Essential Rubber Formulary: Formulas for Practitioners

Chellappa Chandrasekaran

• Publisher: William Andrew
• Year: 2007
• eBook ISBN: 9780815517092
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

The author, a seasoned rubber technologist of four decades, provides more than 180 essential rubber formularies, some of which have never been published, that are used by practitioners the world over on a frequent basis. A special feature of the formulations is that they are designed for factory scale applications.The opening chapter of this indispensable book gives practical information on compounding techniques, coloring, ingredients, as well as a whole section on typical rubber testing methods. The book concludes with appendices useful for the technologist that include seven conversion tables and three tables on scorching of rubber, specific gravity and volume cost, equivalent chemical names for trade names.Designing a rubber formula on the factory floor demands knowledge of the whole undertaking, such as the physical nature of ingredients, the interaction of additives and the base rubber during compounding and processing, as well as making sure that the finished product conforms to specification and requirements. This book provides all the necessary knowledge for practitioners and students alike.

Part 1

About Rubber

1 Introduction

The term “rubber” is used for any material which when subjected to an external force deforms with a comparatively low load/deflection ratio and regains its original shape quickly and forcibly when the forces applied to it are withdrawn. Based on this definition there are many materials which can be generally classified into the following:

1. Natural rubber

2. Synthetic rubber

Natural rubber is obtained from the bark of the tree Hevea brasiliensis, originally discovered in Brazil. The traditional and centuries old method of slitting the bark and letting the milk-like substance drip down as a thick fluid called “latex” still continues to be the sole method of obtaining natural rubber. The history of natural rubber in Brazil is an exciting tale that changed the lifestyle of the world. The Industrial Revolution and the discoveries that followed were reflected in all sectors of human necessities. Automobiles, locomotives, telephones, electricity, and many innovations in engineering and chemical industries changed the topography, customs, and pace of life in towns and cities. Thanks to its multiple uses in the ever-expanding industries, rubber became a commodity that was in demand worldwide.

In 1927 when Reimer and Tiemann published their work on amino acids, it blew open a new avenue for process industries. Rubber technology became an interesting area for study and research work in this field yielded a wide range of new rubbers. Research work on natural rubber yielded polyisoprene which was found to have similar properties as natural rubber. This led to an avalanche of many distinct rubber types based on styrene, isobutylene, butadiene, isoprene, and chloroprene, which in turn heralded the birth of synthetic rubber. The scientific community felt the inappropriateness of the term “rubber” and coined a new term to cover the entire range of man-made rubbers namely “elastomers” or “polymers.” A wide variety of synthetic rubbers have been developed, and the production technology for these rubbers was in the hands of global giants such as Dupont, Bayer, Shell, BASF, Goodyear, Polysar, ICI, Dow, and Exxon.

The use of this material became widespread because the characteristics and properties of both natural and man-made rubbers made them useful in almost all sectors namely automobiles, footwear, pharmaceuticals, steel, paper, transport, electrical and electronics, and chemical engineering. Tens of thousands of product types were in use in these sectors. Rubber became a scarce commodity in the United States during World War II. The United States faced an economic crisis due to the shortage in rubber supply. War tanks, warplanes, and warships required huge quantities of rubber for their spare parts. Every factory, home, office, and military facility throughout the United States used rubber. Due to depletion of stocks, the US government banned the use of rubber other than for defense purposes. The post-war situation had similar impacts worldwide. The industrial and manufacturing sectors were forced to develop new methods and innovative compounding technologies for the manufacture of rubber products for critical, noncritical, and consumer needs.

The rubber products manufacturing sector also saw a revolution in compounding and processing technologies for the various types of natural and synthetic rubbers, with the availability of diverse types of rubber ingredients.

It is interesting to know that the first rubber factory in the world was established near Paris in the early 1800s, and the first in England was established by Thomas Hancock during the same period. Charles Goodyear’s discovery of vulcanization and Hancock’s discovery of mastication revolutionalized the rubber manufacturing industry from its infancy.

The wide range of rubber products manufactured by industries worldwide catered to defense, civil, aviation, railways, agriculture, transport, textiles, steel, health, sports, and practically every conceivable field. Therefore, designing and developing rubber formulations was a tricky and challenging job for the rubber technologist.

2 Brief Notes on Compounding Ingredients

In order to produce a useful end product, the base rubbers are admixed with suitable ingredients. This process is called compounding. The ingredients used for compounding are classified into accelerators, activators, antioxidants, coloring agents, fillers and reinforcing agents, retarders, rubber process oils, softeners, and vulcanizing agents. Certain other classes of products which do not come under the above classes are dusting and anti-tack agents such as talc powder and mold lubricants such as silicones, reclaimed rubbers, and solvents. Addressing a complete treatise on rubber compounding ingredients would be a voluminous task and it is also not within the scope of this book; however, brief notes are provided for readers to acquire a basic idea of each class of ingredients.

The unit “phr” that appears frequently in the formulations listed throughout this book stands for “parts per hundred rubber,” which means the parts by weight of an ingredient per hundred parts by weight of rubber. For example, 40 phr of carbon black means 40 parts by weight of carbon black per hundred parts by weight of rubber, where the unit of weight can be either kilograms or pounds.

2.1. Accelerators

Accelerators of vulcanization are classified into organic and inorganic types. Organic accelerators are known to the rubber industry for over a century. Their use in rubber compounding has become universal. Some examples of organic accelerators are hexamine, mercapto-N-cyclohexyl benzothiazole sulfenamide, sodium diethyl dithiocarbamate, tetramethylthiuram disulfide, tetramethylthiuram monosulfide, etc. These compounds represent almost the entire range of organic accelerators from moderate to ultra accelerators. Inorganic accelerators such as lime and litharge are used in slow curing products like rubber lining. Accelerators reduce the time required for vulcanization. The benefits of using accelerators are economy of heat, greater uniformity of finished goods, improved physical properties, improved appearance, and better resistance to deterioration.

2.2 Vulcanizing Agents

Sulfur is the most well-known vulcanizing agent. It is easily available in powder and prilled form packed in polyethylene bags. Sulfur vastly improves the properties of raw rubber which is sticky and soluble in solvents. With the addition of sulfur, rubber is converted into a nontacky, tough, and elastic product.

2.3 Activators

Activators help accelerators in the vulcanization process. Zinc oxide and zinc stearates are the most popular activators. Zinc oxide is also a reinforcing filler.

2.4 Antioxidants

Rubber is degraded by oxidation. In order to prevent this, inhibitors are used during rubber compounding. These inhibitors are called antioxidants. The commercially available antioxidants are grouped into amine types and phenolic types. Products derived from amines, mostly aniline or diphenylamine, are called staining antioxidants because they tend to discolor nonblack vulcanizates on exposure to light, and products derived from phenol are referred to as nonstaining antioxidants.

2.5 Fillers and Reinforcing Agents

Fillers are classified into reinforcing and inert fillers. They can be either black or nonblack fillers. Those which have a pronounced effect on the physical properties of rubbers, such as tensile strength, abrasion resistance, tear resistance, and fatigue resistance, are cal...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• Preface
• Part 1: About Rubber
• Part 2: Formulary
• Appendix 1: Scorching of Rubber—A Study Formula
• Appendix 2: Specific Gravity and Volume Cost
• Appendix 3: Equivalent Chemical Names for Trade Names
• Appendix 4: Useful Conversion Tables
• Bibliography
• Index