What Are the Technical Issues and Solutions for Polyurethane Foam Raw Materials?

Section 1: Raw Material Ratio and Reaction Control

Q1: Why is foam density uneven during production?

A: Possible causes include: inadequate mixing of polyols and isocyanates (TDI/MDI); uneven distribution or imbalanced reaction of blowing agents (e.g., water); and an imbalanced catalyst system for the blowing and gelling reactions.

Solution: Optimize mixing equipment and process parameters, such as increasing mixing head speed and pressure; adjust the ratio of chemical and physical blowing agents; and use a balanced catalyst system to control the blowing and gelling reactions.

Q2: What causes abnormal foam cell structures, such as large pores or unstable open cells?

A: Possible causes include: inappropriate type or amount of silicone surfactants; temperature gradients during the foaming process; and an excessively high raw material system viscosity.

Solution: Use a suitable silicone surfactant to stabilize bubbles and control cell openness; strictly control the ambient and raw material temperatures during foaming (25–35°C); and lower the system's viscosity by optimizing the formulation.

Section 2: Environmental Compatibility and Process Safety

Q3: Why do finished foams emit excessive VOCs?

A: Common reasons include: the presence of low-molecular-weight volatiles in raw materials; residual, unreacted amine catalysts; and the use of outdated or non-eco-friendly physical blowing agents (e.g., dichloromethane).

Solution: Choose low-emission or reactive amine catalysts (e.g., Dabco NE200); use eco-friendly blowing agents like water, liquid CO₂, or cyclopentane; and strictly control the reaction to minimize unreacted low-molecular-weight substances.

Q4: Why does the foam fail flame retardancy standards like UL94 or GB8624?

A: Likely causes include: inadequate flame retardant dosage; and poor compatibility or thermal degradation of the flame retardant during foaming.

Solution: Combine reactive (e.g., phosphorus polyols) and additive retardants (e.g., phosphate esters or expandable graphite); and control the foaming temperature to prevent flame retardant degradation.

Section 3: Production Stability Issues

Q5: What causes large performance variations between foam batches?

A: Main causes include: inconsistent hydroxyl value or moisture content in raw materials; and poor control of the isocyanate index (NCO/OH ratio).

Solution: Ensure stable hydroxyl value and moisture content of polyols, controlling variations within ±5 mg KOH/g and ±0.05%; and apply closed-loop control to keep the isocyanate index between 1.05–1.10.

Section 4: Special Functional Foam Challenges

Q6: Why does slow-rebound foam deform or recover poorly?

A: Likely due to: an irregular open-cell structure; and improper glass transition temperature (Tg) or phase separation.

Solution: Choose high-molecular-weight, low-reactivity polyols to achieve a suitable glass transition temperature (Tg); and optimize the silicone surfactant and isocyanate type to fine-tune the cell structure and microphase separation.

Final Tips to Enhance Foam Quality

Q: What are the 3 key factors to improve polyurethane foam production?

A:

Strict control of raw material quality (polyol, isocyanate).

Fine-tuned process parameters (temperature, mixing, pressure).

Regular equipment maintenance (cleaning, calibration, servicing).

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