition velocity of a polymer solution with a high Darcy viscosity and the ignition velocity of a Newtonian oil with approximately the same high shear viscosity.

Numerous similarities are described between flow-induced birefringence of dilute polymer solutions with opposed capillary jets and viscoelastic resistance of dilute polymer solutions in packed tubes. These similarities suggest that the maximum Darcy viscosity is associated with a condition of almost complete extension and alignment of the polymer molecules.     

Rheology and viscosity scaling of the polyelectrolyte xanthan gum

The viscosity as a function of concentration for xanthan gum in both salt‐free solution and in 50 mM NaCl is measured and compared with a scaling theory for polyelectrolytes. In general, the zero shear rate viscosity and the degree of shear thinning increase with polymer concentration. In addition, shear thinning was observed in the dilute regime in both solvents. In salt‐free solution, four concentration regimes of viscosity scaling and three associated critical concentrations were observed (c* ≈ 70 ppm, c_e ≈ 400 ppm, and c_D ≈ 2000 ppm). In salt solution, only three concentration regimes and two critical concentrations were observed (c* ≈ 200 ppm and c_e ≈ 800 ppm). In the presence of salt, the polymer chain structure collapses and occupies much less space resulting in higher values of the critical concentrations. The observed viscosity‐concentration scaling is in very good agreement with theory in the semidilute unentangled and semidilute entangled regimes in both salt‐free and 50 mM NaCl solution. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Lyotropic liquid crystalline solutions of hydroxypropyl cellulose in water: Effect of salts on the turbidity and viscometric behavior

Effect of addition of salt on the viscometric behavior of the dilute or concentrated aqueous solution of hydroxypropyl cellulose (HPC) was determined by means of an Ubbelohde or a cone-plate viscometer. That effect on the turbidity of the dilute system was also determined. As salts, NaCl, LiCl, and thiourea were chosen. The turbidity and viscometric behavior for the dilute system, and the viscometric behavior for the concentrated system were greatly affected by salt type and concentration. With increasing NaCl or LiCl concentration, the cloud point decreased, [η] showed a maximum, Huggins' constant k′ showed a minimum, and the shear viscosity for concentrated isotropic solutions showed a maximum. The 45 wt % solution with no salt showed a viscometric behavior which was characteristic of lyotropic liquid crystals; however, with increasing NaCl concentration, a critical temperature at which the shear viscosity showed a maximum with respect to temperature shifted to lower temperature. This behavior was due to an increase in the turbidity, not due to a phase transformation. On the other hand, an addition of thiourea did not affect so greatly the turbidity and viscometric behavior as an addition of NaCl or LiCl did. We speculated different actions of NaCl and thiourea.     

Dilute solution properties of anionic poly(potassium-2-sulphopropylacrylate)

The dilute solution properties of an anionic polyelectrolyte, poly(potassium-2-sulphopropylacrylate) (poly(SPA)) are studied by measurements of intrinsic viscosity, degree of binding, ionic strength and critical micelle concentration. The intrinsic viscosity of this polyelectrolyte is related to the type and concentration of the salt added. The intrinsic viscosity behaviour of an anionic polyelectrolyte resulting from the electrostatic repulsive force of the polymer chain is in contrast to that of a polyampholyte. The polyelectrolyte in high concentration of NaCl has a low degree of binding, indicating that the proton ion (H⁺) is relatively difficult to bind to the sulphonate group (SO⁻₃) at the polymer end. An increase in ionic strength causes the pK_a to decrease at the half-neutralization point. The monomer solutions exhibit a plot typical of those observed for detergents, with a break in the curve occurring at the critical micelle concentration. For the polymer solutions, no break in the equivalent conductance curve was found for the concentrations studied.     

Molecular degradation of concentrated polystyrene solutions in a fast transient extensional flow

The extensional degradation of concentrated polymer solutions is studied. Extensional flows are prevalent in the polymer processing industry, but their effect on polymer degradation is often overlooked. Previous research into dilute solution extensional degradation proved that this type of flow is much more effective than shear flow in causing chain scission. This research extends these dilute solution studies into the concentrated regime, where intermolecular entanglements are expected to affect chain scission. A concentrated polystyrene solution is degraded in an opposed pistons device. This device cycles the solution across a sharp contraction, imposing a strong extensional flow. The flow field is modeled to determine the extension rate along the centerline, and the degradation is quantified by measuring the zero shear viscosity and the molecular weight distribution. The results show that degradation is more significant compared to dilute solutions. The zero shear viscosity drops 30% after a single pass across the orifice at high strain rates. As in a dilute solution, the extensional flow leads to preferential cleavage of the high molecular weight chains. All chains longer than a measured critical molecular weight are ruptured. Multiple passes across the orifice increase chain scission, although degradation is the most significant in the first pass through the high strain rate region.     

Dilute solution properties of anionic poly(potassium-2-sulfopropylmethacrylate)

The dilute solution properties of an anionic polyelectrolyte, poly(potassium-2-sulfopropylmethacrylate) [poly(SPM)], are studied by measurements of polymerization rate, intrinsic viscosity, degree of binding, ionic strength, and critical micelle concentration. The polymerization of SPM in 0.5M NaCl aqueous solution proceeded more easily than that of SPM in pure water. The polymerization rate of SPM is found to pass through an extreme value as a function of pH. The intrinsic viscosity of this polyelectrolyte is related to the type and concentration of the salt added. The intrinsic viscosity for anionic polyelectrolyte resulting from the electrostatic repulsive force of the polymer chain is in contrast with the polyampholyte. The polyelectrolyte in a high concentration of NaCl has a low degree of binding, indicating that the proton ion (H⁺) is relatively difficult to bind to the sulfonate group (SO⁻₃) at the polymer end. An increase in ionic strength causes the pKa (dissociation constant) to decrease at the half-neutralization point. The monomer solutions exhibit a plot typical of those observed for detergents, with a break in the curve occurring at the critical micelle concentration. For the polymer solutions, no break in the equivalent conductance curve was found for the concentrations studied. The polymer is adapted for use as viscosity-controlling agents in secondary oil recovery operations by water flooding. We have the proposed models to account for the poly(SPM) solution viscometrics. © 1997 John Wiley & Sons, Inc.