Factors influencing the resilience of PU foam include the following aspects:
(1) Cell opening rate:
When the open-cell rate of the product is high, most polymers are evenly distributed in the naturally open-celled foam network, resulting in higher resilience. When the open-cell rate decreases, the product’s resilience decreases. Therefore, increasing the amount of foaming agent can be considered, adjusting the surface tension of the cell wall to achieve a moderate level of cell wall rupture, thereby increasing the open-cell rate of polyurethane foam plastic.
(2) Cell shape:
As the regularity of cell shape increases, the resilience of polyurethane foam plastic increases. Polyurethane foam plastic with a spherical cell structure exhibits better resilience. Needle-shaped cell structures are prone to collapse. Therefore, reducing the foaming temperature can help avoid cell collapse due to excessive expansion and mutual compression deformation.
(3) Cell pore size and distribution:
In the same system, foaming bodies with a larger proportion of small cells will have a higher rebound rate. However, there is an optimal value for cell pore size, and the rebound rate of foam plastic increases with the increase of cell density. Properly increasing the pore stabilizer can achieve the maximum cell density.
(4) Polyether polyol:
Within a certain range, the higher the relative molecular weight of polyether polyol, the better the flexibility of the molecular chain and the better the resilience. However, measures should be taken to reduce its degradation when using polyether polyols with a large relative molecular weight, such as adding an appropriate amount of antioxidant before the polymerization reaction.
(5) Isocyanate:
It is important to control the isocyanate index, or TDI index, which is the ratio of the actual TDI usage to the theoretically calculated usage. Within the TDI index range of 105~115, the foam hardness can be conveniently and safely controlled. Within a certain range, an increase in the TDI index leads to an increase in foam hardness and resilience. Therefore, the TDI index can be appropriately increased.
(6) Other factors:
The resilience of foam plastic first increases and then decreases with the increase of the mass ratio of water to polyol. Adjusting the water addition amount can maintain higher resilience. As the mass ratio of chain extender to polyol increases, the tensile strength of the product increases, and resilience decreases. Therefore, reducing the amount of chain extender can be considered.
