Comparison of various solvents for determination of intrinsic viscosity and viscometric constants for cellulose

Different solvents used to determine the intrinsic viscosity and the viscometic constants, a and K, published in the literature for cellulose, were compared. The various parameters affecting the viscometric constants were also evaluated. The main conclusions obtained from the experimental data available in the literature are that (1) the intrinsic viscosities in various solvents are ordered as follows: [η]_LiCl/DMAc > [η]_NH3/NH4SCN ≥ [η]_FeTNa > [η]_CED > [η]_Cadoxen > [η]_Cuoxam; (2) the reported intrinsic viscosities and molecular weights for cellulose are lower than the true value due to degradation of cellulose in the solvents; (3) the rate of degradation was the smallest in LiCl/DMAc and NH₃/NH₄SCN, moderate in cadoexn and FeTNa, and the highest in CED and cuoxam; (4) the plot of log K versus exponent a was linear and inversely related; (5) the curve was used for estimation of the constant K for cellulose in a solvent (NH3/NH4SCN) with a known exponent a; and (6) among various reported solvents, LiCl/DMAc and NH₃/NH₄SCN are advantageous over other solvents because of a complete dissolution of the polymer with a negligible reduction in its intrinsic viscosity. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2189–2193, 2002     

不同特性粘数PBT切片的流变性能研究

采用毛细管流变仪研究了5种不同特性粘数的聚对苯二甲酸丁二醇酯(PBT)的流变性能,计算得到了PBT的非牛顿指数和粘流活化能。结果发现:不同特性粘数的PBT熔体能够达到的最大剪切速率不同,随着特性粘数的增大,PBT熔体的非牛顿指数逐渐减小,粘流活化能先是逐渐减小,然后又变大。     

提高羧甲基纤维素钠酸黏比的研究

以乙醇为溶剂,精棉、氯乙酸和氢氧化钠为原料,加入价廉的、对人体无害的添加剂来加深碱化与醚化反应的深度,可制备出高酸黏比(小试达1.00左右)的羧甲基纤维素钠(CMC)。运用数理统计与正交试验法研究了物料配比、添加剂种类与用量、反应温度、反应时间以及其它强化碱化与醚化深度的多种因素,从而确定了提高CMC酸黏比的优化反应条件,为中试与扩大试验提供了参考的依据。     

Conformational change studies by intrinsic viscosity of cellulose tricarbanilate as a function of temperature

Summary The experimental variation of the intrinsic viscosity [] as a function of temperature for various molecular weights of cellulose tricarbanilate in solution in dioxane displays a S-shaped character with two plateau regions, respectively at low and high temperatures. The use of the Yamakawa model leads to two distinct values for the chain stiffness q, one which may be_o associated to a rather rigid conformation of the macromolecule (q=139 Å), the other which may correspond to a rather flexible conformation (q = 84Å).     

On the single-point determination of intrinsic viscosity

In the present paper we have analytically derived a single-point equation for determining the intrinsic viscosity of a polymer. It is observed that the proposed equation gives a much better agreement with the extrapolated value of [η] over a wide range of concentration for good as well as poor polymer–solvent systems.     

Determination of intrinsic viscosity by single specific viscosity measurement

Single point determination of intrinsic viscosity saves considerable amount of time, effort and materials. Quite a few equations are available in the literature which require relative viscosity of the polymer solution at a single concentration for calculation of [η]. A comparative assessment of the applicability of two such equations and that of a proposed one has been made by using reported data as well as the practical data on viscosity of alkyd solutions in different solvents. It is inferred from the findings that, for good results from single point methods, the concentration should not be the sole criterion, as suggested by earlier workers; η_sp may also be considered as one of the criteria. The single point technique is found to be applicable to alkyd solutions in different solvents.     

Relation between intrinsic viscosity and molecular weight

The connection between intrinsic viscosity and number-average and weight-average molecular weight has been revealed by calculations from distribution curves. Log-normal distributions, and moderate variations thereon, were chosen as typical for polystyrene and other thermoplastics. Intrinsic viscosity and number-average molecular weight are unlikely to be related because of the highly disturbing effect of small variations in molecular weight distribution. Conversely, intrinsic viscosity is a good practical measure of weight-average molecular weight up to a ratio of 10 for weight-to-number average.     

氯化聚丙烯甲苯溶液的特性黏数及其黏均分子量

分别用乌氏黏度计和旋转黏度计测定了氯化聚丙烯甲苯溶液的特性黏数和黏度,把特性黏数和黏度进行关联,发现ηsp/C与浓度C(ml/g)的关系用多项式ηsp/C=[η]+k1[η]2C+k2[η]2C2拟合,可以得到很好的结果。并且用特性黏数和Mark-Houwink方程求出了不同氯化聚丙烯(CPP)的黏均分子量。     

Determination of intrinsic viscosity of polyelectrolyte solutions

Intramolecular hydrodynamic contribution η_intra/C to the reduced viscosity η_SP/C of polyelectrolyte solutions is derived as a function of polymer concentration C by separating the theoretically calculated intermolecular electrostatic contribution η_inter/C from the observed reduced viscosity, assuming an additivity, η_SP/C=η_intra/C+η_inter/C. The resulting intramolecular part η_intra/C reflects nearly the net effect of the polyion conformation; it increases monotonously with decreasing polymer concentration and levels off to a constant in sufficiently dilute concentrations. The leveling-off value of η_intra/C corresponds to the intrinsic viscosity [η]. From the estimated values of [η], the ionic strength I dependence of the polyion conformation has been visualized, resulting in a similarity between two relations, η_intra/C vs. C and [η] vs. I.     

聚酯特性粘数测试方法的比较

阐述了相对粘度仪法和传统玻璃毛细管粘度仪法的测试原理,实验验证了Y501相对粘度仪和LAUDACD30粘度仪测试结果的差异性。结果表明其差异性不大,相比LAUDACD30粘度仪,5（501相对粘度仪的测试精度及自动化程度更高、有利环保,更具有实用性和快捷性。     

聚合物特性黏度与在线黏度测量相关性实例分析

通过不同配方的特性黏度和在线黏度的实测案例,对特性黏度和在线黏度测量结果的相关性、数据转换和偏差进行分析,结果表明,聚合物特性黏度和在线黏度测量值之间有很好的相关性,通过适当的数据转换,在线黏度计可用于快速、实时、连续测量特性黏度。     

Solubility of sodium cellulose xanthate in aprotic solvents

Conclusions The solubility of sodium cellulose xanthate of various degrees of substitution in dipolar aprotic solvents has been examined.It has been shown that a xanthate with a low degree of substitution is soluble only in dimethyl sulfoxide, while a highly substituted one dissolves also in dimethylformamide, dimethylacetamide, and N-methylpyrrolidone.A water content in the aprotic solvent improves the solubility of the cellulose xanthate, but a sharp decrease in the degree of polymerization and degree of substitution also takes place.Translated from Khimicheskie Volokna, No. 1, p. 27, January–February, 1984.     

Practical use of intrinsic viscosity for polyethylenes

Although usually derived from measurements at several concentrations, intrinsic viscosity (IV) can be determined with good precision from a single measurement. IV tends to be a regular and distinct function of melt index (MI) for each family of high-density polyethylenes. The tendency to regularity suggests a use in routine control, uniform production being marked by a small scatter about the IV–MI line. The distinctiveness marks one family of medium high and high-density resins from another, and becomes a rapid means of identifying the production method of a resin. Further, IV at a given MI correlates roughly with properties, and can be used to characterize a resin. These attributes of the IV–MI relationship arise from the correlation of IV a t a given MI with width of molecular weight distribution. Such width varies considerably among commercial high-density polyethylenes, causing a commensurate variation in IV. Among low-density polyethylenes the IV–MI relationships is less useful, being confused by long-chain branching.     

Prediction of solubility parameter from intrinsic viscosity

Polymer for coating such as epoxy and alkyd resin use additives for enhancing physical properties, hardening acceleration, and decreasing viscosity. Therefore, diluent selection is important for blending of additives in the resin. The choice of these solvents is determined by comparing the solubility parameters. In this study, it is a measure of the intrinsic viscosity of epoxy resin by Ubbelohde viscometer and epoxy resin is calculated solubility parameter through intrinsic viscosity. The epoxy and alkyd resins’ solubility parameters were calculated from their intrinsic viscosities to be epoxy resin (${\delta }_{2d}=16.55$, ${\delta }_{2p}=5.98$, ${\delta }_{2h}=6.53$) and alkyd resin (${\delta }_{2d}=19.11$, ${\delta }_{2p}=3.96$, ${\delta }_{2h}=4.86$), respectively. Their total solubility parameters were calculated to be epoxy resin (${\delta }_{2t}=18.77$) and alkyd resin (${\delta }_{2t}=20.11$), respectively.     

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.     

聚酯切片特性粘度分析的误差来源

叙述了在落实聚酯切片特性粘度国家标准的过程中出现的一些问题 ,讨论了特性粘度分析误差的主要来源于测试仪器、所用试剂、过滤设施等 ,并提出了解决办法。