Polyvinyl alcohol, referred to as PVA. Molecular formula: (C2H4O) n. A polymer organic compound made of polyethylene acetate through saponification. Polyvinyl alcohol is a white powdery, flake or flocculent solid with a glass transition temperature of 60-85 ° C. Polyvinyl alcohol contains many alcohol groups, has polarity, and can form hydrogen bonds with water, so it can be soluble in polar water; also soluble in hot hydroxyl solvents such as glycerol, phenol, etc., insoluble in general organic solvents such as methanol, benzene, acetone, gasoline, etc. Mainly used in the manufacture of polyvinyl alcohol acetal, gasoline-resistant pipes and vinylon fibers; also used as an adhesive for temporary protection films, fabrics, leather, etc., a rubber for binding, a sizing agent for fabrics, an emulsifier and a protective colloid, etc.

Polyvinyl alcohol is a water-soluble polymer obtained by hydrolysis of polyvinyl acetate without monomer polymerization, abbreviation. White flaky, flocculent or powdery solid, odorless. The physical properties of polyvinyl alcohol are affected by chemical structure, degree of alcoholysis, and degree of polymerization. There are two chemical structures in polyvinyl alcohol molecules, namely 1, 3 and 1, 2 ethylene glycol structures, but the main structure is 1, 3 ethylene glycol structure, i.e. "head · tail" structure.

Soluble in water, in order to completely dissolve generally need to be heated to 65~ 75 ℃. Insoluble in gasoline, kerosene, vegetable oil, benzene, toluene, dichloroethane, carbon tetrachloride, acetone, ethyl acetate, methanol, ethylene glycol, etc. Slightly soluble in dimethyl sulfoxide. Soluble in glycerol at 120~ l50 ℃. But cold to room temperature to become gelatinized. To dissolve polyvinyl alcohol should first add the material to room temperature water under stirring. After dispersing evenly and then heating up to speed up the dissolution, this can prevent agglomeration and affect the dissolution rate. Polyvinyl alcohol aqueous solution (5%) is very sensitive to borax and boric acid, easy to cause gelation. When borax reaches 1% of the solution mass, irreversible amination will occur. Chromate, dichromate, permanganate can also make polyvinyl alcohol gel.

Polyvinyl alcohol, a water-soluble obtained by alcoholysis, has a molecular backbone containing -CH-CH (OH) -groups, and can be divided into various industrial products according to the degree of polymerization and alcoholysis. According to the degree of polymerization: it can be divided into ultra-high degree of polymerization (molecular weight 25~ 300,000), high degree of polymerization (molecular weight 17~ 220,000), medium degree of polymerization (molecular weight 12~ 150,000) and low degree of polymerization (molecular weight 2.5~ 35,000).

According to the degree of alcoholysis: it can be divided into three types: complete alcoholysis (alcoholysis degree 98~ 100%), partial alcoholysis (alcoholysis degree 87~ 89%) and alcoholysis degree 78%.

Polyvinyl alcohol with high degree of polymerization and alcoholysis is the main raw material of polyvinyl alcohol formaldehyde shrinkage fiber. As the degree of alcoholysis increases, its solubility in water decreases significantly. For polyvinyl alcohol, the thousand or hundred digits of the degree of polymerization are generally placed in the front of the product brand, and the degree of alcoholysis is placed in the back. For example, polyvinyl alcohol 17-99 means that the degree of polymerization is 1700, and the degree of alcoholysis is 99%. Generally speaking, when the degree of polymerization increases, the viscosity of the aqueous solution increases, and the strength and solvent resistance after film formation increase, but the solubility in water and the elongation after film formation decrease.

PVA L7-88 aqueous solution gradually increases in viscosity with time at room temperature. However, the viscosity at a concentration of 8% is absolutely stable and has nothing to do with time. The special phenomenon c polyvinyl alcohol has good film-forming properties and is highly uncomfortable to many gases other than water vapor and ammonia. Good light resistance, not affected by light. Can burn when open flame, has a special smell. Aqueous solution sometimes becomes toxic when stored. Non-toxic, non-irritating to human skin.

Used as an emulsion stabilizer for polyvinyl acetate emulsion polymerization. Used in the manufacture of water-soluble adhesives. Used as a modifier for starch adhesives. Can also be used in the preparation of photographic adhesives and sealants resistant to benzene-based solvents. Also used as a mold release agent, dispersant, etc. Store in a cool, dry warehouse. Moisture-proof and fire-resistant.

Polyvinyl alcohol 17-92 referred to as PVAl 7-92, white granules or powder. Easily soluble in water, dissolution temperature 75~ 80 ℃. Other properties are basically the same as PVA17-88. Used as an emulsion stabilizer for emulsion polymerization. Used in the manufacture of water-soluble adhesives. Store in a cool, dry warehouse, fireproof and moisture-proof.

Polyvinyl alcohol 17-99 is also known as sizing resin, referred to as PVAl7-99. White or slightly yellow powder or flocculent solid. Glass transition temperature 85 ° C, saponification value 3~ 12mgKOH/g. Soluble in hot water at 90~ 95 ° C, almost insoluble in cold water. Aqueous solutions with a concentration greater than 10% will gel to freeze at room temperature, and will become thinner at high temperature to restore fluidity. To stabilize the viscosity, an appropriate amount of sodium thiocyanate, calcium thiocyanate, phenol, butanol and other viscosity stabilizers can be added to the solution. PvAl7-99 solution is more sensitive to gelation than PvAl7 and 88. 0.1% borax by mass of the solution will gel 5% PVAl7-99 aqueous solution, while the amount of borax that causes the gelation of PVA 17-88 aqueous solution at the same concentration needs to be 1%.

For aqueous solutions of polyvinyl alcohol with the same concentration and the same degree of alcoholysis, borax is more likely to gelate than boric acid. PVAl7-99 is more resistant to solvents such as benzene, chlorinated hydrocarbons, esters, ketones, ethers, hydrocarbons, etc. than PVAl7-88. It gradually changes color when heated to above 100 ° C. It changes color quickly when it is above 150 ° C. It will decompose when it is above 200 ° C. The discoloration properties of polyvinyl alcohol when heated can be inhibited by adding 0.5% to 3% boric acid. Good light resistance and is not affected by light. It has chemical reactivity such as esterification, etherification, and acetalization of long-chain polyols. Open flame will burn and has a special odor. Non-toxic and non-irritating to human skin.

• Calcium ash-based putty: A very small amount of putty can significantly improve the cohesion strength, adhesion and water resistance of the putty coating, reduce the amount of calcium ash powder, and significantly improve the phenomenon of delamination and scarring during grinding. Improve the surface fineness of putty after polishing.
• In cement-based exterior wall putty: improve the solidification speed of cement, improve the early strength of putty, good film formation, excellent durability, thin batch is not easy to depowder.
• Polishing putty (imitation porcelain paint): It can improve the surface film formation, making the coating surface denser, harder, brighter, and more resistant to scrubbing. Adding only one kilogram per ton can achieve obvious results.
• Neutral putty for interior walls: 6 kg of polyvinyl alcohol powder is added to one ton of heavy calcium, and an appropriate amount of cellulose (hydroxypropyl, carboxymethyl) can be used to obtain ordinary putty powder with far better quality than starch and 821 types. The hardness of this putty is between the gray calcium-based putty and the starch putty, and it has excellent batch scraping. The adhesion, flexibility, grinding fineness and durability of the two putties are far inferior. If combined with gypsum powder and retarding technology, a higher grade of excellent home improvement putty powder can be obtained. This putty powder has a long service life and good decorative effect, and will become the development direction of the putty industry in the future.
• In instant glue powder, it is the main binder. It is combined with an appropriate amount of hydroxypropyl methylcellulose and supplemented with an appropriate amount of thickening complexing aids, which can be convenient for environmental protection, high bonding strength, and can be mixed with cement gypsum for wet wall leveling. It can also be used as a separate batch of high-performance glue powder without powder removal.
• In dry mortar. PVA1788 powder has good film-forming properties. It is used in combination with cellulose ether water-retaining agents to improve the flexibility and water retention of various cement mortars and gypsum building materials, improve the bonding strength of the mortar, and effectively prevent peeling, cracking, and hollowing.