What Factors Affect the Internal Temperature of Polyurethane Soft Foam?

The internal temperature of foam is as indispensable as vitality is to a person. If the post-cure temperature of the sponge is too low, its physical properties will not be optimal, and there will be significant fluctuations in these properties.

Once the foam is well developed, its internal temperature rapidly rises to over 120 degrees Celsius due to the exothermic reaction occurring under poor heat dissipation conditions, becoming one of the fire hazard risks.

The internal temperature of the foam is crucial for forming its superior properties. Foam matured at specific external temperatures exhibits exceptionally superior physical properties like tensile strength. Some calculate the foam temperature through formulas, while others use software to input formulas and automatically calculate the internal temperature of the foam. So, what factors influence the internal temperature of the foam? Is it significant to know these factors? It's akin to how modern phone cameras are high-resolution, but does that render professional photography useless? Are adjustments like aperture, focal length, and exposure time pointless? To better control things, one must grasp more of the key variables of that thing. Let's start with basic principles to understand the changes in internal foam temperature.

First, let's grasp a few basic rules.

The temperature of a space is directly proportional to the amount of heat energy injected into that space and inversely proportional to its size.

For example, if 10 kilojoules of heat are distributed in an 8-liter space, the temperature of that space is 20 degrees Celsius. If the same 10 kilojoules of heat are distributed in a 4-liter space, the temperature becomes 40 degrees Celsius.

The amount of heat input is directly proportional to the heat input value and the speed of heat input.

For instance, if 100 kilojoules of heat are released at speed "v," the heat input is "A." If the same 100 kilojoules of heat are released at 2v speed, the heat input becomes 2A.

The size of a space is directly proportional to the absolute temperature.

For example, a 1-liter space at 0 degrees Celsius becomes 1.366 liters at 100 degrees Celsius because (273.15 + 100)/(273.15 + 0) = 1.366.

The size of a space is inversely proportional to atmospheric pressure.

The lag in methane vaporization needs to be considered.

Next, let's examine how fine-tuning the formula affects the internal foam temperature.

Since this is fine-tuning, we'll approximate that the surrounding environment remains unchanged before and after the adjustments. Let's consider the effects of adjusting water and methane on the internal foam temperature.

For example, if a formula increases methane by 5%, we can be certain that the internal foam temperature decreases because methane vaporization absorbs heat, reducing the heat input to the foam, and increasing the space to accommodate heat. Similarly, if the water content is increased by 5%, the added water releases heat upon injection into the foam, raising the heat input, and the reaction of the added water generates gas, increasing the space for heat. So, does the internal foam temperature increase or decrease in this case? Experience indicates that the internal foam temperature increases. This suggests that the increased heat input due to this change contributes more to the increase in internal foam temperature than the gas produced by water diluting the temperature.

The changes involving foam index, heat release, and heat dissipation all increasing can make it difficult to intuitively guess whether the internal foam temperature will rise or fall. One might need to insert a probe after foaming to compare internal temperatures or calculate to reach a conclusion.

For calculations, several formulas (algebraic expressions) derived from the earlier basic rules are needed, along with some data: the heat released when water reacts with TDI to form carbon dioxide in kilojoules per mole, the heat absorbed during methane vaporization in kilojoules per mole. To estimate the total foam internal temperature, one must know the heat released when forming amino methyl formate, urea methyl formate, urea, and biuret (polyurea), in kilojoules per mole, and the reaction rate (reaction time).

This also explains why the density calculated from the foam index drastically differs from the theoretical and actual values for foams without fillers at 50 densities. The lower the density, the more closely the theoretical and actual values of foam density match.