New Generation Sponge Hardener: ORTEGOL ® HA 1

Polyurethane block sponge production has long required an easy and user-friendly method for adjusting sponge hardness. Sponge hardness can be adjusted through various methods.

Normally, reducing sponge hardness—softening the sponge—does not significantly affect other properties of the sponge. However, increasing sponge hardness without unwanted effects on other sponge properties is not possible. Hardness increase can be achieved through multiple methods. The first method that comes to mind is increasing sponge hardness by raising sponge density. A 1 kg/m³ increase in sponge density provides approximately 1.0 kPa (CLD 40%) hardness increase, but this also brings cost increases. Following the same logic, filler materials (CaCO₃ and BaSO₄) can also provide hardness increase, but this increase will not be permanent and will cause weakening in the sponge's physical properties. One of the most common methods is using polymeric polyol in certain ratios. This method provides hardness increase but significantly increases sponge cost as well. Another method is strengthening the sponge's three-dimensional structure—increasing the number of cross-links. This is possible by increasing the TDI index. However, when hardness is increased this way, changes occur in the sponge's pore structure, air permeability decreases, and closed cell count increases. In addition, reaction temperature will rise, increasing yellowing risk and even fire risk within the block.

Another method to strengthen polymeric bonds is accelerating the gelling reaction—increasing the tin catalyst. However, in this method too, the sponge's pore structure changes and air permeability decreases.

A third approach is using additives that increase cross-linking, but as with tin increase, the pore structure will change in this method as well. Evonik, in line with industry demands, conducted long-term research on the sponge hardness mechanism. As a result of this research, a specially developed new additive ORTEGOL® HA 1 was introduced to the industry to meet manufacturer demands. Ortegol® HA 1 provides important advantages to users through significant hardness increase, low usage rate, and minimal impact on the sponge's physical properties. ORTEGOL® HA 1, unlike other hardening additives on the market, provides significant hardness increase on one hand while having minimal impact on the sponge's pore structure on the other. When ORTEGOL® HA 1 is added to the formulation, there is no need to make changes to TDI or tin quantity to maintain the open pore structure. Usage rate ranges from 1 to 5 pphp depending on the desired hardness increase. Depending on sponge density, formulation, and production parameters, a hardness increase of up to 35% is possible without significant changes in pore structure. As shown in Table 1, for 16 kg/m³ density, the hardness increase achieved with 3 pphp ORTEGOL® HA 1 in sponge produced in-box under laboratory conditions with the reference formula is 25%, reaching 35% with 5 pphp. ORTEGOL® HA 1 can be used not only for hardness increase but also for reducing TDI, polymeric polyol, or tin quantity in the formula while maintaining sponge hardness. In this direction, it can be used either for cost reduction if desired or for facilitating process conditions (reaction temperature).  

As shown in Table 2, for 21 kg/m³ density, with the reference formula and in-box sponge produced under laboratory conditions, reducing the index from 105 to 100 and adding 3 pphp ORTEGOL® HA 1 keeps hardness nearly constant while providing significant improvement in the yellowing problem.

             

ORTEGOL® HA 1 should ideally be fed to the system through a separate line, but due to its water solubility, it can also be supplied with water/amine mixture.

  Selim Kubat Area Group Manager / Evonik Ticaret Ltd. Şti.