Dynamical considerations of network properties

Elasticity is discussed as an aspect of viscoelasticity, which is described by the tube model. The effects of both crosslinks and entanglements contribute to this model and a discussion of how these effects can be quantified is given. At high enough concentration, entanglements ensure the existence of elastic effects even without crosslinks, and a theory is presented on how this dynamical phase change comes about.     

Network topology and the theory of rubber elasticity

The earliest investigations on rubber elasticity, commencing in the 19th century, were necessarily limited to phenomenological interpretations. The realisation that polymers consist of very long molecular chains. commencing c. 1930, gave impetus to the molecular theory of rubber elasticity (1932-). according to which the high deformability of an elastomer, and the elastic force generated by deformation, stem from the configurations accessible to long molecular chains. Theories of rubber elasticity put forward from 1934-1946 relied on the assumption that the junctions of the rubber network undergo displacements that are affine in macroscopic strain. The theory of James and Guth (1947) dispensed with this premise, and demonstrated instead that the mean positions of the junctions of a ‘phantom’ network consisting of Gaussian chains devoid of material properties are affine in the strain. The vital significance of the distinction between the actual distribution of chain vectors in a network and their distribution if the junctions would be fixed at their mean positions went unnoticed for nearly 30 years. Experimental investigations, commencing with the incisive work of Gee in 1946. revealed large departures from the relationship of stress to strain predicted by the theories cited. This discrepancy prompted extensive studies, theoretical and experimental, during succeeding years. Inquiry into the fundamentals of polymer networks, formed for example by interlinking very long polymer molecules, exposed the need to take account of network imperfections, typically consisting of chains attached at only one end to a network junction. Various means were advocated to make corrections for these imperfections. The cycle rank ζ of the network has been shown (1976) to be the fundamental measure of its connectivity, regardless of the junction functionality and pattern of imperfections. Often overlooked is the copious interpenetration of the chains comprising typical elastomeric networks. Theories that attempt to represent such networks on a lattice are incompatible with this universal feature. Moreover, the dense interpenetration of chains may limit the ability of junctions in real networks to accommodate the fluctuations envisaged in the theory of phantom networks. It was suggested in 1975 that departures from the form predicted for the elastic equation of state are due to constraints on the fluctuations of junctions whose effect diminishes with deformation and with dilation. Formulation of a self-consistent theory based on this suggestion required recognition of the non-affine connection between the chain vector distribution function and the macroscopic strain in a real network, which may partake of characteristics of a phantom network in some degree. Implementation of the idea was achieved through postulation of domains of constraint affecting the equilibrium distribution of fluctuations of network junctions from their mean positions. This led in due course to a theory that accounts for the relationship of stress to strain virtually throughout the ranges of strain accessible to measurement. The theory establishes connections between structure and elastic properties. This is achieved with utmost frugality in arbitrary parameters.     

NBR/PP热塑性弹性体研究进展

阐述了NBR／PP共混热塑性弹性体动态硫化胶的国内外研究进展、微观相态结构、性能、应用及展望。     

橡胶卷材挤出连续硫化生产线的结构特色与工作原理

介绍了橡胶防水防腐卷材挤出连续硫化生产线的结构、特点和工作原理;指出在目前国内同类设备中,该生产设备具有先进性,并可替代引进设备。     

KZON-50/120空分设备的安装调试及设计改造

在KZON-50/120空分设备的安装调试和试运行过程中,对其机械和电器部分进行了多处改造,克服了原设计中存在的不足之处。改造后,机械和电器性能更加趋于合理,操作简单,便于维护,降低了制气费用,提高了制气纯度和经济效益,保证了空分设备更加安全可靠运行。     

某铅锌矿选矿尾矿综合利用试验研究

针对选矿尾矿的特性，采用高选择性的3ACH捕收剂、F—1抑制剂，回收了绢云母含量分别达96％和64％以上的一、二级绢云母产品。经应用试验表明：绢云母一级品在橡胶中的补强性能基本达到了沉淀法白炭黑水平，二级品也全面超过硅铝炭黑的补强性能。     

顺丁橡胶后处理新型交替运输机

在顺丁橡胶后处理生产线上，用处行开发的新型交替运输取代原有运输机。试用结果表明，采用新型交替运输机后，胶块的导向到位率由７０％提高到９８％；减轻了劳动强度，提出了生产开工率，运行周期可达１ａ以上。     

Some factors affecting the electrical properties of carbon-black-loaded butyl rubber during vulcanization

Butyl rubber mixtures loaded with 70 phr general purpose furnace black (GPF) and tetramethyl thiuram disulphide (TMTD)/S as vulcanizing system were prepared. The kinetics of their electrical conductivity development during the vulcanization process were followed by using an especially devised system. It was found that the increase in the electrical conductivity during vulcanization obeys an exponential growth function with time constant τ, which markedly decreases with increasing vulcanization temperature as well as with the efficiency of the vulcanizing system. After completion of the vulcanization process, about 80 min, the samples obtained possess reasonable stability and reproducibility of electrical conductivity.     

直流电动机参数测定

根据直流电机的可逆原理并利用常规的实验仪表，可以简便、准确地测出直流电动机的主要参数－电磁转矩、输出转矩和效率．