O slideshow foi denunciado.
Utilizamos seu perfil e dados de atividades no LinkedIn para personalizar e exibir anúncios mais relevantes. Altere suas preferências de anúncios quando desejar.

Natural rubber

221 visualizações

Publicada em

N.R

Publicada em: Educação
  • Seja o primeiro a comentar

  • Seja a primeira pessoa a gostar disto

Natural rubber

  1. 1. NATURAL RUBBER RAW MATERIAL Access to know-how and raw materials are the fundamental elements of a competitive manufacturing industry. While we are somewhat self-sufficient in know-how, the story of raw materials is somewhat different. Europe is import-dependent of many crucial raw materials, one of which being the natural rubber whose trade is affected by concentrated suppliers, skyrocketing prices and unprecedented global competition for its supply. Fair and sustainable supply of raw materials remains a challenge. This topic is here to stay. For example, price volatility in natural rubber markets and a foreseen shortage thereof, a shortage of different oils, ambitious recycling and resource-efficiency targets put forward both by industry itself and the European Commission are but a few examples. In the beginning of 2011, the Commission named natural rubber as one of the raw materials under the scope of the raw materials policy in its communication on commodity prices and raw materials. This will be of increasing importance as the global demand of our industry for raw materials is likely to continue or even grow given the expected increase in demand for transportation. At the next revision of the list of the critical raw materials, the challenges raised by fair supply of natural rubber should be properly assessed. Supply shortages in some sectors may have consequences which will have effect on strategically important societal sectors such as healthcare, medical science and transport. NATURAL RUBBER: Who discovered rubber? The Indians of Central and South America were the first to utilize rubber’s unique properties. Christopher Columbus watched them play a game called “Tlachtlic,” a vigorous cross between basketball and football, with the object of directing a rubber ball through a stone ring. What was the first practical use of rubber? In England, Joseph Priestley, best known for his discovery of oxygen, noted that pencil marks could be “rubbed out” by the substance. From this early use, rubber derived its name. What discovery marked the beginning of modern rubber technology? Prior to 1839, the properties of rubber were dictated by the surrounding temperature. During the hot summer, rubber was sticky and malleable, while it became hard and brittle in the colder months. This was finally remedied by the discovery of the process of vulcanization. A mixture of rubber, white lead and sulphur was dropped accidentally upon a hot stove. When it was removed, the material was no longer affected by temperature. Despite stretching, it
  2. 2. always returned to its original shape. This process of vulcanization made it possible to use rubber in raincoats, overshoes, and eventually many other products, including tires. THE TWO TYPES OF RUBBER What are the two types of rubber? The two types of rubber in common use today are natural and synthetic. Natural rubber comes from the rubber tree (Hevea brasiliensis). When a tree matures at the age of six or seven years, the latex is collected from a diagonal incision in the tree trunk. The tapping process does not affect the health of the tree and the tree wound later heals itself. Synthetic rubber is made by man from petrochemical feedstocks. Crude oil is the principal raw material. What is natural rubber? Natural rubber (abbreviated to NR) primarily comprises polyisoprene and is harvested from the milky white latex of a number of species of plants which flourish in the tropics, above all from the Spurge family (Euphorbiaceae). The rubber tree (Hevea brasiliensis) has achieved considerable commercial importance. The tree is native to the Amazon region and is now cultivated in virtually all tropical regions of South America, Africa and Asia. 90% of the world's production of natural rubber is harvested from the rubber tree. A diagonal incision is made in the bark, allowing the latex to exude. The latex has approximately the following composition: Constituents Percentage Water 55...70 Rubber 30...40 Resins 1.5...2 Protein 1.5...3 Ash 0.5...1 Sugar 1...2 The latex, which is rich in rubber, can be preserved by adding ammonia and for special purposes it can be transported to the countries in which it is processed as latex concentrate in liquid form. This is done in barrels or in tank containers. It is far more common to filter the harvested latex, dilute it with water and then to cause it to coagulate using substances such as acetic acid or formic acid or by means of electrophoresis. This separates the raw natural rubber from the water, forming a solid mass (coagulum) that is then further processed. Coagulation can also take place in the form of auto-coagulation on the tapping panel (tree
  3. 3. lace) and the collection cups (shell scrap and cup lumps). Such coagulum has a greater degree of contamination, and is hence used in the natural rubber grades which have less stringent requirements with respect to contamination. Where is natural rubber produced? Today more than 90% of the natural rubber supply comes from Southeast Asia. As rubber trees require a hot, damp climate, they grow only in the “Rubber Belt,” an equatorial zone that stretches around the world. In 1876, the English, in recognition of the difficulties of securing quality rubber from the jungle, hit upon the idea of growing rubber on plantations. From their efforts, the cultivated rubber tree plantations of Southeast Asia and Africa have developed. Does the industry utilize more natural or synthetic rubber in its manufacturing process? Approximately 70% of all rubber used is synthetic. How many chemical types of rubber are there? There is only one chemical type of natural rubber. However, there are approximately twenty different chemical types of synthetic rubber, and within each type there are many distinguishable grades. The different types of rubber, each with its own properties and advantages, allow industry to choose the rubber that most clearly meets the demands of an intended use. Processing of Natural Rubber
  4. 4. Processing of natural rubber involves the addition of a dilute acid such as formic acid. The coagulated rubber is then rolled to remove excess water. Then a final rolling is performed using a textured roller and the resultant rubber sheet is dried. Following this, the rubber is ready for export of further processing. This type of natural rubber accounts for about 90% of natural rubber production. Natural rubber is used in a pure form in some applications. In this case, the latex tapped from trees is concentrated using centriguges, removing water and proteinaceous materials. It is then preserved using a chemical such as ammonia.

×