Polyurethane Fillers and Release Agents

Fillers

To reduce the production cost of foam and sometimes improve the hardness or other properties of the foam, organic or inorganic fillers are occasionally added.

Organic fillers like melamine and plant fibers can be used in both soft and rigid polyurethane foams. Inorganic fillers such as calcium carbonate, barium sulfate, kaolin, diatomaceous earth, and talc are generally used as fillers for polyurethane soft foams. For every 100 parts of polyether polyol, the filler dosage can reach 50 to 150 parts or even higher.

In rigid and semi-rigid polyurethane foams produced via RIM (Reaction Injection Molding) and in microcellular elastomer products, special fillers like glass fibers have been widely used. Suitable fillers in RIM and microcellular elastomers can significantly increase the elastic modulus over a wide temperature range, improve thermal stability, and reduce the coefficient of thermal expansion. Details on reinforced fillers for RIM can be found in the RIM chapter.

It should be noted that fillers used in polyurethane must be dried before use. For water-foaming systems, the water content must be measured.

Additionally, vinyl polymers in polymer polyols are classified as organic fillers, serving as a unique type of internally filled polyol.

Release Agents

Polyurethane foam exhibits good adhesion to many materials. Therefore, during molding, release agents must be applied to the mold surface to form a very thin isolation layer between the foam skin and the mold, facilitating product demolding.

Release agents are divided into internal and external types. The former is added directly to the material. However, external release agents are the most commonly used and are mainly composed of two types: silicone and paraffin wax.

Besides requiring excellent release performance, external release agents must also be chosen carefully to avoid adversely affecting the surface quality of the product. For instance, paraffin wax with melting points of 90°C or 110°C in organic solvent solutions or aqueous dispersions, polyethylene wax hydrocarbon solutions, and silicone solutions are typical options.

To improve production efficiency, internal release agents have been developed as important auxiliaries for RIM polyurethane (urea) systems. Internal release agents are added to formulations to assist with demolding. Types of internal release agents include polysiloxane compounds with active organic groups, fatty acid polyesters, higher fatty alcohol or amine ethoxylates, and zinc stearate.