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3. May 2021 | Production & Lab

Water-borne polyurethane with good water resistance and mechanical strength

Researchers report on a terpene derivative-containing silicone two-component waterborne polyurethane for coatings.
The water absorption test showed that the modified polyurethane membrane nearly doubled its ability to prevent water penetration. 
Image source: BillionPhotoscom - stock.adobe.com (symbol image).

With increasing desires to protect the environment, volatile organic solvent emissions have been restricted, and there is a trend in developing waterborne polyurethanes. However, poor water resistance and low mechanical strength of waterborne polyurethane are major obstacles.

Now researchers propose a terpene-modified polysiloxane-based polyurethane that solves the above-stated problems. In the presence of the Karstedt catalyst, isobornyl acrylate (IBOA) was introduced into the branch of hydrogen-containing silicone oil (HSO) through the hydrosilylation reaction. Then, it was mixed with an alkaline aqueous solution to convert the remaining Si-H bonds to Si−OH bonds, which can be used as a polyol component (IBOA-Si-OH). Then, the mixtures of IBOA-Si-OH and polypropylene glycol-400 (PPG-400) were used as polyol components to react with polyisocyanate-3100 (PI-3100) in preparing a two-component waterborne polyurethane.

Tensile strenght

Compared with the unmodified polyurethane film, the contact angle of the polyurethane film modified with IBOA-Si-OH was greater than 102°, which increased by 28°. The water absorption test showed that the modified polyurethane membrane nearly doubled its ability to prevent water penetration (from 18.11 % to 9.38 %). Although the introduction of silicone improved the water resistance of waterborne polyurethane, the mechanical properties were reduced. The introduction of IBOA into the silicone side chain improved the mechanical properties of polyurethane. Comparing WPU-Si with WPU-2, the tensile strength improved by 85.56 % (from 3.47 MPa to 6.44 MPa).

Thermogravimetric analysis and dynamic thermomechanical analysis indicated that silicone reduced Tg and thermal stability, but participation of IBOA made up for this deficiency.

The study has been published in Progress in Organic Coatings, Volume 153, April 2021.

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