Influence of polyether polyols on foam products

1, hydroxyl value

Generally, the polyols have high functionality and hydroxyl value, and the foams have high hardness, good mechanical and physical properties and good temperature resistance. However, it has poor solubility with other components such as isocyanate.

The reaction of hydroxyl compounds with isocyanate is one of the most common and basic reactions in the synthesis of polyurethane. When the hydroxyl content is the same, the reaction rate with higher functionality is higher and the viscosity of the reactant increases faster. With the same functionality, the reactivity of polyether with high hydroxyl value to TDI was enhanced, while the reactivity of polyether with low hydroxyl value to TDI was weakened. As the two main reactions in the foaming process, the reactivity of TDI with water is equivalent to that with secondary alcohols, so the fluctuation of hydroxyl value of polyether will destroy the reaction balance between TDI and 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 be enhanced, resulting in the main reaction rate not keeping up with the foaming reaction rate, and easy to cause foam collapse.

The fluctuation of polyether hydroxyl value has a great effect on the 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 adding too little TDI, resulting in foam crack, poor resilience, poor strength and compression permanent deformation. Conversely, the amount of TDI added to it will make the foams form large pores and closed pores, increase hardness and longer curing time, and cause heartburn.

2. Unsaturation

The reaction temperature of polyether and the number of catalysts directly affect the unsaturation degree of polyether products. If the reaction temperature is high or the catalyst content is high (the number of activation centers of polyether chain is large), the side reaction will increase and the unsaturation degree will increase. The increase of unsaturation degree indicates that the number of unsaturated substances such as aldehydes increases during the reaction process. The end group of polyether loses its reactivity after forming unsaturated double bond. The chain growth terminates, which affects the average molecular weight of polyether, lowers the average molecular weight, increases the hydroxyl value and decreases the functionality of polyether. The degree of functionality directly affects the performance of foam products. Therefore, in production control, the lower the degree of unsaturation, the less the side reaction, the smaller the impact on the foam products.

3. Moisture

As a foaming agent, water is one of the most important reactions in foamed plastics. A small amount of water can consume a large amount of TDI, produce a large amount of gas and emit heat. Increasing the concentration of water in the reaction mixture can accelerate the reaction rate. If the water content in polyether (calculated by TDI index is ignored), it will not only consume a lot of TDI, but also reduce the activity of polyether, resulting in bubbles and bubbles. At the same time, a large amount of CO[sub]2[/sub] and heat will be released from the reaction, which will reduce the density of foam products. If the heat generated can not be removed rapidly, it will cause yellow heart and even fire. If the moisture content of polyether is too high, the amount of urea bond and CO[sub]2[/sub] will increase, the foam density will become smaller, the foam products will harden, and a large amount of heat will be released to cause heartburn. If customers use it without knowing it, it is equivalent to increasing the water volume, but the amount of TDI and catalyst is not adjusted, which is easy to cause cracking bubbles. Bubble collapse will occur when exceeding the standard seriously. Therefore, the lower the moisture content during the control of polyether, the better the formulation and performance of foam products.

4. acid value

AV can be expressed in the form of hydroxyl value, so high acid value consumes more TDI, but the amount is negligible. The higher reaction temperature and the increase of catalyst concentration will increase the side reaction and increase the acid value. The higher the acid value is, the more the amine catalyst consumed in the foam formation process, and the lower the reaction activity.

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, but the solubility is opposite. The relationship did not change significantly when the molecular weight increased to a certain value. The molecular weight of polyether can be calculated by hydroxyl value and functionality. For the same brand, the size of molecular weight is affected by unsaturated bonds, so the influencing factors of molecular weight change are similar to those of unsaturation. The two factors are mutually reinforcing, that is, the unsaturation degree increases the molecular weight decreases; the unsaturation degree decreases the molecular weight increases.

6. Potassium ion

The presence of residual catalysts in polyether will directly affect the physical properties of polymer preparation and polyurethane products, because potassium ions promote the formation of rigid and cross-linked urethanates and two ureas in polyurethane chemical reaction, which makes the foam products harden, and the elasticity decreases. At the same time, the content of potassium is high. When foaming is used as raw material and TDI, the foaming heat can not be released in time, resulting in foam heartburn.

7. Antioxidants

In order to improve the antioxidant capacity of foam products, we add antioxidants in the process of polyether production and foaming, which can increase the combustion temperature of foam products to more than 180 degrees Celsius, and the amount of added products is related to the amount of water added. The combustion temperature of foam products can be improved to avoid the occurrence of heartburn.

8. Color value

The color value is the most intuitive apparent index of polyether. The quality of polyether can be directly reflected by the color value. The carbon atoms on polyether ether bonds are easy to oxidize, especially in alkaline media and at higher temperatures, which may cause an increase in side reactions and generate unsaturated bonds. If the chromatic value is deep, other indicators such as AV and unsaturation will also change accordingly, and the color of foam products will change accordingly.