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How Foam Made In a Factory? PU Foam, HR foam & Memory Foam कैसे बनता है?

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Polyurethane foam is used primarily for bedding and furniture stuffing.

Isocyanates and Polyols

We have two foundational chemicals involved in the foaming of PU. Isocyanates and Polyols contain multiple hydroxyl.

In the foaming, the two most common isocyanates are TDI (for flexible and semi-rigid foaming) and MDI (for rigid foaming).
TDI + polyol has made polyurethane polymer, which now can be expanded to make foam. To do that, we add water. Isocyanate is highly reactive, and produces two things with water: urea linkages/urethane, and carbon dioxide (CO2) gas.

Blowing the Foam
The CO2 is considered primary blowing agent. As a gas, it blows little air pockets into the PU to form the foam. Just like blowing soap bubbles though, there is a point when the liquid casing cannot withstand the pressure of the air inside and bursts.
To successfully make material foam, the polyurethane must gel into shape once air has been blown to it. It’s harder than it sounds, and it’s also why foam technicians can make or break your factory production. The art of foam-making revolves around this sensitive balance between expansion, or blowing, and gelling.
Once they’re formed inside the polyurethane, we’re going to call the air bubbles cells. If the foam expands and gels before any air bubbles burst, you get closed-cell foams, which are semi-rigid (not truly rigid like foam made of MDI) since the material doesn’t bend as easily. To go back to our ladder metaphor, closed-cell foams are like wood ladders, whereas open-cell foams are like rope ladders. If some or all cell walls are allowed to rupture before gellation, you get a much more flexible material that bends, twists, and even breaks easier.
what is polyurethane foam? Basically: TDI, polyol, water, polymer, open versus closed-cell.
Additives.
see PU foaming additives by function. One of the most important additives is the catalyst, which can affect the basic reactions in several ways. It can speed the expansion, speed the gelling, cool the reaction (so you have less of a fire hazard on your hands), etc. There are also curing agents, which include chain-extenders and cross-linking agents. Chain-extenders, like their name suggests, extend polymer chains, which increases material flexibility. Cross-linking agents promote and strengthen cross-linkages, increasing structural integrity for more rigid foams.
Think of surfactants like emulsifiers. Oil and water on their own do not mix, but once you add some dish soap, they can be emulsified into a uniform mixture. Surfactants work like the soap. A more uniform mixture means a smoother reaction, and you get more even cell sizes, steadier reaction speeds, and finer control between gellation and foam collapse.
(The reason they’re called surfactants is because they reduce the surface, or interface tensions between two compounds. As in, the oil doesn’t just sit neatly on top of the water surfactants blend that interfacing surface between them.)

PU Foaming Chemistry oil
Remember that CO2 gas from the reaction with water acts as a blowing agent? other blowing agents may also be used or added. The main inconvenience of water blowing is the high temperature of the reaction, making PU foaming a fire hazard. Physical blowing agents (additives that physically encourage the expansion of cells instead of that initial CO2, which is chemically blown) reduce that fire hazard.

A similar additives is fillers. They come as particles or fibers. Particulate fillers can reduce flammability and add weight to foam (good for cushioning foams). Fibrous fillers reinforce cell structure. All fillers function to 1) add physical properties like tensile or compressive strength to foam, and 2) save on costs by reducing the amount of liquid chemicals used per batch.

The main ingredients are.
Isocyanate: TDI
Polyol: polyol
Blowing Agents: water, methylene-chloride (MC)
Catalysts: amine, tin
Surfactant: silicone

Now we understand what each element does during the foaming process. TDI + polyol begins the creation of polyurethane. A mixing head first injects small amounts of air into the liquid mix to kickstart the foaming process. TDI + water chemically produces the CO2 gas that blows the liquid into foam. In addition, we add MC so that less water is used in the initial reaction and the overall reaction temperature is lower, all while cell expansion is retained.

Meanwhile, the amine additive is doing multi-purpose catalysis (speeding the reaction) and tin provides a stable gelling catalyst, increasing foam structural elasticity. Silicone smooths and steadies the entire blowing process, maintaining cell structure evenness until gellation occurs.

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