As one of the main basic raw materials of polyurethane foams, polyether polyols have an important impact on the performance of the final product.Among the parameter indicators of polyether polyol quality, moisture content is an important parameter that cannot be ignored.
This article will discuss the presence of moisture in polyether polyols, the analysis method and its influence on material properties.
1. The form of moisture in polyether polyols
The moisture in polyether polyols usually exists in two forms: freeze-able water and non-freeze-able water.The state of these two water molecules depends on their degree of restraint in the molecular chain of polyether polyols.
1. Freezable water: This part of the water molecules interact weakly with the molecular chain of polyether polyols. Their existence is similar to free water and can freeze at low temperatures.
2. Non-freezing water: This part of the water molecule has a strong interaction with the molecular chain of the polyether polyol, usually directly coordinated with the hydroxyl group (OH) at the end of the polyether polyol chain, or combined with the ethoxy (EO) chain in the polyether polyol.The maximum absorption peak frequency of these water molecules in the high-frequency spectrum does not move as the moisture content increases, so it is called non-freezing water.
2. Analysis method of moisture in polyether polyols
Accurate determination of the moisture content in polyether polyols is essential to control their quality.Currently, commonly used analysis methods include differential scanning calorimetry (DSC) and high frequency spectroscopy, as well as Karl Fischer titration.
1. Differential scanning calorimetry (DSC): DSC distinguishes between freeze-able and non-freeze-able water by measuring the heat change of the sample during heating.This method can visually display the state distribution of water molecules in polyether polyols.
2. High-frequency spectroscopy: High-frequency spectroscopy is very sensitive to changes in solution structure and intermolecular association state, and is suitable for studying the binding state of water molecules in polyether polyols.Through this method, the specific form of non-freezing water can be analyzed and the differences between it and the DSC analysis results can be compared.
3. Karl Fischer titration method: Karl Fischer titration method is a method for directly determining the moisture content, which is suitable for the determination of the moisture content of most polyether polyols.This method extracts the moisture in the sample from anhydrous methanol, and then titrates it with Karl Fischer reagent to accurately calculate the moisture content in the sample.However, it should be noted that the Karl Fischer titration method is not suitable for polyether polyols containing thiols, peroxides, or equivalent aldehydes.3. The effect of moisture on the properties of polyether polyols