Anticorrosive Rubber Lining

A Practical Guide for Plastics Engineers

Chellappa Chandrasekaran

• Publisher: William Andrew
• Year: 2017
• Print ISBN: 9780323443715
• eBook ISBN: 9780323444859
• Topic: Technology & Engineering
• Subtopic: Engineering General
• Index: Technology & Engineering

Anticorrosive Rubber Lining discusses the state-of-the-art in this evolving industry, including sections on the best materials and formulations to use, what's best for a particular application, which repair technique is best for a given application, how long a rubber lining is likely to last, vulcanization parameters, and more.This book deals with the important field of anticorrosive rubber lining and its applications in various industries, including oil and gas, nuclear, aerospace, maritime, and many more, highlighting many of the technological aspects involved. The author offers a unique perspective due to the exclusiveness of the case histories presented, including many industrial rubber lining practices which are mostly kept within the industry.The technical information on rubber presented here is a practical tool to enable engineers to make the best use of rubber linings to prevent corrosion in chemical plants. The book includes valuable insights into bonding systems, surface preparation, and coating methodologies, and also covers failure analysis of failed systems.- Includes up-to-date technical information on special compounding and processing technology of recently developed synthetic rubbers- Provides detailed case studies from industry sectors, including aerospace, nuclear energy, and mining- Presents rare, valuable insider knowledge of current industry practice

1

Rubber—A Miracle Material

Abstract

We encounter the miracle material rubber everywhere and every day without even realizing it—in cars, toothbrushes, mobile phones, computers, chewing gum, balloons, surgical gloves, bathroom mats, rubber corks, rubber bands, erasers, roads, hospitals, and in aircraft and space craft. When combined with other materials, rubber has an almost infinite number of uses. It is one of the most hardy, robust, and versatile materials in existence. The oldest traces of rubber were found in a fossil estimated to be 55–60 million years old, discovered in 1924 in lignite deposits in Germany. Amazingly, after being treated, the rubber still had its elastic properties!

Keywords

Butyl rubber; Crosslinking; Ebonite; Elasticity; Elastomeric lining; Elastomers; Natural rubber; Polymers; Saturation and unsaturation; Vulcanization

We encounter this miracle material everywhere and every day without even realizing it—in cars, toothbrushes, mobile phones, computers, chewing gum, balloons, surgical gloves, bathroom mats, rubber corks, rubber bands, erasers, roads, hospitals, and in aircraft and space craft. When combined with other materials, rubber has an almost infinite number of uses. It is one of the most hardy, robust, and versatile materials in existence. The oldest traces of rubber were found in a fossil estimated to be 55–60 million years old, discovered in 1924 in lignite deposits in Germany [1]. Amazingly, after being treated violently, the rubber still had its elastic properties!

Rubber, an Elastic Concept

But what actually is the material that we refer to in everyday language as rubber? The short answer is that rubber is our most elastic material, with unique properties of sealing fluid leakages, damping, resisting acids, and protecting in a variety of different contexts. However, the concept of rubber is far from uniform. There are many different types of rubber and closely related materials, which can be given widely differing properties through the addition of various chemicals. Rubber elasticity is identified as the capacity to sustain very large deformations followed by complete recovery. It is exhibited exclusively by polymeric materials consisting predominantly of long molecular chains. The essential requirement for a material to be rubbery is that it consists of long flexible chain-like molecules. It is to be understood that there is a limit to the amount of stress one can apply to a material before it reaches its “elastic limit” and deforms irreversibly. Materials like rubber have high elasticity because they are made up of millions of long and bendable chains of molecules. Many theories exist on the concept of rubber elasticity but they are centered on the fact that although stress can be applied to the millions of chains in the rubber in any direction, it will always return to its original shape.

On Icy Roads and in Ablative Flame

Chemical additives and combinations with other materials such as metals, textiles, and plastics determine the final characteristics of the end product. It might be a hose that must be resistant to corrosive chemicals, or a rubber sheet applied to a metal surface for chemical resistance, or a seal in an aircraft that must withstand extreme differences in temperature, or a sound-absorbing material that silences the humming of a hard disk, or a tire that rides on icy roads or on runways as well as on tropical roads, which develops high friction temperature, or in the rocket industry an ablative material that is flame retardant. Icy roads in snowy winter are topped up with sodium chloride salt crystals to lower the freezing point of the slippery ice. Whatever our needs, human beings can be relied on to constantly find new applications for this remarkable material.

In the Beginning

Natural rubber is obtained from the bark of the tree Hevea brasiliensis, originally discovered in Brazil. The traditional and century-old method of slitting the bark and letting the milk to drip to form a solid mass called latex continues to be the sole method of obtaining natural rubber. This was the only material serving humanity until the advent of polymer technology. Hence the term “rubber,” until the arrival of polymers, only meant natural rubber. Hevea brasiliensis is found in African countries too. Comparing the climatic conditions of these countries, it is obvious that these rubber trees prefer humid tropical climates.

Since its discovery the use of rubber became widespread and when worldwide demand increased during the world war periods, the natural rubber produced all over the world was inadequate. This necessitated scientists to look for substitutes for natural rubber. From the discovery of natural rubber to the development of modern-day thermoplastic elastomers, elastomeric materials have found a mind-boggling variety of applications that make them an integral part of an industrial and civilized society. In a diverse variety of products ranging from automobile tires to lifesaving implantable medical devices, their unique ability to be greatly deformed and return to their original shape fills an important niche in the world of engineering materials. It would be difficult to identify a manufacturing process that does not use elastomers in one form or another. Elastomeric materials have found widespread acceptance because of the virtually limitless combinations of elastomer types, fillers, and additives, which can be compounded at relatively low cost and processed by a wide variety of methods. This gives end users the ability to develop specific formulations with properties tailored to their needs.

Saturation and Unsaturation

The traditional view that rubber properties are related to high unsaturation led to numerous theories about the elastic behavior of rubbers, which were based on geometric structures resulting from the unsaturated linkages [2]. Susceptibility to chemical attack is attributed to the unsaturation of natural rubber molecules. Physical properties that appear not to be intrinsically dependent upon the carbon–carbon double bond (C

C) configuration are tensile strength, elasticity, rebound, elasticitic recovery, mechanical orientation, electrical properties, and solubility, which are mostly dependent on the molecular weight distribution, entanglement, and coiling up of long chain molecules.

Chemical unsaturation, which is extremely important from the point of view of allowing crosslinking or vulcanization to take place, is the greatest weakness of natural rubber molecules since it also allows oxidation reaction. One has therefore to reasonably believe that in the case of soft rubber goods, molded, extruded, or sheeting, only a fraction of the available double bonds is utilized in the vulcanization process with sulfur. The large residual unsaturation is responsible for the pronounced chemical reactivity of the soft rubber. It is this unsaturated character that makes natural rubber very susceptible to oxidation by O₂, O₃, and other oxidizing chemicals with consequent deterioration on aging and disintegration. It is also responsible for its lack of resistance to chemical agents such as strong mineral acids and also to its lack of heat stability.

Hardening and Softening Degradations

In this context, it may be interesting to compare the saturation levels of both natural and butyl rubber where the latter has a low level of unsaturation and the former has a high level. Cured butyl rubber with its predominant saturation is resistant to many acids making it a viable protective lining, while cured natural rubber in spite of its predominant unsaturation is again a protective lining because it forms an acid-resistant protective layer by reacting with acids especially HCl, the layer being known as chlorinated rubber, a highly chemically resistant material.

In appearance, butyl rubber resembles natural crêpe rubber, since it is an aliphatic, hydrocarbon polymer, whose density is the minimum (0.91) attainable for elastic materials of this type. In butyl rubber the original unsaturation level is very small and this low unsaturation is greatly reduced and may even be entirely eliminated during the compounding and curing process. The fact that vulcanized butyl rubber is extremely resistant to chemical attack is understandable because after vulcanization it becomes not only a nonthermoplastic, strong elastic material, but also an essentially chemically saturated product. This means that from a physical standpoint, vulcanized butyl rubber resembles soft vulcanized natural rubber and from the point of view of chemical resistance it may be considered most similar to ebonite, which is almost devoid of any unsaturation.

It is extremely resistant to acids and other deterioration influences. Like natural rubber, butyl rubber is not resistant to aliphatic hydrocarbon, but it does show a surprising resistance to benzene, ethylene dichloride, and oxygenated solvents. On resistance to aging and chemicals, Staudinger [3] says: “Every reaction which shortens the length of molecules liquefies to mass and conversely every reaction which lengthens the atomic chain tends to solidify the mass. These two actions correspond exactly to the chief transformations which rubber undergoes, which are nothing more than changes in consistency namely a fluidizing degradation and hardening degradation.” How true it is when both natural rubber and butyl rubber are compared after an accelerated aging test, butyl of low unsaturation undergoing only the degradative softening type of deterioration under the severe influence of heat, light, and air, and natural rubber predominantly of high unsaturation undergoing hardening deterioration.

Crosslinking

For the most effective development of rubber-like elasticity, permanent interlocking of the chain molecules at a few points along their length to form a three-dimensional network is desirable. The crosslinks should be sufficient in number to ensure a permanence of structure that is a suppression of viscous flow and yet not so numerous as to seriously restrict the internal segment mobility of the polymer chain. A very convenient way of effecting this crosslink is to make natural rubber react with sulfur. Sulfur linkages are formed between the chain with strengths comparable to those linking the carbon atoms to the polyisoprene chains in the starting material. This process, known as vulcanization, occurs as a consequence of the presence of highly reactive double bonds in the polyisoprene chains. The effect of vulcanization is to raise the glass transition temperature of the amorphous polymer and to lower the melting point of the crystallites formed on stretching the amorphous material.

Crosslinked polymers are to be regarded as giant three-dimensional molecules of indeterminate molecular weight [4–9]. Such molecules swell in solvents to an extent that depends on the nature of the swelling agent and also on the extent of crosslinking. The more highly crosslinked a given solvent is, the less the swelling. As the number of crosslinks is increased, these polymers, e.g., ebonites containing upward of 30% sulfur combined with rubber, show progressively less segmented mobility of the chains between the crosslinking points and consequently lose their long-range elasticity and resemble ordinary brittle solids in their elastic behavior.

Many of the mechanical properties of the high polymers are molecular weight dependent although the effect may be overshadowed by other factors such as chain orientation or crystallinity. A polymer of low molecular weight...

Table of contents

• Cover image
• Title page
• Table of Contents
• Series Page
• Copyright
• Disclaimer
• Dedication
• About the Author
• Preface
• Acknowledgment
• Introduction
• 1. Rubber—A Miracle Material
• 2. Rubber for Corrosion Protection
• 3. Wear-Resistant Rubbers for Ore and Mining Industries
• 4. Chemical Resistance of Biopolymers
• 5. Corrosion Resistance of Fluoropolymers
• 6. Rubber Lining for Sea Water Systems
• 7. Rubber Linings for Oilfield Equipment
• 8. Curing Technology
• 9. Rubber Lining for Nuclear Equipment
• 10. Rubber Lining for a Sulfur Dioxide Scrubbing System
• 11. Raw Materials for Rubber Lining Compounds
• 12. Rubbers Mostly Used in Process Equipment Lining
• 13. Compounding Rubbers for Lining Applications
• 14. Technoeconomic Aspects of Nonrubber Linings—Glass, FRP, and Lead
• 15. Manufacturing Rubber Sheets and Application Procedures
• 16. Adhesive Formulations for Rubber-to-Metal Bonding Systems
• 17. General Rubber Lining Guidelines
• 18. Fabrication of Equipment for Rubber Lining Suitability
• 19. Testing of Rubber Lining
• 20. Specifications and Codes of Practice
• 21. Some Typical Process Conditions in Chemical Industries
• 22. Aging, Service Life, and Prediction
• 23. Failure Analysis Methodology
• 24. Implications of Forensic Engineering on Rubber Lining
• 25. Basic Chemical-Resistant Ebonite Formulations
• 26. Practical Corrosion-Resistant Rubber Formulations
• 27. Infrastructure for Setting up a Rubber Lining Shop
• 28. Case Studies
• Appendix I
• Appendix II
• Appendix III
• Appendix IV
• Appendix V
• Appendix VI
• Appendix VII
• Appendix VIII
• Appendix IX
• Appendix X
• Bibliography
• Glossary of Terms
• Index