Polyvinyl alcohol powder
Polyvinyl alcohol (PVA) is made of vinyl acetate (VAM) by alcoholysis polymerization. It is a kind of water-soluble and environmental friendly polymer.
1. Physical properties
Appearance: white powder, odorless, tasteless, with liquidity.
Solubility: polyvinyl alcohol powder (PVA) 17-88 and 24-88 belong to partial alcoholysis PVA, which can be dissolved in room temperature water.
Thermal stability: when polyvinyl alcohol is heated, it will soften without obvious change below 40 ℃. When it is heated for a long time at 160 ℃, it will gradually color. When it is heated above 220 ℃, it will decompose and generate water, acetic acid, acetaldehyde and butenal.
Chemical resistance: hardly affected by weak acid, weak base or organic solvent, high oil resistance.
Storage stability: PVA is a low viscosity polymer, its aqueous solution is very stable at room temperature. PVA aqueous solution will not deteriorate during storage.
Film forming property: due to the high adhesion between PVA molecules, PVA film is easy to form, the film formed is colorless and transparent, with good mechanical strength, smooth surface without stickiness, and good solubility resistance. PVA film has good light transmittance, high moisture permeability, no electricity, no dust collection, and good printability.
2. Chemical properties
PVA can be regarded as a kind of linear polymer with secondary hydroxyl. The hydroxyl groups in PVA molecules have high activity, which can carry out typical chemical reactions of low alcohols, such as esterification, etherification, acetalation, etc., and can also react with many inorganic or organic compounds. Note: the difference of PVA properties is mainly determined by its degree of polymerization and alcoholysis.
3. PVA dissolution method
Powder mixing method: PVA powder particles and equal or larger amount of other powder ingredients are fully dispersed by dry mixing, and then water is added for dissolution, then PVA can be dissolved without agglomeration.
4. Product use
PVA polymer powder is especially suitable for building mortar additive. It can be used with HPMC water retaining agent to improve cement
The flexibility and water retention of mortar can improve the adhesion of mortar. In addition, it can reduce the friction of mortar, thus enhancing the working efficiency and quality.
(prevent the plastering layer from cracking and falling off, increase the adhesion strength and smoothness). PVA is a fine particle polymer, which is easy to disperse in cold water and in water
It can disperse rapidly, and its viscosity stability is good, so it can improve many properties of cement mortar, and it also has the function of capillary, which has the function of adsorption.
Note: the difference of PVA properties is mainly determined by its polymerization degree and alcoholysis degree. The influence of polymerization degree on its properties:
◇ with the increase of polymerization degree, molecular weight and viscosity
◇ increase of polymerization degree, decrease of solubility and permeability
◇ protective colloid characteristics increase with the increase of cohesion
Recommended dosage: 0.3-1.2% of total mixture
5. Packaging, transportation and storage
Polyvinyl alcohol powder products are packed in paper plastic composite bags, lined with high-density polyethylene plastic bags, 25kg / bag. When PVA products are transported, clean and covered means of transportation shall be used to prevent moisture, rain and sun. When carrying, handle them with care to prevent the package from being scratched or broken. PVA powder shall be stored in a dry and well ventilated room with room temperature of 5-30 ℃. Keep away from heat, keep away from humidity and sunlight. It is strictly prohibited to store together with volatile chemicals to prevent absorption deterioration.