Application and Properties of Hydroxypropylmethylcellulose HMPC

Plaster is a substrate treatment for the inside of walls, render refers ro the substrate for the outside of walls, it is sometimes also referred to as putty, though in British English putty also refers to a linseed paste that is used in the installation of traditional wooden windows. Plaster or Render is often applied in a maleable putty like format, which helps to achieve to a sealed and smooth finish, prior to final coating. The main function is to fill in defects in the base wall and to microfine the base surface.

[edit] What is Hydroxypropyl Methylcellulose (HPMC)?

Hydroxypropyl methylcellulose (HPMC) is a non-ionic cellulose ether. It is an odourless and tasteless white powder. It is produced from purified cotton or wood pulp by a series of etherification reactions.

[edit] Properties of HPMC

Hydroxypropylmethylcellulose (HPMC) has thermal gelation properties, as its aqueous solution precipitates and gels, and dissolves when cooled. The gelation temperature varies depending on the specification, and its solubility varies with viscosity, the lower the viscosity, the higher the solubility. HPMC is essentially methane-epoxide-modified methyl cellulose and therefore has similar properties to methyl cellulose, being readily soluble in cold water and insoluble in hot water. The solution does not contain an ionic charge and therefore will not react with metal salts or ionic compounds.

HPMC has good dispersability, emulsification, thickening, adhesion, water retention, and glue retention properties and is therefore widely used in pharmaceuticals, petrochemicals, construction, ceramics, textiles, food, daily chemicals, synthetic resins, coatings and other fields, as well as electronic products.

[edit] Application of HPMC in putty powder

Depending on the application, hydroxypropyl methyl cellulose (HPMC) can be classified as construction grade, food grade and medical grade. In construction, HPMC is mainly used in laster (also called putty powder), with varying percentages used in the gypsum mix.

HPMC powder is mainly used as a thickener, water retention agent and lubricant.

• Thickeners: HPMC is added to putty powder to thicken it, enhance its suspension, resist sagging and keep it in a homogeneous solution.
• Water Retainer: HPMC is added to putty powder to keep it moist and to allow the auxiliary grey calcium to act as an underwater agent.
• Lubricant: Hydroxypropyl methylcellulose has a lubricating effect. The use of HPMC in putty powder gives the putty powder a good compatibility, keeps it flat during construction and saves labour.

Hydroxypropylmethylcellulose (HPMC) does not chemically react, except as an auxiliary molecule. Though adding water to the powder causes a chemical reaction, during which a new substance (calcium carbonate) is formed. Because of the formation of this new substance (calcium carbonate) it can't be reused in the same way twice.The main components of grey calcium powder are:Ca(OH)2, CaO and a small amount of CaCO3 mixture.CaO+H2O=Ca(OH)2 - Ca(OH)2+CO2=CaCO3↓+H2O gray calcium in water and air under the action of CO2, the formation of calcium carbonate, and HPMC only water, auxiliary gray calcium better reaction, its own did not participate in any reaction.

The formulation of the putty can vary from one size to another. As a result, the viscosity and dosage of hydroxypropyl methylcellulose (HPMC) vary. In practice, it is recommended to use a lower viscosity HPMC product in winter, which is more conducive to construction. Otherwise, when the temperature is low, the viscosity will increase and this may cause problems for further applications.

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