1. Hydroxyl value

Generally, the polyol compound has high functionality and high hydroxyl value, so the foam produced will have high hardness, good mechanical and physical properties, and good temperature resistance. But the miscibility with other components such as isocyanate is poor.

The reaction of hydroxyl compounds and isocyanates is one of the most common and basic reactions in polyurethane synthesis. When the hydroxyl content is the same, the reaction rate with greater functionality is greater, and the viscosity of the reactant increases quickly. In the case of the same functionality, polyethers with a high hydroxyl value have higher reactivity and stronger reactivity with TDI, and polyethers with a low hydroxyl value have lower reactivity and weaker reactivity with TDI. As the two main reactions in the foaming process: the reactivity of TDI with water is equivalent to its reaction with secondary alcohols, so fluctuations in the hydroxyl value of polyether will disrupt the reaction balance of TDI with polyether and water during the foaming process. If the hydroxyl value is high, the reactivity of TDI with polyether is enhanced, and the main reaction is enhanced. If the hydroxyl value is low, the reaction between TDI and water will increase, causing the main reaction rate to fail to keep up with the foaming reaction rate, and it is easy to cause bubble collapse.

The fluctuation of the hydroxyl value of polyether has a greater impact on foam products. The hydroxyl value of polyether directly affects the amount of TDI added. If the hydroxyl value is high, the amount of TDI will increase. If the user does not adjust the amount of TDI, it is equivalent to Too little TDI is added, resulting in foam cracks, poor resilience, poor strength, and increased compression set. On the contrary, it is equivalent to adding too much TDI, which will cause the foam to form large and closed cells, increase the hardness, and cause heartburn due to long curing time.

2. Unsaturation

The reaction temperature of the polyether and the amount of catalyst directly affect the unsaturation of the polyether product. If the reaction temperature is high or the catalyst content is high (the number of activated centers of the polyether chain is large), the side reactions will increase and the unsaturation will increase. The increase in unsaturation indicates that the aldehydes and other unsaturated substances generated during the reaction increase. The end groups of the polyether lose the reactivity after forming an unsaturated double bond, and the chain growth is terminated, which affects the average molecular weight of the polyether and reduces the average molecular weight. , The hydroxyl value increases, and the functionality of the polyether decreases. The level of functionality directly affects the performance of foam products. Therefore, in production control, the lower the degree of unsaturation, the less side reactions and the smaller the impact on foam products.

3. Moisture

Water as a foaming agent is one of the most important reactions in foam plastics. A small amount of water can consume a large amount of TDI, generate a large amount of gas and release heat. The increase of the water concentration in the reaction mixture can speed up the reaction. If the moisture in the polyether (which is ignored when calculating the TDI index) increases, not only will a large amount of TDI be consumed, which will reduce the activity of the polyether and cause cracking and collapse, but also release a large amount of CO[sub]2[/sub] and Heat will reduce the density of the foam product. If the generated heat cannot be removed quickly, it will cause a yellow heart or even catch fire in severe cases. If the water content of the polyether exceeds the standard, the amount of urea bonds and CO[sub]2[/sub] will increase, the density of the foam will decrease, the foam product will become hard, and a large amount of heat will be released, which may cause heartburn. If the customer uses it without knowing it, it is equivalent to an increase in the amount of water, but the amount of TDI and catalyst has not been adjusted, which is likely to cause cracking and foam collapse when it exceeds the standard. Therefore, in the control process of polyether, the lower the moisture, the better, which is conducive to the stability of the foam product formulation and performance.

4. Acid value

AV can be expressed in the form of hydroxyl value, so high acid value consumes more TDI, but because the amount is small, it can be ignored. The high reaction temperature and the increase of the catalyst concentration will increase the side reaction and increase the acid value; the high acid value consumes more amine catalysts in the foam formation process and reduces the reaction activity. In severe cases, it will be caused by too much amine catalyst consumption. Shrinkage and closed cells of foam products.

5. Molecular weight

The properties of most polymers increase with the increase of molecular weight, such as tensile strength, elongation, melting point, hardness and glass transition temperature, etc. increase with the increase of molecular weight, while solubility is the opposite. This relationship does not change significantly after the molecular weight is increased to a certain value. The molecular weight of polyether can be calculated from hydroxyl value and functionality. For the same brand, the size of molecular weight is affected by unsaturated bonds, so the influencing factors that cause molecular weight changes are similar to those of unsaturation. The two are in a complementary relationship, that is, the same brand of polyether, the degree of unsaturation increases → molecular weight Decrease; decrease of unsaturation → increase of molecular weight.

6. Potassium ion

The presence of residual catalyst in the polyether will directly affect the preparation of prepolymer and the physical properties of polyurethane products, because potassium ions promote the formation of rigid and cross-linked allophanate and biuret groups during the chemical reaction of polyurethane, making foam products It hardens, reduces elasticity, and gels in severe cases. At the same time, the potassium ion content is high. When it is used as a raw material for foaming with TDI, the foaming heat cannot be dissipated in time, resulting in foam heartburn.

7. Antioxidant

In order to improve the oxidation resistance of foam products, we add antioxidants in the production and foaming process of polyether (the combustion temperature of foam products can be increased to above 180°C, and the amount of addition is related to the amount of water added). Increase the combustion temperature of foam products to avoid the occurrence of heartburn.

8. Color value

Color value is the most intuitive appearance index of polyether, and the quality of color value can directly reflect the quality of polyether. The carbon atom on the polyether ether bond is very easy to oxidize, especially in alkaline medium and at higher temperature, it will cause the increase of side reactions and the formation of unsaturated bonds. If the color value is deep, the corresponding other indicators (such as Indexes such as AV, unsaturation, etc.) will also change accordingly, and at the same time cause the color of the foam product to change accordingly.