共查询到19条相似文献,搜索用时 255 毫秒
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非晶高聚物的结构研究,包括玻璃态、橡胶态、粕流态、结晶高聚物中的非晶部分以及结晶熔融态的结构研究。有关非晶态高聚物的结构,过去都认为由Flory(1949)从统计热力学的理论推导出来的“无规线团模型”(random coil model)是正确的。根据Flory理论,非晶态高聚物分子链的构象服从无规行走统计学,亦即 相似文献
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基于作者提出的纯气体吸收机理,并引入吸收竞争因子的概念,导出了混合气体在非晶态高分子膜内的吸收机理模型.针对PMMA—CO_2/CH_4、PMMA—C_2H_4/CH_4以及PS-C_2H_4/CH_4等3种系统,在308K的温度下进行了等温吸收实验.实验结果表明了上述模型能较好地描述混合气体的等温吸收数据. 相似文献
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纯气体在非晶态高分子膜内的吸收机理模型(Ⅱ)应用 总被引:1,自引:1,他引:0
对CO_2、CH_4、C_2H_4和C_2H_6等4种纯气体进行了吸收等温线的测试,通过数据表明在(Ⅰ)报中提出的吸收机理模型是普遍适用的,模型参数也能较好地与高分子和渗透分子的物性数据关联. 相似文献
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以自由体积理论为基础 ,提出改良的玻璃态高分子中溶剂扩散系数的数学模型 .模型推导过程中考虑了溶剂可塑化效应对高分子凝聚态的影响 ,并以明确的物理概念计算玻璃态聚合物的自由体积 .对橡胶态适用的自由体积参数在此模型中保持有效 ,所引入的表达溶剂可塑化效应的唯一参数 β可以通过计算玻璃化温度来确定 .所以 ,本模型中无可调节参数存在 ,具有完全可预测性 .以芳香族溶剂苯、甲苯、乙苯在玻璃态聚苯乙烯和聚甲基丙烯酸甲酯中的扩散系数为例对模型进行验证 ,理论计算结果和实验值取得良好一致 相似文献
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针对有机溶剂在玻璃态高分子膜中的渗透现象,提出基于物性推算法的膜分离材料选择方法.基于溶解-扩散机理模型,使用统计热力学和状态方程式为基础的GCLF-EOS模型进行溶解度计算、自由体积模型推算扩散系数,同时考虑填充型复合膜的基膜影响,建立膜渗透通量计算模型.本研究充分考虑有机溶剂对高分子的塑化效应,通过引入塑化固子,重新评价对传质过程有效的"空穴自由体积",改进现有的自由体积理论模型.利用芳香族溶剂苯的实验数据和理论预测比较,验证溶解性和扩散性理论模型的正确性.在此基础上对芳香族有机溶剂在玻璃态高分子膜中传递行为进行成功预测. 相似文献
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高分子聚合物中溶剂扩散系数的预测 总被引:2,自引:2,他引:0
溶剂分子在高分子聚合物中的扩散现象广泛存在于日常生活和工业生产中,对其研究具有普遍意义.Vrentas-Duda模型以自由体积理论为基础,所有参数不需扩散实验测量,由溶剂和高分子的分子性质独立确定,可用于预测高分子聚合物中低相对分子质量溶剂扩散系数.研究Vrentas-Duda模型对典型高分子/溶剂体系中溶剂扩散系数的预测准确性,通过将预测值与实验值比较,评价该模型在不同高分子体系中的适用情况.对处于橡胶态的各向同性高分子聚合物体系,Vrentas-Duda模型能够准确计算除存在氢键以外多数体系的溶剂扩散系数;相对于溶剂互扩散系数而言,溶剂自扩散系数的预测精度更高. 相似文献
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The processes of gas sorption and permeation in a polymer membrane at temperatures above and below the glass-transition point were examined using poly-4-methylpentene-1 (glass-transition temperature reported to be 40°C) as a membrane material. The permeabilities to O2 and N2 were independent of applied gas pressure at every temperature; the mean permeability coefficient to CO2 increased with increasing gas pressure. The logarithm of the mean permeability coefficient to CO2 increased linearly with gas pressure due to the plasticization effect induced by sorbed CO2. From the sorption isotherms for CO2 at 20 and 30°C it was judged that the glass transition was brought about by sorbed CO2 at temperatures below the glass-transition point of the pure polymer. © 1994 John Wiley & Sons, Inc. 相似文献
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Seong-Youl Bae Du-Hyon Cho Sang-Wook Ko Hee-Taik Kim Hidehiro Kumazawa 《Korean Journal of Chemical Engineering》1993,10(1):44-48
When the glass-transition temperature of the polymer is not so much higher than the experimental temperature, the pressure
dependence of the mean permeability coefficient of the poly-mer membrane to a gas is apt to deviate from the prediction by
the conventional dual-mode mobility model, and to obey a similar model with concentration-dependent diffusivities because
of the plasticization action of sorbed gas in the polymer membrane. In this work, sorption and permeation for oxygen and carbon
dioxide in a membrane of polystyrene whose glass-transition temperature is 95°C, were measured to discuss the mechanism of
gas diffusion in glassy polymer membranes with relatively low glass-transition temperature at 30, 40 and 50°C respectively. 相似文献
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A new version of the free-volume theory of diffusion is used to describe polymer–solvent diffusion both above and below the glass transition temperature. Expressions are derived for the temperature dependence of the mutual diffusion coefficient and for the effective activation energy in the limit of zero penetrant concentration. The theory also describes the effect of the glass transition on the diffusion process. Predictions of the theory are compared with available diffusivity data for amorphous polymer–solvent systems. 相似文献
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Conclusions 1. The authors have studied the principal laws of polycondensation of the hydrochloride of m-aminobenzoyl chloride. A polymer with a logarithmic viscosity of 0.7–0.9 has been obtained by the procedure developed.2. It has been established that poly-m-benzamide is an amorphous polymer with a glass-transition temperature of about 300°C. The weight loss of the polymer at 500°C is 2.5–3.5%.3. Fibre with a breaking length of 36 rkm (breaking length expressed in kilometers), high-heat resistance, and excellent thermal stability has been formed from solutions of the polymer.All-Union Scientific-Research Institute for Synthetic Fibres (VNIIV). Translated from Khimicheskie Volokna, No. 5, pp. 2–4, September–October, 1969. 相似文献
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Two methods based on the free-volume theory of transport are developed for the estimation of diffusion coefficients for trace amounts of solvents in amorphous polymers. The first method uses diffusivity data for a polymer–solvent system above the glass transition temperature to estimate the temperature dependence of the mutual diffusion coefficient below this temperature. In the second method, mutual diffusion coefficients are estimated for a particular polymer–solvent system both above and below the glass transition temperature using no diffusivity data for the system. The predictions of the proposed theory are compared with diffusivity data for the n-pentane–polystyrene and ethylbenzene–polystyrene systems. 相似文献
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General correlations were developed to estimte polymer thermal conductivities for four cases—amorphous polymers above the glass temperature; amorphous polymers below the glass temperature; semicrystalline polymers above the melting temperature, and semicrystalline polymers below the melting temperature. The correlations based on readily available parameters (mer weights, densities at 25°C, specific heats) yielded calculated thermal conductivities that deviated by only 1%–2% from experimental values. 相似文献
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The fracture properties and deformation behaviour of a linear amorphous polymer (1,2-polybutadiene) above the glass-transition temperature (?18°C) in liquid media have been studied. In accordance with data published earlier it is found that when fractured above Tg polymers behave like cured elastomers. Experiments conducted in low-molecular alcohols at 10°C show that the ultimate strength, durability (time-to-fracture) and development of irrecoverable deformation of viscous flow depend very strongly on the nature of the liquid medium, whereas the development of the elastic component of deformation is independent of the nature of the alcohols. It has been established that the dependence of durability on true fracture stress for the polymer studied is described by a power function. A simple correlation has been found between the surface tension at the polymer-liquid interface and the durability and ultimate strength of the polymers. 相似文献
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The biaxial stretch blow molding is an established process for manufacturing plastic containers, in which preforms are stretched both in circumferential and axial directions while being blown into a mold. In the development phase of these products, computer-aided analysis tools are extensively used to increase the material and process efficiency. The accuracy of these tools depends on the underlying material models and parameters. The aim of this article is to investigate the suitability of reptation theory for the prediction of the strain-dependent rheological behavior of polyethylene terephthalate (PET) in the stretch blow molding process. Reptation theory has already been successfully applied to a number of polymer melts in the past decades. However, the practical applicability of reptation theory for predicting the strain-dependent rheological behavior of highly viscous polymers slightly above the glass-transition temperature, as is the case with stretch blow molding, has not yet been fully investigated. In the first step, the constitutive material model equation of reptation theory is implemented and the necessary model parameters are determined using various measurement methods. However, the measurements could not be conducted with the same accuracy as in the case of polymer melts, because the measurement methods used showed instabilities in the glass-transition temperature range, which led to high measurement uncertainties. Consequently, the application of the material model does not match quantitatively to biaxial stretch tests. Qualitatively, on the other hand, the material model successfully reproduces the stress–strain behavior of PET films at low strains. In case of temperature dependence, the model results are neither qualitatively nor quantitatively satisfactory. The temperature dependency of the material model has been further investigated in the second step. It was shown that the derivative of the Doi–Edwards memory function with respect to the temperature has an inflection point if the stretching duration is equal to the disengagement time. For very small disengagement times compared to the stretching duration, the results of the model match the experimental observations. For high disengagement times induced by the large viscosities near the glass-transition temperature and for low stretching times induced by high strain rates; however, the Doi–Edwards memory function cannot predict the experimental observations correctly. The investigations show that reptation model qualitatively predicts the strain behavior of biaxial stretched PET films at low strains correctly. However, different measurement approaches for a more accurate and reproducible determination of the material properties and a modification of the model are required in order to adapt the model to highly viscous melts above the glass-transition temperature. The results have shown that the process conditions of the two-stage stretch blow molding, such as high strain rates and low processing temperatures, exceed the validity limits of reptation theory. POLYM. ENG. SCI., 60:765–772, 2020. © 2020 The Authors. Polymer Engineering & Science published by Wiley Periodicals, Inc. on behalf of Society of Plastics Engineers. 相似文献