Polyvinyl alcohol has unique strong adhesion, film flexibility, smoothness, oil resistance, solvent resistance, protective colloid properties, gas barrier properties, abrasion resistance and water resistance through special treatment. It is one of the essential production materials in life.
(1) The importance of polyvinyl alcohol
Polyvinyl alcohol (PVA for short) is white powder in appearance. It is a water-soluble polymer with a wide range of uses. Its performance is between plastic and rubber. Its uses can be divided into two major uses: fiber and non-fiber.
Polyvinyl alcohol is an important chemical raw material used in the manufacture of polyvinyl acetal, gasoline-resistant pipes and vinylon, fabric treatment agents, emulsifiers, paper coatings, adhesives, glues, etc.
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PVA is used as a sizing agent to give textile yarns greater strength and make paper more resistant to oil and grease. It is also used as a component of adhesives and emulsifiers, a water-soluble protective film, and a raw material for preparing other resins.PVA can also make films. PVA is the only vinyl polymer that can be used by bacteria as a carbon source and energy source.
Under the action of bacteria and enzymes, it can degrade 75% in 46 days. It is a kind of biodegradable polymer material and can be produced on a large scale by non-petroleum routes. The price is low, its oil resistance, solvent resistance and gas barrier properties are outstanding, and it has unique advantages in food and pharmaceutical packaging. The application of PVA is based on the solution method. Thin film materials are prepared by casting film. However, the solution processing and molding need to undergo dissolution and drying processes. It has disadvantages such as complex process, high cost, and low yield. It is difficult to prepare thick-walled and complex-shaped products. At the same time, it cannot be co-extruded and blown with other materials to prepare a multilayer composite film.
(3) The chemical structure and safety of polyvinyl alcohol
Polyvinyl alcohol is soluble in water and generally needs to be heated to 65～75℃ in order to dissolve completely. Slightly soluble in dimethyl sulfoxide. It is soluble in glycerol at 120～150℃, but it becomes a jelly when cooled to room temperature.
To dissolve polyvinyl alcohol, the materials should be added to room temperature water under stirring. After the dispersion is uniform, the temperature is increased to accelerate the dissolution, which can prevent agglomeration and affect the dissolution rate. The aqueous solution of polyvinyl alcohol (5%) is very sensitive to borax and boric acid and easily causes gelation. When borax reaches 1% of the solution mass, irreversible gelation will occur.
Chromate, dichromate, and permanganate can also make polyvinyl alcohol gel. The viscosity of PVA 17-88 aqueous solution gradually increases with time at room temperature. But when the concentration is 8%, the viscosity is absolutely stable, regardless of time. It is a special phenomenon c. Polyvinyl alcohol has good film-forming properties and is highly uncomfortable for many gases except water vapor and ammonia.
It has good light resistance and it is not affected by light. 5.It can burn in a brightly lit fire with special smell. When the aqueous solution is stored, it sometimes becomes toxic. Non-toxic, non-irritating to human skin.