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In today’s industrial landscape, the demand for polyurethane sandwich panels has been increasing due to their exceptional insulation properties, especially in cold storage applications. Two common types of polyurethane foam used in these panels are PUR (Polyurethane) and PIR (Polyisocyanurate). While both materials share similarities, they also have key differences that make them suitable for different applications.

1. Chemical Composition

PUR (Polyurethane) is a polymer composed of organic units joined by urethane links. It is produced by the reaction of an isocyanate with a polyol. PUR foam is known for its versatility, being available in flexible, rigid, and semi-rigid forms. It is widely used in various industries due to its excellent performance characteristics.

PIR (Polyisocyanurate) is chemically similar to PUR but with a higher proportion of isocyanate, which leads to the formation of a trimer, a more complex chemical structure. This results in PIR having enhanced thermal stability and fire resistance compared to standard PUR foam.

2. Fire Performance

One of the primary differences between PUR and PIR foam is their fire performance:

• PUR Foam: Typically classified as B3 for flammability. By adding flame retardants, it can be improved to B1 or B2 classification, making it more resistant to fire.
• PIR Foam: Usually classified as B2 but can reach B1 classification with modifications in the formulation, particularly by adjusting the concentration of the polyisocyanurate rings.

3. Thermal Insulation

Thermal insulation is a critical factor in cold storage applications:

• PUR Foam: Has a thermal conductivity ranging from 0.022 W/mK to 0.026 W/mK at 25°C. This makes it an effective insulator for many applications.
• PIR Foam: Offers superior insulation with a lower thermal conductivity, potentially reaching as low as 0.019 W/mK at 25°C.

4. Density

The density of the foam affects its strength and thermal performance:

• PUR Foam: Generally has a density of 38-40 Kg/m³, which provides a satisfactory balance between strength and insulation.
• PIR Foam: Slightly denser, with a typical range of 40-45 Kg/m³, offering greater strength and improved insulation.

5. Temperature Resistance

The operating temperature range is another crucial distinction:

• PUR Foam: Can generally withstand temperatures between -185°C to +110°C. For continuous use, PUR sandwich panels are recommended for temperatures below +85°C.
• PIR Foam: Has a broader temperature range, from -196°C to +205°C, making it suitable for more extreme conditions. PIR panels with an index of 250 or higher can be used continuously at temperatures up to +150°C.

6. Water Absorption

Water absorption is a key factor in determining the longevity and effectiveness of insulation materials:

• PUR Foam: Typically has a water absorption rate of 2.5% to 3%.
• PIR Foam: Exhibits significantly lower water absorption, often as low as 0.9%, which enhances its durability in humid environments.

Conclusion

Both PUR and PIR polyurethane foams are valuable materials for cold storage panels, each offering distinct advantages. PUR is versatile and widely used across industries, while PIR provides enhanced fire resistance, better thermal insulation, and greater durability, making it the preferred choice for more demanding applications. Understanding these differences allows engineers and builders to select the most appropriate material for their specific needs.