Processing technology

Fiber sizing: Covestro waterborne dispersions enable strong polymer resins

Fiber sizing is a thin coating applied to fibers to provide protection and boost fiber properties and adhesion in composites. Covestro waterborne polyurethane dispersions work well as film formers and crosslinkers in high-performance resins and glass, carbon and basalt fiber surfaces.
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Waterborne PU dispersions for fiber sizing

Fibers are coated with sizing for two important reasons. First, fiber sizing provides  protection to the filaments during production processes such as the handling winding and weaving . Second, sizing enhances the fiber’s adhesion properties so it firmly bonds with the resin .  In the composition of the sizing, film formers and crosslinkers are crucial components in achieving the required mechanical properties: bonding, tensile strength and shear strength. Waterborne polyurethane dispersions from Covestro work as high-performance film formers and crosslinkers in sizing formulations used for the carbon, basalt and glass fibers found in both fiber-reinforced thermoplastic  and in thermoset composites.  

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The  components of a sizing are what determine its performance. The film former serves to hold the fibers together before the composite is manufactured.During compounding the film former also enables a proper distribution of the fibers in the matrix. Crosslinkers on the other hand are mainly used to improve the bonding to the resin. This helps to optimize the mechanical properties of the composite part, including its tensile strength and impact resistance, as well as its fatigue performance and thermal and hydrolytic stability. 

In an optimal sizing composition, both components should offer excellent film-forming properties, dilutability and shear strength. Characteristics such as polarity and compatibility with common sizing additives should also be considered to ensure maximum formulating flexibility.  

Our line of Baybond® waterborne polyurethane dispersions (PUDs) is engineered for specific requirements of thermoplastic  and thermoset resins. Our film formers are based on aliphatic isocyanates, and our crosslinker range offers thermal activation at different temperatures. We also produce grades approved for food contact, in line with EU 10/2011.   

 Baybond® film formers and crosslinkers offer solutions tailored to glass, carbon and basalt fiber surfaces and a wide range of thermoplastic and thermoset manufacturer requirements.

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