Views: 88 Author: Site Editor Publish Time: 2022-09-16 Origin: Site
PVA is obtained by the suspension polymerization of vinyl acetate initiated by free radicals at low temperatures to obtain polyvinyl acetate, and then it is obtained by alkali-catalyzed alcoholysis. Due to the diversity of structure, alcoholysis degree, and polymerization degree, PVA has various properties.
Here is the content list:
l Chemical reactivity
l Thermal stability
PVA is a typical water-soluble polymer, and its molecular chain contains a large number of hydroxyl groups, so it has strong hydrophilicity. The solubility of PVA is largely affected by the degree of polymerization and alcoholysis: the complete alcoholysis type PVA has less acetate content and high crystallinity, and its water solubility is poor due to the strong interaction between polymer chains, such as PVA with an alcoholysis degree above 99% is only soluble in hot water at 90-95 °C. With the decrease of the alcoholysis degree, the solubility of PVA increases; PVA with an alcoholysis degree of 87-89% dissolves in hot and cold water. PVA can dissolve quickly and show the maximum solubility; as the alcoholysis degree further decreases, the proportion of hydrophilic groups in the polymer molecule also decreases, and the solubility of PVA also deteriorates. Below 50% PVA is insoluble in water. In addition to water, PVA is also soluble in ethanolamine, glycerol, formamide, etc.; soluble in glycerol at 120-150 °C; slightly soluble in dimethyl sulfoxide; insoluble in methanol, acetone, benzene, toluene, dichloroethane, tetrakis organic solvents such as carbon chloride, ethylene glycol, ethyl acetate, gasoline, vegetable oil, etc.
PVA has good film-forming properties and can form a transparent, tough, tear-resistant, abrasion-resistant, and relatively soft film. The tensile strength of the film increases with the increase of the degree of polymerization and alcoholysis. The permeability of PVA film to gases (such as H2, N2, O2, etc.) is low.
PVA aqueous solution has good adhesion, so PVA is an excellent organic binder in the application field. In general, the higher the degree of polymerization and alcoholysis, the higher the bond strength of the PVA aqueous solution, whereas the lower the bond strength. PVA has high bonding strength, easy plasticization, and high economic efficiency, so it has been used as a reliable adhesive.
PVA is widely used as an emulsifier or dispersant because of its surface activity, its contact angle with water at room temperature is within 22°-54°, and it can reduce the surface tension of water. PVA with different degrees of polymerization, alcoholysis, and microstructure has different surface activities, among which block type PVA has the highest surface activity and the smallest surface tension.
The hydroxyl group in the PVA molecule is similar to the hydroxyl group of some low-molecular-weight organic compounds and has chemical reactivity such as etherification, esterification, and acetalization of long-chain polyols. Among them, acetalization is the most important chemical reaction property of PVA.
When the PVA powder is heated above 100°C, the appearance begins to change; when it is above 150°C, it quickly changes color and undergoes chemical changes, such as dehydration; when heated to above 200°C, it decomposes. Partial alcoholysis PVA starts to melt when heated to about 190°C, and decomposes at 200°C; complete alcoholysis PVA starts to melt when heated to about 230°C and decomposes at 240°C. PVA thermal cracking experiments show that: the lower the degree of polymerization, the faster the weight loss; the higher the degree of alcoholysis, the shorter the decomposition time.
PVA is an extremely safe polymer, which is non-toxic to the human body, has no side effects, and has good biocompatibility. It is widely used in the fields of food, medicine, cosmetics, and packaging, especially in the medical field, such as PVA water gel is used in artificial joints and ophthalmology, wound dressings; PVA1799 film is used as medicinal film, artificial kidney membrane, etc.
The above is the relevant content about the properties of polyvinyl alcohol, if you are interested in PVA 1599, PVA 0599, PVA2488, PVA2688, PVA1799, Polyvinyl Alcohol Powder, you can contact us, our website is https://www.eastchem. com.cn/.