Iodine in industry
Photography
Film used in photography represents one of the oldest industrial uses of iodine. All forms of non-digital photography that still involve films, are based on the light-sensitive properties of silver halide crystals, chemical compounds of silver and halogens. Photographic films contain those crystals within a thin layer of gel, forming a photo-sensitive emulsion where, with light incidence, image is recorded. Also, this chemical process applies to radiographic films for X-ray procedures.
Cesium iodide has the ability to absorb X-rays, gamma and particle radiation, emitting visible light. This so-called scintillation effect is used in medical diagnostics, exploration for natural resources and in nuclear physics research.
LCD Polarizing Films
Liquid crystal displays (LCDs) are widely used in modern visual appliances such as smart phone touch screens or high definition television screens. The display consists of liquid crystals that are activated by electric current. Depending on the activation state of the crystals, they block or allow polarized light to pass through. Polarizing films are used to increase the visibility of the image created on the LCD, by polarizing light so that it has a constant and precisely defined direction.
Iodine containing polarizing films are made by adsorbing iodine onto a stretched polyvinyl alcohol surface.
Chemical Synthesis of Polymers
Iodine and its compounds are very active catalysts for many reactions. One of the principal uses is as catalyst in the production of synthetic rubber or stereospecific polymers, such as polybutadiene rubber and polysoprene polymers. Iodine as a catalyst is also found in the processing of rosins, tall oil, and other wood products, for their conversion to more stable forms.
Iodine plays a significant role in the synthesis of intermediate compounds for the production of polymers. For instance, Iodine pentafluoride (IF5) is widely used in the production of alkyl iodides containing fluoride, valuable intermediates in the synthesis of perfluor-organic compounds. These are used to produce water and oil repellent emulsions for the treatment of textiles and leathers and for fire extinguishing foams.
Organic Compounds
Organic iodine derivatives have wide uses as final or intermediate reagents in numerous organic syntheses to manufacture pharmaceuticals, agrochemicals and dyestuffs, as well as in the synthesis of other specialty organic chemicals.
Nylon
Potassium and cuprous iodides are used as heat stabilising agents in the manufacturing of Nylon. A main use of nylon fibers is in the manufacturing of tires, where heat resistance of the polymer is essential. For example, the tires of a light vehicle while driving can easily reach a temperature near 120°C.
The iodide and the cuprous ions inserted within the nylon polymer net prevent the cracking of the chemical chains. On average, the use of potassium and cuprous iodides allows stabilization up to 170°C.
Colorants and Dyes
Iodine is used in the production of Erythrosine (tetraiodo fluorescein, also named Red #3). Erythrosine is a most efficacious food, drug and cosmetic colorant, providing a deep cherry color.
Other dyes containing iodine, include reds 4′, 5’-diiodo fluorescein, rose bengal and blues from cyanine groups like kriptocyanine, cyanine and pinachrome. Those last are used in printer inks, photographic sensitizers or textile dyes.
Biocides for Industrial Use
Iodine-based alternatives with a lower environmental risk and toxicological profile, have replaced toxic biocides such as pentachlorophenol (PCP) and tributyltinoxide (TBTO). This allows for control of microbial degradation of industrial products. Many diverse applications require preservatives: including cosmetics, paints, adhesives, wood preservation, metalworking fluids, leather processing, inks and starches.
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