Windows and façades are a common source of heat loss. To reduce this heat loss, it is important not only to use multi-pane glazing but also to ensure that the window frames are well insulated. Bayer MaterialScience has developed an efficient, robust and durable material solution for heat-insulating yet small window frames, based on polyurethanes (PUs). This enables profiles to be manufactured with a narrow visible height and low installation depth, for example, for the glazing for roofs or elements where space is limited.
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 fibre composites with a tailored polyurethane (PU) matrix.
“These composites are noted for their very good thermal insulation”, explains Dr Andreas Hoffmann, Project Leader for the Europe, Middle East and Africa region. It has a low thermal conductivity similar to that of wood and polyvinyl chloride (PVC)”. In favourable cases, the window frames satisfy the requirements of energy-saving regulations and passive house standards”, says Hoffmann.
Strong and stable
The material’s good mechanical properties are attributable primarily to the high glass fibre content of around 80% by weight. This enables profiles to be manufactured with a narrow visible height and low installation depth, for example, for the glazing for roofs or elements where space is limited, such as sliding doors for balconies and terraces. A heat-insulating lift-and-slide door of Internorm International is a current example (see photo). Due to a ground sill with a height of only 4cm and a small framework construction the door has a huge glass façade and floods the room with light.
Detail of a lift-and-slide door from Internorm company (photo: Internorm International)
Alternatively, large profiles can also be produced for particularly large glass façade 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. Due 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.
Pultrusion process
The fibre reinforced profiles are produced by a continuous process known as pultrusion. This involves pulling rovings of, for instance, glass or carbon fibres from rolls through a closed injection box, where they are impregnated by the liquid PU matrix. Under the influence of heat, the fibre composite is formed and fully cured in the die – in this case, a window profile. It is then cut to size by a saw.
Pultrusion process (video: Bayer MaterialScience)
Finally, the parts – possibly after further machining by grinding, milling or drilling – are integrated into the window or façade elements. Bayer MaterialScience says that working with PU systems generally enables higher production speeds than with alternative matrix materials such as polyester, vinyl esters or epoxy resins.
Further potential applications
The possibilities for PU pultrudates do not end with their use in windows and façades. Promising applications also exist in the transport sector, where, compared with metal, they are said to exhibit good mechanical properties and lower weight. Other examples include infrastructure projects such as bridge construction and utility poles. Because of their high breaking resistance and wear resistance, U-shaped sections made from pultrudate are used for the construction of industrial facilities.
Rotor blade exhibited at K
At the K show, Bayer MaterialScience showcased a glass fibre reinforced rotor blade for a wind turbine. In this case, the special PU resin developed by the company for this application is processed using the vacuum infusion process.
One exhibition highlight at the Bayer MaterialScience booth: the glass fibre reinforced rotor blade for a wind turbine
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