Chemistry, Manufacture and Applications of Natural Rubber

Shinzo Kohjiya, Yuko Ikeda

• Publisher: Woodhead Publishing
• Year: 2014
• Topic: Technology & Engineering
• eBook ISBN:
  9780857096913
• Subtopic: Physical & Theoretical Chemistry
• Index: Technology & Engineering

The growing demand for more sustainable materials has led to increased research on the properties of natural rubber. Chemistry, Manufacture and Applications of Natural Rubber summarizes this research and its significance for the industrial applications of natural rubber. Chapters in part one explore the properties and processing of natural rubber, including the biosynthesis of natural rubber in different rubber-producing species, chemical modification of natural rubber for improved performance, and the effect of strain-induced crystallization on the physical properties of natural rubber. Further chapters highlight hydrophobic and hydrophilic silica-filled cross-linked natural rubber and computer simulation of network formation in natural rubber. Part two focusses on applications of natural rubber, including eco-friendly bio-composites using natural rubber matrices and reinforcements, soft bio-composites from natural rubber and marine products, natural rubber for the tire industry, the application of epoxidized natural rubber in pressure sensitive adhesives (PSAs), and the use of natural rubber for vibration isolation and earthquake protection of structures. Finally, chapters in part three consider environmental and safety issues associated with natural rubber, including improving the sustainable development of natural rubber, the recycling of natural and synthetic isoprene rubbers and of sulfur cross-linked natural rubber, and recent research on natural rubber latex allergy. Chemistry, Manufacture and Applications of Natural Rubber is a comprehensive resource for academics, chemists, chemical engineers, mechanical engineers, and other professionals in the rubber industry, as well as those industries, including automotive, civil, and medical engineering, using natural rubber products. - An updated review with systematic and comprehensive coverage of natural rubbers - Covers a broad range of topics, including the chemistry, processing, sustainability, and applications of natural rubbers - Coverage of the best international research, including key experts from Asia, the United States, South America, and Europe

Part I

Properties and processing of natural rubber

Outline

1 Biosynthesis of natural rubber (NR) in different rubber-producing species

2 Natural rubber (NR) biosynthesis: perspectives from polymer chemistry

3 Chemical modification of natural rubber (NR) for improved performance

4 Understanding network control by vulcanization for sulfur cross-linked natural rubber (NR)

5 The effect of strain-induced crystallization (SIC) on the physical properties of natural rubber (NR)

6 Generating particulate silica fillers in situ to improve the mechanical properties of natural rubber (NR)

7 Hydrophobic and hydrophilic silica-filled cross-linked natural rubber (NR): structure and properties

8 Computer simulation of network formation in natural rubber (NR)

1

Biosynthesis of natural rubber (NR) in different rubber-producing species

K. Cornish, The Ohio State University, USA

Abstract:

Rubber biosynthesis in plants underpins the production of this strategically vital polymer. A fundamental understanding of the regulation of rate and polymer quality is essential to the development of alternate rubber-producing crops and new rubber materials with novel properties. Alternate rubber crops are needed to meet the projected shortfalls in global rubber production caused by the burgeoning economies of China and india.

Key words

biochemistry; initiator; monomer; natural rubber; polyisoprene; polymer

1.1 Introduction

Natural rubber is the fourth most important natural resource of the modern earth, after air, water, and petroleum (History Channel, June 9, 2004). However, due to its pervasive utility, it is also one of our most underrated, taken-for-granted natural products. There are at least 40,000 different products made with natural rubber and over 400 medical devices (Mooibroek and Cornish, 2000). The large amount of irreplaceable natural rubber needed in the military, industrial, transportation, medical and consumer sectors have led to natural rubber being repeatedly defined as a strategic raw material over the last 70 years. Although many synthetic rubber (derived from petroleum) applications can be met with natural rubber, the converse is not true. For example, although all tires contain a significant proportion of natural rubber, the higher the performance required, the greater the amount of the natural rubber component: truck tires are 90–100%, airplane tires are 100%, and navy jet tires on aircraft carriers are single-use 100% natural rubber tires. Almost all commercial natural rubber is tapped from a single species, Hevea brasiliensis, the para rubber tree. Production predominately occurs in plantations and small holdings in South-east Asia, a region which produces about 90% of global natural rubber. Africa produces around 10% and South America less than 1% because of the endemic South American leaf blight, a fatal fungal disease caused by Microcyclus ulei infection (Furtado et al., 2008; Lieberei, 2007; Rocha et al., 2011). The genetic diversity of cultivated H. brasiliensis is extremely low, advanced lines are grown as clonal scions on seedling root stocks, and most, if not all, modern lines are M. ulei sensitive. Thus, H. brasiliensis is at constant risk of crop failure.

The expanding economies of China and India have already eroded the small gains achieved in the rubber supply during the economic downturn of 2008–11, and shortages are burgeoning (Fig. 1.1). The independent International Rubber Study Group (IRSG, Singapore) has predicted a 1.5–3 million metric ton global shortfall between supply and demand by 2020 – the United States imports 1.2 million MT/yr. Like many countries, the United States is currently totally dependent upon the import of natural rubber (NR); in its case, for more than 1.2 million metric tons per year from tropically-grown sources. The economic importance of maintaining a steady supply of NR is highlighted by the fact that the United States rubber products trade in 2011 was worth over $18 billion.

1.1 Annual global production and consumption of natural rubber from 1995 to 2012 with projections to 2020. The economic downturn reduced the rate of consumption from 2007 to 2009, allowing earlier projected shortfalls to be halved. It should be noted that some of the shortfall could be made up by increased tapping of existing trees (Dock No, IRSG, personal communication), labor permitting. (data from the International Rubber Study Group)

The use of a single species to generate the global supply of a strategy commodity is not necessary, and has happened for rubber more as a matter of chance than anything else. In contrast, many crops are used to supply starch to humans even though the composition and quality of the different crops is dissimilar (e.g., potatoes, wheat, and rice). Similarly, many different plants (Mooibroek and Cornish, 2000), and some Lactarius sp. fungi (Mekkriengkrai et al., 2004; Ohya et al., 1997, 1998) make rubber and a few of these, as wild plants, have been used over past centuries and still could be developed as crops. Hevea brasiliensis is actually quite a recent crop because, until 120 years ago, we did not know how to compound rubber and generate desired product performance (Finlay, 2013). Wild rubber was used but had few applications. Since then, the enormous investment in all aspects of commercial production has led to the remarkable expansion of the crop that we have seen, particularly in South-east Asia, and until 2005, consumption of rubber has closely matched production (Fig. 1.2).

1.2 Annual global production and consumption of natural rubber from 1900 to 2008. The impact of World War II is clear and led to the Emergency Rubber Project. However, the world needs ten times more rubber than it needed in the 1940s, and demand will at least double by 2030. (data from the International Rubber Study Group)

Of the many plants capable of natural rubber production, two temperate species stand out as commercial candidates, Parthenium argentatum (guayule) and Taraxacum kok-saghyz (Kazak dandelion, also known as Russian dandelion and Buckeye Gold). These alternate rubber species are under development at a number of universities and companies on several continents. At the present time, P. argentatum is ahead of T. kok-saghyz, commercially. However, there is a large pilot plant for T. kok-saghyz processing in Wooster, Ohio, USA. Also, rubber and latex from T. kok-saghyz is similar to that from H. brasiliensis in composition and performance (Cornish et al., 2012). This similarity includes latex and rubber-particle bound proteins that cross react with Type I latex allergy, and so this rubber is a supplement to H. brasiliensis rubber, but not a circumallergenic rubber or latex, like that from P. argentatum (Cornish, 2012).

Future improvements in rubber yield per area of H. brasiliensis and the development of alternate natural rubber crops require an understanding of how the rubber is made, and how these mechanisms relate to both yield and quality. This understanding can direct both genetic engineering approaches, and plant breeding. Without such knowledge, such efforts rely heavily on serendipitous discoveries, and research over many years is required. In this chapter, I attempt to describe some of the commonalities and complexities of rubber biosynthesis and what we know, at this time, about the regulation of rubber biosynthetic rate, chain transfer and final molecular weight in evolutionarily-divergent rubber-producing species.

1.2 Rubber biosynthesis

Rubber biosynthesis requires two distinct pyrophosphate substrates and a divalent cation activator, usually magnesium ions in the living plant system (Archer and Audley, 1967, 1987; Cornish, 2001a, 2001b; Cornish and Backhaus, 1990). The Mg^{2 +} is essential for binding the pyrophosphate (PP) substrates into the active site. The first substrate, which initiates the polymerization reaction, is an allylic pyrophosphate (APP), which appears to be the C₁₅ farensyl-PP (FPP) in vivo (Fig. 1.3c). However, apart from a single initiator, the rest...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributor contact details
• Introduction
• Part I: Properties and processing of natural rubber
• Part II: Applications of natural rubber
• Part III: Environmental and safety issues
• Index