Composition dependence of viscosity of some binary solutions

Viscosities of eleven binary liquid systems, mostly regular solutions, have been measured over the entire composition ranges at 25°C. Most of the systems had not been investigated before. The procedure, the precautions observed for the measurement of viscosity, and the calibration of the viscometers have been discussed. Of the many empirical and semi-empirical equations tested for their validity the McAllister equation has been found to fit best the experimental data for all the solutions. Non-ideality of a solution, as expressed in terms of excess activation energy for viscous flow or in terms of excess molal volume, has also been briefly discussed.     

Molecular weight and temperature dependence of intrinsic viscosity of polymer solutions

The molecular weight and temperature dependence of the intrinsic viscosity of polymer solutions have been predicted by combining the calculated radius of gyration, R_G, and hydrodynamic radius, R_H, with either the static empirical approach of Mandelkern—Flory or the dynamic argument of Weill—des Cloizeaux. It is found that experimental results can be successfully represented by the dynamic model for a range of five decades of molecular weight and temperature. The discrepancy between the calculated and experimental data at $\text{N ? N}{}_{\mathrm{т}}$ reveals the crudeness of the discontinuity at the temperature cut-off assumed by current temperature blob theory.     

高氨基甲酸酯含量PIPA多元醇的制备及应用

通过大量实验寻找出合适的特殊分散剂,通过添加此分散剂,可制备出高聚氨酯含量的多元醇PIPA,并用此多元醇制备聚氨酯泡沫,泡沫性能良好。     

Temperature dependence of the zero-shear melt viscosity of oligomeric epoxy resins

The melt viscosities of a homologous series of five epoxy resins based on bisphenol A and epichlorohydrin have been measured over a wide range of temperatures. It is shown that the temperature dependence of the zero-shear viscosity can be well described by the three-parameter Vogel equation. The Vogel parameters B and T_o were found to increase with increasing glass transition temperature, T_g, of the resin, while the ratios $\text{B}\text{T}{}_{\mathrm{<mtext>g</mtext>}}$ and $\text{T}{}_{\mathrm{<mtext>o</mtext>}}\text{T}{}_{\mathrm{<mtext>g</mtext>}}$ remained approximately constant. This constancy of the reduced Vogel parameters implies that T_g can be used as a corresponding states parameter to superimpose the viscosity-temperature data of all five resins onto a single master curve. The existence of such a master curve is of practical use, as it enables melt viscosities of epoxy resins to be predicted over a fairly extensive temperature range from only two quantities, viz. the value of T_g and one single viscosity value at a given temperature.     

Temperature dependence of pH for solubilized collagen solutions

The temperature dependence of the pH for an acid-soluble collagen in solution was measured, so that the pH largely increased in the temperature region including ca. 40°C of the thermal denaturation temperature. As the changes of the optical rotation, α_D, and the electrical conductivity, σ, were observed in this temperature region, the change of the pH is due to the thermal denaturation of collagen. The differential curve of pH vs. t gave clear deflection points and a large peak at ca. 40°C. The thermal denaturation temperature, t_d, could be estimated from the peak temperature. The t_d obtained by the measurement of the α_D, t_dαD, decreased with the decrease in the heating rate and with the increase in the concentration of collagen. However, the t_d obtained through the measurement of the pH, t_dpH, was independent of the variations of the heating rate and the concentration of collagen. These measurements were carried out for different kinds of collagens prepared by various methods. Some of them had one kind of peak; others had two kinds of peaks. The t_dpH correlated with the t_dαD for different kinds of collagen preparations. Therefore, the measurement of the temperature dependence of the pH was useful for the determination of the t_d. © 1994 John Wiley & Sons, Inc.     

Concentration dependence of zero-shear viscosity for polymer solutions: A test of the lyons-tobolsky equation

The empirical equation proposed by Lyons and Tobolsky (1) to describe the concentration dependence of zero-shear viscosity in polymer solutions was tested on a variety of data taken from the literature, covering different polymer-solvent systems, molecular weight, temperature, and the whole concentration range. This equation was fitted to each set of experimental viscosity-concentration data by a least squares method. The validity of this equation is verified. The dependence of the optimal values obtained for the three parameters intrinsic viscosity, [η], Huggins constant, k, and new empirical constant, b, on molecular weight, temperature, and solvent is also discussed.     

Characterisation of polyurethane networks based on vegetable derived polyol

A polyurethane (PU) network based on vegetable derived polyol has been characterised and compared to a synthetic based network. Fracture mechanics studies showed the lowest tear strength for the vegetable networks, which decreased as molecular weight of the vegetable based polyol increased. Swelling studies were carried out to determine the molecular weight between crosslinks and polymer networks made from wholly synthetic polyols were shown to have higher molecular weight between crosslinks. Moreover, vegetable networks showed higher solubles' content. Sol-fractions were analysed by several techniques. It was found that vegetable networks based sol-fraction was mainly its correspondent raw polyol while low molecular weight oligomers were detected for the most part in synthetic networks based sol-fraction.     

Melt viscosity of polyethylene: Shear dependence

Apparent viscosities of linear polyethylene melts may be simply related to molecular weight at various shear stresses. One gets constant slopes on a log–log scale with higher critical M?_w at higher shear stresses. The validity of Ferry's equation and the dependence of its coefficients are extensively analyzed.     

Temperature and concentration dependence of diffusion coefficient in dilute solutions

Temperature and molecular weight dependence of k_D in D(C) = D(O) [1 + Ck_D], where D(C) is the diffusion coefficient for the density fluctuations in a dilute polymer solution, is investigated by first expressing D(C) as a function of the static structure factor S(q,C) within the framework of the Kirkwood-Riseman theory. The continuous transition of k_D from negative values under theta conditions to positive values in good solvents is calculated using various models for the intermolecular interaction potential and the results are presented graphically as function of a reduced variables $\text{S}\text{?}\text{R}{}_{\mathrm{H}}$ that combines both molecular weight and temperature effects. It is shown that the negative value of k_D at the theta temperature can be explained at least partially, in terms of an increase in the chain dimensions of two overlapping molecules. The concentration dependence of the self-diffusion coefficient is also discussed.     

Pressure dependence of newtonian viscosity

Recently, a new method of generalization of the zero shear viscosity of liquids has been proposed. The method utilizes a modified Doolittle formula and the temperature-dependent volume, as expressed by the corresponding states theory of liquids. Furthermore, the glass-transition temperature has been employed as the scaling parameter. The proposed treatment allowed prediction of the correlation between: (i) viscosity, η, and temperature, T, (ii) η and the molecular weight of polymer, (iii) η and concentration, and (iv) the combined effect of these variables. At present, the method is extended to the pressure, P, effect. Furthermore, by substituting the free volume fraction in the Doolittle formula by the theoretical “hole fraction,” a master-relation is proposed that provides means for predicting η = h(T, P) dependence.     

The viscosity dependence on concentration,molecular weight and shear rate of xanthan solutions

Summary This paper concerns the viscosity dependence of Xanthan as a function of polymer concentration, shear rate and molecular weight in the ordered conformation. The different samples with various molecular weights are obtained by ultrasonication. A unique curve is obtained for the reduced specific viscosity ( ) as a function of γ · γ _r ⁻¹ for the different molecular weight samples and polymer concentrations below an overlap concentration C [η]₀⩽ 1.5. The master curve giving the relation as a function of C [η]₀ is drawn and compared with that of polystyrene in good solvent. The largest increase of in semidilute solution may be due to larger interchain interactions and to larger stiffness of the Xanthan molecule.     

低氟发泡聚醚多元醇

低氟(里昂)发泡聚醚多元醇是当代聚醚多元醇的新品种,它的问世为聚氯酯泡沫塑科生产中减少和最终完全替代CFC类物质创造了条件。本文介绍了低氟发泡聚醚多元醇结构设计原则、合成工艺及应用实例,建议在冰箱行业首先推广应用。     

聚酯多元醇M_r对热塑性聚氨酯弹性体性能的影响

以聚己二酸乙二醇/丁二醇酯(PEBA)、4,4′–二苯基甲烷二异氰酸酯(MDI)和1,4–丁二醇(BDO)为原料,合成了热塑性聚氨酯弹性体(TPU)。通过控制异氰酸酯指数(R值)和TPU硬段含量,研究了PEBA相对分子质量(Mr)对TPU综合性能的影响。实验结果表明:当R值和硬段含量维持不变时,随聚酯多元醇Mr增加,TPU的回弹性、力学性能、耐磨耗性能和耐低温性能增强。     

Temperature dependence of reinforcement in the composites polyurethane rubber–crosslinked polymeric filler

The temperature dependence of the components of the complex tensile and shear modulus of composites thermoplastic polyurethane rubber (Estan 5707)–crosslinked polymeric filler has been determined using torsional pendulum and Rheovibron viscoelastometer techniques. For comparison, dynamic mechanical properties of the system Estan 5707–glass beads were determined. The temperature dependence of the relative modulus (modulus of composite/modulus of matrix) of the former composites exhibited a pronounced maximum at about 50°C above the glass transition temperature of the matrix. This maximum of reinforcement was discussed in terms of (a) immobilized interfacial layer, (b) broadening of the spectrum of relaxation times, and (c) increase in the glass transition temperature of the matrix. From the excess reinforcement, i.e., the discrepancy between experimental data and theoretical prediction, an apparent thickness of the immobilized layer was calculated.     

Temperature dependence of rheological properties of poly(methyl methacrylate) filled with silica nanoparticles

Creep-recovery experiments up to the steady state were performed on neat poly (methyl methacrylate) and on composites filled with 2.1 vol.% silica nanoparticles in order to get information on the long retardation times that occur due to polymer-particle interactions. The temperature dependence of the elasticity was investigated, varying the temperatures between 170 °C and 200 °C. For the neat polymer it was found that it behaves thermorheologically simple, whereas the composite exhibits a thermorheological complexity. An interpretation of these findings can be given, if the corresponding retardation spectra are regarded. The interactions between the polymer molecules and the particle surface is reflected by a particular maximum at longer retardation times, which exhibits a different temperature dependence compared to the spectra of the unfilled polymer matrix. This thermorheological complex behaviour is not seen in the usual dynamic-mechanical measurements down to angular frequencies of ω = 10⁻² s⁻¹. If the frequency range of the dynamic moduli is extended, however, by making use of the retardation spectra, a thermorheological complexity can be found, too. These results demonstrate that appropriate experimental time windows have to be applied to obtain a comprehensive picture of the rheological behaviour of nano particle-filled polymer melts.     

高固体分低粘度羟基丙烯酸树脂的合成

报道了高固体分低粘度羟基丙烯酸树脂的合成方法，讨论了羟基单体、溶剂、引发剂、分子量调节剂、工艺条件等因素对产品的影响，介绍了该树脂的特性和应用效果。     

On the factors governing the pressure dependence of the viscosity of moderately concentrated polymer solutions

Viscosity measurements were carried out as a function of pressure and temperature with solutions of polystyrene in eight (endothermal) θ-solvents at the respective critical composition by means of a Searle-type apparatus. A rolling-ball viscometer was used for the investigation of the pure solvents. In all cases the viscosity coefficient increases in a more or less exponential manner when the pressure is raised. For θ-conditions, the volumes of activation of the solutions exceed that of the pure solvent by typically 10–15%. The exact amount of this extra efffect stemming from the presence of the polymer and its variation with temperature can be qualitatively correlated with the heats of mixing. The ratio of the viscosity of the solution at 1000 and 1 bar, respectively, can be varied for a given solvent power (θ-temperature) by the choice of the solvent from ca. 2 (cyclopentane) to 4 (trans-decalin). Within a given system, the maximum effects that can be realized by a change of the solvent power via the variation of temperature ranges from ca. 3 to 6 (tert-butylacetate).