The physical properties of polyvinyl alcohol are affected by chemical structure, alcoholysis degree and polymerization degree. The main structure of the polyvinyl alcohol molecule is 1, 3-propylene glycol, that is, the "head and tail" structure. The degree of polymerization of PVA is divided into 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 (250,000-35,000). Alcoholysis degree is generally 78%, 88%, 98% three. The alcoholysis degree of partial alcoholysis is usually 87% to 89%, and the alcoholysis degree of complete alcoholysis is 98% to 100%. The thousands and hundreds of the average degree of polymerization are usually placed in the front, and the percentage of alcoholysis is placed behind, such as 17-88, that is, the table polymerization degree is 1700, and the alcoholysis degree is 88%. Generally speaking, as the degree of polymerization increases, the viscosity of 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. The relative density of polyvinyl alcohol (25 ° C /4 ° C) is 1.27 ~ 1.31 (solid), 1.02 (10% solution), the melting point is 230 ° C, the glass transition temperature is 75 ~ 85 ° C, and the temperature is heated to more than 100 ° C in the air. Heating to 160 ~ 170℃ dehydration etherification, loss of solubility, heating to 200 ℃ began to decompose. Above 250℃ becomes a polymer containing conjugated double bonds. Refractive index 1.49 ~ 1.52, thermal conductivity 0.2W/(m·K), specific heat capacity 1 ~ 5J /(kg·K), resistivity (3.1 ~ 3.8) × 10Ω ·cm. Soluble in water, in order to completely dissolve generally need to be heated to 65 ~ 75℃. It is 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 ~ 150℃, but becomes jelly when it is cold to room temperature. To dissolve PVA, the material should first be added to room temperature water under stirring, dispersed evenly, and then heated to accelerate the dissolution, which can prevent caking 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, it will produce irreversible gelation. Chromate, dichromate, permanganate can also make PVA gel. At room temperature, the viscosity of PVA 17-88 aqueous solution gradually increases with time, but the viscosity is absolutely stable when the concentration is 8%, which is independent of time. Polyvinyl alcohol has good film-forming properties and is highly resistant to many gases except water vapor and ammonia. Good light resistance, not affected by light. When open flame can burn, there is a special smell. Water solutions sometimes become mildewed when stored. Non-toxic, no irritation to human skin. [2]
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. It can also be used to prepare photosensitive adhesives and benzol-resistant sealants. Also used as release agent, dispersant and so on. Store in cool, dry warehouse. Moisture-proof, fire-proof.
Polyvinyl alcohol 17-92, abbreviated PVA 17-92, white granules or powder form. Soluble in water, solubility temperature 75 ~ 80℃. Other performance is basically the same as PVA17-88. Used as an emulsion stabilizer for emulsion polymerization. Used in the manufacture of water-soluble adhesives. Store in cool, dry warehouse, fire, moisture.
Polyvinyl alcohol 17-99, also known as Sizing resin (Sizing resin), referred to as PVA17-99. White or yellowish powder or flocculent solid. The glass transition temperature is 85℃ and the saponification value is 3 ~ 12mg KOH/g. Soluble in 90 ~ 95℃ hot water, almost insoluble in cold water. An aqueous solution with a concentration greater than l0% will gel into freeze at room temperature, and will dilute to restore fluidity at high temperatures. In order to stabilize the viscosity, appropriate amount of sodium thiocyanate, calcium thiocyanate, phenol, butanol and other viscosity stabilizer can be added to the solution. PVA17-99 solution is more sensitive to the gel induced by borax than PVA17-88 solution, and 0.1% of the solution mass will gelate 5%PVA17-99 solution, while the amount of borax causing the same concentration of PVA17-88 solution gelation needs 1%. For polyvinyl alcohol aqueous solution with the same concentration and alcoholysis degree, borax is more likely to gel than boric acid. PVA17-99 is more resistant to benzene, chlorinated hydrocarbon, ester, ketone, ether, hydrocarbon and other solvents than PVA17-88. Heating to more than 100℃ gradually change color, more than 150℃ quickly change color, more than 200℃ will decompose. The discoloration of PVA when heated can be inhibited by adding 0.5% ~ 3% boric acid. Good light resistance, not affected by light. It has the chemical reactivity of esterification, etherification and acetalization of long chain polyols. Open fire will burn, have a special smell. Non-toxic, no irritation to human skin.
Polyvinyl alcohol 17-99B is mainly used in the manufacture of high viscosity polyvinyl butyral. Widely used as a dispersant for sizing materials. Other types of 17-99 are used as emulsifying stabilizers for polyvinyl acetate emulsion polymerization, but the effect is not as good as 17-88, and 17-99 is generally mixed with 17-88. 17-99 is used for the manufacture of PVA aqueous solution (mainly 107 construction glue). 17-99 is also used in the preparation of benzene solvent resistant sealant. Store in cool, dry warehouse, moisture-proof, fireproof.
