Editing Polymer (section)

===Modification of natural polymers===
Naturally occurring polymers such as [[cotton]], [[starch]], and rubber were familiar materials for years before synthetic polymers such as [[polyethene]] and [[perspex]] appeared on the market. Many commercially important polymers are synthesized by chemical modification of naturally occurring polymers. Prominent examples include the reaction of [[nitric acid]] and [[cellulose]] to form [[nitrocellulose]] and the formation of [[vulcanized rubber]] by heating natural rubber in the presence of [[sulfur]]. Ways in which polymers can be modified include [[oxidation]], [[cross-link]]ing, and [[endcapping|end-capping]].

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Especially in the production of polymers the gas separation by membranes has acquired increasing importance in the [[petrochemical industry]] and is now a relatively well-established unit operation.
The process of polymer [[degassing]] is necessary to suit polymer for extrusion and pelletizing, increasing safety, environmental, and product quality aspects. Nitrogen is generally used for this purpose, resulting in a vent gas primarily composed of monomers and nitrogen.<ref name="Improvement Economics Program">{{cite book|url=http://www.slideshare.net/intratec/membranes-on-polyolefins-plants-vent-recovery |title= Membranes on Polyolefins Plants Vent Recovery, Improvement Economics Program|publisher=Intratec|isbn= 978-0615678917|url-status=dead |archive-url= https://web.archive.org/web/20130513040249/http://www.slideshare.net/intratec/membranes-on-polyolefins-plants-vent-recovery|archive-date= 2013-05-13|date= 2012-08-02}}</ref>
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