Polyether polyol cas number is one of the most commonly used chemical materials. The technical indicators of polyether include hydroxyl value, acid value, moisture and so on. In general, manufacturers will announce other technical indicators other than molecular weight. Below Nanjing Chemical Material Corp. will analyze the importance and significance of common indicators for you.
The hydroxyl value is the basis for calculating the amount of substances and the number average molecular weight. It is used to accurately control the mass ratio of isocyanate and polyol (--NCO/--OH) in the formula, predict the viscosity of PET and its prepolymers, determine the soft segment content and it is very important to obtain the finished polyurethane foam with stable performance, and it is also an important indicator to monitor the reaction degree of polyester polyol.
The pH in polyols directly affects the reactivity of isocyanates, and may have a higher or lower impact on the measured value of hydroxyl value. When measuring hydroxyl value, the measured value of acidic polyols should be corrected, that is, the corrected hydroxyl value is equal to the sum of the measured hydroxyl value and the acid value. Generally, the acid value of polyether polyol cas number is extremely low, which can be ignored when calibrating the hydroxyl value; while polyester polyol uses organic acid as raw material, it often has a small amount of acid compound residue in the product, which makes the product have a certain acidity value. The acid value of polyester polyol must be less than 2.0mgKOH/g, otherwise it will bring adverse effects on processing and product performance, so it is particularly important to determine the acid value of polyester polyol.
In addition, during the synthesis of polyols, since the use of catalysts may also bring and produce alkaline impurities, polyols should try to avoid alkaline residues, because it can promote many unpredictable side reactions in the synthesis of polyurethane materials. Therefore, the pH value can be measured to quickly determine the approximate degree of contamination of polyols by acid and alkaline substances.
Moisture control in polyols is also extremely important. Isocyanate is extremely sensitive to water, and a trace amount of water will consume nearly 10 times the amount of isocyanate, and it will also affect the viscosity of the prepolymer and the physical properties of the product; when measuring the hydroxyl value, the water in the polyol will consume part of the acylating agent, and also it will affect the accuracy of hydroxyl value determination; because of the existence of water, it is also difficult to accurately calculate the ratio of isocyanate to hydroxyl in the formula; usually polyurethane polyols require water content below 0.2%, higher than this value, determine the hydroxyl value must be dehydrated first.
In addition, in the polyol synthesis process, a small amount of water can also be used as a starting agent to react with the epoxy compound monomer, so that the amount of starting agent in the prescribed formula increases, resulting in a decrease in the design molecular weight of the synthetic polyol, that is, when the moisture exceeds the standard, the molecular weight may also be different from the usual.