聚合物熔体挤出胀大的三维数值模拟

采用粘弹性PTT模型对聚合物熔体的矩形口模挤出胀大进行了三维等温数值模拟,得出了不同条件下的口模外流动速度和挤出胀大率沿挤出方向的分布规律.模拟时利用罚函数有限元法和把动量方程转化成椭圆类方程的去耦算法以降低模拟对计算机内存的要求和增加计算收敛的稳定性,采用用路线法对挤出胀大自由表面进行更新迭代.模拟结果表明:We数越大,则挤出胀大率越大,而且对于矩形口模挤出而言,高度方向的挤出胀大率比宽度方向的挤出胀大率大.     

聚合物挤出过程中的数值模拟技术

介绍了计算流体力学中常用的数值计算方法,并从螺杆挤出过程、口模的设计以及挤出胀大等方面综述了数值模拟技术在聚合物挤出过程中的应用,最后针对聚合物挤出过程数值模拟发展的方向作了简要论述。     

高分子熔体和浓溶液流变性能的研究

基于多重缠结网络结构模型和高分子链上缠结点在流动中可进行动态解缠和再缠结的多重蠕动机理,用统计力学和动力学相结合的方法,分别计算出了缠结链组的末端距分布函数;处于缠结状态下高分子链构象统计分布函数;受力下聚合物熔体粘弹性形变自由能和解除外力下高分子挤出体可回复性粘弹性形变自由能,提出了高分子挤出体可回复形变的粘弹性分子理论。推导出的高分子熔体的回忆函数、简单剪切流下的本构方程和物料函数,并采用一种新的方法测定出物料的四种参数： η0、 GN0、 n′和 a。对于高分子挤出体,可回复性粘弹性形变由快速弹性形变和慢速粘弹性形变两者组成,当把两种形变量的复合结构参数－分子链的反式构象分数引入两种形变自由能表达式后,就从理论上得到了可回复形变量同挤出胀大比间的定量表达式,从而建立起一个具有分子链结构参数的新的挤出胀大比方程,可回复形变量同挤出条件（温度、挤出速率和量以及口模长径比不同的挤出机）和树脂结构特征（分子量及分布）的关系式以及在特殊情形下的简化表达式,并用几种高分子熔融体系的挤出胀大比和可回复性形变量的实验数据对理论进行验证,理论方程同实验数据较好的符合。     

几种典型含氟树脂流变行为研究概述

主要对乙烯-四氟乙烯共聚物(ETFE)、聚全氟乙丙烯(FEP)、聚偏氟乙烯(PVDF)、全氟磺酸树脂(PFSA)和全氟羧酸树脂(PFCR)这几种典型含氟树脂的加工流变行为和线性粘弹性进行了综述。FEP高速挤出时稳定流动区非常窄,并且进行模型拟合时发现其剪切流动行为符合Carreau模型。ETFE为热流变简单高分子,其剪切粘度、拉伸粘度、挤出胀大和动态模量等流变函数均可进行时温叠加。在低剪切速率下,PVDF熔体表现出牛顿流体行为;在高剪切速率下,PVDF熔体呈现出剪切稀化现象。PFSA和PFCR熔体的表观黏度随剪切速率、温度的升高而降低,流动曲线显示该熔体属于假塑性流体。     

通用聚丙烯的偶联反应

通过熔融接枝的方法在聚丙烯(PP)分子链上接枝甲基丙烯酸缩水甘油酯(GMA),制得PP接枝物PP-g-GMA,然后采用多个胺基的偶联剂聚六亚甲基胍(PHMG)对其进行偶联反应,制备偶联的聚丙烯(MPP)。通过与通用聚丙烯(EPS)以及进口专用料(PF-814)的对比,考察了经过偶联改性的MPP熔体的流变特性。结果表明:与原料EPS和PF-814相比,改性后MPP熔体的低频剪切区储能模量、挤出胀大、稳态柔量、零剪切黏度及熔体强度等都有明显增大。     

数值模拟法在聚合物流变学教学中应用

聚合物流变学多学科交叉特点致使其教学和科研均落后于高分子科学其它分支的发展。针对流变学教学过程中的诸多抽象概念和理论,将计算流体力学(CFD)数值模拟的方法引入到教学中,本文采用Weissenberg效应、二次流、挤出胀大和螺杆共混几个实例说明黏弹与牛顿流体本质差异,并引导学生如何将流变学的原理和方法应用到工程设计实践中,同时借用其工程设计应用功能来讲解经典流变学基本原理和理论。CFD数值模拟方法的引入使课程结构得到优化,教学方法也更为直观生动,提高学生学习的积极性。     

冷态模型系统模拟介质糖浆溶液粘弹性的分析

利用旋转流变仪和毛细管流变仪研究了不同葡萄糖浆溶液的粘弹性,结果表明:不同除水量的糖浆溶液的零剪切粘度(η0)呈现指数增长规律;不同PAM添加量对糖浆溶液的储能模量(G′)和损耗模量(G″)影响较大,且对G′的影响较为显著;随着PAM(聚丙烯酰胺)含量的增加,松弛时间和挤出胀大比(B)逐渐增大,糖浆溶液弹性越来越明显;其它条件相同,零剪切粘度越大,糖浆溶液的弹性效应越明显;糖浆溶液在20~80℃温度范围内粘度可逆,温度对糖浆溶液粘度的影响非常显著,且粘度变化相差可达1000倍。     

线型聚乙烯及其共聚物的挤出畸变与熔体粘弹性的关系

采用恒速型双筒毛细管流变仪研究了一类线型聚乙烯熔体的挤出畸变与熔体非线性粘弹性的关系。实验研究了发生畸变时挤出压力的振荡规律,发现线型大分子或带小侧基的大分子熔体,容易发生壁滑和挤出压力振荡;而有较大侧基、或分子量分布宽、或带大量短支链的熔体,挤出畸变现象较轻。挤出畸变与熔体的弹性及熔体．壁面吸附状态紧密相关。容易发生壁滑和挤出压力振荡的熔体,弹性较大(入口压力降大);在壁面的吸附作用强(壁面临界剪切应力大)。稳态剪切粘度大小与挤出畸变和压力振荡的关系不大;而拉伸应力和拉伸粘度大的熔体较易发生壁滑和挤出压力振荡。     

新型旋转挤出流变仪

聚合物加工是决定塑料制品最终结构性能的中心环节,其重要的理论基础是聚合物流变学,研究聚合物流变行为的关键仪器是流变仪.但现有流变仪大多基于简化的流动模型,与实际复杂加工条件不符,难有效揭示聚合物在复杂应力场/温度场作用下的流变行为.我们基于前期发明的聚合物管旋转挤出加工技术和装备,研制了新型旋转挤出流变仪,可实现挤出/旋转的不同组合和管内外壁双冷,实施和调控旋转挤出中多种运动模式和应力场及温度场,实时检测挤出/旋转速度、应力、温度场,显示记录有关数据,既可用于研究实际加工复杂条件下聚合物加工流变行为,也可用于制备高性能多功能聚合物微导管.本文综述了新型旋转挤出流变仪的结构特点和原理及其在流变测试与聚合物微导管制备方面的应用.     

混合方式对增容尼龙-6/聚苯醚体系的影响

研究了三种混合方式对于Nylon 6 PPO TPEg共混体系的影响 .混合是在双螺杆挤出机上进行的 .即(A)尼龙 6、聚苯醚和TPEg的混合物直接进行熔融挤出 ;(B)尼龙 6与TPEg的混合物预挤出 ,然后与聚苯醚熔融挤出 ;(C)聚苯醚和TPEg的混合物预挤出 ,然后与尼龙 6熔融挤出 .实验结果表明 ,混合方式不仅会影响共混物的形貌结构 ,而且会影响复合材料的最终性能 ,如力学性能、热性能和尺寸稳定性 .采用混合方式C所得的尼龙 6 聚苯醚复合材料的抗冲击强度高于用混合方式A和B所制备的复合材料 .这是因为聚苯醚和TPEg预共混时 ,聚苯醚上的OH基团和TPEg上的一部分马来酸酐发生化学反应 .然后预混物和尼龙 6熔融挤出时 ,剩下的马来酸酐再与尼龙分子上的NH2 基团反应 .这样就会形成一个好的界面层 ,它使复合材料的抗冲击强度大幅度提高 ,材料达到了超高韧性     

Progress of diffraction enhanced imaging at the Beijing Synchrotron Radiation Facility

A simple framework that allows a new general diffraction enhanced imaging (DEI) equation to be derived is presented. This latter equation may explain all open problems associated with the equation introduced by Chapman and those not explained by the first DEI equation, such as the noise background due to the small-angle scattering reflected by the analyzer. Combing the DEI equation with computed tomography (CT) theory, we propose a new DEI–CT formula that explains qualitatively the contour contrast caused by extinction of the refraction. Two formulae with a new method to extract the refraction angle are also introduced. Within this new theoretical framework the three components of the gradient of the refractive index can be reconstructed.     

Equation for calculating surface coverage from end-capping of chromatographic bonded phases.

An equation was derived to calculate the surface density of trimethylsilyl groups (alphaTMS) on bonded chromatographic stationary phases that have undergone primary as well as secondary ('end-capping') chemical modification. The new equation is an extension of that published by Berendsen-de Galan for calculating primary surface coverage and, likewise, alphaTMS is calculated in terms of the carbon content (% by weight) of the bonded material before and after end-capping, specific surface area of the starting silica and structural information (molecular weight and number of carbon atoms) of the anchored groups. The new equation is valuable when a thorough characterization of bonded stationary phases is desirable and, if used along with the Berendsen-de Galan equation, it affords total ligand coverage information. Application of the new equation to correct for measurable carbon content of the starting support leads to a more accurate expression for surface coverage from primary as well as secondary bonding. The scope and limitations of the new equation are discussed.     

An explicit linear six-step method with vanished phase-lag and its first derivative

An explicit linear sixth algebraic order six-step method with vanished phase-lag and its first derivative is constructed in this paper. We will study the method theoretically and computationally. Theoretical investigation contains the building of the method, the calculation of the local truncation error, the comparative error analysis of the new method with the method with constant coefficients and the stability analysis of the new method using scalar test equation with different frequency than the frequency of the scalar test equation used for the development of the method. Computational investigation contains the application of the new obtained linear six-step method to the resonance problem of the radial time independent Schrödinger equation. The theoretical and computational study lead us to the summary that the new proposed linear scheme is computationally and theoretically more efficient than other well known methods for the numerical solution of the Schrödinger equation and related periodic initial or boundary value problems.     

聚合物共混物脆韧转变性能研究 Ⅱ准韧性聚合物共混物脆韧转变的几何模型

给出了分散相粒间基体层厚度Ｔ与分散相粒径（ｄ）、粒径分散度（σ）和分散相体积分数（）的定量关系式．发现σ对Ｔ的影响与有关，不仅Ｔ随σ的增大而增大，而且越大，这种影响越显著．用计算机图像分析仪直接测定了聚氯乙烯／丁腈橡胶、聚丙烯（ＰＰ）／三元乙丙橡胶、ＰＰ／乙烯 醋酸乙烯酯共聚物共混物的Ｔ，发现这三种共混物的Ｔ近似于对数正态分布．理论预示与实验结果很好符合．     

Calculation of interparticle spacing in colloidal systems

Interparticle spacing (IPS) is a very important parameter for estimation of the viscosity of a suspension. A new equation for calculating IPS was derived on the assumption that each particle is surrounded by a virtual cell, which is the free volume that each particle can occupy. This idea was originated by Kuwabara and widely used for calculating electrophoretic mobility in concentrated suspensions. Our new IPS equation was evaluated and compared with a pre-existing IPS equation proposed by Dinger and Funk using experimental data from three commercial sources of titania. Our equation was found to give reasonable values, including cases where the equation of Dinger and Funk gave anomalous values.     

Improved g-level calculations for coil planet centrifuges

Calculation of the g-level is often used to compare CCC centrifuges, either against each other or to allow for comparison with other centrifugal techniques. This study shows the limitations of calculating the g-level in the traditional way. Traditional g-level calculations produce a constant value which does not accurately reflect the dynamics of the coil planet centrifuge. This work has led to a new equation which can be used to determine the improved non-dimensional values. The new equations describe the fluctuating radial and tangential g-level associated with CCC centrifuges and the mean radial g-level value. The latter has been found to be significantly different than that determined by the traditional equation. This new equation will give a better understanding of forces experienced by sample components and allows for more accurate comparison between centrifuges. Although the new equation is far better than the traditional equation for comparing different types of centrifuges, other factors such as the mixing regime may need to be considered to improve the comparison further.     

Prediction of the Conductance of Strong Electrolytes and the Calculation of the Ionization Constant of Weak Electrolytes in a Dilute Solution by a New Equation

In order to predict the conductance for dilute 1-1 valent electrolyte solutions,a new conductance equation was proposed based on the Onsager and Onsagar-Fuoss-Chen conductance equation.It has only one parameter A,which can be obtained directly from the data of ionic limiting molar conductivity Λ∞m,and its expression is very simple.The new equation has been verified by the experimental molar conductivities of some single strong electrolyte and mixed electrolyte solutions at 298.15 K reported in literatures.The results are in good agreement with the experimental data.Meanwhile the ionization constants of some weak electrolyte solutions were calculated by a modified equation of this new equation,and it was also found that the calculation results are in good agreement with the data in the literature.     

一个适用于Huggins常数K′较大的新的一点法特性粘数方程

本文提出了一个适用于Huggins常数较大(0.472≤K＇≤0.825)的聚合物-溶剂体系的新的一点法特性粘数方程[η]=ηsp/Cη~(1/2).并与其它四个一点法方程分别对19种聚合物的27种聚合物-溶剂体系的192个文献数据进行计算比较,发现本方程所得结果是十分满意的.因此,本方程的建立,扩大了用一点法求算聚合物特性粘数方法中K＇值的范围.     

A quartic hard chain equation of state for normal fluids

A new empirical equation of state is proposed which is applicable to mixtures of chain-like molecules. The equation is based on a simple model which uses an approximate chain theory and an approximation of the Carnahan—Starling equation. The results for pure component properties of normal fluids are comparable to the common cubic equations of state. For mixtures of chain-like molecules, the new equation is as good or better than the Peng—Robinson equation.     

平衡时溶液的表面吸附

溶液的表面吸附仍是表面热力学当中的一个具有挑战性的问题.在本文中我们定义了一个新的热力学态函数,表面吸附的平衡条件是这个态函数的微分为零.基于这个条件,我们推导了描述平衡时表面吸附的新方程.在推导过程中没有采用假想分界面.新的表面吸附方程和Gibbs表面吸附方程完全不一样.还通过分子动力学方法模拟了氯化钠溶液,模拟结果和我们的理论预测符合较好.