Introduction and application of polyvinyl alcohol (PVA) materials

Science name: polyvinyl alcohol

English name: Polyvinyl alcohol

English abbreviation: PVA

Polyvinyl alcohol (PVA) is made from vinyl acetate through polymerization and alcoholysis. It is a white, stable, non-toxic water-soluble polymer, powder, flake or flocculent solid.

Polyvinyl alcohol contains many alcohol groups, has polarity, and can form hydrogen bonds with water, so it can be dissolved in polar water; It is also soluble in hot hydroxyl containing solvents such as glycerin and phenol, and insoluble in methanol, benzene, acetone, gasoline and other general organic solvents.

1 Physical and chemical properties

1、 Physical properties

A. Solubility: PVA powder can be dissolved in water. Polyvinyl alcohol resin (PVA) with alcoholysis degree less than 95% can be dissolved in normal temperature water, while polyvinyl alcohol resin (PVA) with alcoholysis degree more than 99.5% can only be dissolved in hot water above 95 ℃.

B. Thermal stability: PVA will soften when heated, and there is no obvious change below 40 ℃. The glass transition temperature: 75~85 ℃, and slowly discolor and embrittle when heated to above 100 ℃. Above 160 ℃, it will gradually color, dehydrate and etherify after heating for a long time, and lose its solubility; When the temperature is above 220 ℃, it will decompose to form water, acetic acid, acetaldehyde and butyraldehyde; Over 250 ℃, it becomes a polymer containing conjugated double bonds.

C. Chemical resistance: PVA is hardly affected by weak acid, weak base or organic solvent, and has high oil resistance.

D. Storage stability: PVA is a low viscosity polymer, and its aqueous solution is stable at room temperature. The aqueous solution will not deteriorate during storage.

E. Film forming property: due to the high adhesion between PVA molecules, PVA is easy to form a film, and the film formed is colorless and transparent, with good mechanical strength, smooth and clean surface without sticking, and good solubility. The molecular film has good light transmittance, high moisture permeability, no electricity, no dust absorption and good printability.

2、 Chemical properties

PVA can be regarded as a linear polymer with secondary hydroxyl groups. The hydroxyl group in the molecule has high activity and can carry out typical chemical reactions of low alcohols, such as esterification, etherification, acetalization, etc., and can also react with many inorganic or organic compounds.

2. Packaging, transportation and storage of polyvinyl alcohol:

Product appearance: white flocculent, flaky and powdery solid. This product is non-hazardous and has no explosion, oxidation, corrosion, radioactivity, toxicity or harm.

1. Packaging

12.5kg, 20kg, 25kg plastic woven bags or paper bags, 750Kg~1000Kg plastic woven ton bags.

2. Transportation

Use clean means of transportation to prevent moisture, rain and sun. Handle with care during handling to prevent scratching or breaking the package.

3. Storage

In a dry and well-ventilated room, the room temperature is 5-30 ℃. Please keep away from heat sources, keep away from humidity and sunlight. It is forbidden to store together with volatile chemicals to prevent adsorption and deterioration.

3 Product application

Polyvinyl alcohol resin (PVA) aqueous solution has good film-forming and emulsifying properties. It can be used as a protective colloid for polymer emulsification and suspension polymerization.

PVA can be used in the fields of textile size, vini fiber, paper coating agent, building materials, adhesives, PVA film, PVB raw materials, food and medicine, etc. PVA can also be used as soil improver, polymerization suspension agent, emulsifier, quenching agent, etc. In addition, with the continuous development and improvement of PVA performance, its use is still expanding.

Use of various types of polyvinyl alcohol (PVA)

1. Vinylon raw material:

Vinylon fiber can be prepared from polyvinyl alcohol after dissolving, spinning, and then acetalization. It can be blended with cotton, wool, viscose fiber, etc. to produce vinylon textiles, which are widely used in clothing, tarpaulin, cord, fishnet rope, etc. Generally, PVA17-99, with an average polymerization degree of 1750 ± 50, should be selected as the spinning material

2. Warp size:

A. The size mainly prepared with polyvinyl alcohol has good adhesion to cotton, hemp, polyester and vinylon viscose fibers, and it is smooth and smooth after film forming, which is both firm and wear-resistant, and promotes the suitability of warp yarn, reducing the friction and bending of warp yarn during weaving. Warp yarn breakage is caused by intense movements such as stretching, which reduces the breaking rate of cloth machine. And the fabric feels crisp. It is smooth and delicate, and the cloth surface is not rough.

B. PVA is a water-soluble polymer compound, which is convenient for sizing, sizing and desizing. Generally, PVA with low average polymerization degree (such as PVA15-99, 16-99, 17-99) is selected as the slurry.

3. Adhesive:

A. The aqueous solution of polyvinyl alcohol has strong adhesion to cellulosic materials (such as paper, cloth, wood, etc.), and has the advantages of safety and non-toxicity. It can be used for the lamination of paperboard, the adhesion of corrugated paperboard, and office glue. PVA is also used as the adhesive for kraft paper bags used for packaging heavy goods such as cement, fertilizer and grain.

B. Urea-formaldehyde resin and phenolic resin modified with polyvinyl alcohol can be used as adhesives for laminates and wood-based panels.

C. PVA aqueous solution (by adding appropriate fillers and additives) is also widely used to prepare adhesives for printing and binding, paper tubes, cartons and other paper products.

D. The condensation of polyvinyl alcohol with formaldehyde, butyraldehyde, glyoxal or other aldehydes under the catalysis of acid can produce polyvinyl acetals (such as PVAF, PVB) with stronger water resistance, adhesion and mechanical strength, which are widely used in construction, coatings, adhesives, safety glass interlayer and other fields. With the increase of polymerization degree of PVA, the viscosity of acetals increased.
E. Polyvinyl alcohol is an excellent protective colloid and dispersant for homopolymerization of vinyl acetate or copolymerization with other monomers to produce lotion (white glue), which is crucial in the production of white glue. Generally, the viscosity of the produced lotion increases as the polymerization degree of polyvinyl alcohol increases. Partial alcoholysis polyvinyl alcohol (17-88) is used in combination with complete alcoholysis polyvinyl alcohol (such as 17-99, 19-99, etc.). The use of partial alcoholysis polyvinyl alcohol can increase the stability of lotion, and the use of complete alcoholysis polyvinyl alcohol can increase the water resistance of lotion.

4. Paper processing:

A. PVA can be used as a paper surface sizing agent in the paper industry. It has the characteristics of good film forming and high film strength, and can improve the printing adaptability, smoothness, friction resistance, folding resistance, oil resistance and chemical resistance of the paper. PVA with an average polymerization degree of 1750 ± 50 should be selected as the paper surface sizing agent.

B. Pigment processing agent: It can improve the whiteness and gloss of coated paper. It has good printing gloss and bright color and improves the paper. It is better to choose polyvinyl alcohol with higher average polymerization degree.

C. As the internal sizing agent of paper: when making paper, add powdered polyvinyl alcohol and pulp to beat and make paper, so as to make paper with high strength. It is better to choose polyvinyl alcohol with higher average polymerization degree.

5. PVA film made from this product has good transparency, high tensile and crack resistance, good moisture permeability and gas insulation, oil resistance, organic drug resistance, and no static electricity, so it is suitable for the packaging of textiles.