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The last four years since the publication of the first of this series have seen further striking developments in both the science and technology of oriented polymers. In particular, polymers possessing very high degrees of molecular orientation are now quite commonplace, and this is reflected by the inclusion of five chapters dealing with ultra-high modulus polyethylene fibres, oriented liquid crystalline polymers (both lyotropics and thermo tropics) and polydiacetylene single crystal fibres. At the same time there is continuing interest in the structure and properties of less highly oriented polymers and in the mechanisms of deformation in polymers. It is therefore good to have these themes represented also. I should like to thank the contributors for adhering to a rather tight time schedule, and the publishers for their cooperation, so that this book can provide up-to-date reviews of the state of the art in a rapidly moving area of polymer science. I. M. WARD v CONTENTS Preface.... . . . .. . . . . .. ... . . . . . . . . . .. . . .. . . . . . . ... ... v List of Contributors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IX 1. Polymer Single Crystal Fibres ........................ .
Modern society makes increasing demands for novelty in materials and their properties which are ever more exacting. Crystalline polymers are in the forefront of this demand and improvements are constantly occurring across the entire range from existing materials of high tonnage to novel materials with application in information technology. The developments recorded in this volume reflect this situation. Chapter 1 is a comprehensive review of the polymer PHB, poly(hydroxybutyrate), which is new to industrial manufacturing but is a naturally occurring substance. It has potentially valuable properties but has excited interest especially because it is biodegradable. It may, therefore, provide one means of reducing environmental pollution. Improvements in existing materials, beyond those which are ob tainable by optimization of known variables, are most likely to come from understanding of structure-property relationships. Polymer is able to make effective science has now reached the stage where it synthesis of information from complementary techniques, leading to rapidly deepening understanding. Chapters 2, 3 and 4 are all con cerned with technical developments which are contributing substan tially to this synthesis. The possibilities of electron microscopy, specifically the characterization of lamellar microstructure, have been transformed by permanganic etching. Now real organization (which can be very different from what had previously been inferred) can be used as a basis for explaining polymeric properties. In Chapter 3, Mitchell and Windle give a critical account of the assessment of orientation in liquid crystalline polymers, a rapidly developing new field in which they have played a leading part.
This volume includes reviews on tackling polymer characterisation problems and on developing specific characterisation techniques. The first two chapters and the last chapter describe progress in providing character isation information for polymers containing long-chain branching, for polymer blends, and for polymers having preferred orientation. The remaining chapters review progress in individual techniques, showing with examples the characterisation results which may be obtained. It is recognised that the degree of chain branching which can evolve in some polymerisation processes can have a marked effect on the flow properties of a polymer, and therefore on polymer processing behaviour. In the first chapter the characterisation of long-chain branching from measurements of the molecular size and molar mass of a polymer in dilute solution is outlined. It is indicated that a complete characterisation of branching requires the combined use of several techniques, emphasising in particular recent developments involving gel permeation chromatography. Thermal analysis and infrared spectroscopy are widely used techniques in polymer characterisation. Both techniques can provide, very quickly, significant results with readily available instrumentation. This is illustrated by the review of the characterisation of polymer blends by thermal analysis in Chapter 2. An assessment of blend morphology, which influences the behaviour of a material consisting of two or more polymers, is presented in terms of transition temperatures. Conventional infrared spectroscopy involves dispersive spectrometers which do not always provide accurate information on composition and structure for complex polymeric materials.