How to Adjust the Formula for PU Foam Burning Inside?--Part One

PU foam burning inside occurs due to excessive internal temperature within the PU foam. The temperature of the PU foam is influenced by the following factors:

1. The volume of gases. This volume includes the sum of carbon dioxide produced from the water reaction and the vaporized methane.

2. The heat value within the foam. When the quantities of water and MC are fixed, the heat value within the foam will fall within a certain range.

3. The reaction rate. These three factors are variables, not constants.

Analyzing based on the gas volume and the heat value within the foam: When the heat value within the foam is constant, the larger the gas volume, the lower the foam temperature. For instance, if there are 1000 joules of heat in a single unit of space, the temperature might be 50°C. If it’s in two units of space, the temperature would be 25°C. In other words, during the steady foaming process of our PU foam, it is a process of diluting the heat.

Analyzing based on the heat value within the foam and the reaction rate: When the heat value within the foam is constant, it is influenced by the reaction rate. The faster the reaction rate, the greater the heat generated.

Therefore, to address PU foam burning inside, we need to adjust based on these three factors.

First Measure: The heat generated during PU foam foaming mainly comes from the reaction between water and TDI. We need to adjust this reaction.

For example, the original formula is for ordinary PU foam foaming:

560S with a molecular weight of 3000, hydroxyl value of 56, and TDI at 80. When this original formula slightly burns, the most common method is to reduce the amount of ammonia. Ammonia catalyzes the reaction between water and TDI. By slowing down the reaction rate, the main heat-producing reaction is reduced, and thus the heat sensation is also lowered. Other aspects remain mostly unchanged.

Second Measure: Increase methane and reduce water. When reducing water and adding methane while keeping the density essentially unchanged, and slightly adjusting the ammonia, the gas volume remains roughly the same, but the heat value within the foam is lowered, thus reducing the overall temperature within the foam.

These are the two main adjustment methods.

Let's look at other scenarios:

For instance, increasing water will increase the gas volume, but it will also increase the heat value within the foam. The increase in the heat value within the foam is much greater than the increase in gas volume, resulting in a rise in the ratio, which typically leads to an increase in PU foam temperature, causing red cores within the foam.

On the other hand, increasing methane will increase the gas volume and decrease the heat value within the foam. This increase and decrease will lower the internal foam temperature.

Another example: If water is increased to 4.3 and methane to 13, will the temperature rise or fall? This requires specific calculations. The previous examples were judged directionally, but this situation needs to be calculated specifically. We need many parameters, such as the reaction heat of water and TDI, which involves two reaction steps, each with its reaction heat, including the reaction heat of polyether, the reaction heat of polyether with TDI, and the vaporization heat of methane. All these parameters need to be considered.

Therefore, our most common adjustment method is to increase methane and reduce water, adjusting A33 as needed.