The Adjustment of Physical Properties of Viscoelastic Foam – the Role of Different Raw Materials

Viscoelastic polyurethane foam, also referred to as memory foam or low resilience foam, is used mainly in home and office furnishings, although a considerable amount of work has been conducted for automotive applications. During a compression cycle, viscoelastic foams exhibit slow recovery and thus, high hysteresis. Viscoelastic foams also typically have low ball rebound values. They are produced from MDI, TDI 65, TDI 80 and other mixtures of these isocyanates. TDI 80 formulations have a tendency toward closed cell structures, whereas TDI 65 and MDI usually result in foams with reasonable porosity. The role of the cell structure – cell fineness and porosity – turns out to be significant for viscoelastic foams relying on the pneumatic as well as the adhesion effect. The major reason for viscoelastic foam properties however is the glass transition temperature, which is mainly defined by the nature of the polyol mixture. By the specific adjustment of the glass transition temperature, also other foam physical properties (such as foam hardness or compression set) are controllable. Evonik has put many resources into the understanding of the different mechanisms, which influence the physical properties of viscoelastic foam. This paper evaluates different ways to control and precisely adjust physical properties of viscoelastic foam. Finally, the influence of different raw materials on the viscoelasticity and other physical properties of the foam are analyzed.