Use and Market of PU Catalysts
2020-05-18    [Source:PUdaily]
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    There are more than 200 catalysts that can be used in polyurethane synthesis, over 20 of which are commonly used. These commonly used catalysts can be divided into two categories, namely, tertiary amines and organometallics.

    Triethylenediamine (ethylenediamine / triethylenediamine) is the most widely used tertiary amines; and the most widely used organometallics are organotin (including dibutyltin dilaurate and stannous octoate) and organobismuth. With a trademark of Dabco, triethylenediamine was developed and commercialized by Air Products in the 1950s. It laid a foundation for the application of tertiary amine catalysts in polyurethane industry. Organotin also began to be used as a catalyst in polyurethane synthesis in 1950s.

 

    Catalysts are used to speed up chain propagation reaction, selectively speed up specific reactions and slow down or inhibit side reactions. In the synthesis of polyurethane, -NCO reacts with H2O to produce CO2; -NCO reacts with terminal hydroxyl groups of polyol to generate NHCOO, and isocyanate self-polymerizes to produce isocyanurate rings. Catalysts can be used to speed up one or more of the three reactions. Catalysts that can speed up the reaction of -NCO with H2O are called blowing catalysts; those speeding up the reaction of -NCO with terminal hydroxyl groups of polyol are called gelling catalysts; those that can speed up the reaction of -NCO with both H2O and terminal hydroxyl groups of polyol are known as balanced catalysts; and those speeding up the self-polymerization of isocyanate are referred to as trimerization catalysts.

    In the presence of catalysts, as the synthesis reaction proceeds, the reaction system sees its viscosity increase and ultimately solidifies to become polyurethane. Besides these conventional catalysts, there are delayed-action catalysts. Delayed-action catalysts and normal ones have largely the same overall activity. but the former have low activity in early stage and high activity in middle stage. These catalysts can be used to improve the fluidity of the reaction system, and win more time for operation.


    In the synthesis of polyurethane, the reaction time varies with catalysts, indicating that the activities of catalysts are varied. In gel reaction, the activity of organometallics is higher than that of tertiary amine. As the amount of catalyst in the reaction system increases, the activity rises. In addition to a single catalyst, a combination of two or more catalysts (i.e., composite catalyst) can also be used. The activity of composite catalyst is significantly higher than that of a single catalyst.

 


    When selecting from the myriad catalysts, we should take into account catalysts’ activity, selectivity, solubility in the raw material system, usage, pricing, chemical toxicity, stability during storage and transportation, and effect of catalyst residues on the finished products.

    There are many catalyst manufacturers at home and abroad. Representative foreign manufacturers include Evonik, Air Products, Huntsman, Tosoh and BASF. Major domestic producers include Yangzhou Dajiang Chemical, Liyang Yutian Chemical, Zhangjiagang Dawei Additives, Nantong Hengguangda and Guangdong Yourun Chemical.

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