How to Adjust the Tear Strength of Flexible PU Foam by Modifying Formulations?--Part 1

The formulations for the same product can vary significantly across different regions, raw materials, machinery, and conditions, so formulations are provided for reference only. We'll illustrate this using the formulation for a regular flexible PU foam. The reasons for using a regular high-formula flexible PU foam as an example are:

Regular foam polyether has low reactivity, so its reaction with water and TDI is not very intense, unlike high-resilience or slow-resilience polyether which reacts very strongly with water and TDI.

The reaction rates of regular polyether with TDI and water with TDI are relatively similar, making them easier to coordinate during the reaction process. Therefore, the regular flexible PU foam formulation effectively demonstrates the reaction principles.

Now let's discuss tear strength.

Tear strength is related to the following three factors: 1. Crosslinking reaction; 2. Hard segments and soft segments; 3. Internal heat of the foam.

The stronger the crosslinking reaction, the higher the tear strength.

The more hard segments in the flexible PU foam, the higher the tear strength.

The internal heat of the foam controls the crosslinking reaction and hard segments. The higher the internal heat, the stronger the crosslinking reaction and the greater the generation of hard segments.

It is important to note that the crosslinking reaction is not controlled by amines and tin; it is controlled by the internal heat of the foam.

Next, let's look at the formulations.

First, we'll compare Formulation 1 with the original formulation. The main difference is that Formulation 1 has one more part of TDI than the original formulation, so the TDI index of Formulation 1 is higher. The crosslinking reaction also has a characteristic that it is related to the TDI index; the higher the TDI index, the faster and stronger the crosslinking reaction. Therefore, the tear strength of Formulation 1 is superior to the original formulation.

Now let's examine Formulation 2. In Formulation 2, the water content has increased, and the methane content has decreased. The reaction between water and TDI is exothermic, while methane is endothermic. This increase in water and decrease in methane result in a higher internal temperature in Formulation 2 compared to the original formulation. As the internal heat increases, the crosslinking reaction and hard segments also increase, so the tear strength of Formulation 2 is significantly better than the original formulation. This is also a primary method for adjusting tear strength.

Finally, let's look at Formulation 3. Formulation 3 has an increased amount of A33, which catalyzes the reaction between water and TDI. Therefore, the increase in A33 also raises the internal heat, resulting in a tear strength greater than the original formulation.

Additionally, it is worth noting that the substances produced by crosslinking reactions and hardening are related to the internal heat of the foam. These substances not only improve tear strength but also enhance the thermal stability of the foam. For example, the British Standard for thermal weight loss is an indicator of the foam's thermal stability. In other words, the thermal stability of Formulations 1, 2, and 3 is superior to the original formulation.