PU Foam delivers efficient gap filling, reliable bonding strength, and thermal and acoustic insulation in light to medium load applications. It is ideal for door and window sealing, panel fixing, and gap filling in renovation projects. For heavy-duty structural bonding, consider dedicated structural adhesives.
1. PU Foam: Composition and Working Principle
PU Foam is a one-component, moisture-curing polyurethane sealing material.
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Composition: polyurethane prepolymer, blowing agent, catalyst, and minor solvents and additives.
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Foaming Mechanism: upon extrusion, moisture in air or on substrate reacts with isocyanate to release CO₂ gas, causing 40–80× expansion into a closed-cell or micro-cell foam. Concurrent polymer chain growth and cross-linking solidify the foam and bond it to the substrate.
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Curing Profile:
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Tack-free time: ~10 minutes
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Cut-through time: 1–48 hours (for a 30 mm diameter bead)
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Final hardness varies with formulation and ambient conditions.
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2. Essential Performance Metrics
Typical performance parameters for PU Foam include:
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Expansion ratio: 40–80×
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Tack-free time: ~10 min
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Cut-through time: 1–48 h
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Recommended application temperature: +5 °C to +35 °C (ideal +18 °C to +25 °C)
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Shear strength: ≥ 80 kPa
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Bond strength to aluminum: ≥ 80 kPa
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Bond strength to cement mortar: ≥ 60 kPa
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Long-term service temperature: –30 °C to +80 °C
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Thermal conductivity: 0.042 W/m·K
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Formaldehyde and benzene: none detected
3. Comparison with Conventional Glues and Structural Adhesives
Unlike rigid structural adhesives, PU Foam expands to fill irregular gaps and provides thermal and acoustic insulation. Conventional glues vary widely by formulation but generally lack significant expansion capacity. Structural adhesives offer the highest load capacity but cannot fill gaps.
4. Factors Influencing Bond Strength
Several factors determine how securely PU Foam bonds materials:
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Substrate Preparation: clean, dry, oil-free, and dust-free surfaces improve contact and adhesion.
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Environmental Conditions:
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Temperature: optimal +18 °C to +25 °C; below +5 °C slows curing.
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Humidity: relative humidity ≥ 60% accelerates curing.
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Foam Quality: high-hardness, low-shrink formulations (including two-component systems) yield stronger bonds.
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Application Technique:
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Shake the can vigorously (15–30 shakes) before use.
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Apply a uniform bead, leaving ~20% free space for expansion.
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Support foam in overhead or vertical joints until initial curing.
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5. Typical Applications and Examples
PU Foam is widely used for:
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Door and window installation: seals and secures frame-to-wall gaps.
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Wood assembly: door casings, panel fixtures, and furniture alignment.
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Electrical enclosures: vibration damping and component potting.
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Hobby and landscaping: model-making, floral arrangements, and display dioramas.
Example: A specialized PU Foam formulation demonstrates excellent penetration and shear strength (≥ 80 kPa) on both high- and low-density wood, making it suitable for furniture assembly and flooring applications.
6. Safety and Handling
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Personal Protection: wear gloves, safety goggles, and a mask to avoid skin or eye contact.
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Ventilation: ensure adequate airflow to minimize odors.
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Fire Safety: keep away from open flames and heat sources; store below 50 °C.
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Equipment Cleaning: use appropriate solvent cleaner immediately after application to prevent nozzle clogging.
7. Selection Guidelines
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For large-area, high-load structural bonding, opt for dedicated structural adhesives or epoxy.
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For gap filling, sealing, insulation, and light to medium load bonding, choose single-component PU Foam.
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Prioritize products with controllable expansion, quick tack-free time, and high hardness. Adjust application based on ambient conditions for optimal results.
