Tensile structures using membrane systems offer a world of possibilities for architects. More and more, projects are turning to Ethylene Tetrafluoroethylene (ETFE), a high-strength fluoropolymer, in their tensile membrane systems.
ETFE is a versatile material – it is self-cleaning, durable, environmentally friendly and can be highly customized during fabrication.
In this blog, we’ll explore ETFE’s production and properties. Then delve into types of systems utilizing ETFE and their real-life applications. By understanding membranes, you’ll be better equipped to utilize the system in your next project.
How is ETFE Made?
ETFE is produced through a chemical process known as free-radical polymerization. This involves the copolymerization of two key ingredients: ethylene and tetrafluoroethylene (ETFE).
An organic peroxide initiator triggers the polymerization process. During polymerization, the molecules of these substances combine to form a long chain, creating the ETFE polymer. The process is conducted in specialized vessels due to the potential risk of explosive decomposition reactions.
The copolymerization takes place at low pressure, using an inert chlorofluorocarbon solvent. Fluorinated peroxides serve as initiators, and methanol is used as a chain transfer agent.
The introduction of an additional termonomer into the mix increases the flexibility of the ETFE. The enhanced flexibility, along with other properties, makes it ideal for large-scale commercial applications.
Once the ETFE polymer is created, it can be formed into membrane structures in various ways. One method is as a single-layer tensioned film, akin to PVC or PTFE films, where ETFE is stretched over a structure.
Alternatively, it can be fashioned into double-layer or multilayer air cushion structures. Here, the ETFE is cut and stitched together to form air cushions between the layers, which can take on a variety of shapes. These cushions are then connected using aluminum alloy frames or cable networks to create expansive coverage spaces.
ETFE Material Properties & Benefits
ETFE membranes have numerous benefits making them a preferred choice for architects and designers worldwide. Its unique blend of properties and benefits makes it the ideal choice for innovative design and construction.
Let’s delve deeper into what makes ETFE such a preferred choice.
Exceptional Durability: With an impressive lifespan exceeding 25 years, ETFE has an anti-aging ability. This durability makes it a long-term investment for any architectural project.
Self-Cleaning Performance: The smooth surface of ETFE film makes it a self-cleaning material. Dust and dirt can be easily removed from the membrane structure of the ETFE film. Reducing maintenance requirements and costs overtime.
Climate Resistance: ETFE’s working temperature range spans from 200 to 150℃, with a melting point of approximately 275℃. This gives ETFE exceptional stability and adaptability to various climatic conditions. It maintains its mechanical and optical properties after more than 15 years of exposure to severe weather. ETFE’s weather resistance makes it a reliable choice for outdoor structures.
Natural Lighting: ETFE boasts high translucency, transmitting up to 95% of light, making it perfect for projects requiring high light and UV transmission, such as large-span roofing, skylights, and facades. Additionally, ETFE film absorbs most infrared light, which can be harnessed to improve a building’s energy efficiency.
Environmentally Friendly: The eco-friendly and recyclable characteristics of ETFE supports sustainability in construction, making it an ideal choice for architectural projects throughout the world.
Fire Safety: ETFE’s high melting point is approximately 260°C. It doesn’t generate flaming droplets or particles in case of fire. Coupled with its ability to self-extinguish – and not promote the spread of flames – makes it a safe choice for construction. With all of its flame-resistant properties, ETFE meets various international and national fire safety standards.
In essence, ETFE’s durability, climate resistance, energy efficiency, and aesthetic appeal make it a versatile and attractive material for architectural design and construction. Its wide range of applications and benefits truly sets it apart.
Types of Tensile Membrane Systems Using ETFE
Novum Structures offers three distinctive system products for architectural membrane enclosures: Air Filled Pillow (AFP), Stressed Skin Membrane (SSM), and Cable Tensioned Fabric (CTF). The AFP and SSM systems utilize ETFE membrane layers.
CTF Systems use woven materials, like PVC or PTFE, instead of ETFE. These make them perfect for lightweight primary structures with heavier foundations. These look more like classical “tent” architecture.
Each system has its unique advantages and is suitable for different applications.
Air Filled Pillow
Air Filled Pillow system utilizes 2, 3, or 4 layers of ETFE membrane that are edge-welded into sealed units. Pillows can be large and take on any shape—be it rectangular, triangular, or octagonal, making them perfect for complex freeform structures, even those extending over 200′ (60m).
AFP systems require less structural steel support than traditional glazed systems. Since they require less support, installation is easier and less cost intensive.
Layers can be customized, offering a wide range of shades and custom options. When using ETFE raw material, pigmentation can be done before extruding to achieve multiple colors and opacities. Membrane printing enables a variety of options, including standard colors and patterns such as:
- Reverse Dots
- Rain Effects
It can also be customized to meet full-screen and logo requirements. This versatility allows for captivating designs and enhances visual appeal.
Novum utilizes dual chamber pumps and advanced sensors to create pillows that are filled with air under low pressure. Our in-house software predicts potential prone areas and adjusts the geometric form to prevent wrinkling.
For enhanced functionality, our air supply systems can be integrated with master control systems, wireless access points, SMS alerts, and other BMS solutions. We also offer bird deterrent systems, color-coated air feeds, and custom-operable vents.
Stressed Skin Membrane
The Stressed Skin Membrane system uses a single layer of ETFE with biaxial tension applied by low-force perimeter tensioning. Making it ideal for a range of applications, including:
- Rain Shelters
- Stadium Roofs
- Glass Skylight Replacements
The Stressed Skin Membrane (SSM) is perfect for areas that require lightweight transparent covering, minimal maintenance, and nominal thermal performance.
These systems comprise perimeters and panel intermediates made from anodized or powder-coated aluminum extrusions. Internal guttering is commonly utilized in the intermediates.
The cable spacing, typically around 2′ (600mm), is determined based on environmental loads. Drainage requires careful planning due to the ultra-light and flexible nature of the system, which deflects easily. The weight of the system is below 1 psf (0.05 kpa), making it arguably the lightest enclosure system available.
To limit membrane spans and avoid the need for cables, the materials are stretched over spaceframe grids or stiff steelwork. The tension forces are held within the steelwork, and clamping bars are applied as required to prevent uplift.
In cases where smaller pre-made aluminum framed panels are feasible, the cables are eliminated, and the system becomes unitized. ETFE is commonly used in a single skin system, offering nominal thermal performance. For shading purposes, colored, solid, or translucent materials can be conveniently employed.
Example ETFE Facade & Canopy Structure Projects
Most projects require one or the other ETFE Membrane System. Some projects require using AFP & SSM Systems to realize the architect’s design intent. For example, the Skylight at Post Houston in Houston, Texas, USA.
Novum engineered, fabricated, and installed three beautiful ETFE skylights for the POST Houston entertainment venue in Houston, TX. The rectangular skylights utilize Novum’s Air Filled Pillow System as cladding with ETFE cushions. The largest skylight measures 139’ long by 82’ wide, with the other two skylights measuring 112’ long by 55’ wide. In total, the ETFE membrane spans 22,520 sq ft above the atriums to provide stunningly transparent roofs.
The architect approached Novum to engineer multiple canopies with transparent roofs to complement existing ETFE air filled pillow structures on the property. As there was no requirement for thermal insulation, Novum proposed an innovative, single layer of tensioned ETFE to achieve maximum transparency. Stainless steel cables are in ETFE pockets below the membrane to resist wind and snow loads. Simple steelwork supports the very light skin. Our expertise relating to each material allowed the concept to be fast-tracked into construction.
ETFE Membrane systems offer a high level of adaptability. The systems have unique aesthetics and distinct approaches to delivering the necessary surface tension.
Connect with Novum’s ETFE Membrane experts to find the solution best suited to realize the design intent of your next project.