Reticulated Polyurethane Foam: Quenching vs. Zapping

Reticulated Polyester

Reticulation is a post process in foam manufacturing that removes the window membranes of the cell. The cells that make up the foam can have a number of variations, which can also be precisely controlled. Different foams have varying cell structures and characteristics, but foams from the same material family can also be made with vastly different density and firmness specifications that will greatly affect their performance.

Reticulated polyurethane foam is created by removing cell membranes through one of two methods in the polyurethane manufacturing process.The first method is chemical etching or quenching. Quenching involves running the loaf of foam through a caustic bath of controlled temperature, concentration and duration. The caustic solution attacks and dissolves the window membranes, leaving only the skeletal structure. The foam is then washed, rinsed and dried. One shortcoming of this process is that it leaves a trace powder in the foam, making it unsuitable for some clinical applications. Quenching is not effective in polyether polyurethanes. One benefit of the quenching process is that it produces a rougher or more etched cell strand which holds liquids better due to surface tension. This method is ideal for polyester-based reticulated polyurethane foam. It also produces a softer feeling foam especially in higher porosities, which can be important for cosmetic applicators.

The second method is called thermal reticulation or “zapping.” Zapping is a process that involves placing a bun of foam in a very large vacuum pressure vessel known as a “zapper.” The vessel is evacuated and filled with an explosive gas mixture. The gas is ignited and a controlled flame front passes through the foam, melting the window membranes and leaving the skeletal structure intact. Zapping works with both polyester and polyether polyurethanes. The benefit of the zapping process is a smooth, clean polished cell stand. This can be important in a clinical application such as a defoamer in a blood oxygenator or other medical applications. Another benefit is that zapping works on polyethers which perform better in applications that require hydrolytic stability at evaluated temperatures. Zapping can be done on buns for producing sheets or logs for producing rolls.

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