As one of the primary raw materials for polyurethane foam, polyether polyols plays a crucial role in determining the final product’s performance. Among the quality attributes of polyether polyols, the moisture content is a significant parameter that cannot be overlooked.

This article will discuss the state of moisture in polyether polyols, analysis methods, and its impact on material performance.

I. State Analysis of Water in Polyether Polyols

Water in polyether polyols typically exists in two states: freezeable and non-freezeable water. The state of these water molecules depends on the state of restraint in the polyol.

1. Freezeable Water: These water molecules have weaker interactions with the polyol chain. Their presence is similar to free water and can freeze at low temperatures.

2. Non-freezeable Water: These water molecules are strongly bound to the polyol chain. They coordinate to the OH group at the end of the polyol chain or bond to the EO chain in the polyol. The frequency of the maximum absorption peak of these water molecules does not shift with increasing moisture content in the high-frequency spectra, hence they are referred to as non-freezeable water.

II. Analysis Methods for Moisture Content in Polyether Polyols

Accurately determining the moisture content in polyether polyols is crucial for controlling their quality. Currently, common analysis methods include differential scanning calorimetry (DSC), high-frequency spectroscopy, and Karl Fischer Titration.

1. DSC: DSC is used to distinguish between freezable and non-freezable water in polyether polyols This method provides a visual representation of the distribution of water molecules in polyether polyols.

2. High-Frequency Spectroscopy: High-frequency spectroscopy is highly sensitive to solution structures and change of state of association between molecules, making it suitable for studying the binding state of water molecules in the polyols. This method can be used to analyze the state of non-freezable water and compare them with the results obtained from DSC analysis.

3. Karl Fischer Titration: Karl Fischer titration is a direct method for determining moisture content and is applicable for most polyether polyols. This method involves extracting water from the sample using anhydrous methanol and then titrating it with Karl Fischer reagent to accurately measure the moisture content in the sample. However, it should be noted that Karl Fischer titration is not suitable for polyether polyols containing thiols, peroxides, or substantial amounts of aldehydes.

III. Impact of Moisture on the Properties of Polyether Polyols

The moisture content in polyether polyols significantly affects their properties.

    Water, as a foaming agent, reacts with isocyanates (TDI) to generate gas and heat.
    Adequate moisture accelerates the reaction rate, but excessive moisture increases TDI consumption, reducing the activity of polyols and potentially leading to foam cracks or collapses.
    Excessive moisture in polyols can increase urethane bonds and carbon dioxide levels, resulting in reduced foam density, harder foam products, and significant heat release. Failure to remove the generated heat quickly can lead to core yellowing or even fires. 
    Therefore, minimizing moisture content in polyols production is essential to ensure the quality and performance of the final products.

Conclusion

Moisture content analysis is crucial for controlling quality of polyether polyols. Methods like differential scanning calorimetry (DSC), high-frequency spectroscopy, and Karl Fischer Titration can accurately determine the content and state of water in polyether polyols. Strict control of moisture content during production and usage is vital to ensure stable performance of foam plastics and to avoid quality and safety issues arising from excessive moisture.