Editing Natural rubber (section)

==Production==
{{More citations needed section|date=March 2019}}
[[File:Rubber trees in Kerala, India.jpg|thumb|Rubber is generally cultivated in large plantations. The image shows a coconut shell used in collecting latex, in plantations in [[Kerala]], India.]]
[[File:Natural rubber.jpg|thumb|Sheets of natural rubber]]

More than 28 million tons of rubber were produced in 2017, of which approximately 47% was natural. Since the bulk is synthetic, which is derived from petroleum, the price of natural rubber is determined, to a large extent, by the prevailing global price of crude oil.<ref>{{cite web |url=http://en.wlxrubber.com/news_detail/newsId=daa867c8-3134-477a-a1aa-4db921ff538f&comp_stats=comp-FrontNews_ranking01-1264986203356.html |title=Overview of the Causes of Natural Rubber Price Volatility |publisher=En.wlxrubber.com |date=2010-02-01 |access-date=2013-03-21  |archive-url=https://web.archive.org/web/20130526213107/http://en.wlxrubber.com/news_detail/newsId%3Ddaa867c8-3134-477a-a1aa-4db921ff538f%26comp_stats%3Dcomp-FrontNews_ranking01-1264986203356.html |archive-date=26 May 2013}}</ref><ref>{{cite web |url=http://www.rubberstudy.com/documents/WebSiteData_Dec2018.pdf |title=Statistical Summary of World Rubber Situation |publisher=International Rubber Study Group |date=December 2018 |access-date=5 February 2019 |url-status=live |archive-url=https://web.archive.org/web/20190205201255/http://www.rubberstudy.com/documents/WebSiteData_Dec2018.pdf |archive-date=5 February 2019}}</ref> Asia was the main source of natural rubber, accounting for about 90% of output in 2021.<ref>{{Cite web |title=Natural rubber leading producers worldwide 2021 |url=https://www.statista.com/statistics/275397/caoutchouc-production-in-leading-countries/ |access-date=2023-02-18 |website=Statista |language=en}}</ref> The three largest producers, [[Thailand]], Indonesia,<ref>{{cite web |last=Listiyorini |first=Eko |url=https://www.bloomberg.com/news/2010-12-16/rubber-exports-from-indonesia-may-grow-6-8-next-year-update1-.html |title=Rubber Exports From Indonesia May Grow 6%–8% Next Year |publisher=bloomberg.com |date=2010-12-16 |access-date=2013-03-21  |archive-url=https://web.archive.org/web/20121104074312/http://www.bloomberg.com/news/2010-12-16/rubber-exports-from-indonesia-may-grow-6-8-next-year-update1-.html |archive-date=4 November 2012}}</ref> and Malaysia, together account for around 72% of all natural rubber production.{{When|date=April 2024}}{{Citation needed|date=April 2024}}  Natural rubber is not cultivated widely in its native continent of South America because of the South American leaf [[blight]], and other natural predators there.

=== Cultivation ===
Rubber latex is extracted from rubber trees. The economic life of rubber trees in plantations is around 32 years, with up to 7 years being an immature phase and about 25 years of productive phase.

The soil requirement is well-drained, weathered soil consisting of [[laterite]], lateritic types, sedimentary types, nonlateritic red or [[alluvium|alluvial]] soils.

The climatic conditions for optimum growth of rubber trees are:
* Rainfall of around {{Convert|250|cm}} evenly distributed without any marked dry season and with at least 100 rainy days per year
* Temperature range of about {{convert|20 to 34|°C|°F}}, with a monthly mean of {{convert|25 to 28|°C|°F}}
* Atmospheric humidity of around 80%
* About 2,000 hours sunshine per year at the rate of six hours per day throughout the year
* Absence of strong winds

Many high-yielding clones have been developed for commercial planting. These clones yield more than {{convert |2,000|kg/ha|lb/acre}} of dry rubber per year, under ideal conditions.

Rubber production has been linked to deforestation. Rubber therefore is one of seven commodities included in the 2023 [[EU Regulation on Deforestation-free products]] (EUDR), which aims to guarantee that the products [[European Union]] (EU) citizens consume do not contribute to deforestation or [[forest degradation]] worldwide.<ref name="eudef">{{cite web|url=https://environment.ec.europa.eu/topics/forests/deforestation/regulation-deforestation-free-products_en|work=[[European Union]]|access-date=24 July 2024|title=Regulation on Deforestation-free products}}</ref>

=== Collection ===
{{main|Rubber tapping}}
[[File:Vintage tobacco card, Tapping a Rubber Tree, India, Products of the World series, Player's Cigarettes, 1909.jpg|left|upright|thumb|Vintage tobacco card, Tapping a Rubber Tree, India, Products of the World series, Player's Cigarettes, 1909]]
In places such as Kerala and Sri Lanka, where coconuts are in abundance, the half shell of coconut was used as the latex collection container. Glazed pottery or aluminium or plastic cups became more common in [[Kerala India|Kerala-India]] and other countries. The cups are supported by a wire that encircles the tree. This wire incorporates a spring so it can stretch as the tree grows. The latex is led into the cup by a [[Galvanization|galvanised]] "spout" knocked into the bark. [[Rubber tapping]] normally takes place early in the morning, when the internal pressure of the tree is highest. A good tapper can tap a tree every 20 seconds on a standard half-spiral system, and a common daily "task" size is between 450 and 650 trees. Trees are usually tapped on alternate or third days, although many variations in timing, length and number of cuts are used. "Tappers would make a slash in the bark with a small hatchet. These slanting cuts allowed latex to flow from ducts located on the exterior or the inner layer of bark ([[cambium]]) of the tree. Since the cambium controls the growth of the tree, growth stops if it is cut. Thus, rubber tapping demanded accuracy, so that the incisions would not be too many given the size of the tree, or too deep, which could stunt its growth or kill it."<ref>{{cite book |title=Encyclopedia of American Indian contributions to the world 15,000 years of inventions and innovations |last=Keoke |first=Emory |publisher=Checkmark Books |year=2003 |page=156}}</ref>

[[File:Ceylon rubber.jpg|thumb|upright|A woman in [[Sri Lanka]] harvesting rubber, {{Circa|1920}}]]
It is usual to tap a panel at least twice, sometimes three times, during the tree's life. The economic life of the tree depends on how well the tapping is carried out, as the critical factor is bark consumption. A standard in Malaysia for alternate daily tapping is 25&nbsp;cm (vertical) bark consumption per year. The latex-containing tubes in the bark ascend in a spiral to the right. For this reason, tapping cuts usually ascend to the left to cut more tubes. The trees drip latex for about four hours, stopping as latex coagulates naturally on the tapping cut, thus blocking the latex tubes in the bark. Tappers usually rest and have a meal after finishing their tapping work and then start collecting the liquid "field latex" at about midday.

====Field coagula====
[[File:MixedFieldCoagula.jpg|thumb|left|Mixed field coagula]]

The four types of field coagula are "cuplump", "treelace", "smallholders' lump", and "earth scrap". Each has significantly different properties.<ref>This section has been copied almost verbatim from the [[public domain]] UN [[Food and Agriculture Organization]] (FAO), ecoport.com article: {{cite web |url=http://ecoport.org/ep?SearchType=earticleView&earticleId=644&page=4363 |title=Processing of Natural Rubber, Manufacture of Latex-Grade Crepe Rubber |first1=John |last1=Cecil |first2=Peter |last2=Mitchell |first3=Per |last3=Diemer |first4=Peter |last4=Griffee |publisher=FAO, Agricultural and Food Engineering Technologies Service |work=ecoport.org |date=2013 |access-date=19 March 2013}}</ref> Some trees continue to drip after the collection leading to a small amount of "cup lump" that is collected at the next tapping. The latex that coagulates on the cut is also collected as "tree lace". Tree lace and cup lump together account for 10%–20% of the dry rubber produced. Latex that drips onto the ground, "earth scrap", is also collected periodically for processing of low-grade product.

===== Cup lump =====
[[File:MyanmarRubber1.jpg|thumb|Cup lump rubber coagula in a [[Myanmar]] road stall]]

Cup lump is the coagulated material found in the collection cup when the tapper next visits the tree to tap it again. It arises from latex clinging to the walls of the cup after the latex was last poured into the bucket, and from late-dripping latex exuded before the latex-carrying vessels of the tree become blocked. It is of higher purity and of greater value than the other three types.

'Cup lumps' can also be used to describe a completely different type of coagulate that has collected in smallholder plantations over a period of 1–2 weeks. After tapping all of the trees, the tapper will return to each tree and stir in some type of acid, which allows the newly harvested latex to mix with the previously coagulated material. The rubber/acid mixture is what gives rubber plantations, markets, and factories a strong odor.

===== Tree lace =====
Tree lace is the coagulum strip that the tapper peels off the previous cut before making a new cut. It usually has higher copper and manganese contents than cup lump. Both copper and manganese are pro-oxidants and can damage the physical properties of the dry rubber.

===== Smallholders' lump =====
Smallholders' lump is produced by smallholders, who collect rubber from trees far from the nearest factory. Many Indonesian smallholders, who farm paddies in remote areas, tap dispersed trees on their way to work in the paddy fields and collect the latex (or the coagulated latex) on their way home. As it is often impossible to preserve the latex sufficiently to get it to a factory that processes latex in time for it to be used to make high quality products, and as the latex would anyway have coagulated by the time it reached the factory, the smallholder will coagulate it by any means available, in any container available. Some smallholders use small containers, buckets etc., but often the latex is coagulated in holes in the ground, which are usually lined with plastic sheeting. Acidic materials and fermented fruit juices are used to coagulate the latex&nbsp;– a form of assisted biological coagulation. Little care is taken to exclude twigs, leaves, and even bark from the lumps that are formed, which may also include tree lace.

===== Earth scrap =====
Earth scrap is material that gathers around the base of the tree. It arises from latex overflowing from the cut and running down the bark, from rain flooding a collection cup containing latex, and from spillage from tappers' buckets during collection. It contains soil and other contaminants, and has variable rubber content, depending on the amount of contaminants. Earth scrap is collected by field workers two or three times a year and may be cleaned in a scrap-washer to recover the rubber, or sold to a contractor who cleans it and recovers the rubber. It is of low quality.

=== Processing ===
[[File:RemovingCoagulumFromCoagulatingTroughs.jpg|thumb|Removing coagulum from coagulating troughs]]

Latex coagulates in the cups if kept for long and must be collected before this happens. The collected latex, "field latex", is transferred into coagulation tanks for the preparation of dry rubber or transferred into air-tight containers with sieving for ammoniation. Ammoniation, invented by patent lawyer and vice-president of the [[United States Rubber Company]] Ernest Hopkinson around 1920, preserves the latex in a colloidal state for longer periods of time. Latex is generally processed into either latex concentrate for manufacture of dipped goods or coagulated under controlled, clean conditions using formic acid. The coagulated latex can then be processed into the higher-grade, technically specified block rubbers such as SVR 3L or SVR CV or used to produce Ribbed Smoke Sheet grades. Naturally coagulated rubber (cup lump) is used in the manufacture of TSR10 and TSR20 grade rubbers. Processing for these grades is a size reduction and cleaning process to remove contamination and prepare the material for the final stage of drying.<ref>{{cite book |title=Basic Rubber Testing |url={{google books |plainurl=y |id=VQVAHZyHyPAC |page=6}} |publisher=ASTM International |pages=6– |id=GGKEY:8BT2U3TQN7G}}</ref>

The dried material is then baled and palletized for storage and shipment.

===Molecular structure===
Rubber is a natural polymer of [[isoprene]] (polyisoprene), and an [[elastomer]] (a stretchy polymer). Polymers are simply chains of molecules that can be linked together. Rubber is one of the few naturally occurring polymers and prized for its high stretch ratio, resilience, and water-proof properties. Other examples of natural polymers include [[Tortoiseshell|tortoise shell]], [[amber]], and [[animal horn]].<ref>{{Cite web |date=2016-07-18 |title=Science of Plastics |url=https://www.sciencehistory.org/science-of-plastics |access-date=2023-02-18 |website=Science History Institute |language=en}}</ref> When harvested, latex rubber takes the form of latex, an opaque, white, milky suspension of rubber particles in water. It is then transformed through industrial processes to the solid form widely seen in manufactured goods.

=== Vulcanized rubber ===
{{Unreferenced section|date=April 2018}}
{{Main|Sulfur vulcanization}}
[[File:Torn latex rubber dry suit wrist seal P8180011.jpg|thumb|Torn latex rubber dry suit wrist seal]]

Natural rubber is reactive and vulnerable to oxidization, but it can be stabilized through a heating process called vulcanization. Vulcanization is a process by which the rubber is heated and [[sulfur]], [[peroxide]], or [[bisphenol]] are added to improve resistance and [[elasticity (physics)|elasticity]] and to prevent it from oxidizing. [[Carbon black]], which can be derived from a petroleum refinery or other natural incineration processes, is sometimes used as an additive to rubber to improve its strength, especially in vehicle tires.<ref>{{Cite journal |last1=Schuster |first1=Jens |last2=Lutz |first2=Johannes |last3=Shaik |first3=Yousuf Pasha |last4=Yadavalli |first4=Venkat Reddy |date=2022-10-01 |title=Recycling of fluoro-carbon-elastomers – A review |journal=Advanced Industrial and Engineering Polymer Research |series=Recycling of Rubbers |language=en |volume=5 |issue=4 |pages=248–254 |doi=10.1016/j.aiepr.2022.08.002 |issn=2542-5048 |doi-access=free |s2cid=251658624}}</ref><ref>{{Cite journal |last1=Asaro |first1=Lucia |last2=Gratton |first2=Michel |last3=Seghar |first3=Saïd |last4=Aït Hocine |first4=Nourredine |date=2018-06-01 |title=Recycling of rubber wastes by devulcanization |journal=Resources, Conservation and Recycling |language=en |volume=133 |pages=250–262 |doi=10.1016/j.resconrec.2018.02.016 |bibcode=2018RCR...133..250A |issn=0921-3449 |s2cid=115671283}}</ref>

During vulcanization, rubber's polyisoprene molecules (long chains of isoprene) are heated and cross-linked with molecular bonds to sulfur, forming a 3-D matrix. The optimal percentage of sulfur is approximately 10%. In this form, the polyisoprene molecules orientation is still random but they become aligned when the rubber is stretched. This sulfur vulcanization makes the rubber stronger and more rigid, but still very elastic.<ref>{{Cite journal |last1=Ducháček |first1=Vratislav |last2=Kuta |first2=Antonín |date=October 1986 |title=Long-time sulfenamide-accelerated sulfur vulcanization of natural rubber/chlorobutyl rubber compounds |journal=Journal of Applied Polymer Science |volume=32 |issue=5 |pages=4849–4855 |doi=10.1002/app.1986.070320507 |issn=0021-8995}}</ref> And through the vulcanization process, the sulfur and latex are meant to be totally used up in individual form.

=== Transportation ===
Natural rubber latex is shipped from factories in [[Southeast Asia]], [[South America]], and [[West Africa|West]] and [[Central Africa]] to destinations around the world. As the cost of natural rubber has risen significantly and rubber products are dense, the shipping methods offering the lowest cost per unit weight are preferred. Depending on destination, warehouse availability, and transportation conditions, some methods are preferred by certain buyers. In international trade, latex rubber is mostly shipped in 20-foot ocean containers. Inside the container, smaller containers are used to store the latex.<ref>[https://web.archive.org/web/20090404081944/http://www.aalatex.com/content/comments.asp?id=193 Transportation of Natural Rubber] – Industry Source</ref>