How to Adjust Soft PU Foam Properties Based on the Characteristics of Common Foam Polyether

Common foam polyether is generally divided into two types. The first type is regular foam polyether (PPG), which has a hydroxyl value of 56, a molecular weight of 3000, and a light yellow color. The second type is polymer polyether (POP) used for regular foam, which is milky white.

PPG is categorized based on its reactivity into fully PO polyether and partially EO polyether. Fully PO-type PPG is now rarely used. Over a decade ago, many factories in Guangdong used fully PO-type PPG for foaming, while many factories in Jiangsu, Zhejiang, and Anhui used EO-type PPG. If the Guangdong formula is used in Jiangsu and Zhejiang, excessive T9 can occur because fully PO-type PPG has low reactivity and requires a high T9 content. Therefore, if partially EO polyether is used for foaming, the tin content must be reduced to 10% to 15%. Otherwise, the foam produced will have poor physical properties due to excessive foaming.

The characteristics of polymer polyether (POP) used in regular foam are:

Higher reactivity than PPG, so adding POP in some formulas can cause slight inside-burnt.

POP aids in foam cell opening. The factors influencing foam cell opening include:

Promoting the gas reaction: After adding POP during foaming, the soft PU foam density did not significantly change, indicating that promoting the gas reaction is not its main function.

Promoting the urea reaction: I believe this is the factor that aids in cell opening.

Affecting the viscoelasticity of the reaction system.

POP also has the characteristic of hardening the foam.

So, how can the properties of POP and PPG be used to adjust the physical properties of the soft PU foam? Here are two formulas:

Formula 1 has more TDI and no POP.

Formula 2 has less TDI and some POP.

Since TDI and POP both contribute to hardening, the hardness of these two formulas is similar. However, in terms of elasticity and the feeling of fullness when squeezed, Formula 2 is superior to Formula 1. The main reasons are:

With the same amount of water, the TDI index in Formula 2 is reduced, which benefits the elasticity of the soft PU foam.

The addition of POP contributes to hardness, and it is a high molecular weight polyether.

Additionally, taking Formula 2 as an example, to harden the soft PU foam, increase the TDI in the formula, and the POP can be increased to 40%-60%. After increasing, the soft PU foam will show slow post-curing, meaning the soft PU foam will still feel powdery four minutes after being removed from the mold. This is because one reaction is inhibited. However, if you want the hardened soft PU foam to be both elastic and hard, the post-curing reaction must be slow, allowing the soft PU foam to react gradually. This way, the elasticity and hardness of the soft PU foam can be appropriately combined. Otherwise, if the reaction is too fast, the resulting soft PU foam will feel very hard but will actually be hollow inside.

Therefore, if you want to produce foam for furniture, you should choose Formula 2.