What Are the Two Stages and Web-Forming Methods for Making Polyurethane Filter Foam?

Manufacturing polyurethane filter foam typically involves two key stages. The first stage involves preparing open-cell or partially open-cell polyurethane foam according to the desired porosity. If the foam is closed-cell, it needs to be subjected to roller compression to rupture the cell walls, thereby creating the necessary porous structure. The second stage is to remove all the cell membranes to form a reticulated structure.

To produce polyurethane filter foam, the size of the pores and the structure of the network of the foam are largely determined by the catalyst, foaming agent, and surfactant.

In practical operations, there are two common methods for forming the network:

First is the alkali hydrolysis method. The steps of this method involve immersing the soft polyester-type polyurethane foam obtained from the first stage in a 10% sodium hydroxide solution at 50 degrees Celsius for about 10 minutes. Then it goes through processes such as washing with water, neutralization with acetic acid, another round of water washing, and drying, resulting in the final product of polyurethane filter foam.

Another method is the combustion method, also known as the explosion method. This method requires placing the soft polyether-type or polyester-type polyurethane foam obtained from the first stage into a sealed container. The container is then evacuated to 13.3 Pa, followed by the introduction of oxygen and natural gas (in a volumetric ratio of 2:1), bringing the internal pressure of the container to a certain level (which increases with the porosity). Next, the gas inside the container is ignited using a spark plug. The heat generated from the combustion process will burn off or melt the cell membranes without damaging the cell struts. Finally, the resulting product after combustion is cleared with air, and the filter foam is removed from the container.

Both of these methods are effective ways to prepare polyurethane filter foam, and the specific choice between them depends on the material of the foam and the desired structural characteristics.