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PH-56; PD-56
Polyester polyols are one of the two primary classes of polyols used in polyurethane chemistry (the other being polyether polyols). In the context of CASE (Coatings, Adhesives, Sealants, and Elastomers), polyester polyols are often the preferred choice due to the superior properties they impart to the final product.
They are formed by the condensation reaction of diacids (or their anhydrides) with glycols (diols), resulting in a polymer chain with ester linkages (-COO-) and terminal hydroxyl groups (-OH).
Compared to polyether polyols, polyester polyols generally offer:
Excellent Mechanical Properties: High tensile strength, tear resistance, and abrasion resistance.
Good Heat Resistance: Higher thermal stability due to the strong polar ester groups.
Superior Oil and Fuel Resistance: The polar ester backbone is less susceptible to swelling and degradation by non-polar solvents, oils, and fuels.
Excellent Adhesion: To a wide variety of substrates (metals, plastics), making them ideal for adhesives and coatings.
UV Resistance: Generally better than polyether polyols, which can be prone to oxidative and UV degradation.
Lower Hydrolytic Stability: This is their main weakness. The ester bond can be susceptible to breakdown in the presence of water, acids, or bases.
The properties can be finely tuned by selecting different raw materials (acids and glycols).
Aliphatic Polyester Polyols:
Description: Made from aliphatic diacids (e.g., adipic acid) and glycols (e.g., 1,4-butanediol, ethylene glycol).
Properties: Offer a good balance of flexibility, strength, and low-temperature performance.
CASE Applications: Flexible cast elastomers, synthetic leather, UV-resistant coatings, soft adhesives.
Aromatic Polyester Polyols:
Description: Made using aromatic diacids or anhydrides (primarily Phthalic Anhydride, Terephthalic Acid (PTA), Isophthalic Acid (IPA), or recycled PET).
Properties: Rigid, high strength, good heat and flame resistance.
CASE Applications: Rigid coatings, high-performance adhesives and sealants, and as a key component in rigid foam for insulation.
Polycaprolactone (PCL) Polyols:
Description: A special class made by ring-opening polymerization of ε-caprolactone.
Properties: Excellent hydrolysis resistance, low-temperature flexibility, and mechanical properties. They are high-performance and more expensive.
CASE Applications: High-performance elastomers, waterproof coatings, and specialty adhesives.
Polycarbonate Diols (PCD):
Description: While technically not polyesters (they have carbonate linkages -O-CO-O-), they are often grouped with them for their similar performance profile.
Properties: Exceptional hydrolysis resistance, UV stability, and mechanical properties.
CASE Applications: Extreme high-performance coatings, automotive and aerospace elastomers.
Standard (Moderate MW): Ranging from semi-solid to waxy solids. Often heated to be processed.
Low Molecular Weight / Oligomeric: Liquid resins that are easier to handle.
Here’s how polyester polyols are used in each segment of CASE:
Use: Formulating two-pack (2K) polyurethane coatings.
Reason: They provide hard, durable, and glossy films with excellent chemical resistance and adhesion.
Examples:
Metal Coatings: For industrial machinery, pipelines (corrosion protection).
Floor Coatings: For factories, warehouses, and gyms (abrasion resistance).
Plastic Coatings: For automotive interiors and consumer electronics.
Wood Coatings: High-end furniture and flooring finishes.
Use: As the base resin in reactive polyurethane adhesives.
Reason: High strength and excellent adhesion to diverse substrates.
Examples:
Laminating Adhesives: Bonding plastic films (e.g., food packaging).
Structural Adhesives: In automotive (bonding plastic components) and construction.
Shoe Manufacturing: Solvent-based or waterborne adhesives for bonding soles.
Use: In high-performance, elastomeric sealants.
Reason: Provide good flexibility, tear resistance, and durability.
Examples:
Construction Sealants: For expansion joints, glazing, and sanitary joints.
Industrial Sealants: For sealing automotive windshields and body seams.
Use: As the soft segment in cast, thermoplastic (TPU), or millable polyurethane elastomers.
Reason: Impart outstanding mechanical properties like tensile strength, tear resistance, and abrasion resistance.
Examples:
Cast Elastomers: Industrial wheels, rolls, and mining screens.
Thermoplastic Polyurethanes (TPUs): For cables, hoses, films, and athletic footwear.
| Property | Polyester Polyols | Polyether Polyols |
|---|---|---|
| Mechanical Strength | High (Tensile, Tear) | Moderate |
| Abrasion Resistance | Excellent | Good |
| Flexibility / Low Temp | Good (Excellent for PCL) | Excellent |
| Hydrolytic Stability | Poor to Moderate | Excellent |
| Microbial Resistance | Good | Poor (can support mildew) |
| Chemical/Oil Resistance | Excellent | Poor to Moderate |
| Cost | Moderate to High | Low to Moderate |
| Product Model | Hydroxyl value (mgKOH/g) | Acid Value (mgKOH/g) | Moisture (%) | Viscosity (CPS 25℃) |
| PH-56 | 56±3 | ≤1.0 | ≤0.05 | 1800 100℃ |
| PD-56 | 56±3 | ≤2.0 | ≤0.05 | ≤0.05 |
When formulating for CASE applications, polyester polyols are selected when the priority is:
Durability and mechanical strength.
Resistance to oils, fuels, and chemicals.
High-temperature performance.
Strong adhesion.
Their main drawback, hydrolytic instability, can be managed through proper formulation (e.g., using additives, aromatic polyols, or high-performance types like polycaprolactone) or by selecting them for applications where prolonged exposure to water is not a primary concern.
Polyester polyols are one of the two primary classes of polyols used in polyurethane chemistry (the other being polyether polyols). In the context of CASE (Coatings, Adhesives, Sealants, and Elastomers), polyester polyols are often the preferred choice due to the superior properties they impart to the final product.
They are formed by the condensation reaction of diacids (or their anhydrides) with glycols (diols), resulting in a polymer chain with ester linkages (-COO-) and terminal hydroxyl groups (-OH).
Compared to polyether polyols, polyester polyols generally offer:
Excellent Mechanical Properties: High tensile strength, tear resistance, and abrasion resistance.
Good Heat Resistance: Higher thermal stability due to the strong polar ester groups.
Superior Oil and Fuel Resistance: The polar ester backbone is less susceptible to swelling and degradation by non-polar solvents, oils, and fuels.
Excellent Adhesion: To a wide variety of substrates (metals, plastics), making them ideal for adhesives and coatings.
UV Resistance: Generally better than polyether polyols, which can be prone to oxidative and UV degradation.
Lower Hydrolytic Stability: This is their main weakness. The ester bond can be susceptible to breakdown in the presence of water, acids, or bases.
The properties can be finely tuned by selecting different raw materials (acids and glycols).
Aliphatic Polyester Polyols:
Description: Made from aliphatic diacids (e.g., adipic acid) and glycols (e.g., 1,4-butanediol, ethylene glycol).
Properties: Offer a good balance of flexibility, strength, and low-temperature performance.
CASE Applications: Flexible cast elastomers, synthetic leather, UV-resistant coatings, soft adhesives.
Aromatic Polyester Polyols:
Description: Made using aromatic diacids or anhydrides (primarily Phthalic Anhydride, Terephthalic Acid (PTA), Isophthalic Acid (IPA), or recycled PET).
Properties: Rigid, high strength, good heat and flame resistance.
CASE Applications: Rigid coatings, high-performance adhesives and sealants, and as a key component in rigid foam for insulation.
Polycaprolactone (PCL) Polyols:
Description: A special class made by ring-opening polymerization of ε-caprolactone.
Properties: Excellent hydrolysis resistance, low-temperature flexibility, and mechanical properties. They are high-performance and more expensive.
CASE Applications: High-performance elastomers, waterproof coatings, and specialty adhesives.
Polycarbonate Diols (PCD):
Description: While technically not polyesters (they have carbonate linkages -O-CO-O-), they are often grouped with them for their similar performance profile.
Properties: Exceptional hydrolysis resistance, UV stability, and mechanical properties.
CASE Applications: Extreme high-performance coatings, automotive and aerospace elastomers.
Standard (Moderate MW): Ranging from semi-solid to waxy solids. Often heated to be processed.
Low Molecular Weight / Oligomeric: Liquid resins that are easier to handle.
Here’s how polyester polyols are used in each segment of CASE:
Use: Formulating two-pack (2K) polyurethane coatings.
Reason: They provide hard, durable, and glossy films with excellent chemical resistance and adhesion.
Examples:
Metal Coatings: For industrial machinery, pipelines (corrosion protection).
Floor Coatings: For factories, warehouses, and gyms (abrasion resistance).
Plastic Coatings: For automotive interiors and consumer electronics.
Wood Coatings: High-end furniture and flooring finishes.
Use: As the base resin in reactive polyurethane adhesives.
Reason: High strength and excellent adhesion to diverse substrates.
Examples:
Laminating Adhesives: Bonding plastic films (e.g., food packaging).
Structural Adhesives: In automotive (bonding plastic components) and construction.
Shoe Manufacturing: Solvent-based or waterborne adhesives for bonding soles.
Use: In high-performance, elastomeric sealants.
Reason: Provide good flexibility, tear resistance, and durability.
Examples:
Construction Sealants: For expansion joints, glazing, and sanitary joints.
Industrial Sealants: For sealing automotive windshields and body seams.
Use: As the soft segment in cast, thermoplastic (TPU), or millable polyurethane elastomers.
Reason: Impart outstanding mechanical properties like tensile strength, tear resistance, and abrasion resistance.
Examples:
Cast Elastomers: Industrial wheels, rolls, and mining screens.
Thermoplastic Polyurethanes (TPUs): For cables, hoses, films, and athletic footwear.
| Property | Polyester Polyols | Polyether Polyols |
|---|---|---|
| Mechanical Strength | High (Tensile, Tear) | Moderate |
| Abrasion Resistance | Excellent | Good |
| Flexibility / Low Temp | Good (Excellent for PCL) | Excellent |
| Hydrolytic Stability | Poor to Moderate | Excellent |
| Microbial Resistance | Good | Poor (can support mildew) |
| Chemical/Oil Resistance | Excellent | Poor to Moderate |
| Cost | Moderate to High | Low to Moderate |
| Product Model | Hydroxyl value (mgKOH/g) | Acid Value (mgKOH/g) | Moisture (%) | Viscosity (CPS 25℃) |
| PH-56 | 56±3 | ≤1.0 | ≤0.05 | 1800 100℃ |
| PD-56 | 56±3 | ≤2.0 | ≤0.05 | ≤0.05 |
When formulating for CASE applications, polyester polyols are selected when the priority is:
Durability and mechanical strength.
Resistance to oils, fuels, and chemicals.
High-temperature performance.
Strong adhesion.
Their main drawback, hydrolytic instability, can be managed through proper formulation (e.g., using additives, aromatic polyols, or high-performance types like polycaprolactone) or by selecting them for applications where prolonged exposure to water is not a primary concern.
