Tài liệu The application of textiles in rubber

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The Application of Textiles in Rubber David B. Wootton Rapra Technology Limited Shawbury, Shrewsbury, Shropshire SY4 4NR, United Kingdom Telephone: +44 (0)1939 250383 Fax: +44 (0)1939 251118 http://www.rapra.net Textiles Title Page etc. 1 31/7/01, 11:34 am First Published in 2001 by Rapra Technology Limited Shawbury, Shrewsbury, Shropshire, SY4 4NR, UK ©2001, Rapra Technology Limited The right of David Wootton to be recognised as the author of this work has been asserted by him in accordance with sections 77 and 78 of the Copyright, Designs and Patents Act 1998. All rights reserved. Except as permitted under current legislation no part of this publication may be photocopied, reproduced or distributed in any form or by any means or stored in a database or retrieval system, without the prior permission from the copyright holder. A catalogue record for this book is available from the British Library. ISBN: 1-85957-277-4 Typeset by Rapra Technology Limited Printed and bound by Polestar Scientifica, Exeter, UK Textiles Title Page etc. 2 31/7/01, 11:34 am Preface Rubber and textiles have been used together, each working with the other to give improved performance in a very wide range of applications, since the earliest days of the rubber industry in the more developed areas of the world. For many years, rubber companies of reasonable size, using textile reinforcement, would employ their own textile technologist working alongside the rubber technologists. Over the last third of the twentieth century, faced with global competition and the need to control and reduce total costs, this luxury has largely disappeared apart from the largest companies (particularly the tyre companies). Most organisations now rely on their textile suppliers to provide technical knowledge and expertise. As a result, the textile component for many applications is now considered in much the same way as the other raw materials, that is as an existing product, which only requires introducing into the manufacturing process, without any special knowledge or understanding, and is supplied against an agreed specification, which was probably drawn up by the textile manufacturer anyway. The aim of this current work is to provide a general background to and a basic awareness of the technology of textiles, to give the rubber technologists an improved understanding of the uses, processes and potential problems associated with the use of textiles in rubber products. The most important and by far the largest use of textiles in rubber is in the tyre industry. This area is not covered in this book, as the field covers such a wide range that it would require a volume on its own. In addition, most tyre companies have their own textile specialists and have developed their own technologies, shrouded in the mysteries of ‘trade secrets’. The first part of this volume covers the basic technology of the textile fibres and the processes used in preparing these ‘ready made’ raw materials for rubber reinforcement. Particular attention is given to various aspects of adhesion, adhesive treatments, the effects of rubber compounding and processing and the assessment of adhesion. In the second half of the book, the major applications of textiles in rubber are described; the aim here is to illustrate the way that the textile component can be designed and engineered to obtain the optimum reinforcement and performance for each particular application. These descriptions are not intended to be definitive technological theses on 1 Preface 1 31/7/01, 11:34 am The Application of Textiles in Rubber the different applications. However, they indicate the balance of properties required and how these can be obtained in the textile component by selection of the fibres used, the physical form of the reinforcement and the processes and treatments required. Over the years since the earliest days of Hancock, Goodyear and Macintosh, there have been many significant breakthroughs and developments, in both textile and rubber technologies. Originally, there were only cotton and natural rubber, now there are wide ranges of both synthetic rubbers and of man-made fibres. There have been great advances in the technologies of vulcanisation and of adhesive treatments; the service requirements have become more stringent and operating conditions more severe, but these issues have largely been overcome by improving expertise and knowledge. However, over the last two decades, there has been relatively little advance in the general technologies of textiles or rubbers; most developments have been targeted either at cost containment or at very high performance (and consequently very high cost) applications, particularly aerospace, with only minor spin-offs for everyday terrestrial applications. Where possible, the general content of the chapters has been kept as simple and practical as possible but where there is a more theoretical discussion of certain aspects, these have been separated into appendices, at the end of the relevant chapters. The general discussion can thus be read without the intrusion of the more theoretical aspects, but these are still available, if desired. A glossary of terms has been included to assist the reader. I wish to thank all those at Rapra who have encouraged and assisted me in the preparation and publication of this book, in particular Clair Griffiths and Steve Barnfield, for their work in preparing the manuscript for publication. David B. Wootton 2 Preface 2 31/7/01, 11:34 am Contents Preface ................................................................................................................... 1 1 Historical Background ..................................................................................... 3 Introduction ..................................................................................................... 3 1.1 The Textile Industry ................................................................................ 3 1.2 The Rubber Industry ............................................................................... 6 1.3 Textile and Rubber Composites ............................................................ 10 References ...................................................................................................... 13 2 Production and Properties of Textile Yarns .................................................... 15 Introduction ................................................................................................... 15 2.1 Production Methods for Textile Fibres ................................................. 15 2.1.1 Cotton ...................................................................................... 15 2.1.2 Rayon ....................................................................................... 21 2.1.3 Nylon ....................................................................................... 24 2.1.4 Polyester ................................................................................... 26 2.1.5 Aramid ..................................................................................... 28 2.2 General Characteristics of Textile Fibres .................................................. 30 2.3 2.2.1 Cotton ...................................................................................... 30 2.2.2 Rayon ....................................................................................... 32 2.2.3 Nylon ....................................................................................... 33 2.2.4 Polyester ................................................................................... 34 2.2.5 Aramid ..................................................................................... 35 General Physical Properties of Textile Fibres ........................................ 36 2.3.1 Cotton ...................................................................................... 36 i Textiles Contents 1 31/7/01, 11:34 am The Application of Textiles in Rubber 2.3.2 Rayon ....................................................................................... 38 2.3.3 Nylon ....................................................................................... 39 2.3.4 Polyester ................................................................................... 40 2.3.5 Aramid ..................................................................................... 40 References ...................................................................................................... 40 3 Yarn and Cord Processes ................................................................................ 41 Introduction ................................................................................................... 41 3.1 3.2 Yarn Preparation Methods .................................................................... 41 3.1.1 Twisting .................................................................................... 42 3.1.2 Texturing .................................................................................. 49 Warp Preparation ................................................................................. 52 3.2.1 Direct Warping ......................................................................... 53 3.2.2 Sectional Warping ..................................................................... 54 3.3 Sizing ....................................................................................................... 57 4 Fabric Formation and Design of Fabrics ........................................................ 59 Introduction ................................................................................................... 59 4.1 4.2 Fabric Formation .................................................................................. 59 4.1.1 Weaving .................................................................................... 59 4.1.2 Knitting .................................................................................... 64 4.1.3 Non-Woven Fabrics .................................................................. 68 The Design of Woven Fabrics ............................................................... 70 4.2.1 Physical Property Requirements ................................................ 70 4.2.2 Selection of Fibre Type .............................................................. 71 4.2.3 Selection of Fabric Construction ............................................... 74 5 Heat-Setting and Adhesive Treatments ........................................................... 83 Introduction ................................................................................................... 83 5.1 Heat-Setting Machinery ........................................................................ 83 ii Textiles Contents 2 31/7/01, 11:34 am Contents 5.2 Heat-Setting .......................................................................................... 90 5.3 Adhesive Treatment .............................................................................. 94 5.3.1 Cotton ...................................................................................... 94 5.3.2 Rayon ....................................................................................... 95 5.3.3 Nylon ....................................................................................... 98 5.3.4 Polyester ................................................................................... 99 5.3.5 Aramid ................................................................................... 101 5.4 The In Situ Bonding System ................................................................ 102 5.5 Mechanisms of Adhesion .................................................................... 103 5.6 Environmental Factors Affecting Adhesion ......................................... 107 Appendix V Interfacial Compatibility .......................................................... 109 References .................................................................................................... 112 6 Basic Rubber Compounding and Composite Assembly ................................ 113 6.1 Compounding ..................................................................................... 113 6.1.1 Polymers ................................................................................. 113 6.1.2 Curing Systems ....................................................................... 114 6.1.3 Fillers ...................................................................................... 116 6.1.4 Antidegradants ....................................................................... 117 6.1.5 Other Compounding Ingredients ............................................ 117 6.2 Processing ........................................................................................... 117 6.3 Composite Assembly ........................................................................... 118 6.3.1 Calendering ............................................................................ 118 6.3.2 Coating ................................................................................... 124 References .................................................................................................... 127 7 Assessment of Adhesion ............................................................................... 129 Introduction ................................................................................................. 129 7.1 Cord Tests ........................................................................................... 129 iii Textiles Contents 3 31/7/01, 11:34 am The Application of Textiles in Rubber 7.1.1 Pull-Out Tests ......................................................................... 130 7.1.2 Cord Peel Test ......................................................................... 130 7.2 Fabric Test Methods ........................................................................... 133 7.3 Testing and Interpretation of Results .................................................. 138 7.4 Adhesion Tests for Lightweight Fabrics and Coatings......................... 140 7.5 Peeling by Dead-Weight Loading ........................................................ 142 7.6 Direct Tension Testing of Adhesion .................................................... 143 7.7 Adhesion and Fatigue Testing ............................................................. 145 7.8 Assessment of Penetration into the Textile Structure ........................... 146 Appendix VII: The Physics of Peeling ........................................................... 148 References .................................................................................................... 153 8 Conveyor Belting ......................................................................................... 155 Introduction ................................................................................................. 155 8.1 8.2 Belt Construction and Operation ........................................................ 160 8.1.1 Carcase ................................................................................... 160 8.1.2 Insulation ................................................................................ 161 8.1.3 Covers .................................................................................... 162 Belt Design .......................................................................................... 165 8.2.1 Plied Belting ............................................................................ 167 8.2.2 Single-Ply and Solid-Woven Belting ........................................ 171 8.2.3 Steel Cord Belting ...................................................................... 172 8.3 8.4 Belting Manufacture ........................................................................... 172 8.3.1 Belt Building ........................................................................... 173 8.3.2 Pressing and Curing ................................................................ 173 8.3.3 Belt Joining ............................................................................. 178 Belt Testing ......................................................................................... 182 8.4.1 Tensile Strength and Elongation .................................... 182 iv Textiles Contents 4 31/7/01, 11:34 am Contents 8.4.2 8.4.3 8.4.4 8.4.5 8.4.6 Gauge ........................................................................... 183 Adhesion ...................................................................... 183 Abrasion ....................................................................... 183 Troughability ................................................................ 183 Fire Resistance .............................................................. 183 References .................................................................................................... 184 9 Hose ............................................................................................................. 187 Introduction ................................................................................................. 187 9.1 Hose Manufacture .............................................................................. 188 9.1.1 Braiding .................................................................................. 188 9.1.2 Spiralling ................................................................................ 190 9.1.3 Wrapped Hose ........................................................................ 191 9.1.4 Knitted Hose ........................................................................... 192 9.1.5 Oil Suction and Discharge Hose ............................................. 192 9.1.6 Circular Woven Hose .............................................................. 193 Appendix IX ................................................................................................ 195 i. Neutral Angle .................................................................................. 195 ii. Bursting Pressure ....................................................................... 196 10 Power Transmission Belts ............................................................................. 199 Introduction ................................................................................................. 199 10.1 Main Types of Power Transmission Belts ............................................ 200 10.1.1 V-Belts .................................................................................... 200 10.1.2 Timing Belts ............................................................................ 203 10.1.3 Flat Belting ............................................................................. 203 10.1.4 Cut-Length Belting.................................................................. 205 10.2 Manufacture of Power Transmission Belting ...................................... 206 10.2.1 Manufacture of V-Belts ........................................................... 206 10.2.2 Manufacture of Timing Belts .................................................. 209 v Textiles Contents 5 31/7/01, 11:34 am The Application of Textiles in Rubber 10.3 Effect of the Textile Reinforcement on Belt Performance .................... 209 References .................................................................................................... 212 11 Applications of Coated Fabrics .................................................................... 213 Introduction ................................................................................................. 213 11.1 Inflatable Structures ............................................................................ 214 11.1.1 Inflatable Boats ....................................................................... 214 11.1.2 Oil Booms ............................................................................... 218 11.1.3 Inflatable Dams ...................................................................... 219 11.1.4 Inflatable Buildings ................................................................. 220 11.1.5 Dunnage Bags ......................................................................... 221 11.2 Non-Inflated Structures ...................................................................... 222 11.2.1 Reservoir and Pond Liners ...................................................... 222 11.2.2 Flexible Storage Tanks ............................................................ 223 11.2.3 Supported Building Structures ................................................ 223 References .................................................................................................... 224 12 Miscellaneous Applications of Textiles in Rubber ........................................ 225 Introduction ................................................................................................. 225 12.1 Hovercraft Skirts ................................................................................ 225 12.1.1 Types of Skirt .......................................................................... 226 12.2 Air Brake Chamber Diaphragms ......................................................... 229 12.3 Snowmobile Tracks ............................................................................. 230 References .................................................................................................... 231 Abbreviations and Acronyms............................................................................. 233 Glossary ............................................................................................................ 234 Index ................................................................................................................. 239 vi Textiles Contents 6 31/7/01, 11:34 am 1 Historical Background Introduction The modern world relies to a great extent, on textile/polymer composites, the majority of which are rubber/textile compositions. In fact, it is difficult to imagine the functioning of modern everyday life without the use of such products. It is only necessary to consider the need for transport systems (relying on textile/rubber tyres), materials handling systems (relying on textile/rubber conveyor belting) and mechanical drive systems (using rubber/ textile drive belts) to see the important role played by such materials. Whereas textiles have been produced and used for many thousands of years, it was only some 500 years ago that rubber was introduced to Europe and really only in the last two hundred years that textiles and rubber have been used together in this region. Since then, however, there has been very great development in the design and use of these materials. Within the last 75 years, there has been a great move away from natural materials (natural rubber and cotton) to synthetic products, both as regards the fibres and the polymers used, resulting in a very wide diversity of engineered composites, to meet many and varied performance requirements. 1.1 The Textile Industry The origin of the textile industry is lost in the past. Fine cotton fabrics have been found in India, dating from some 6-7000 years ago, and fine and delicate linen fabrics have been found from two to three thousand years ago, at the height of the Egyptian civilisations. More recent archaeological excavations, among some of Europe’s oldest Stone Age sites, have found imprints of textile structures, dating back some 25,000 years, but in the humid conditions obtaining in these more northerly areas, all traces of the actual textiles have long disappeared, unlike those from the dry areas of India and Egypt. Until more recent times, the spinning of the yarns and the weaving of the fabrics were generally undertaken by small groups of people, working together – often as a family group. However, during the Roman occupation of England, the Romans established a 3 Chapter 1 3 31/7/01, 11:34 am The Application of Textiles in Rubber ‘factory’ at Winchester, for the production, on a larger scale, of warm woollen blankets, to help reduce the impact of the British weather on the soldiers from southern Europe. In the family context, it generally fell to the female side to undertake the spinning, while the weaving was the domain of the men. Spinning was originally done using the distaff to hold the unspun fibres, which were then teased out using the fingers and twisted into the final yarn on the spindle. In the 1530s, in Brunswick, a ‘spinning wheel’ was invented, with the wheel driven by a foot pedal, giving better control and uniformity to the yarns produced. Often, great skill was developed, as shown by the records of a woman in Norwich, who spun one pound of combed wool into a single yarn measuring 168,000 yards, and from the same weight of cotton, spun a yarn of 203,000 yards. In today’s measures this is equivalent to a cotton count of 240, or approximately 25 decitex. Cotton count is the number of hanks of 840 yards (768 metres) giving a total weight of 1 lb (453.6 g). A Tex is a measurement of the linear density of a yarn or cord, being the weight in grams of a 1,000 m length; a decitex is the weight in grams of a 10,000 m length. By the eighteenth century, small co-operatives were being formed for the production of textiles, but it was really only with the mechanisation of spinning and weaving during the Industrial Revolution, that mass production started. Up to this time, both spinning and weaving were essentially hand operations. Handlooms were operated by one person, passing the weft (the transverse threads) by hand, and performing all the other stages of weaving manually (see Chapter 4 for a description of the weaving process). In 1733, John Kay invented the ‘flying shuttle’, which enabled a much faster method for inserting the weft into the fabric at the loom and greatly increased the productivity of the weavers. Until the advent of the flying shuttle, the limiting factor in the production chain for fabrics was the output of the individual weaver, but this now changed and with the more rapid use of the yarns, their production became the limiting factor in the total process. In 1764, this was partly resolved by the invention, by James Hargreaves, of the ‘Spinning Jenny’, which was developed further by Sir Richard Arkwright, with his water spinning frame, in 1769, and then in 1779, by Samuel Crompton, with his ‘spinning mule’. Alongside these developments in spinning, similar changes were taking place in the weaving field, with the invention of the power loom by Edmund Cartwright, in 1785. With this increase in mechanisation of the whole industry, it was logical to bring the production together, rather than keeping it widely spread throughout the homes of the producers. Accordingly, factories were established. The first of such was in Doncaster in 4 Chapter 1 4 31/7/01, 11:34 am Historical Background 1787, with many power looms powered by one large steam engine. Unfortunately, this was not a financial success, and the mill only operated for about 3 or 4 years. Meanwhile, other mills were being established, in Glasgow, Dumbarton and Manchester. A large mill was erected at Knott Mill, Manchester, although this burnt down after only about 18 months. The first really successful mill was opened in Glasgow in 1801. However, this industrialisation was not to everyone’s liking; many individuals were losing their livelihoods to the mass production starting to come from the increasing number of mills. This led to a backlash from the general public, resulting in the Luddite Riots in 1811-12, when bands of masked people under the leadership of ‘King Ludd’ attacked the new factories, smashing all the machinery therein. It was only after very harsh suppression, resulting in the hanging or deportation of convicted Luddites in 1813, that this destruction was virtually stopped. However, there were still some outbreaks of similar actions in 1816, during the depression following the end of the British war with France, and this intermittent action only finally stopped when general prosperity increased again in the 1820s. Following this, the textile industry expanded considerably, particularly in the areas where the raw materials were readily available. For example, the woollen mills in East Anglia, where there was good grazing for the sheep, and in West Yorkshire and Eastern Lancashire, where either coal was available for powering the new steam engines, or where fast flowing streams existed to provide the energy source for water-powered mills (particularly in central Lancashire). The main woollen textile production developed in Yorkshire, as it was easier and cheaper to transport the raw wool there, than to carry the large quantities of coal required to power the mills to the wool growing areas. In Lancashire, with the ports of Liverpool and Manchester close by for the importation of cotton from America, the cotton industry grew and flourished. However, in the 1860s, due to the American Civil War, the supply of cotton from America dried up and caused great hardship among the cotton towns of south and east Lancashire. On account of this, and with the great strides being made in chemistry, research was begun to try to find ways of making artificial yarns and fibres. The first successful artificial yarn was the Chardonnet ‘artificial silk’, a cellulosic fibre regenerated from spun nitrocellulose. Further developments lead to the cuprammonium process and then to the viscose process for the production of another cellulosic, rayon. This latter viscose was fully commercialised by Courtaulds in 1904, although it was not widely used in rubber reinforcement until the 1920s, with the development of the balloon tyre. Research continued into fibre-forming polymers, but the next new fully synthetic yarn was not discovered until the 1930s, when Wallace Hume Carothers, working for DuPont, discovered and developed nylon. This was first commercialised in 1938 and was widely 5 Chapter 1 5 31/7/01, 11:34 am The Application of Textiles in Rubber developed during the 1940s to become one of the major yarn types used. Continuing research led to the discovery of polyester in 1941, and over the ensuing decades, polyolefin fibres (although because of their low melting/softening temperatures, these are not used as reinforcing fibres in rubbers) and aramids. As the chemical industry greatly increased the types of yarns available for textile applications, so the machinery used in the industry was being developed. Whereas the basic principles of spinning and weaving have not significantly changed over the millennia, the speed and efficiency of the equipment used for this has been vastly been improved. In weaving, the major changes have been related to the method of weft insertion; the conventional shuttle has been replaced by rapiers, air and water jets, giving far higher speeds of weft insertion. Other methods of fabric formation have similarly been developed, such as the high speed knitting machines and methods for producing fabric webs known as ‘non-wovens’. 1.2 The Rubber Industry Whereas the basic properties of rubber, or caoutchouc as it was then called, were known to the natives of South America, the first reports of it in Western Europe were given by Christopher Columbus in 1492 and then more detailed accounts were given by Gonzalo Fernandez d’Ovideo y Valdas, in his Universal History of the Indies [1], in which he describes the game of ‘batos’ as like a game of balls, ‘But played differently and the balls are of other material than those used by Christians’. Later, Juan de Torquemada [2] describes the use of elastic balls from the sap of the Ulaqahil tree, which juice was also used for painting on linen fabrics, to protect the wearer from the rain; water did not penetrate but the sun’s rays ‘had an evil effect on the coating’. In 1731 the French government sent the geographer Charles Marie de La Condamine to South America on a geographical expedition. In 1736 he sent back to France a report to the Paris Academy, together with several rolls of crude rubber and a description of the products fabricated from it by the people of the Amazon Valley. In this report, he stated that the resin (caoutchouc) from the Hévé tree was used, in the province of Quito, to cover linen material, which was then used like oilcloth. Fresnau, an engineer, later reported more fully on this use and suggested other possible applications, such as waterproof sails, divers’ hoses and bags for keeping food, etc. He also commented, however, that such goods could only be produced in those areas where the trees grew, as the juice dries very quickly and looses its fluidity. During the 18th century, small quantities of rubber were sent to Europe and found some limited applications. For example, in 1770, Joseph Priestly drew attention to the 6 Chapter 1 6 31/7/01, 11:34 am Historical Background fact that small pieces of caoutchouc could be used for rubbing out pencil marks. Since 1775, small pieces have been available in stationers’ shops for this purpose, called ‘India Rubbers’, by which name this material has been known ever since, in English speaking countries. More important uses were found for this material, however, and in spite of the comments by Fresnau some fifty years earlier, one of these earlier applications was for coating fabrics, to render it waterproof, where the ‘loss of fluidity’ was overcome by solution of the rubber in turpentine; this was the subject of one of the earliest patents for the use of rubber, granted to Samuel Peal in 1796 [3]. All the rubber available at this time, was, of course, wild rubber, gathered from the rain forests of Central and Southern America. This rubber was mainly in the form of ‘bottles’, from the wooden formers on which the latex was dried and smoked, or roughly spherical ‘negro-heads’, consisting of many small lumps of dried rubber stuck together. Originally, products could only be made by cutting the rubber from these rough blocks or by dissolving it in a suitable solvent, such as turpentine, and spreading it onto fabric or some similar substrate. However, in 1820 Thomas Hancock [4] noted that on heating, rubber became soft and plastic; also on kneading it in a dough mixer, without solvent, it would become soft and more easily worked. Accordingly, he designed a machine to enable the rough lumps and offcuts to be worked together into a soft mass. This could then be pressed into a heated mould to give a regular and uniform block of rubber, which was much easier to handle and work with. From these prepared blocks, sheets of various sizes and thicknesses were cut for many applications; one of these was for use as pads between the railway lines and the sleepers, to reduce vibration. More complicated mouldings were also made and textiles were plied up with thinly cut sheets or coated for solution. One of the best known names in this latter context was that of Charles Macintosh, who patented many applications e.g., [5] for proofing fabrics. In 1823 he established a factory in Glasgow and then later moved to Manchester, building his plant in Cambridge Street, which site is still used for rubber manufacture and coating. Many other uses were found for rubber; by 1825, hoses were being built on mandrels, with reinforcement of two or more plies of fabric, and with wire spiralling for suction hose. In 1826, rubber insulated cables were use by Baron Schilling, for detonating explosives in mines; drive belts made from layers of fabric bonded together with rubber were used by Isambard Kingdom Brunel to drive the machines used in sinking the Thames Tunnel. Inflatables of many kinds were produced from coated fabrics. Hancock [4] in collaboration with Macintosh produced air beds and pillows, such as were used by King George IV on his deathbed. Large floating pontoons, for floating bridges, were produced 7 Chapter 1 7 31/7/01, 11:34 am The Application of Textiles in Rubber and tested to the satisfaction of the Duke of Wellington. Throughout this period, waterproof cloaks were worn by the passengers on the stagecoaches. All these products, however, had severe service limitations. They would soften and become sticky in warm weather or would harden and become brittle in the cold. Much work was done to overcome these problems and, independently, Charles Goodyear in the USA and Hancock in England, discovered the effects of sulphur in vulcanising rubber. This discovery of vulcanisation gave a great boost to the rubber industry. The properties, and especially the service life, of all the rubber articles were vastly improved and new outlets and applications were continually being found. In 1845 a Scotsman, Robert William Thomson, invented the pneumatic tyre [6]. However, this was designed for use with steam road engines, which were not in favour with the Government of the time, it was not developed further until the advent of the bicycle and motor car, when it was reinvented by John Boyd Dunlop [7, 8]. Between these times, the solid tyre sufficed and indeed was given royal approval, in 1846, by Queen Victoria. This was all accomplished with supplies of wild rubber. In 1836, the consumption of rubber in Western Europe was some 65 tonnes per annum. As the industry grew, so did consumption, reaching 2,250 tonnes in 1853 and 15,600 tonnes by 1887. At this time, rubber from sources other than the Hevea brasiliensis, such as Ficus elasticus and the shrub Guyale, was being imported into Europe. By this time it was obvious that the industry could not survive on wild rubber only. In 1876 the British explorer Sir Henry Wickham collected about 70,000 seeds of Hevea brasiliensis, and, despite a rigid embargo, smuggled them out of Brazil. The seeds were successfully germinated in the hothouses of the Royal Botanical Gardens at Kew in London, and were used to establish plantations first in Ceylon in 1888 and then in other tropical regions of the eastern hemisphere. During the next decade, plantations were more widely established in Ceylon and Malaya but significant imports of plantation rubber into Europe were not made until 1901, by which time the consumption of wild rubber had increased to 27,000 tonnes per year. The plantations soon proved their worth, and by 1936 over 1,000,000 tonnes of rubber were being produced annually, generally within the geographical range of around 1,100 km either side of the Equator. While the production of rubber and its uses were expanding, so the technology was developing. It was quite soon found that the addition of certain metal oxides assisted in vulcanisation. In 1880, while trying to use ammonia to produce sponge rubber, T. Rowley found that this vastly increased the rate of vulcanisation [9]. Work in this area continued and in 1906, George Oenslager discovered two much more readily applicable materials, to accelerate vulcanisation, aniline and thiocarbanilide. 8 Chapter 1 8 31/7/01, 11:34 am Historical Background Research continued and, in 1912, the use of piperidine was patented [10] to be followed by the thiuram disulphides, which were also shown, in 1919, to be able to cure rubber without the addition of sulphur. Then, in 1923, mercaptobenzthiazole, the basis of many modern accelerators, was discovered. Meanwhile, chemists were also studying the composition of the rubber itself. It had been shown to possess the same empirical formula as isoprene and, in 1860, Charles Greville Williams established that it was in fact a linear polymer of isoprene. By the 1890s, it was shown that isoprene could change, on standing, into a rubbery solid, albeit with rather different properties from those of natural rubber itself. This reaction is now known as polymerisation. The generally poor properties of the spontaneously polymerised isoprene arise from the lack of steric regularity, a problem only overcome some 60 years later. The search for a synthetic rubber continued and was spurred on, in the early 20th century, by the increasing price of natural rubber and then by the First World War. Various dienes were investigated for their potential for polymerisation. The most promising of these was dimethyl butadiene and, during the period from 1915 to 1918, Germany was able to produce some 2,500 tonnes of ‘methyl rubber’ using the sodium polymerisation route still in use today. These early synthetic rubbers left much to be desired in their overall properties; the use of carbon black for reinforcement was not known in Germany and the technology of vulcanisation and the use of protective anti-oxidants were in the very early stages of development. On account of these shortcomings, research into synthetic rubbers was largely allowed to drop. However, Father Julius Nieuwland, of the University of Notre Dame but working for the DuPont Company, discovered polychloroprene in 1930, which was first marketed under the trade name of ‘Duprene’ but latterly called ‘Neoprene’. This group of synthetic rubbers, as they became available during the 1930s, largely changed the attitude of the rubber industry towards synthetics. The general properties of these rubbers were quite good but the ageing and properties, such as the resistance to oils and solvents, were very much better than with the natural rubber. This gave a further boost to research and in 1935, the chemists of IG Farbenindustrie in Germany, developed the ‘Buna’ rubbers, the name being derived from butadiene, one of the common monomers, and Na, the chemical symbol for sodium, used as the catalyst. The major types developed were the standard Buna rubbers, copolymers of butadiene with styrene, and the Buna N types, with acrylonitrile as one of the monomers. A further great impetus was given to research by the advent of the Second World War, when supplies of natural rubber from the Far East were completely cut off and the US Government launched a crash programme to develop a viable alternative. This quickly 9 Chapter 1 9 31/7/01, 11:34 am The Application of Textiles in Rubber led to the development of the GR-S rubbers (styrene-butadiene rubber, now known as SBR) and the rapid establishment of large scale production of these polymers. In the 1950s work by Natta and Ziegler on catalysation processes led to the discovery of novel methods for obtaining highly stereo-regular polymers, including the high cispolyisoprene, ‘synthetic natural rubber’, which had been sought since the composition of natural rubber had been established a century before. Today, there are many synthetic polymers available, ranging from the general purpose hydrocarbons with properties largely similar to those of natural rubber; to the special purpose types with excellent resistance to ageing, oils and solvents; to highly sophisticated (albeit very expensive) polymers with outstanding resistance to the most hostile of environments, as found in aerospace, marine and oil exploration applications. 1.3 Textile and Rubber Composites From the very first references to rubber in South America, its use with textiles has been noted. This is not very surprising, as from the earliest times, one of the major drawbacks of textiles was their performance under wet conditions; in the dry, they gave excellent protection and warmth, but in the wet they soon became saturated and, if anything, made things seem worse. Many treatments were tried over the years to overcome this deficiency, using coatings of tars, resins and waxes; the most successful of these was the treatment with natural drying oils, to give the waterproof oilcloths. The main disadvantage of these was the stiffness and brittleness imparted to the fabrics. With rubber, many of these disadvantages virtually disappeared, giving a soft, flexible and waterproof material (at least at normal ambient temperatures). This is essentially the stage that Macintosh and Hancock started. Macintosh improved the coating process, with his single and double textures (this latter consisting of two layers of fabric adhered together with a thin film of rubber) but it was largely Hancock, with his imaginative approach, who developed a wide range of applications. Apart from waterproof coats and cloaks for travellers, he produced waterproof bags. Some were used by Captain Parry on his expedition to the North Pole, who, in his report on the voyage, refers to saving a bag of cocoa, which fell off an ice-floe during unloading, but ‘…the bag being made of Macintosh’s waterproof canvas, did not suffer the slightest injury.... I know of no material which, with an equal weight, is equally durable and waterproof’ [11]. Hancock realised the advantages of combining the strength of the textile with the other properties of rubber. He produced hose by wrapping successive layers of rubber and 10 Chapter 1 10 31/7/01, 11:34 am Historical Background fabric onto a mandrel. In spite of fierce opposition from the traditional leather hose makers, he persuaded Barclays Brewery, in London, to completely re-equip with rubber hose. This quickly proved its worth as, being seamless, leakage, which had always been a problem with the stitched leather hose, was reduced to negligible levels. In the same way that bags could be made waterproof, so also could they be made airtight and a great many applications for inflatable articles were found, covering air cushions and pillows, air beds and inflatable boats. A development from these, using inflatable bags, connected with rubber/fabric air hose, was used for lifting sunken ships. The concept worked well, but in the end, the project failed because of difficulties in attaching the bags to the object to be lifted. In the early days, many of these applications foundered simply because of the poor service life of the raw rubber. Being unvulcanised, the rubber was susceptible to changes in temperature but the major problem arose from the poor ageing characteristics. As all these applications relied on only thin layers of rubber, they were very susceptible to oxidation and the service life was accordingly very short. It is only over the last few decades, with the development of effective anti-ageing products, that this has satisfactorily been overcome and many of Hancock’s inventions have been ‘rediscovered’ and proved to be sound concepts. Not all the early products were doomed to failure, however. One of the early successes was in the field of textile machinery. One of the processes in the spinning of cotton is carding (for more detail of this, see Chapter 2). The carding engine is equipped with rollers to which are attached a multitude of fine steel wires; originally these wires were fixed by means of a leather backing, but the variability of the natural product led to considerable problems in achieving uniformity when these wired leather strips were wound onto the steel rollers. Hancock solved this problem by producing a backing of textile laminated with rubber: this enabled a very uniform ‘card clothing’ to be provided, with significant advantages in consistency and life of the clothing. The advantages of this material were rapidly recognised and within a few years, the textile/rubber backed clothing had completely replaced the original leather version on the cotton cards, and in fact is still used today. The earlier products were, with the exception of hose, flat composites. The next great development, however, was the pneumatic tyre. The tyre, developed by Dunlop, was originally based on a tube strapped to the wheel by means of rubberised fabric, but soon, the inner tube with a separate outer tyre was evolved. The outer tyre was made from layers of square woven cotton canvas and rubber, with wire beads to hold it in place on the rim of the wheel. By 1915, however, the canvas was replaced by cord fabrics. These gave improved properties and performance to the tyres, but the limiting properties were 11 Chapter 1 11 31/7/01, 11:34 am The Application of Textiles in Rubber still those of the rubber. At this time, carbon black was starting to be used: this effectively doubled the life of the tyres, which now lasted up to 4,000 miles. Further improvements in tyre life were achieved by the introduction of the balloon tyre in 1923: this used a much larger cross-section tyre, operating at considerably lower pressure (200-300 kPa) than the earlier narrow section tyres, which required pressures of up to 700 kPa. These improvements in tyre performance now threw the restrictions on performance back to the textile component. The answer to this was to employ the relatively new artificial fibre, rayon, for the reinforcing plies of fabric. But this introduced another problem. This was the first major use of fibres other than cotton. Up to now there had been no problem in adhering the rubber to the textile inserts: the techniques of spreading or frictioning had resulted in good mechanical adhesion, due to the embedding of the fibre ends of the staple yarns into the rubber. With the continuous filament artificial fibre, there were no fibre ends to embed. The search to find some system to give adequate adhesion led to the first adhesive dips. These were originally based on natural latex and casein, but the casein component was soon replaced with a resorcinol/formaldehyde resin. When natural rubber had to be replaced with synthetic, this, of course, applied to the adhesive systems too. The SBR latex behaved similarly to natural and gave adequate adhesion to rayon, albeit with some loss of building tack. When nylon was introduced, it was found that these resorcinol/formaldehyde/latex (RFL) dips did not give satisfactory adhesion. Research led to the development of a terpolymer latex, containing vinyl pyridine as the third monomer, which gave significantly improved adhesion with nylon and rayon. With the introduction of polyester, further adhesion problems arose: the standard RFL systems did not work. The first systems found to give good adhesion to polyester were based on very active isocyanates from solvent solution, either on their own, to be subsequently treated with RFL, or in a rubber cement, in which case, no further treatment was required. Solvent systems not being popular, much effort was devoted to the search for a satisfactory aqueous based process and this was finally achieved. Then, several years later, a similar exercise had to be undertaken to find a system suitable for use with the newly introduced aramid fibres. Similarly, with each new synthetic polymer introduced, special adhesive systems have had to be developed in order to obtain the optimum performance from the resultant textile/rubber composite. Thus, over the years, the two technologies, those of rubber and of textiles, have developed side by side. Today, composites are available which satisfy the stringent performance requirements met under such diverse and hostile environments as those of outer space or the depths of the sea and at extremes of temperature. 12 Chapter 1 12 31/7/01, 11:34 am
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