How to Control Memory Foam Performance? Core Raw Material Selection Guide

High-quality memory foam production begins with precise matching of the main material system, key additives, and process parameters. The core challenge lies in balancing the polyurethane network’s crosslinking density with the segmental activity to achieve stable viscoelasticity and shape recovery.

I. Main Material System: The Chemical Basis of Slow Rebound

The microstructure of memory foam is a phase-separated system formed by high molecular weight soft segments and low molecular weight hard segments. The selection and ratio of main raw materials are critical to rebound speed, density, and compressive resistance.

1. Combination Strategy of Polyether Polyols

The skeleton of memory foam is built from a combination of polyethers with different hydroxyl values and molecular weights.

Selection of memory foam polyols:
Use low-molecular-weight, high-hydroxyl-value polyethers. Adjust the ratio of slow-rebound polyether to regular polyether to control the weighted hydroxyl value. At a fixed TDI index, the higher the weighted hydroxyl value, the slower the foam’s elastic recovery, and the more pronounced the slow rebound effect.

Improving compression resistance:
To overcome the weakness of poor compression durability in memory foam, introduce high-EO polyether (blowing polyether) or a small amount of polyether-modified polyester. This strategy reduces phase separation and crystallinity, improving cohesion and compression resistance.

Hardness and structural stability:
Combine regular polyethers (e.g., hydroxyl value 56) or polymer polyols (POP) to adjust the final hardness and support strength of the foam.

2. Isocyanates (TDI/MDI) and Crosslink Density Control

The isocyanate index (NCO/OH ratio) is the key parameter controlling polyurethane network crosslink density.

TDI index golden range:
For memory foam, the TDI index must be strictly controlled between 80–95. An index below 100 means some hydroxyl groups remain unreacted, forming an incomplete network that slows recovery. When the index approaches 100, the slow rebound property essentially disappears.

High-compression applications:
For applications requiring high compression resistance and thermal stability, use MDI or a blended TDI/MDI system. MDI provides better structural stability and lower heat loss than pure TDI.

II. Key Additives: Selection and Precise Control

Additives fine-tune foaming rate, cell structure, and product stability, ensuring consistent production quality.

1. Catalyst System Balance

Memory foam uses a mixed system of amine and tin catalysts.
Preferred amine catalyst: Dabco 33-LV (0.3–0.8 parts). Its solvent (DPG) has a high molecular weight, minimizing TDI consumption and closed cells.
Preferred tin catalyst: Dibutyltin dilaurate (D22/T-12) (0.03–0.05 parts), which resists hydrolysis and promotes post-curing.
In practice, precisely balance amine to tin, ideally around 0.35:0.06 to 0.45:0.10, to ensure good cell opening and flowability.

2. Surfactants and Blowing Agents

Silicone oil (surfactant):
Use a memory-foam-specific silicone oil, about 1.0–1.8 parts. It stabilizes bubbles and promotes cell opening. Adjust dosage with density—reduce for high density, increase for low density. Too much or too little leads to coarse cells or collapse.

Cell opener:
Use SK-1900 or similar (1.5–2.5 parts) to control open-cell structure and prevent shrinkage from excessive polyether crosslinking.

Water (blowing agent):
Typically 1.5–2.5 parts to achieve longer rebound time. Excess water produces urea formation, reducing comfort and rebound performance.

III. Process Coordination and Quality Control for Application Fit

Raw material performance only fully develops under strict process control.

1. Strategies to Eliminate Production Defects

Common defects directly reflect dosage imbalance and require rapid adjustments:

Closed-cell swelling: Increase cell opener by 3–10% or reduce tin catalyst by 3–5%.

Cracking: Lateral cracking indicates insufficient tin catalyst—add about 5%.

Other adjustments: In black foam, carbon black’s hydrophobicity affects compatibility and catalyst efficiency; adjust catalyst dosage accordingly.

2. Process Parameters Affecting Density

Temperature control:
Memory foam foaming is temperature-sensitive. Raw material temperature should stay between 22–25 °C. Higher temperatures accelerate reactions, making control harder, while slightly elevated mold temperatures help reduce final foam density.

Chain speed and mixing:
On continuous lines, chain speed should be slower than regular foam (about 3.8 m/min) to accommodate the slower gelling of memory foam. Mixing speed and time should be moderate to prevent rough cells caused by excessive shear.

Manufacturing memory foam is a precise art. Success depends on a deep understanding of the TDI index, polyether system, and fine control of additive dosages. Only by mastering these fundamentals can manufacturers consistently produce high-performance, application-ready memory foam products.