Polyvinyl Alcohol (PVA)
Polyvinyl alcohol is an organic compound that appears as white flaky, flocculent, or powdery solid, odorless. It is soluble in water (above 95°C), slightly soluble in dimethyl sulfoxide, and insoluble in gasoline, kerosene, vegetable oil, benzene, toluene, dichloroethane, carbon tetrachloride, acetone, ethyl acetate, methanol, ethylene glycol, etc. As an important chemical raw material, it is used in the production of polyvinyl acetal, gasoline-resistant pipelines, vinylon synthetic fibers, fabric treatment agents, emulsifiers, paper coatings, adhesives, glues, and other products.
Technical Specifications
Polyvinyl Alcohol Product Standard (CP2010)
- Appearance: White solid powder
- Viscosity: 3–70
- pH value: 4.5–6.5
- Loss on drying: ≤5.0
- Residue on ignition: ≤0.5
- Acid value: ≤3.0%
- Degree of alcoholysis: 85–89
- Heavy metals: ≤10 ppm
Polyvinyl Alcohol Product Standard (USP25)
Low Viscosity Grade
- Appearance: White solid powder
- Viscosity: 4.0–7.0
- pH value: 5–8
- Average molecular weight: 16,000–20,000
- Loss on drying: ≤5.0
- Residue on ignition: ≤2.0
- Water-insoluble impurities: ≤0.1%
- Degree of hydrolysis: Complies
- Volatile organic impurities: Complies
- Assay: 85.0%–115.0%
Medium Viscosity Grade
- Appearance: White solid powder
- Viscosity: 21.0–33.0
- pH value: 5–8
- Average molecular weight: 110,000–130,000
- Loss on drying: ≤5.0
- Residue on ignition: ≤2.0
- Water-insoluble impurities: ≤0.1%
- Degree of hydrolysis: Complies
- Volatile organic impurities: Complies
- Assay: 85.0%–115.0%
High Viscosity Grade
- Appearance: White solid powder
- Viscosity: 40.0–65.0
- pH value: 5–8
- Average molecular weight: 180,000–200,000
- Loss on drying: ≤5.0
- Residue on ignition: ≤2.0
- Water-insoluble impurities: ≤0.1%
- Degree of hydrolysis: Complies
- Volatile organic impurities: Complies
- Assay: 85.0%–115.0%
Physicochemical Properties
Characteristics
White flaky, flocculent, or powdery solid, odorless.
The physical properties of polyvinyl alcohol are affected by its chemical structure, degree of alcoholysis, and degree of polymerization. Two chemical structures exist in PVA molecules: 1,3- and 1,2-ethylene glycol structures, with the 1,3-ethylene glycol (head-to-tail) structure being dominant. The degree of polymerization of PVA is classified as ultra-high (molecular weight 250,000–300,000), high (170,000–220,000), medium (120,000–150,000), and low (25,000–35,000). Common degrees of alcoholysis are 78%, 88%, and 98%. Partially hydrolyzed PVA typically has a degree of alcoholysis of 87%–89%, while fully hydrolyzed PVA is 98%–100%. The naming convention uses the thousands and hundreds digits of the average degree of polymerization followed by the percentage of alcoholysis; for example, 17–88 denotes a degree of polymerization of 1700 and alcoholysis of 88%.
Generally, increasing the degree of polymerization raises the viscosity of aqueous solutions and improves film strength and solvent resistance, but reduces water solubility and film elongation.
Relative density (25°C/4°C): 1.27–1.31 (solid), 1.02 (10% solution).
Melting point: 230°C.
Glass transition temperature: 75–85°C.
When heated above 100°C in air, it gradually discolors and embrittles. Dehydration and etherification occur at 160–170°C, losing solubility. Decomposition starts at 200°C, and above 250°C it forms conjugated double-bond polymers.
Refractive index: 1.49–1.52.
Thermal conductivity: 0.2 W/(m·K).
Specific heat capacity: 1–5 kJ/(kg·K).
Resistivity: (3.1–3.8)×10⁷ Ω·cm.
It dissolves in water, usually requiring heating to 65–75°C for full dissolution. 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°C, but gels upon cooling to room temperature.
To dissolve PVA, it should be dispersed in room-temperature water under stirring before heating to prevent agglomeration. A 5% PVA aqueous solution is highly sensitive to borax and boric acid, causing gelation; irreversible gelation occurs at 1% borax by mass. Chromates, dichromates, and permanganates also induce gelation. The viscosity of PVA 17–88 solution gradually increases at room temperature, but remains stable at 8% concentration.
PVA has excellent film-forming properties and high gas barrier properties against most gases except water vapor and ammonia. It has good light resistance and burns with a characteristic odor when exposed to open flame.
Aqueous solutions may occasionally become moldy during storage. Non-toxic and non-irritating to human skin.
Used as an emulsifying stabilizer for polyvinyl acetate emulsion polymerization, in water-soluble adhesives, as a modifier for starch adhesives, in photosensitive adhesives, sealing compounds resistant to benzene solvents, mold release agents, and dispersants. Store in a cool, dry warehouse, protected from moisture and fire.
PVA 17–92
White granular or powdery, readily soluble in water at 75–80°C. Other properties are similar to PVA 17–88. Used as an emulsifier for emulsion polymerization and in water-soluble adhesives. Store in a cool, dry warehouse, protected from fire and moisture.
PVA 17–99 (Sizing Resin)
White or slightly yellowish powder or flocculent solid. Glass transition temperature 85°C, saponification value 3–12 mgKOH/g. Soluble in hot water at 90–95°C, nearly insoluble in cold water. Aqueous solutions above 10% gel at room temperature but thin and flow at high temperatures. Viscosity stabilizers such as sodium thiocyanate, calcium thiocyanate, phenol, or butanol may be added.
PVA 17–99 is much more sensitive to borax than PVA 17–88: 0.1% borax gels a 5% 17–99 solution, while 1% is required for 17–88. Borax induces gelation more easily than boric acid. PVA 17–99 has stronger resistance to benzene, chlorinated hydrocarbons, esters, ketones, ethers, and hydrocarbons. It discolors above 100°C, rapidly above 150°C, and decomposes above 200°C. Discoloration can be inhibited by 0.5%–3% boric acid. It undergoes esterification, etherification, and acetalization reactions. Non-toxic and non-irritating.
PVA 17–99B
Mainly used for high-viscosity polyvinyl butyral (PVB) and as a dispersant for sizing materials. Other 17–99 grades are used as emulsifiers for polyvinyl acetate emulsions (less effective than 17–88, often blended), in 107 construction adhesives (polyvinyl formal), and solvent-resistant sealants. Store in a cool, dry warehouse, protected from moisture and fire.
Key Physical Constants
- Ignition temperature (powder): 410°C
- Lower explosive limit: 125 g/m³
Main Applications
Used in the production of polyvinyl acetals, gasoline-resistant pipelines, vinylon fibers, fabric treatments, emulsifiers, paper coatings, and adhesives.
Water-Soluble PVA Fiber
Prepared from PVA with a degree of polymerization of 500–2000 and alcoholysis of 75–99 mol% using a DMSO/water (90–70:10–30) solvent system at 80–120°C under reduced pressure. The fiber has a water solubility range of 10–90°C, strength ≥3.5 cN/dtex, fineness 1.5–10 dtex, elongation 15–30%. Used in blended yarns, non-woven fabrics, embroidery backings, and papermaking.
Excellent Properties
- Solubility: Soluble in water (more soluble at higher temperatures), nearly insoluble in organic solvents. Solubility depends more on alcoholysis than polymerization. Partially hydrolyzed/low-polymerization grades dissolve rapidly; fully hydrolyzed/high-polymerization grades dissolve slowly. Dissolution proceeds through wetting → swelling → unlimited swelling → dissolution.
- Film-forming: Easily forms strong films; tensile strength increases with polymerization and alcoholysis.
- Adhesion: Strong bonding to hydrophilic celluloses; strength increases with polymerization and alcoholysis.
- Thermal stability: Begins to change at ~100°C. Partially hydrolyzed grades melt at ~190°C and decompose at 200°C; fully hydrolyzed grades melt at ~230°C and decompose at 240°C. Lower polymerization = faster weight loss; higher alcoholysis = shorter decomposition time.
Pharmaceutical Grades
PVA 05–88, 17–88, 124 are used pharmaceutically. PVA 05–88 and 17–88 have 88±2 mol% hydrolysis and DP 500–600 / 1700–1800. PVA 124 has 98–99 mol% hydrolysis and DP 2400–2500.
PVA is a promising pharmaceutical excipient due to its easy synthesis, low toxicity, consistent quality, low cost, and ease of use.
Cold-Water Soluble Polyvinyl Alcohol Powder
PVA is produced by polymerizing vinyl acetate to polyvinyl acetate, followed by saponification under varying alkali conditions to achieve different degrees of alcoholysis.
Cold-water soluble PVA powder is made by cryogenic grinding of partially hydrolyzed PVA. It is a water-soluble, eco-friendly polymer.
Physicochemical Properties
- Solubility: Dissolves in water at room temperature; low-polymerization grades dissolve faster.
- Adhesion: Excellent
- Wear resistance: Good
- Thermal stability: Softens when heated; stable below 40°C, discolors above 160°C, decomposes above 220°C to form water, acetic acid, acetaldehyde, and crotonaldehyde.
- Chemical resistance: Nearly unaffected by weak acids, weak bases, or organic solvents; high oil resistance.
Main Applications
- Dry-mix mortars, putties, and coatings
- Interface agents, finishing plasters, tile grouts
- Industrial ceramics (silicon carbide, silicon nitride)
- Additives for gypsum and cement
- Oil-well cement additives
- Pharmaceutical industry, agricultural seed coatings
Cold-water soluble PVA powder can replace redispersible polymer powders in dry-mix mortars with two key advantages:
- Only 0.5% dosage (by total solids) is needed to achieve tensile bond strength >0.1 MPa, much lower than polymer powder.
- Higher viscosity improves mortar consistency, with excellent anti-sagging and anti-slip properties.
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