Hydroxypropyl cellulose

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Structural formula
Hydroxypropyl Cellulose.png
General
Surname Hydroxypropyl cellulose
other names
  • HPC
  • E  463
CAS number 9004-64-2
Monomers / partial structures Hydroxypropyl cellobiose
Brief description

yellowish-white powder

properties
Physical state

firmly

solubility

soluble in water (temperature <48 ° C) and organic solvents such as methanol , ethanol or propylene glycol

safety instructions
GHS labeling of hazardous substances
no GHS pictograms
H and P phrases H: no H-phrases
P: no P-phrases
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Hydroxypropyl cellulose ( HPC ) is a collective term for cellulose ethers ( derivatives of cellulose ) in which some of the hydroxyl groups are linked as ethers with hydroxypropyl groups. In Europe, hydroxypropyl cellulose is approved as a food additive under the E number E 463 .

Manufacturing

In the production of hydroxypropyl cellulose, some of the hydroxyl groups in cellulose are first reacted with alkali hydroxide in a polymer-analogous reaction and then converted into hydroxypropyl groups with propylene oxide . In addition to the OH groups of the cellulose, the OH groups of the propyl groups are also converted, so that polyether chains are also formed. In this way, the degree of substitution can rise above what is actually theoretically possible. The original cellulose structure is retained during the conversion.

Properties / use

Hydroxypropyl cellulose is soluble in both water and organic solvents. In aqueous solutions, the viscosity is greatly increased and the surface tension is reduced due to the surface-active properties, the increase in viscosity clearly depending on the molar mass of the HPC used. These solutions are pH stable - the viscosity does not change between pH 2 and 11. HPC is soluble in cold to lukewarm water. When heated above the critical solution temperature of around 48 ° C, the solubility decreases sharply and an initially clear solution becomes cloudy and, depending on the concentration, flocculation can occur. This process is reversible and the HPC dissolves again when it cools down. HPC is therefore one of the thermoresponsive polymers . This effect, which also occurs with polyethylene glycols and polypropylene glycols , can be explained by the fact that, from a certain temperature, the hydrogen bonds between the PEG chains and water break and the polymer becomes more hydrophobic. The addition of ethanol or methanol increases the flocculation temperature; the addition of salts reduces the solubility (salting out). HPC is thermoplastic and can be processed like thermoplastics.

HPC is used, among other things, as a pharmaceutical excipient , as a binder for ceramic compounds, for coatings and adhesives, in cosmetic articles, in printing inks and in polymerization technology (production of suspension polyvinyl chloride). It is used in food as a stabilizer, protective layer and gloss coating.

Individual evidence

  1. Entry on E 463: Hydroxypropyl cellulose in the European database for food additives, accessed on August 6, 2020.
  2. a b c Entry on hydroxypropyl celluloses. In: Römpp Online . Georg Thieme Verlag, accessed on November 13, 2016.
  3. a b c Tanja Wüstenberg: Cellulose and cellulose derivatives. Behr's Verlag DE, 2013, ISBN 978-3-95468-188-4 , pp. 225-238 ( limited preview in the Google book search).
  4. a b data sheet hydroxypropyl cellulose, average Mw ~ 80,000 from Sigma-Aldrich , accessed on November 14, 2016 ( PDF ).
  5. a b c technical data sheet hydroxypropyl cellulose Retrieved on November 16, 2016.
  6. EA Bekturov, Z. Kh Bakauova. Synthetic Water-Soluble Polymers in Solution . Huethig & Wepf, Basel Heidelberg New York 1986, ISBN 3-85739-110-3 , p. 139 .