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So what are porous plastics? Generally speaking, the term porous plastic defines a molded, open-cell, porous material made from any number of thermoplastic polymers. By molded, we mean a rigid body that has 3D features. By open-cell, we mean a material that enables air (or fluid) to flow from one side of the part to the other as water flows through a sponge. The porous network that enables fluidic communication throughout the thermoplastic material is created in a basic sintering process.
Sintering is a production process that is used to make porous components from thermoplastic powders. In most cases, the powder is subjected to a thermal/compression cycle that causes adjacent powder particles to adhere to one another. During the formation cycle, a neck forms at the contact point between adjacent particles when the thermoplastic begins to soften. The neck serves as the connecting point between the two particles and is a reaction to the material's attempt to lower its surface energy by reducing its collective surface area. As a result, this favorable reaction enables adjacent particles to bond to one another.
As an example of this sintering process in action, imagine filling a coffee cup with a handful of marbles. If the coffee cup and marbles were subjected to a sintering process, the marbles contained within the coffee cup will bind to each other without changing their shape. In other words, each marble will stick to its adjacent neighbor without eliminating the air space between each of the marbles. Remove the marble mass from the cup and voila, you have a porous plastic component. Now, instead of using marbles as described in the example above, use thermoplastic particles. Subject the coffee cup filled with thermoplastic particles to its own sintering process and again, a porous component will be created.
By using the sintering process described above with a variety of different raw materials, ThermoPore can produce porous plastic components with different pore size (the size of the opening between adjacent particles), pore volume (the percentage of air per unit volume present in the porous part). In addition, by using various raw materials at the onset of the sintering process or by creating a raw material blend composed of multiple raw material types, ThermoPore can create porous plastic components that offer a variety of functional options in a single porous plastic component.
One of the most exciting design variables associated with porous plastic concerns the flexibility that engineers are afforded with the raw materials used in the porous plastic sintering process. The table below shows a correlation between the design variable inputs and the corresponding functional outputs.