Editing Natural rubber (section)

==Properties==
[[File:Latex being collected from a tapped rubber tree.jpg|thumb|Rubber latex]]
Rubber exhibits unique physical and chemical properties. Rubber's stress–strain behavior exhibits the [[Mullins effect]] and the [[Payne effect]] and is often modeled as [[hyperelastic material|hyperelastic]]. Rubber [[strain crystallization|strain crystallizes]]. Because there are weakened [[allyl]]ic C–H bonds in each [[repeat unit]], natural rubber is susceptible to [[vulcanisation]] as well as being sensitive to [[ozone cracking]]. The two main [[solvent]]s for rubber are [[turpentine]] and [[naphtha]] (petroleum). Because rubber does not dissolve easily, the material is finely divided by shredding prior to its immersion. An [[ammonia solution]] can be used to prevent the [[flocculation|coagulation]] of raw latex. Rubber begins to melt at approximately {{Convert|180|C}}.

===Elasticity===
{{More citations needed section|date=August 2015}}

{{Main|Rubber elasticity}}
[[File:Koh Chang, Thailand, Rubber tapping, Latex.jpg|thumb|Rubber latex elasticity]]
On a microscopic scale, relaxed rubber is a disorganized cluster of erratically changing wrinkled chains. In stretched rubber, the chains are almost linear. The restoring force is due to the preponderance of wrinkled conformations over more linear ones. For the quantitative treatment see [[ideal chain]], for more examples see [[entropic force]].

Cooling below the [[glass transition temperature]] permits local conformational changes but a reordering is practically impossible because of the larger [[activation energy|energy barrier]] for the concerted movement of longer chains. "Frozen" rubber's elasticity is low and [[strain (materials science)|strain]] results from small changes of [[chemical bond|bond]] lengths and angles: this caused the [[Challenger disaster|''Challenger'' disaster]], when the American [[Space Shuttle]]'s flattened [[o-ring]]s failed to relax to fill a widening gap.<ref>{{cite web |title=Casing Joint Design |work= Report – Investigation of the Challenger Accident |publisher=US Government Printing Office |url=http://www.gpo.gov/fdsys/pkg/GPO-CRPT-99hrpt1016/pdf/CHRG-101shrg1087-2.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.gpo.gov/fdsys/pkg/GPO-CRPT-99hrpt1016/pdf/CHRG-101shrg1087-2.pdf |archive-date=2022-10-09 |url-status=live |access-date=29 August 2015}}</ref> The glass transition is fast and reversible: the force resumes on heating.

The parallel chains of stretched rubber are susceptible to crystallization. This takes some time because turns of twisted chains have to move out of the way of the growing [[crystallite]]s. Crystallization has occurred, for example, when, after days, an inflated toy balloon is found withered at a relatively large remaining volume. Where it is touched, it shrinks because the temperature of the hand is enough to melt the crystals.

[[Vulcanization]] of rubber creates [[disulfide|di-]] and [[polysulfide]] bonds between chains, which limits the [[degrees of freedom (mechanics)|degrees of freedom]] and results in chains that tighten more quickly for a given strain, thereby increasing the elastic force constant and making the rubber harder and less extensible.

===Malodour===
Raw rubber storage depots and rubber processing can produce malodour that is serious enough to become a source of complaints and protest to those living in the vicinity.<ref>{{cite journal |url=https://pdfs.semanticscholar.org/b74a/c9bfbe91a9cc5625c7dd980bc1de3ec8a0de.pdf |title=Determination of Volatile Fatty Acids from Raw Natural Rubber Drying Activity by Thermal Desorption-Gas Chromatography |journal=Chemical Engineering Transactions |year=2012 |volume=30 |s2cid=7469231 |doi=10.3303/CET1230030 |access-date=14 December 2017  |archive-url=https://web.archive.org/web/20171215053437/https://pdfs.semanticscholar.org/b74a/c9bfbe91a9cc5625c7dd980bc1de3ec8a0de.pdf |archive-date=15 December 2017|author1=Nur Fadhilah Idris |author2=Nor Hidayaty Kamarulzaman |author3=Zairossani Mohd Nor }}</ref> Microbial impurities originate during the processing of block rubber. These impurities break down during storage or thermal degradation and produce volatile organic compounds. Examination of these compounds using [[gas chromatography]]/[[mass spectrometry]] (GC/MS) and gas chromatography (GC) indicates that they contain sulfur, ammonia, [[alkene]]s, [[ketone]]s, [[ester]]s, [[hydrogen sulfide]], nitrogen, and low-molecular-weight fatty acids (C2–C5).<ref>{{cite journal |title=Determination of Chemical Components that Cause Mal-Odor from Natural Rubber |first1=Vipavee P. |last1=Hoven |first2=Kesinee |last2=Rattanakaran |first3=Yasuyuki |last3=Tanaka |date=1 November 2003 |journal=Rubber Chemistry and Technology |volume=76 |issue=5 |pages=1128–1144 |doi=10.5254/1.3547792}}</ref><ref name="aidic.it">{{cite web |url=http://www.aidic.it/cet/12/30/021.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.aidic.it/cet/12/30/021.pdf |archive-date=2022-10-09 |url-status=live |title=Info |website=aidic.it}}</ref> When latex concentrate is produced from rubber, [[sulfuric acid]] is used for coagulation. This produces malodourous hydrogen sulfide.<ref name="aidic.it" /> The industry can mitigate these bad odours with [[scrubber|scrubber systems]].<ref name="aidic.it" />