Bayer composites develops energy efficient windows

Large windows that flood the room with light are highly fashionable at the moment, particularly in public buildings. The frames are therefore becoming smaller, yet they must still offer correspondingly high rigidity and dimensional stability. To comply with all these requirements, Bayer MaterialScience has developed an efficient, robust and durable material solution based on fiber composites with a tailored polyurethane matrix.

“These composites are noted for their very good thermal insulation,” explains Dr. Andreas Hoffmann, head of the project in the Europe, Middle East and Africa region. It has a low thermal conductivity similar to that of wood and polyvinyl chloride (PVC). “In favorable cases, the window frames satisfy the requirements of energy-saving regulations and passive house standards,” says Hoffmann.

Excellent strength and dimensional stability

The material’s outstanding mechanical properties are attributable primarily to the high glass fiber content of around 80 percent by weight. This makes it possible to manufacture profiles with a very narrow visible height and low installation depth, for example for the glazing for roofs or elements where space is limited, like sliding doors for balconies and terraces. A heat-insulating lift-and-slide door of Internorm International GmbH is a current example. Thanks to a ground sill with a height of only four centimeters and a small framework construction the door has a huge glass facade and floods the room with light.

Alternatively, large profiles can also be produced for particularly large glass facade windows. The good mechanical properties also help to reduce overall weight. This facilitates assembly and later opening of the window elements.

The composite materials are protected from the weather by a suitable coating or by the application of a laminating film. This eliminates any risk of rotting as in the case of a wooden frame or of embrittlement as with PVC. Thanks to the material’s good dimensional stability, only minor stresses occur at the joint between the glass and the window frame when subjected to marked changes of temperature. The joint remains permanently air-tight.

Continuous production by pultrusion

The fiber-reinforced profiles are produced by a continuous process known as pultrusion. This involves pulling rovings of e.g. glass or carbon fibers from rolls through a closed injection box, where they are impregnated by the liquid polyurethane matrix. Under the influence of heat, the fiber composite is formed and fully cured in the die – in this case, a window profile. It is then cut to size by a saw.