Polymer such as rubber, suberin, melanin and lignin. 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-linking and endcapping. Especially in the production of polymers the gas separation by membranes has acquired increasing
Flowers of sulfur Flowers of sulfur Flowers of sulfur (older British spelling flowers of sulphur) is a very fine, bright yellow sulfur powder that is produced by sublimation and deposition. It is known as ' by apothecaries and in older scientific works. Natural sulfur was also known as brimstone, hence the alternative name flowers of brimstone. Flowers of sulfur were traditionally produced by subliming naturally occurring sulfur, known as "sulphur vivum". Impurities and moisture could cause acid residue in the product, so it was often washed, the result being known as "washed flowers of sulfur" (in Latin, "flores sulphuris loti"). Flowers of sulfur