聚合物共混体系界面层厚度的表征方法

聚合物共混体系的界面层厚度取决于聚合物分子相互扩散的程度,与两相体系的相容性、微相分离程度、分子量及其分布有关。界面层厚度的结构表征一直受到人们的重视,精确的测量聚合物界面层厚度,对研究多相聚合物的性能有着重要意义。文中介绍了界面层厚度测量的基本原理和表征方法,这些测定方法是:小角X散射法、小角激光散射法和椭圆偏振法三种,列出了每种方法的理论计算公式,对每种方法的优缺点及适用范围进行了简单说明。     

燃烧条件下聚合物熔体流滴行为研究现状及思考

燃烧过程中聚合物的熔体流动和滴落对材料阻燃和火灾动力学有重要影响。文中综述了聚合物熔体流动相的形成机理,中大型实验和小型实验中的熔体流滴行为及其主要影响因素,熔体相对聚合物点燃、燃烧、火蔓延和火灾动力学的影响。并分析认为评价熔体流滴的燃烧测试标准、裂解温度以上聚合物熔体流动性的表征和预测、以及熔体流滴过程动力学等方面尚有待研究。     

茂金属催化的乙烯-辛烯共聚物/聚苯乙烯体系界面张力的研究

采用椭球回缩模型研究了茂金属催化的乙烯-辛烯共聚物(POE)和聚苯乙烯(PS)体系界面张力。结果表明,该体系的界面张力随温度线性降低,其温度系数为-0.024 mN/(m.℃)。此外,还采用了粘弹体系的乳液模型对聚合物的粘弹性对界面张力的测量的影响进行了分析。基体和分散相液滴的松弛时间比值q对测量有重要的影响。     

FM全新卡车顶篷把手气辅成型技术

研究了气辅成型过程中气体穿透聚合物熔体的扩散特征和气.熔界面形态.以FM全新卡车顶篷把手为典型件进行气辅成型实验研究,研究了气体保压压力、熔体温度、气体保压时间、气体注射延迟时间四个重要工艺参数对气熔界面的影响规律.结果表明,在气体注射点近区,气体对聚合物熔体冲击程度较大.呈现出复杂流动形态及扩散特征;低的保压压力和熔体温度,较短的保压时间和较长的气体注射延迟时间可获得较好的气熔界面.     

利用耗散颗粒动力学方法模拟优选合成聚表剂的可聚合季铵盐单体

为研究聚合物表面活性剂(聚表剂)分子结构变化对聚表剂和油-水界面性质的影响,优选出最佳性能的聚表剂。以正十六烷基为油相,水为水相,采用耗散颗粒动力学方法(DPD)模拟含有不同可聚合季铵盐表面活性基团的聚表剂在油-水界面的性质,研究了聚表剂摩尔分数及季铵盐基团种类等因素对油-水界面性质的影响。模拟结果表明,模拟体系中聚表剂摩尔分数范围以0.02~0.06为宜;通过模拟优选出最佳季铵盐单体为对甲基苯乙烯基十二烷基二甲基溴化铵(R4),聚表剂AMR4在油水体系中最佳摩尔分数为0.06,此时界面张力值最低、界面效率最佳且聚表剂分子均方根末端距最大。聚表剂分子几乎全都分布在油-水界面层,其界面活性使得油-水界面厚度增大,油-水界面张力降低。     

气辅共挤出界面位置对挤出胀大的影响

基于聚合物流变学理论,运用有限元方法,建立了半圆形共挤口模成型的理论模型,并对理论模型进行了数值模拟,研究了口模入口端熔体层间界面位置及熔体入口流率对共挤出胀大和熔体层间界面位置的影响。研究表明,气辅共挤过程中,当两熔体流率相等时,使得两熔体入口面积近似相等的r值(共挤口模入口处界面位置)能将熔体的离模膨胀率降为零值,同时保证熔体层间界面位置稳定;当两熔体流率不等时,熔体离模膨胀率随着自身流率的增大而增大,随着另一熔体流率的增大而减小,界面位置则向流率较低的一侧偏移。     

SBS改性沥青相态结构的参数化表征方法

聚合物改性沥青是典型的两相共混物,相态结构分析是研究其改性机理和改性效果最直接、最有效的方法。为参数化表征SBS改性沥青的相态结构,通过荧光显微系统对沥青观测样本进行图像采集,运用专业软件对荧光显微图像进行预处理并提取聚合物相显微形态参数,对4种典型的显微形态参数长短轴之比最大值、面积百分率、分形维数、最大面积代表值进行量化分析。结果表明:最大面积代表值较其他参数更适合表征SBS改性沥青的相态结构。当聚合物最大面积代表值小于2500μm2时,改性沥青一般形成沥青相连续而聚合物相分散结构;当最大面积代表值大于15000μm2时,一般形成聚合物相连续而沥青相分散结构,即网络结构。荧光显微分析为SBS改性沥青相态结构的参数化表征提供了技术手段。     

反应性共混中原位接枝及嵌段共聚物的界面拔出

在最新实验结果的基础上论述了一种在聚合物反应性共混过程中的相态控制新方法－－共聚物分子的界面拔出。通过选择组分高聚物的种类和调节反应性高分子共混物两相相对组成，可控制在两相界面上原位生成共聚物分子的构造，从而可系统分析分子构造与界面提出之间的关系；通过改变熔融共混剪切速率或共混物的熔体粘度，评述了外界流场的作用强度对共聚物分子的界面提出的影响。     

共混聚合物界面张力的测定方法

综述了共混聚合物界面张力的测定方法。这些方法包括动态法(断裂丝线法、嵌入纤维回缩法、变形液滴回缩法)和平衡法(悬滴法)。对这些方法的优缺点及适用体系给予了简要评述。     

超支化聚合物合成的研究进展

超支化聚合物是一类具有高度支化结构的体型大分子,其独特的结构赋予其具有不同于传统线性聚合物的性能,显示出广阔的应用前景.超支化聚合物的合成是超支化聚合物研究的重要内容,合成方法对超支化聚合物的结构和性能有重要影响.对该领域的最新研究进展进行了归纳介绍,其中主要涉及传统的缩聚聚合、活性聚合、离子聚合、开环聚合以及一些新型的聚合反应,同时论述了各种合成方法的优点和局限性.     

Relationships Among Liquid–Vapor Interfacial Region Properties: Predictions of a Thermodynamic Model

In theoretical models and molecular dynamics simulations of the interfacial region between a liquid and vapor phase, three properties are usually of primary interest: the interfacial tension, the interfacial region thickness, and the density gradient in the interfacial region. While these properties can be determined from molecular dynamics simulations by collecting appropriate statistics, such results do not explicitly provide an indication of the interrelationship among these characteristics. This paper presents theoretical predictions of the relationships among interfacial tension, the interfacial region thickness, and the density gradient in the interfacial region that are derived from a theoretical model of the thermodynamic properties of the interfacial region. Explicit relations among interfacial region properties are obtained from a modified version of the classical mean field model that incorporates Redlich-Kwong fluid properties. Comparisons are presented that indicate that the theoretical relations among the interfacial region properties are consistent with trends indicated by experimental data. Use of the theoretical model relations to determine the interfacial tension using the mean density profile obtained from a molecular dynamics simulation is also explored. This method is shown to predict values comparable to traditional methods for determining interfacial tension in molecular dynamics simulations while requiring significantly less computational effort.     

Failure processes in particulate filled polypropylene

In this paper the common degradation effect of silicon oxide filler on fracture strain and fracture toughness of isotactic polypropylene is investigated by analysing the failure processes in the composite material by microscopic methods. Experiments demonstrate that, although fracture of the polymer regions absorbs considerable energy by plastic deformation, void formation and cracking of the interface between the polymer and the filler usually requires very little energy. These weak interfaces do not resist cracking and are the cause of brittleness in particulate filled systems. The crucial parameters influencing the fracture data of the composite were found to be the volume fraction of the filler and the interfacial adhesion between polymer matrix and particles. As the interfacial fracture energy is usually much smaller than the polymer fracture energy, the composite toughness drops when filler is added. Using a model which describes the individual steps of crack formation and final fracture, an attempt is made to explain the decrease of crack resistance of the polymer matrix with increasing filler fraction and to calculate the fracture energy of the composite by introducing partial values of crack resistance of the matrix and the interface, respectively. In addition, it is discussed how a coarse spherulitic morphology of the matrix, as produced by isothermal crystallization from the melt, can modify this behaviour.     

Measurement of transient behavior of the thermal diffusivity of flowing polymer melt

Molecular orientation of polymer molecules created by shear force due to the flow of the polymer melt in a duct rapidly relaxes after the change in the shear rate. This relaxation causes the changes in anisotropic behavior of mechanical. thermal, and optical properties which have strong effect in precision forming of casted polymer products. Among these properties, thermal diffusivity is one of the most difficult properties to measure by the conventional techniques. The present paper describes and discusses the subsecond measurement of relaxation characteristics in thermal dilfusivity anisotropy of flowing polymer melt in conjunction with measurements of some typical flow characteristics. The method used was the forced Rayleigh scattering method, an optical method which was developed and modified by the authors' group for applying to oriented polymer materials. The measuring lime of I ms can trace the relaxation occurred in the order of several seconds. Measured results of thermal diffusivity anisotropy were compared with transient characteristics of the now and quantitatively showed a good agreement with estimated behavior of oriented polymer molecules.Paper presented at the Fourth International Workshop on Subsecond Thermophysics, June 27–39, 1995, Köln, Germany.     

纳米尼龙丝的制备及性能

用静电纺丝这种制备直径在纳米级到微米级间超细纤维的新技术，成功地制备出纳米级尼龙6纤维丝及其平行丝。研究了纺丝过程中的工艺参数对纤维形态的影响，以及尼龙6电纺丝的力学性能。     

Discrete element modelling of unidirectional fibre-reinforced polymers under transverse tension

The mechanical behaviour of unidirectional fibre-reinforced polymer composites subjected to transverse tension was studied using a two dimensional discrete element method. The Representative Volume Element (RVE) of the composite was idealised as a polymer matrix reinforced with randomly distributed parallel fibres. The matrix and fibres were constructed using disc particles bonded together using parallel bonds, while the fibre/matrix interfaces were represented by a displacement-softening model. The prevailing damage mechanisms observed from the model were interfacial debonding and matrix plastic deformation. Numerical simulations have shown that the magnitude of stress is significantly higher at the interfaces, especially in the areas with high fibre densities. Interface fracture energy, stiffness and strength all played important roles in the overall mechanical performance of the composite. It was also observed that tension cracks normally began with interfacial debonding. The merge of the interfacial and matrix micro-cracks resulted in the final catastrophic fracture.     

反应挤出法制备PPO/PA6/SEBS共混物的研究EI

研究了 PPO- g- MA对 PPO/PA6 /SEBS共混体系的原位增容作用和 SEBS对 PPO/PA6的增韧作用。 PPO/PA6 /SEBS共混物的 TEM结果表明 ,SEBS分散在 PPO中 ,而 PPO又分散在 PA6基体中。 TEM和 SEM的结果均表明 ,PPO- g- MA细化了分散相的相畴 ,增加了界面强度 ;冲击实验的结果表明 ,PPO- g- MA和 SEBS的用量分别为 2 0 %～ 2 5 %和 10 %～ 15 %时 。     

Processing of B4C Particulate-reinforced Magnesium-matrix Composites by Metal-assisted Melt Infiltration Technique

In fabricating magnesium-matrix composites, an easy and cost-effective route is to infiltrate the ceramic preform with molten Mg without any external pressure. However, a rather well wettability of molten Mg with ceramic reinforcement is needed for this process. In order to improve the wettability of the metal melt with ceramic preform during fabricating composites by metal melt infiltration, a simple and viable method has been proposed in this paper where a small amount of metal powder with higher melting point is added to the ceramic preform such that the surface tension of the Mg melt and the liquid-solid interfacial tension could be reduced. By using this method, boron carbide particulate-reinforced magnesium-matrix composites （B4C/Mg） have been successfully fabricated where Ti powder immiscible with magnesium melt was introduced into B4C preform as infiltration inducer. The infiltration ability of molten Mg to the ceramic preform was further studied in association with the processing conditions and the mechanism involved in this process was also analyzed.     

Preparation of composite dispersed phase morphologies in incompatible and compatible blends during melt processing

Most processing/morphology studies of multi-phase polymer blends have been concerned with controlling the size and shape of the dispersed phase. The dispersed phase is generally a pure homo- or copolymer (apart from low levels of interfacial modifier). This paper describes the preparation during melt processing of a complex polymer blend morphology known as a composite dispersed phase system. Microscopically this structure can be seen to be composed of three parts: two distinct phases with sub-inclusions within one of the phases. This system is a type of blend within a blend. Various microscopic techniques are used to show that a composite multi-phase morphology can be prepared in an incompatible polypropylene/ polycarbonate (PP/PC) blend as well as in a compatible polyethylene copolymer/polyamide blend. This structure has been generated at two compositions for polypropylene/ polycarbonate through melt blending. At 50% volume fraction (near the region of dual-phase continuity), simultaneous addition of components results in co-continuous polypropylene and polycarbonate phases with the latter containing small PP spherical sub-inclusions. At 25% PC (volume fraction) the generation of a composite dispersed phase in a polypropylene matrix is obtained by imposing phase inversion followed by controlling the mixing time. The morphology in this case consists of a polypropylene matrix, a polycarbonate dispersed phase and spherical polypropylene sub-inclusions within the dispersed polycarbonate. Partial stabilization of the composite morphology in incompatible blends with mixing time can be obtained through control of the viscosity of the dispersed phase. Polyethylene copolymer/polyamide blends have also been prepared by the phase inversion process and show that strong interfacial interactions between the polyamide sub-inclusions and polyethylene copolymer dispersed phase material results in complete stabilization of the composite dispersed phase morphology with very high retention of sub-inclusions persisting even after long mixing times.     

高聚物共混及掺混材料界面形态与力学性能的关系

利用扫描电子显微镜(SEM)对共混及掺混材料的界面形态进行了观察,并讨论了界面形态与力学性能的关系。结果表明,力学性能的差异,明显地反映在材料的界面形态上。通过观察还表明,两相之间的粘结强度越高,表现出的力学性能越优异,这主要是改性后界面相的形成所做出的贡献。同时,还讨论了增韧增强机理。     

Effect of modification melt treatment on casting/chill interfacial heat transfer and electrical conductivity of Al–13% Si alloy

For successful modelling of the solidification process, a reliable heat transfer boundary condition data is required. These boundary conditions are significantly influenced by the casting and mould parameters. In the present work, the effect of sodium modification melt treatment on casting/chill interfacial heat transfer during upward solidification of an Al–13% Si alloy against metallic chills is investigated using thermal analysis and inverse modelling techniques. In the presence of chills, modification melt treatment resulted in an increase in the cooling rate of the solidifying casting near the casting/chill interfacial region. The corresponding interfacial heat flux transients and electrical conductivities are also found to be higher. This is attributed to (i) improvement in the casting/chill interfacial thermal contact condition brought about by the decrease in the surface tension of the liquid metal on addition of sodium and (ii) increase in the electronic heat conduction in the initial solidified shell due to change in the morphology of silicon from a acicular type to a fine fibrous structure and increase in the ratio of the modification rating to the secondary dendrite arm spacing.