How to Prepare High-Performance Slow Rebound Foam?

The unique properties of viscoelastic polyurethane foam (slow rebound foam) make it highly valued in precision engineering and material science. However, achieving stable viscoelasticity and precise physical performance requires a deep understanding and strict control of all parameters in the manufacturing process. This article systematically analyzes the key factors that influence slow rebound foam performance—including catalyst, silicone oil, foaming agent, cell opener dosage, TDI index, and mold temperature—with the aim of providing professional insights into improving manufacturing processes and product quality.

1. Effect of Amine-Tin Catalyst Dosage on Foaming and Cell Structure

Catalysts play a crucial role in polyurethane foam formation, directly affecting the reaction rate, gelation, and gas expansion balance. Optimizing the balance between foaming and gelling speeds, as well as improving cell openness and flowability, is essential for slow rebound foam.

When the catalyst dosage is increased from 0.30-0.04 phr to 0.55-0.30 phr, both emulsifying and rise times are significantly shortened, indicating a faster reaction. Dosages around 0.35-0.06 to 0.40-0.08 phr yield fine, open-cell structures ideal for slow rebound characteristics. Higher dosages lead to closed-cell structures that reduce breathability and increase rebound speed, thus compromising viscoelastic performance. The optimal range is 0.35–0.40 phr.

2. Effect of Foaming Agent Dosage on Hand Feel and Rebound Time

Water was used as the environmentally friendly foaming agent in controlled trials.

At 1.50–2.50 phr, the foam offers the longest rebound time and best feel. Excessive water causes poor cell structures due to premature gelation before sufficient CO₂ is formed. Moreover, the urea linkages from water-isocyanate reactions reduce foam comfort and slow rebound effect. Thus, water dosage must be tightly controlled.

3. Effect of Silicone Oil Dosage on Cell Structure

Silicone oil stabilizes the foam structure during formation. Using B8002 silicone oil from Evonik, tests show:

Too little causes collapse, while excessive dosage coarsens the structure again. Ideal dosage is 1.00–1.80 phr.

4. Effect of Cell Opener Dosage on Cell Fineness

Cell openers improve breathability and structure. With SK-1900 (Momentive):

The optimal range is 1.50–2.50 phr to ensure fine and open cells.

5. TDI Index and Its Constraint on Rebound Performance

The TDI index (molar ratio of isocyanate to active hydrogen compounds) significantly affects slow rebound behavior. Higher TDI index speeds up rebound and reduces softness. When the index reaches 100, foam becomes high-rebound. To maintain slow rebound, keep the index within 80–95.

6. Effect of Mold Temperature on Foam Density

Mold temperature directly influences foam density. As mold temperature increases, density decreases due to faster heat transfer and expansion. However, the optimal mold temperature range is 40–60°C. Higher values may cause over-foaming or surface defects.

Preparing high-performance slow rebound foam involves tightly controlling interconnected variables: catalyst, silicone oil, water, cell opener, TDI index, and mold temperature. Their interactions affect foam’s structure, rebound time, hand feel, and density. A deep understanding and precise formulation optimization are key to developing quality foam for diversified applications. Future research should include the effect of humidity, polyol hydroxyl values, and multi-parameter response surface optimization to support product innovation.