Polyvinyl Alcohol powder as a kind of water-soluble film-forming bonding material, it has also been widely used in some dry mortar products in recent years, especially the appearance of powder polyvinyl alcohol products, which provides a cheaper bonding material for powder and paste putty. Although polyvinyl alcohol powder can be added to dry powder mortar products like redispersible polymer powder to increase its bonding strength, its comprehensive performance is far from the protective colloid function of redispersible polymer powder, but it really realizes low-temperature flexible bonding, reflecting better impermeability, alkali resistance, abrasion resistance, impact resistance, water retention, it is still made of vinyl acetate ethylene and vinyl acetate -Ethylene TERT carbonate copolymer to complete. Therefore, the prices of the two are quite different, but for the production of some low-cost dry mortar products, polyvinyl alcohol powder can be used, but the addition amount should be increased appropriately. Due to the strong hydrophilicity of PVA, its water resistance is poor.
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The alcoholysis degree of polyvinyl alcohol powder is about 88%, which can be well dissolved in water, and the water-soluble viscosity is also large. Therefore, polyvinyl alcohol powder can be easily prepared into glue, which can be used as paste internal wall putty and white cement, talcum powder and as adhesive of external wall putty and interface agent.
Main applications
The application of polyvinyl alcohol in the construction industry mainly includes the following aspects:
(1) Emulsifier in water-soluble coating;
(2) emulsifying agent in vinyl acetate emulsion.
(3) Make protective colloid in redispersible latex powder;
(4) As the main raw material of 802 glue production;
(5) In dry mortar products, adding polyvinyl alcohol powder can improve the adhesion and flexibility of cement mortar, and prevent the plaster from cracking and falling off.
Basic characteristics of polyvinyl alcohol
1.Viscosity: Its viscosity changes with variety, concentration and temperature. When the concentration increased, the viscosity value increased sharply, and the temperature increased, the viscosity decreased obviously.
2.Cohesiveness:PVA has strong binding force for hydrophilic porous surface materials, such as paper, textile, wood, concrete, mortar and smooth non absorbent surface.
3.Film forming ability: It can form better flexible film, and the mechanical strength of PVA film can be adjusted by plasticizer.
4.Gas impermeability: after PVA film forming, it has high impermeability for many gases, especially for oxygen, carbon dioxide, hydrogen, helium, hydrogen sulfide, etc. But for chlorine and water vapor, the permeability is high, and the gas passing rate for polyvinyl alcohol is high.
5.Chemical resistance: It has high corrosion resistance to sodium hydroxide, acetic acid, most inorganic acids, sodium nitrate, aluminum chloride, calcium chloride,calcium carbonate, sodium sulfate and potassium sulfate.
6.Water solubility: the solubility of polyvinyl alcohol is closely related to the degree of alcoholysis of the product. The product with 87%-89% alcoholysis degree has the best water solubility. For example, PVA 24-88 has 88% alcoholysis degree. It can be well dissolved in cold water or hot water. Of course, in actual production, the use of hot water can speed up the dissolution. For products with alcoholysis degree of 89%-90% in order to dissolve completely, they need to be heated to 60-70℃;for products with alcoholysis degree of 90%, they only need to dissolve in hot water of 95℃;.
At present, PVA 17-88 and PVA 24-88 are the most widely used PVA products. PVA 17-88 indicates that the polymerization degree of the product is and alcoholysis degree is 88%. PVA 24-88 indicates that the polymerization degree is and alcoholysis degree is 88%. Generally speaking, the greater the degree of polymerization, the greater the water-soluble viscosity, the better the strength and solvent resistance of the film, the greater the degree of alcoholysis, the lower the solubility in cold water, and the higher the solubility in hot water. Therefore, the Picture 4.11-1 lists the product characteristics of PVA 24-88.
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Polyvinyl alcohol (PVOH, PVA, or PVAl) is a water-soluble synthetic polymer. It has the idealized formula [CH2CH(OH)]n. It is used in papermaking, textile warp sizing, as a thickener and emulsion stabilizer in polyvinyl acetate (PVAc) adhesive formulations, in a variety of coatings, and 3D printing. It is colourless (white) and odorless. It is commonly supplied as beads or as solutions in water.[3][4] Without an externally added crosslinking agent, PVA solution can be gelled through repeated freezing-thawing, yielding highly strong, ultrapure, biocompatible hydrogels which have been used for a variety of applications such as vascular stents, cartilages, contact lenses, etc.[5]
Although polyvinyl alcohol is often referred to by the acronym PVA, more generally PVA refers to polyvinyl acetate, which is commonly used as a wood adhesive and sealer.
PVA is used in a variety of medical applications because of its biocompatibility, low tendency for protein adhesion, and low toxicity. Specific uses include cartilage replacements, contact lenses, laundry detergent pods and eye drops.[6] Polyvinyl alcohol is used as an aid in suspension polymerizations. Its largest application in China is its use as a protective colloid to make PVAc dispersions. In Japan its major use is the production of Vinylon fiber.[7] This fiber is also manufactured in North Korea for self-sufficiency reasons, because no oil is required to produce it. Another application is photographic film.[8]
PVA-based polymers are used widely in additive manufacturing. For example, 3D printed oral dosage forms demonstrate great potential in the pharmaceutical industry. It is possible to create drug-loaded tablets with modified drug-release characteristics where PVA is used as a binder substance.[9]
Medically, PVA-based microparticles have received FDA 510(k) approval to be used as embolisation particles to be used for peripheral hypervascular tumors.[10] It may also used as the embolic agent in a Uterine Fibroid Embolectomy (UFE).[11] In biomedical engineering research, PVA has also been studied for cartilage, orthopaedic applications,[12] and potential materials for vascular graft.[13]
PVA is commonly used in household sponges that absorb more water than polyurethane sponges.[citation needed]
PVA may be used as an adhesive during preparation of stool samples for microscopic examination in pathology.[14]
Polyvinyl acetals are prepared by treating PVA with aldehydes. Butyraldehyde and formaldehyde afford polyvinyl butyral (PVB) and polyvinyl formal (PVF), respectively. Preparation of polyvinyl butyral is the largest use for polyvinyl alcohol in the US and Western Europe.
Unlike most vinyl polymers, PVA is not prepared by polymerization of the corresponding monomer, since the monomer, vinyl alcohol, is thermodynamically unstable with respect to its tautomerization to acetaldehyde. Instead, PVA is prepared by hydrolysis of polyvinyl acetate,[3] or sometimes other vinyl ester-derived polymers with formate or chloroacetate groups instead of acetate. The conversion of the polyvinyl esters is usually conducted by base-catalysed transesterification with ethanol:
The properties of the polymer are affected by the degree of transesterification.
Worldwide consumption of polyvinyl alcohol was over one million metric tons in .[7]
PVA is an atactic material that exhibits crystallinity. In terms of microstructure, it is composed mainly of 1,3-diol linkages [−CH2−CH(OH)−CH2−CH(OH)−], but a few percent of 1,2-diols [−CH2−CH(OH)−CH(OH)−CH2−] occur, depending on the conditions for the polymerization of the vinyl ester precursor.[3]
Polyvinyl alcohol has excellent film-forming, emulsifying and adhesive properties. It is also resistant to oil, grease and solvents. It has high tensile strength and flexibility, as well as high oxygen and aroma barrier properties. However, these properties are dependent on humidity: water absorbed at higher humidity levels acts as a plasticiser, which reduces the polymer's tensile strength, but increases its elongation and tear strength.
Polyvinyl alcohol is widely used, thus its toxicity and biodegradation are of interest. Tests showed that fish (guppies) are not harmed, even at a poly(vinyl alcohol) concentration of 500 mg/L of water.[3]
The biodegradability of PVA is affected by the molecular weight of the sample.[3] Aqueous solutions of PVA degrade faster, which is why PVA grades that are highly water-soluble tend to have a faster biodegradation.[15] Not all PVA grades are readily biodegradable, but studies show that high water-soluble PVA grades such as the ones used in detergents can be readily biodegradable according to OECD screening test conditions.[16]
Orally administered PVA is relatively harmless.[17] The safety of polyvinyl alcohol is based on some of the following observations:[17]