Compiled by Revathy RoyerB.Arch (ID)7th sem

PLASTIC FAÇADE SYSTEMS

POLYCARBONATEPTFE (Teflon)

POLYCARBONATE FAÇADE SYSTEMS

INTRODUCTION :Polycarbonate panels are used mainly for facade glazing and cladding, as an alternative to glass or GRP (glass reinforced plastic) curtain walling and cladding, as well as conventional rain-screen systems. They can also be used for roofing, canopies and interior design elements.

Polycarbonate is a type of thermoplastic — that is, a polymer that becomes pliable or moldable above a specific temperature and returns to a solid state upon cooling. Polycarbonate falls under “engineering thermoplastics”. These are grouped together because of specific properties that allow them to be used in rigorous applications, particularly in the electronics, automotive, construction and manufacturing fields.

Polycarbonate provides a number of advantages when used for glazing.

• Aesthetics Polycarbonate panels come in a range of colors and degrees of translucency. Blocks of colored panels can be arranged into patterns and illuminated facades can be created by combining translucent panels with LED or ambient lighting systems. As a thermoplastic, polycarbonate can also be molded into curved panels to create bespoke facade treatments.

• Thermal performance Trans-lucent polycarbonate wall panels can be manufactured with U-values of 0.71-0.77 W/m2K as a single-wall construction and 0.36-0.43 W/m2K as a double-wall construction. These panels can be used to allow natural daylight to enter a building without compromising its thermal efficiency. Light transmission through translucent panels can be up to 65%.

• Weight Polycarbonate panels are lighter than glass or solid wall systems, so require lighter support structures, which can help to reduce costs.

• Strength : Polycarbonate has excellent impact properties and are up to 200 times stronger than glass. Polycarbonate elements do not crumble or splinter.

• Weather resistance: Polycarbonate panels have been tested for air and water permeability, including a simulated hailstorm test at Swiss testing laboratory EMPA.

• Solar resistance : Ultraviolet filters can be extruded into the polycarbonate, reducing solar gain without blocking natural daylight or the need for a separate film over the panel.

• Fire resistance : Polycarbonate has a very high ignition temperature of about 450ÞC and, in case of fire, produces very little smoke.

• Acoustic protection Despite their light weight, polycarbonate elements have a good sound insulation value of up to 27dB .With a double-wall construction, a value of up to 43dB is achievable.

A typical wall system will use a framing system that is both air- and watertight. This will be composed of perimeter aluminium channels with head, base, side and corner sections and front and rear thermoplastic elastomer gaskets. This framing is fixed to the structure and can be supplied mill-finished, anodised or polyester powder-coated to any RAL colour.

INSTALLING A POLYCARBONATE WINDOW WALL SYSTEM

front-wall installation installation in

embrasure with weatherboard

installation in embrasure without weatherboard

Panel ends are sealed with a combination of aluminium/ butyl tape and vent tape to prevent water, insects, gases and other fine particles from gaining access to the panel chambers. All sealants and tapes must be polycarbonate-compatible, and all silicone must be neutral and solvent-free.

The translucent building elements are delivered — depending on the finish — with one-sided or both-sided protective foil. This film must be kept on throughout installation.

wall profile

bracing bottom profile corner profile System with reinforced aluminium profile

System with 32mm square pipe

• polycarbonate is not as clear as the glass and in office installations you need to leave open parts on the facade to be filled with glass.

• A disadvantage of polycarbonate compared to glass is that degradation occurs with time. Sheet degradation is measured using a yellowness index called ∆YI

• In addition to change in color correlates with a proportionate amount of loss of the sheet's ability to transmit light.

DISADVANTAGES

• A 10 year warranty is the industry standard for polycarbonate sheet products while the working life is considerably longer.

• Actual performance depends on many aspects like individual applications and local environmental factors. With the addition of special coating UV layers 20 years of lifespan is also possible.

• Most thermoplastic materials suffer from slow deterioration as a result of UV exposure. Build ups of moss and dirt will also lead to lower levels of light transmission and thus a lowering of performance.

• During installation workers should always be careful to fix the panels with the UV protected side on the exterior elevation. This is marked on the protective film and may also be discreetly printed along the side of the sheet.

The architect designed the folded angles of polycarbonate at anywhere from 60 to 150 degrees, so the slightly differing angles of elevation create a rhythmical flow with the speed of the vehicles on the road. Meanwhile, the polycarbonate panels on the rear side, facing the downtown buildings, don’t have any angles, a strategy intended to harmonize with the rigidness of the back street.

The polycarbonate facade of the Herma Parking Building

EXAMPLE

For the facade, the architect chose five-layered polycarbonate, coating the inside white and the outside purple, with IR and UV coating increasing the light diffraction. As a result, according to the viewing angle, the facade seems to show through and sometimes has an opaque purple elevation. Dependent on sunlight or night-time illumination, it displays totally different colors and elevation effects.

PTFE (Teflon)

• PTFE, or polytetrafluoroethylene, is a Teflon®-coated woven fiberglass membrane that is extremely durable and weather resistant.

• The woven fiberglass gives the PTFE fiberglass membrane its mechanical strength. These filaments, known as beta glass, are the smallest diameter available and provide the membrane with maximum flexibility. The fibers are drawn from hot melt glass through platinum dies into continuous filaments, and are then twisted and plied into yarn bundles.

• The yarns are woven into a wide structural fabric, which is then coated with PTFE fiberglass to complete the process.

PTFE fiberglass membranes can be installed in climates ranging from the frigid arctic to the scorching desert heat with a project life in some cases exceeding 30 years.

• PTFE fiberglass coating is chemically inert, capable of withstanding temperatures from -100°F to +450°F (-73°C to +232°C).

• The low-surface free energy of the material results in an electrical grade fabric membrane which is readily rinsed by rainwater. It is also completely immune to UV radiation. This unique combination of inertness, thermal stability and surface properties make PTFE-coated fabric membrane ideal for projects requiring superior weather and fire resistance.

• PTFE fiberglass membranes reflect as much as 73 percent of the sun’s energy while holding just seven percent on its exterior surface. Certain grades of PTFE fiberglass can absorb 14 percent of the sun’s energy while allowing 13 percent of natural daylight and seven percent of re-radiated energy (solar heat) to transmit through.

New Bangkok International Airport (NBIA)

• PTFE's fiberglass yarns maintain ultimate tensile strength of 500,000 PSI and a modulus of elasticity of 10.5 PSI x 106 compared to steel, which offers 40,000 PSI and 29 PSI x 106respectively. Under normal conditions, the fabric behaves elastically and does not undergo significant stress relaxation or creep.

The screen that encloses the third side of the Burj al Arab atrium is made of 1mm thick glass fibre fabric with a Teflon coat to stop the dirt sticking. The screen is the largest of it’s type and covers an area of one and a half football pitch and is hung from the top of the building by over a kilometre of 52mm cable.

EXAMPLE

The façade of the recently expanded King Fahd National Library . The bold, yet contextual, design is crucial to the performance of the building, which is located in the extreme climate of Riyadh, Saudi Arabia.Functionally speaking, the approximately 1,000 twisted squares of textile shade the building and infuse its interior spaces with natural light without completely blocking occupant views.

The design also pays homage to the region’s culture. The tensile structure references the local nomadic tradition—as recently as 1950, 40 percent of the country’s population lived in tents—while the intricate pattern echoes the rich history of geometric Islamic ornamentation.

In the extreme temperatures of Riyadh, Saudi Arabia, the glass-enclosed expansion to King Fahd National Library gets dimensional and heat relief with a tensile fabric façade.

:Fahd National Library .

In a city that often experiences temperatures exceeding 100 F, “a glass building is nonsense,” Lücking says. But the firm clung to its concept of wrapping the existing library with a glass edifice by shading the glazing with a polytetrafluoroethylene (PTFE)-coated, woven-glass-fiber membrane 

3D-diagram of the tensile-cable structure that supports the awnings

The awnings block 93 percent of the incoming sunlight all day, save for about 30 minutes at daybreak and 30 minutes at sunset. To avoid turning their glass building into a greenhouse, the designers left a 2-meter gap between the tensile fabric façade and the building. Convection circulates hot air up and out of the cavity.That geometry was the starting point, Lücking says. “The rhythm of the façade dictated everything else ... the grid of structural elements and the interior space.”