Window frames of plastic and aluminium usually consist of profiles filled with thermal insulation of foamed polyurethane or polystyrene. Some products use aluminium and timber, where timber is the insulating and structural material. Lower quality timber can be used, as the outer layer of aluminium protects against climate exposure. Aluminium products are usually coated with a thin polymer powder coating. Plastic windows are usually made of hard polyvinyl chloride (PVC) stabilized by cadmium, lead and tin compounds and with added colour pigments. A structural core of steel is always used. In recent years, window frames made from specially developed plastic composites have also appeared which have less heat loss than both aluminium and PVC.
A flush door.
Plastic and aluminium products have a very limited reserve of raw materials, and pollution during processing is considerable. The manufacture of an aluminium window uses 6 to 10 times more energy input than a timber window; a window of PVC uses about 3 times more and a wooden window with aluminium cladding approximately 50% more.
The lifetime for PVC windows will be shorter than for aluminium ones. This is mainly due to their sensitivity to temperature changes and ultraviolet radiation. However, if not protected well by coatings, aluminium gets easily damaged under corrosive conditions especially in coastal and industrial areas.
Many aluminium and PVC window frames are assembled in situ and likely to fall to pieces when removed. But both plastic and aluminium windows can be re-used if they are initially installed for easy dismantling. Pure aluminium windows can be material-recycled. This is unlikely for the other products, as they all contain complex combinations of different materials. Waste has to be deposited at special tips. From combustion of PVC dioxins and heavy metals can be emitted. Special care for disposal of the ash must be exercised.
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