Slow rebound sponge

17 . Nov . 2023

The typical characteristic of slow rebound sponges is that when external forces are applied and withdrawn, the deformation process and recovery trajectory are not nearly instantaneous and synchronous response as common sponges. In particular, when reducing, it starts from the outer edge of the stress core point, gradually recovers from the outside, and finally recovers from the stress core point. According to this characteristic of slow rebound sponge, many cushioning products, cushion materials and crafts have been developed.

This property of the slow rebound sponge can evenly distribute the pressure exerted on it by irregularly shaped objects, hence the name zero pressure sponge. At the same time, the weak rebound force can maintain the external objects pressed on the sponge to form the geometric shape, which is also the nickname of memory sponge.

Formation mechanism of slow rebound sponge

As we all know, sponge is made of polyether polyols and isocyanate as the main material, and add the necessary additives.

Under normal circumstances, the use of relatively large molecular weight polyether polyols (such as molecular weight 3000 and above 3000) and polymer polyols (molecular weight 60000 and above 6000) and isocyanate reaction, the preparation is a fast rebound sponge, known as ordinary sponge in the industry.

In the preparation of slow recovery sponges, high molecular weight polyether polyols/polymer polyols are al always used in combination with low molecular weight polyether polyols (such as molecular weight 700 and 550).

In general, we mix polyethers with molecular weight 3000 or above and polyethers with molecular weight 550 or 700 and react with isocyanate to prepare slow recovery sponges. After the reaction of polyether with isocyanate, chain segments of different molecular weight will be formed. The substance produced by the reaction of high molecular weight polyether with isocyanate is called soft segment, and the substance produced by the reaction of low molecular weight polyether with isocyanate is called hard segment. These segments are held together by chemical and physical bonds, which both intertwine, pile up, and cause slight phase separation due to steric effects.

As we all know, high molecular weight polyether has low hydroxyl value and low crosslinking density in reaction with isocyanate, so the soft segment has large intramolecular and intermolecular activity space, easy deformation and recovery, that is to say, the soft segment activity is high. However, low molecular weight polyether has high hydroxyl value, high crosslinking density with isocyanate reaction, small intramolecular and intermolecular activity space, and difficult deformation and recovery, that is, low hard segment activity.

The above properties of the soft and hard segments, combined with the slight phase separation within the polymer, cause the slow rebound sponge to show asynchronous deformation and recovery of the soft and hard segments during the process of applying and withdrawing external forces. The reason is that soft section deformation and recovery speed is fast, hard section deformation and recovery speed is slow. This is how a slow rebound sponge is formed.

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