How to Increase the Foaming Ratio of Flexible PU Foam?

This article provides a quantitative adjustment scheme to improve the foaming ratio of flexible PU foam. The scheme is based on weight parts (per 100 parts polyether). A basic reference formulation is given at the beginning as a calculation benchmark, which can guide further production adjustments.

Basic Reference Formulation (Conventional Density)

Usage logic: All subsequent adjustment schemes can be regarded as overriding modifications to the parameters in this basic formulation.

I. Core Parameter Preset

• 1. Density baseline (water dosage)

Starting point: Set water to 3.2 parts.

Adjustment: For each 0.2 parts reduction in water, density increases by ~1.5 kg/m³.

• 2. Ultra-low density (physical blowing agent)

Condition: For target density < 21 kg/m³.

Adjustment: Increase MC from 0–5 parts to 10–15 parts.

Warning: Above 15 parts, shrinkage risk rises significantly.

• 3. Crosslinking strength (TDI index)

Adjustment: Increase TDI index from 110 to 115–125 to prevent collapse at high foaming ratio.

• 4. Flexible backbone (polyether composition)

Ensure ≥70% is 2-functional polyether with MW ≥ 6000.

Final average functionality should be <2.6.

II. Functional Additives

• 1. Tear resistance reinforcement (POP)

Increase POP from 5 parts to 8–12 parts.

III. Reaction Pace Adjustment

• 1. Delay curing

If gelation is too fast → Reduce T-9 by 0.05 parts.

• 2. Accelerate foaming

If weak rise or shrinkage → Increase A33 from 0.4 to 0.5 parts (max +0.1 extra if severe).

• 3. High temperature response

Replace 40% of A33 with delayed amine catalyst (e.g., DMDEE).

IV. Cell Structure Stabilization

• 1. Stabilizer selection

Must use highly active branched silicone stabilizers.

Dosage linked to MC. When MC = 12 parts, silicone ≥2.0 parts.

• 2. Auxiliary opening measures

Add small-molecule crosslinker (e.g., DEG).

Strictly ≤0.5 parts.

V. Quick Defect Calibration

• 1. Foam scorch (burning core):

Lower TDI index by 5 points.

Increase MC by 3 parts.

• 2. Severe shrinkage after cooling:

If TDI <115 → Raise by 5–10 points.

If sufficient → Increase T-9 by 0.05 parts.

• 3. Too soft, poor resilience:

Reduce 2-functional polyether by 10%.

Replace with equal amount of 3-functional polyether.

Summary

This handbook provides a systematic pathway—core parameter presetting, functional additives, reaction fine-tuning, structural stabilization, and quick defect calibration—to achieve efficient high-ratio foaming of flexible PU foam. Small-scale trials are recommended before production to ensure optimal process adaptation.