Polyvinyl alcohol, abbreviated as PVA. Molecular formula: (C₂H₄O)ₙ. It is a high-molecular-weight organic compound obtained by saponification of polyvinyl acetate. Polyvinyl alcohol is a white powder, flake, or flocculent solid with a glass transition temperature of 60–85℃. Containing many alcohol groups, polyvinyl alcohol is polar and can form hydrogen bonds with water, thus it is soluble in polar water; it is also soluble in hot hydroxyl-containing solvents such as glycerol and phenol, but insoluble in common organic solvents such as methanol, benzene, acetone, and gasoline. It is mainly used in the manufacture of polyvinyl acetal, gasoline-resistant pipes, and vinylon fibers; it is also used as a temporary protective film, adhesive for fabrics and leather, binding adhesive, fabric sizing agent, emulsifier, and protective colloid.
Polyvinyl alcohol is a water-soluble polymer obtained by the hydrolysis of polyvinyl acetate, not by monomer polymerization. It is a white, flaky, flocculent, or powdery solid, odorless. The physical properties of polyvinyl alcohol are affected by its chemical structure, degree of hydrolysis, and degree of polymerization. Polyvinyl alcohol (PVA) molecules contain two chemical structures: 1,3-ethylene glycol and 1,2-ethylene glycol, but the dominant structure is 1,3-ethylene glycol, i.e., a "head-tail" structure.
PVA has a relative density (25℃/4℃) of 1.27–1.31 (solid) and 1.02 (10% solution), a melting point of 230℃, and a glass transition temperature of 75–85℃. When heated above 100℃ in air, it slowly discolors and becomes brittle. Heating to 160–170℃ causes dehydration and etherification, resulting in loss of solubility. Decomposition begins at 200℃. Above 250℃, it transforms into a polymer containing conjugated double bonds. Its refractive index is 1.49–1.52, thermal conductivity is 0.2 W/(m·K), specific heat capacity is 1–5 J/(kg·K), and resistivity is (3.1–3.8) × 10⁷ Ω·cm. It is soluble in water, but complete dissolution generally requires heating to 65–75℃. Polyvinyl alcohol (PVA) is insoluble in gasoline, kerosene, vegetable oil, benzene, toluene, dichloroethane, carbon tetrachloride, acetone, ethyl acetate, methanol, and ethylene glycol. It is slightly soluble in dimethyl sulfoxide (DMSO). It is soluble in glycerol at 120–150°C, but gels when cooled to room temperature. To dissolve PVA, the material should be added to room temperature water with stirring first. After even dispersion, the temperature should be increased to accelerate dissolution, preventing clumping and affecting the dissolution rate. A 5% aqueous solution of PVA is very sensitive to borax and boric acid, easily causing gelation. When borax reaches 1% of the solution mass, irreversible gelation occurs. Chromates, dichromates, and permanganates can also gel PVA.
Polyvinyl alcohol (PVA) is a water-soluble compound obtained through alcoholysis. Its molecular backbone contains -CH-CH(OH)- groups. It can be classified into various industrial products based on the degree of polymerization and degree of alcoholysis. Polyvinyl alcohol (PVA) can be classified by degree of polymerization: ultra-high degree of polymerization (molecular weight 250,000–300,000), high degree of polymerization (molecular weight 170,000–220,000), medium degree of polymerization (molecular weight 120,000–150,000), and low degree of polymerization (molecular weight 25,000–35,000).
Based on degree of hydrolysis: PVA can be classified into three types: complete hydrolysis (98–100%), partial hydrolysis (87–89%), and 78% hydrolysis.
High-degree-of-polymerization and high-degree-of-hydrolysis polyvinyl alcohol (PVA) is the main raw material for PVA formaldehyde fiber. As the degree of hydrolysis increases, its solubility in water decreases significantly. In PVA product designations, the degree of polymerization (thousands and hundreds digits) is usually placed first, followed by the degree of hydrolysis. For example, PVA 17-99 indicates a degree of polymerization of 1700 and a degree of hydrolysis of 99%. Generally, increasing the degree of polymerization increases the viscosity of the aqueous solution, improving the strength and solvent resistance of the film after formation, but decreasing water solubility and elongation after film formation.
The viscosity of PVA 17-88 aqueous solution gradually increases over time at room temperature. However, the viscosity at an 8% concentration is absolutely stable and independent of time, which is a special phenomenon. Polyvinyl alcohol has good film-forming properties and is highly resistant to many gases except water vapor and ammonia. It has good light resistance and is unaffected by light exposure. It is flammable in open flame and has a characteristic odor. Aqueous solutions may sometimes become toxic during storage. It is non-toxic and non-irritating to human skin.
It is used as an emulsifying stabilizer in polyvinyl acetate emulsion polymerization. It is used in the manufacture of water-soluble adhesives. It is used as a modifier for starch adhesives. It can also be used to prepare photosensitive adhesives and sealants resistant to benzene solvents. It is also used as a release agent and dispersant. Store in a cool, dry warehouse, protected from moisture and fire.
Polyvinyl alcohol 17-92, abbreviated as PVA 17-92, is a white granular or powdery substance. It is readily soluble in water, with a dissolving temperature of 75-80℃. Other properties are basically the same as PVA 17-88. Used as an emulsifying stabilizer in emulsion polymerization. Used in the manufacture of water-soluble adhesives. Store in a cool, dry warehouse, protected from fire and moisture.
Polyvinyl alcohol 17-99, also known as sizing resin, abbreviated as PVA17-99. White or slightly yellow powder or flocculent solid. Glass transition temperature 85℃, saponification value 3-12 mgKOH/g. Soluble in hot water at 90-95℃, almost insoluble in cold water. Aqueous solutions with a concentration greater than 10% will gel at room temperature, and will thin and regain fluidity at high temperatures. To stabilize viscosity, appropriate amounts of viscosity stabilizers such as sodium thiocyanate, calcium thiocyanate, phenol, and butanol can be added to the solution. PVA17-99 solution is more sensitive to gelation caused by borax than PVA17-88. 0.1% borax by mass will gel a 5% PVA17-99 aqueous solution, while 1% borax is needed to gel the same concentration of PVA17-88.
For polyvinyl alcohol aqueous solutions of the same concentration and degree of alcoholysis, borax gels more readily than boric acid. PVA17-99 is more resistant to solvents such as benzene, chlorinated hydrocarbons, esters, ketones, ethers, and hydrocarbons than PVA17-88. It gradually changes color when heated above 100℃, changes color rapidly above 150℃, and decomposes above 200℃. The color-changing property of polyvinyl alcohol upon heating can be inhibited by adding 0.5%–3% boric acid. It has good light resistance and is unaffected by light exposure. It exhibits chemical reactivity such as esterification, etherification, and acetalization of long-chain polyols. It burns in an open flame and has a characteristic odor. It is non-toxic and does not irritate human skin.
Polyvinyl alcohol 17-99B is mainly used in the manufacture of high-viscosity polyvinyl butyral. It is widely used as a dispersant in sizing agents. Other types of 17-99 are used as emulsion stabilizers in polyvinyl acetate emulsion polymerization, but their effects are not as good as 17-88; generally, 17-99 and 17-88 are mixed. 17-99 is used in the manufacture of polyvinyl formal aqueous solutions (mainly 107 construction adhesive). 17-99 is also used in the preparation of sealants resistant to benzene solvents. Store in a cool, dry warehouse, protected from moisture and fire.
Product Applications:
1. Gray Calcium-Based Putty: Even a very small amount added can significantly improve the cohesive strength, adhesion, and water resistance of the putty coating, reduce the amount of gray calcium powder used, and significantly improve the phenomenon of delamination and scarring during sanding. It improves the surface smoothness of the putty after sanding.
2. For cement-based exterior wall putty: Improves cement setting speed, increases early strength of the putty, provides good film-forming properties, excellent durability, and prevents powdering even when applied thinly.
3. For polishing putty (imitation porcelain paint): Improves surface film-forming properties, resulting in a denser, harder, glossier, and more scrub-resistant coating. Only one kilogram per ton of cement-based putty is needed for noticeable results.
4. For interior wall neutral putty: Adding 6 kilograms of polyvinyl alcohol powder and an appropriate amount of cellulose (hydroxypropyl or carboxymethyl) to one ton of heavy calcium carbonate produces a superior quality putty powder compared to starch-based and 821-based putty powders. This putty has a hardness between that of lime-based and starch-based putty, excellent workability, and superior adhesion, flexibility, sanding smoothness, and durability compared to both. Combining it with gypsum powder and retarding technology yields an even higher-grade, excellent home decoration putty powder. This type of putty powder has a long service life and excellent decorative effect, and will become the future development direction of the putty industry.
5. In instant adhesive powders, it is the main binder. Combined with an appropriate amount of hydroxypropyl methylcellulose and supplemented with suitable thickening and complexing agents, it produces a convenient, environmentally friendly, high-strength adhesive powder that can be mixed with cement gypsum for wet wall leveling and can also be applied alone without powdering.
6. In dry mortars, PVA1788 powder has excellent film-forming properties. When used in combination with cellulose ether water-retaining agents, it improves the flexibility and water retention of various cement mortars and gypsum building materials, increases mortar bonding strength, and effectively prevents peeling, cracking, and hollowing.
Other uses: thin-layer adhesive, flexible adhesive, mineral plaster, cement additive, PVC latex, wet adhesive, office paste, cosmetics, screen printing photosensitive film, cement additive, coated paper coating agent, zinc plate printing photosensitive film, long fiber yarn sizing agent, wet adhesive PVC latex, and oil well cement additive.
Wet-mixed mortar stabilizer, dry-mixed mortar additive, gypsum mortar additive, new type of concrete binder reducing and strengthening agent, cement grinding aid and raw materials!
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