Hydroxypropyl cellulose
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'''Hydroxypropyl cellulose (HPC)''' (cellulose, 2-hydroxypropyl ether) is a derivative of [[cellulose]] with both water solubility and organic solubility.
==Chemistry==
Hydroxypropyl cellulose is an [[ether of cellulose]] where some of the hydroxyl groups of the cellulose have been hydroxypropylated forming -OCH<sub>2</sub>CH(OH)CH<sub>3</sub> groups. The average number of hydroxyl groups in the [[glucose]] ring substituted is referred to as the [[degree of substitution (DS).]] Complete substitution would provide a DS of 3.0. Because the hydroxypropyl group added contains a hydroxyl group, this can also be etherified during preparation of hydroxypropyl cellulose. When this occurs, the number of moles of hydroxypropyl groups per glucose ring ([[moles of substitution]] - MS) can be higher than 3.
Because of the fact that cellulose is very crystalline HPC must have an MS about 4 in order to reach a good solubility in water. HPC has a combination of [[hydrophobic]] and [[hydrophilic]] groups, so it has a [[Lower Critical Solution Temperature]] (LCST) at 45°C: under the LCST HPC is readily soluble in water, over 45°C HPC is not soluble.
An interesting property of HPC is the fact that forms [[liquid crystals]] and many [[mesophases]] according to its
concentration in water. Such mesophases include [[isotropic]], [[anisotropic]], [[nematic]] and [[cholesteric]] ([[cholesteric liquid crystal]]).
The last one gives many colors, like violet, green and red.
The [[CAS registry number]] of hydroxypropyl cellulose is 9004-64-2.
==Uses==
Lacrisert, manufactured by Aton Pharma, Inc., is a formulation of it used for artificial [[tears]]. It is used in syndromes of insufficient tear production ([[keratoconjunctivitis sicca]]), recurrent [[cornea]]l [[ulcer|erosions]], decreased corneal sensitivity, exposure and neuroparalytic [[keratitis]], and as a lubricant for artificial [[eye]]s.
As a [[food additive]], hydroxypropyl cellulose is used as a [[thickener]] and as an [[emulsion]] [[Food additive#Categories|stabiliser]] with [[E number]] E463.
==See also==
* [[Carboxymethyl cellulose]]
* [[Methylcellulose]]
[[Category:Excipients]]
[[Category:Food additives]]
[[Category:Cellulose]]
[[hu:Hidroxipropil-cellulóz]]