PVC window frames exceed user demands in many respects, especially in cost and durability, but the relatively low stiffness and rigidity has proved to be a drawback.
Frame producers often have had to reinforce profiles for large windows, which typically has involved adding internal reinforcing bars - though producers also have experimented recently with bonding profiles to the frames to create ``structural'' windows.
However, window makers continue to explore alternatives, with the goals of reducing cost and opening the way to more demanding commercial applications.
Middelfart, Denmark-based pultrusion specialist Fiberline Composites A/S introduced its first translucent, pultruded fiberglass window profile in 2006. Since then, development has accelerated, with several new options launched this year.
A pultruded profile made by Comfort Line Inc., based in Toledo, Ohio, gained an innovation award in March from the European Pultrusion Technology Association in Rome for its introduction of a 65 percent glass-fiber-reinforced polyester window profile.
Comfort Line said the reinforcement system, supplied by Toledo-based Owens Corning, consists of a weft-fiber textile stitched to a random mat. The mat is impregnated with a low-profile polyester resin applied by preform injection as opposed to the more common open-bath or dip-tank techniques.
Bayer MaterialScience AG recently displayed a fiberglass-reinforced, pultruded polyurethane window profile system made using a new BayDur Pul 2500 PU resin developed specifically for pultrusion.
Inline Fiberglass Ltd. of Toronto is using the technology to make profiles used by Alpen Fiberglass Windows of Boulder, Colo., among others. According to Alpen, fiberglass is the fastest-growing window sash and frame material in North America.
Inline Fiberglass founder and chief engineer Stanley Rokicki said: ``The fact that we now have the capability to produce lighter profiles that are strong enough to be used in large frames, even curtain walls, is extremely exciting for us.''
The PU pultrusion process allows the use of high glass-fiber content, making the profile eight time stronger than PVC frames, BMS claimed. It also offers 40 times lower thermal conductivity than aluminum, the firm said.
But PVC producers are responding to the potential challenge from fiberglass and PU.
In April at the JEC 2008 composites fair in Paris, Owens Corning's Christophe Ducret and Virginie Lartisien, application center manager and new business development manager respectively at OCV Reinforcements, described a new thermoplastic pull extrusion system for producing pultruded glass-reinforced PVC profiles.
The system is based on Twintex commingled glass and PET copolyester fibers. French PVC and aluminum profile producer Bouvet SA, which consumes 15 million pounds of PVC and 22 million pounds of aluminum annually, introduced the profiles to the market in March.
Bouvet, in La Membrolle-sur-Longuenee, France, said the technology has eliminated the need for steel reinforcement in its designs and enables straight, rigid and totally insulated profiles to be made in thin designs.
Bouvet has halved the width of a sliding window's central column from 3.6 inches to 1.8 inches and reduced side frames from 4.3 inches to 3 inches. Even then, the thermal conductivity value is 30 percent less than for a slim aluminum design, according to the company.
OCV's Lartisien was careful not to disclose details of the pull extrusion process, but said the copolyester fiber has a low melting temperature and high adhesion to PVC.
PVC also figures in the Geneo window profile announced recently by Rehau, Germany-based window profile producer Rehau AG + Co. Geneo profiles are made in ``Rau-Fipro'' material, which is a glass-fiber-reinforced PVC compound developed by Rehau and processed at its Wittmund, Germany, plant in a standard extrusion process with pultrusion.
According to Rehau, high rigidity of the multichamber profiles allows steel reinforcement elements to be eliminated in 80-90 percent of applications. That reduction cuts the cost and weight of the system, easing transport and handling, Rehau said.
There is also less exposure to continually rising steel prices, the company noted.
