Views: 251 Author: Site Editor Publish Time: 2023-07-24 Origin: Site
Polyvinyl Alcohol (PVA) is made from vinyl acetate by polymerisation and alcoholysis, it is a white, stable, non-toxic, water-soluble polymer, powder, flake or flocculent solid.
Polyvinyl alcohol contains many alcohol groups, polar, and can form hydrogen bonds with water, so it can be soluble in polar water, but also soluble in hot hydroxyl-containing solvents such as glycerol, phenol, etc., insoluble in methanol, benzene, acetone, gasoline and other general organic solvents.
A. Solubility: polyvinyl alcohol powder can be dissolved in water. Alcohol solubility less than 95% of polyvinyl alcohol (PVA) can be dissolved in water at room temperature, alcohol solubility greater than 99.5% of polyvinyl alcohol can only be dissolved in hot water above 95 ℃.
B. Thermal stability: polyvinyl alcohol will soften when heated, there is no significant change below 40 ℃, the glass transition temperature of 75 ~ 85 ℃, heated to more than 100 ℃ slowly discoloured, brittle. 160 ℃ or more, a long time to heat will be gradually coloured, dehydrated etherification, loss of solubility. 220 ℃ or more decomposition occurs, generating water, acetic acid, acetaldehyde and butylene aldehyde. More than 250 ℃ into a polymer containing conjugated double bonds.
C, chemical resistance: PVA is almost unaffected by weak acids, weak bases or organic solvents, high oil resistance.
D, storage stability: PVA is a low-viscosity polymer, its aqueous solution at room temperature is very stable, the aqueous solution will not deteriorate in the storage process.
E, film-forming properties: due to the high adhesion between the PVA molecules, PVA is easy to form a film, the formation of the film is colourless and transparent, with good mechanical strength, the surface is smooth and not sticky, good solubility. The molecular film has good light transmittance, high moisture permeability, non-electricity, non-absorbent dust, and good printability.
PVA can be regarded as a linear polymer with secondary hydroxyl groups. The hydroxyl group in the molecule is highly reactive and is able to carry out the typical chemical reactions of lower alcohols, such as esterification, etherification, acetalisation, etc. It can also react with many inorganic or organic compounds.
Polyvinyl alcohol (PVA) aqueous solution has good film-forming and emulsifying properties. It can be used as a protective colloid for polymer emulsification and suspension polymerisation.
Polyvinyl alcohol can be used in textile pulp, vinyl fibre, paper coating agent, building materials, adhesives, PVA film, PVB raw materials, food and medicine, etc. PVA can also be used as a soil conditioner, polymerisation suspending agent and emulsifying agent, quenching agent and so on. In addition, as people continue to develop and improve the performance of PVA, its use is still expanding.
