The new composite material meets strict fire protection requirements while reducing the weight of battery boxes for ships, rail cars, electric vehicles and airplanes. #outofautoclave #polyacrylonitrile#precursor

SAERcore LEO, a flame-retardant material used in a series of resin-infused structures, includes chopped glass fiber mats and flame-retardant PP foam cores, which can provide drape and resin fluidity for complex shapes. Source | Certes    

  SAERTEX LEO COATED FABRIC, the flame-retardant material used in a series of resin-infused structures, meets the external burn-through requirements of the track floor through an intumescent material that generates insulating foam when exposed to fire. Source | Certes    

Figure 1 An intumescent veil, multiple versions. Tecnofire fiber and particle composition are tailored for each application-more than 100 versions have been developed so far. Source | Total Factor Productivity    

Figure 1 A kind of intumescent veil, various versions of Tecnofire intumescent non-woven veil is very suitable for pultrusion (as shown in the picture), RTM and resin infusion process. Source | Total Factor Productivity  

Lightweight FR for bridges and bus structures. Technofire was used on the Whitestone Bridge in New York City. The steel wind fairing was replaced with FR-resistant FRP (see the white curved plate on the left side of the bridge deck) to reduce the bridge load 6,000 metric tons. Source | Continuous Wave  

Lightweight flame retardants for bridges and bus structures This example structure comes from a vinyl ester-infused bus body panel and demonstrates how the Tecnofire intumescent non-woven fabric veil blends into the surface of the sandwich structure. Source | Total Factor Productivity

Figure 2 Light-duty RTM track floor SMT is using SAERTEX LEO system and light-duty RTM process to produce 25,000 square meters of composite track car floor to replace the plywood in the ICE version 3 high-speed train of Deutsche Bahn. Source | Deutsche Bahn        

Figure 2 Lightweight RTM track floor SMT The light weight RTM process used for the ICE version 3 train floor incorporates Alan Harper Composites' reusable membranes. Source | Certes

Figure 3 Bio-based PFA prepreg replaces phenolic resin in track components. TRB Lightweight Structures launched its CFRP rail car door leaf in June 2018. The use of bio-based PFA prepreg reduces weight by 35% compared with bonded aluminum. . Source | TRB Lightweight Structure

Figure 3 Bio-based PFA prepreg replaces the phenolic resin Bercella in the track assembly. The cantilever rail car seat support also uses the carbon fiber/PFA prepreg provided by Composites Evolution. Source | Evolution of composite materials, Bercella

Figure 4 1200°C 2 hours without burning through CFP composite material Combine chopped carbon fiber and inorganic resin to produce FR.10 material, after direct burning and 1200°C without burning through for 2 hours, fully put your bare hands on the back of the heat insulation Floor. Source | CFP Composite  

The list of mechanical functions expected to be provided by composite materials is well known and long: strength, stiffness, toughness, durability, weather resistance, corrosion resistance, impact resistance, and fire resistance. The last requirement is a requirement that composite materials have been addressing for many years. However, due to the development of electric vehicles (EV)-whether on the ground or in the air-and eventually penetrate into the fire-conscious railway, ship, and construction sectors, the industry's demand for fire protection performance is on the rise in the market.

As will be revealed here, material suppliers are responding to this market pull, but the industry cannot just rely on traditional refractory solutions to meet the needs of this market. For example, furan and phenolic resins have long been solutions for refractory composites. However, they are cross-linked through a condensation reaction, which makes processing more difficult, usually produces porosity, and requires multiple operations to obtain a good surface finish. They also tend to be brittle. At the same time, flame retardants such as aluminum trihydroxide (ATH), which are added to the resin to provide fire resistance, usually require a volume load of 20%, which can adversely affect processing, mechanical properties, and surface finish. At the same time, halogenated flame retardants used to be an attractive alternative and are now banned by pan-European regulations including REACH and RoHS. Therefore, the composite material industry is constantly researching and developing new solutions.

Fireproof materials must also provide enough time and protection for the occupants to escape in the event of a fire. In the most stringent applications, this means not only preventing flame spread, heat release, temperature transfer and formation of toxic fumes, but also maintaining a load-bearing capacity in the composite for up to 60 minutes.

Generally, inorganic fibers (eg, glass, carbon, basalt, ceramic) and inorganic matrix materials (eg, ceramic/carbon, metal, polysialic acid/geopolymer) do not burn, and many can withstand high temperatures. However, most organic fibers and polymer matrix decompose when exposed to high temperature and fire (Figure 1), and may also release flammable gases and toxic fumes. KEVLAR para-aramid and NOMEX meta-aramid organic fibers are notable exceptions, which are organic fibers with an inherent flame-retardant chemical structure.

The fire performance of composite materials is measured by a variety of characteristics, including ignition, self-extinguishing ability, flame spread, burn through, heat release, smoke generation, and smoke toxicity. Another frequently mentioned requirement is the Limited Oxygen Index (LOI), which measures the minimum oxygen concentration (expressed as a percentage by volume) required for combustion; therefore, a higher LOI means higher flame resistance. The standard tests for these performance measurements vary by industry and the range of test sample sizes, from small specimens to full-scale structures that represent in-service use. More detailed information is available in the online sidebar "Measuring and improving the fire resistance of composite materials".

There are two main ways to improve the fire resistance of composite materials: to improve the flame retardancy of the matrix and/or reinforcing fibers, or to provide a protective coating.

Fibers can be treated with flame retardants (FR), such as borax/boric acid mixtures and ammonium salts of strong acids. The flame retardancy of the matrix resin can be improved by three basic methods: incorporating flame retardant compounds into the polymer backbone; mixing flame retardant compounds, particulates and/or nanomaterials into the resin; or adding expansion agents to the matrix. Expansion agent is a substance that is activated by heat to expand and form porous carbonaceous carbon, which can insulate the underlying composite material and inhibit the generation of flammable volatiles. The coating can use flame retardant additives or expansion agents.

Flame retardant additives can use a variety of mechanisms to slow down the decomposition, heat release and flame spread of composite materials. For example, the additive can be decomposed through an endothermic reaction to cool the composite material. This decomposition may also produce water and incombustible gases, thereby diluting the concentration of combustible gases. Additives may also scorch and/or create a gaseous layer, which removes oxygen and suffocates the fire. Usually, two or more flame retardants are synergistically combined to increase and expand the fire performance of composite materials-for example, one flame retardant compound may reduce heat release, while another reduces smoke, and the third Produce coke.

The systematic approach is exactly what the material supplier SAERTEX (Salbeck, Germany) pursues in its LEO series of FR products, which include the company's non-crimp fabric (NCF) reinforcement, FR foam core and ATH filled or intumescent coating. The first product in the series, LEO SYSTEM, was launched in 2013, combining flame-retardant treated SAERTEX fabric with flame-retardant resin and flame-retardant or intumescent gel coat. "We want to close the gap between fire performance and mechanical performance," explains Jörg Bünker, head of LEO R&D/Application Services SAERTEX. "With LEO SYSTEM, you can get high fiber content and high fire resistance. We never use ATH or other filler modified fabrics and vinyl ester infusion resins, but use liquid flame retardants for treatment. It also avoids all Halogens and bromides, so there are no toxic materials, which means there is no toxic fumes."

SAERTEX LEO SYSTEM is being used in the floors of 66 ICE version 3 high-speed trains in Germany, which is 50% lighter than the previous plywood (Figure 2). The average size of the composite board is 2.4 x 1.2m, including SAERfoam core, glass fiber NCF surface layer, LEO infused vinyl ester resin and LEO protective layer in the veneer. Reusable silicone film from Alan Harper Composites (Cornish, UK) is used for vacuum infusion. The floor panels are manufactured by SMT Montagetechnik (Foster, Germany), the exclusive supplier of Deutsche Bahn, which produces 25,000 square meters for 66 eight-car trains. Meter panel.

Bünker stated that LEO SYSTEM has received wide acclaim, “but some customers want to use epoxy, polyester or thermoplastic resins, so we developed LEO COATED FABRIC.” SAERTEX applies intumescent coatings after fabric manufacturing. "It will slightly impregnate the fibers, thus forming a good connection with the composite material," he explained. "It cannot be worn or scraped off like some paints. In the event of a fire, the intumescent coating will create foam, which protects the composite from flame and heat. It provides fire resistance to the load-bearing structure without smoke or toxic fumes. Meet the highest requirements." LEO COATED FABRIC is available in roll form and used like any other impregnated fabric. "The only thing you need to pay attention to is," Bünker warned, "if you use it as the top layer before the vacuum bag, because you can't impregnate through this layer to any laminate layer below."

Bünker said that the third product, SAERcore LEO, "is a micro sandwich material that contains chopped strand mats (glass fibers) on both sides of a polypropylene (PP) core material that has undergone a special flame-retardant treatment." "This combination of materials It is easy to drape and provides good resin fluidity during the infusion process." SAERcore LEO is placed in a molding tool with a reverse mold in the light resin transfer molding (light RTM) process. "You can adjust the thickness of the part through the cavity between the mold and the sub-mold," he pointed out, "and you can pre-calculate how much resin content you need." SAERcore LEO has a variety of densities and thicknesses to choose from, and can be combined with vinyl Ester, epoxy resin and polyester resin are used together. "If you want to combine the FR method, you can add ATH to the resin," Bünker said. "This material is most commonly used in polyester RTM applications. We recommend filling resin and gel coat from Scott Bader because it has been tested and works well."

All three SAERTEX LEO products have passed the European railway application standard EN 45545, including the most stringent HL3 level for underground and high-speed trains. The global rail product supplier BARAT Group (Saint-Aignan, France) is using SAERcore LEO to produce inspection doors for Stadler (Busnain, Switzerland) SMILE high-speed trains. The door has a complex molded area and is made into a single piece using RTM and FR resin.

SAERTEX LEO products have also passed the architectural application of ASTM E84 and are used by Carbures Civil Works Spain (Porto Santa Maria, Cádiz) as the headquarters of the Norman Foster Foundation (Madrid, Madrid, Spain). "This type of application is also very suitable for SAERTEX COATED FABRIC, because they usually use large plates with insulation requirements similar to ship bulkheads, for example, a certain temperature profile is mandatory after exposure to fire for 30 and 60 minutes," Bünker said.

Another refractory solution for composite materials is intumescent veils. Tecnofire is a series of expanded nonwoven products manufactured by Technical Fiber Products (TFP, Burneside Mills, UK and Schenectady, New York, USA) using a wet process (Figure 1). Made into rolls, the product thickness ranges from 0.4-10 mm (0.5-2.0 mm is the most common). It has a maximum width of 50 inches and can be cut into tapes as narrow as 0.25 inches wide. Tecnofire can be used in pultrusion, RTM and vacuum infusion processes. It is suitable for a range of resins, including epoxy resins and vinyl from Ashland (Columbus, Ohio, USA) and Polynt (Carpentersville, Illinois, USA) Esters, unsaturated polyesters, thermoplastics and FR modification systems.

“When Tecnofire materials reach 190°C, they will activate unidirectionally in the z-direction and expand to 35 times their original thickness,” explains Scott Klopfer, TFP Business Development Assistant. "This irreversible expansion forms an insulating carbon layer. Tecnofire is usually used on the surface of the part, where it will be exposed to heat and flame in a fire." Tecnofire is specially designed to remain stable and stable in the event of a fire. Protect the underlying structure.

"What we can add to this material, including different types of fibers and particles, we have a lot of freedom," Klopfer explained. "We tailor the ingredients for each application. For example, we can add ATH in powder form during the manufacturing process of Tecnofire and disperse it evenly throughout the material." He did this with the addition of ATH to the matrix resin. The traditional process is compared, the latter will lead to an increase in viscosity. "ATH may also migrate or filter unevenly during the molding process," Klopfer said. "Tecnofire avoids these problems."

Since the establishment of Tecnofire in 2005, TFP has created more than 100 versions, of which 10-15 levels have been put into commercial use. An epoxy resin has been injected to provide 4 x 8 feet panels, such as plywood. "This was created for an industry that requires veneer-type materials," he explained. "It is one of the highest expanders. We also have a patented version that uses metal-coated fibers for electrical activation to make a conductive and fire-resistant composite material. But regardless of the grade, Tecnofire becomes a composite material. An indispensable part."

Applications include continuous profiles with built-in fire protection for roof systems, door and window frames, steel beam coverings, and modular composite housing kits. "It is also used for 45-minute and 90-minute rated doors, providing a solution for passing the UL 10C positive pressure test of the door assembly," Klopfer said. "The standard ensures that the door remains intact to prevent flames and heat from spreading between rooms. At the end of the test, the door must be able to withstand the high-pressure water fire hose and still have integrity to remain in place."

For more applications of Tecnofire, please refer to "Tecnofire adds fire resistance to traffic and infrastructure applications."

Polyfurfuryl alcohol (PFA) is a thermosetting resin that can meet phenolic properties, has better surface treatment and sustainability. Its manufacturing starts with hemicellulose derived from biomass-corn cobs, rice and oat husks or sugarcane waste (bagasse)-which is converted into furan-based furfuryl alcohol and then polymerized (through acid catalysts or temperature). PFA. “Glass/phenolic resin has long been the material of choice, but if you want to accelerate weight reduction, you can consider carbon fiber and PFA,” said Gareth Davies, commercial manager of Composites Evolution (Chesterfield, UK), a prepreg supplier. Its Evopreg PFC prepreg combines PFA resin and reinforcement materials such as linen, glass, aramid, basalt or carbon fiber, and has passed the FAR 25.583 flame, smoke and toxicity (FST) test for aircraft interiors and EN 45545 grade HL3 railway .

Another company that provides PFA prepreg is SHD Composites (Sleaford, Lincolnshire, UK). The company was founded in 2010 by Steve Doughty, a 20-year process development engineer for Advanced Composites Group. SHD Composites has grown rapidly, adding factories in Slovenia and Mooresville, North Carolina, USA. It offers two PFA-based phenolic resin products: FR308 and PS200.

FR308, developed as a phenolic alternative to aircraft interiors, passed all aircraft FST requirements and EN 45545 HL3 railway requirements. PS200 complies with the European Aviation Safety Agency (EASA) fire protection requirements for aircraft batteries and has been used by general aviation aircraft manufacturers. In laboratory tests to rebuild thermal runaway conditions for lithium-ion batteries, a prototype battery box made using PS200 proved its performance. "Although the internal temperature reached 1,100°C, the external temperature never exceeded 250°C, and the box never burned or decomposed," said Nick Smith, technical director of SHD Composites. The company is currently working with several electric vehicle engineering companies to develop battery boxes for automobiles and other types of vehicles.

The formulations of PS200 and FR308 are treated like epoxy resin, usually curing at 120-130°C within one hour. Both have passed the British building interior materials code BS 476, which Smith believes is a fairly large emerging market.

Smith emphasized that railways are another fast-growing PFA material market. "We are bidding on fairly large projects," he added. Davis agreed and cited several exhibits at the 2018 InnoTrans International Transportation Technology Trade Fair in Berlin, including CETROVO from the world's largest rolling stock manufacturer China Railway Rolling Stock Corporation (CRRC, Beijing) Subway train, the train uses carbon fiber composite material body, bogie frame and cab equipment cabinet. At the same time, Composites Evolution collaborated with composite structure manufacturer Bercella (Varano de Melegari, Italy) to develop a lightweight composite bracket for rail seats (Figure 3). "This is a fairly thick, heavy metal part," Davis said. However, a 1-meter-long part made of carbon fiber Evopreg weighs less than 5 kg. "Multiply the weight reduction by the number of seat supports per rail car, and the redesign of the composite material greatly reduces the axle load."

The carbon fiber reinforced plastic (CFRP) sandwich panel door leaf developed by TRB Lightweight Structures (Huntington, UK) also uses bio-based PFA prepreg. Compared with bonded aluminum door leaves, this sustainable CFRP alternative uses 100% recycled foam core material, which reduces weight by 35% — from 40 kg to 26 kg — and the cost of parts is comparable. TRB's lightweight door leaf meets the EN 45545 HL3 standard, with an expected service life of 40 years. Compared with aluminum, it has excellent fatigue resistance and lower maintenance costs, as well as a lighter door operating system, which can further increase weight and energy. benefit.

Although Composites Evolution and SHD Composites also offer FR epoxy resins, Davies stated that in terms of test data, “they cannot provide the full FST performance provided by PFA-based resins and are more expensive.” Smith pointed out that FR epoxy resins are still Has higher toughness, "but PFA resin has better toughness than phenolic resin, and we are studying formulations to further improve this. In addition, the flame retardant in FST epoxy resin can slow down the impact of fire, but they will still It burns and releases toxic fumes. When PFA burns, it only releases carbon dioxide-no toxic gases."

The surface finish of PFA is also better than traditional phenolic resin. "This is a big problem with aircraft interiors," he explained. “Manufacturers want better part quality for the first time without rework. Historically, FR composites are more difficult to machine and require multiple rounds of surface preparation due to porosity. PFA systems provide improved surface finish and higher This is confirmed by the Horizon 2020 project IntAir, which shows that directly using PFA prepreg instead of phenolic resin can shorten the molding cycle time by 34% and the manual finishing time by 70%, and the final interior components Cost reduction is 58%.

There are also some new composite technologies that completely abandon organic materials and completely rely on inorganic fibers and polymers to achieve fire protection. Traditionally, inorganic polymers are often expensive and/or difficult to process. Some are also brittle and/or sensitive to chipping and impact damage. However, polysiloxanes, polysilanes, and polysialic acid/geopolymers can be mixed into the resin or synthesized into the backbone of the organic polymer, as are the basic inorganic monomers. This method has been successfully used in the flame retardant development of polypropylene, polyethylene, epoxy resin, polyethylene, polyester, polyamide and polyurethane resins. In particular, geopolymers seem to have potential in current research.

CFP Composites (Solihull, UK) combines chopped carbon fiber and inorganic resin to produce the so-called FR.10, which has passed the seven-hour fire resistance test at 1,500°C and emits almost no smoke or gas (Figure 4) ). These materials provide a cost-effective structural alternative to lightweight metals-2 mm thick FR.10 weighs less than 3 kg/m², and 5 mm thick FR.10 weighs less than 6 kg/m². FR.10 also passed the structural test under load. It withstood a direct flame at 1,200°C for two hours without burning through. At the same time, it provided enough heat insulation to allow bare hands to fully touch the back. It has a 1.3 x 0.8m sheet with a thickness of up to 20 mm and can be easily connected or bonded using traditional fasteners or adhesives.

The process used to make FR.10 combines chopped fibers and inorganic resin in a water-filled mixture. This mixture is then released to produce a fully resin-infused flat and net-like preform with a fiber structure in the x, y, and z directions within a few seconds. They are then transferred to a 1,000-ton press and compression molded to form flat plates or molded parts. “We can produce lightweight parts very quickly without waste,” said Simon Price, managing director of CFP Composites. The process has obtained a global patent, and compared with traditional composite materials, the cost is lower, and the inorganic composition can provide higher fire resistance. "The two key barriers to the adoption of composite materials in construction/construction, heavy ships, and oil and gas are cost and fire regulations," Price said. "We are opening up new applications for composite materials, replacing metals or ceramics."

Another new solution is fi:resist for pultrusion of non-flammable profiles. It was developed by FISCO GmbH (Zusmarshausen, Germany), a joint venture established in 2015 by German fastening expert Fischer (Waldachtal) and on-board equipment manufacturer Sortimo (Zusmarshausen). On the 2018 European Maritime Light Application Network (E-LASS) Symposium Day (June 26, Pornichet, France), Fisco product manager David Thull described fi:resist as using 100% inorganic materials, Will not produce smoke when in flames. In addition, it is reported that the matrix and glass fiber maintain their strength at temperatures as high as 1,000°C and 600°C, respectively. The material also provides high thermal insulation and is reported to meet DIN 4102-1 and EN 13501-1 requirements for the most stringent A1 class building materials.

Thull described the use of fi:resist for fire-resistant cable ducts. Due to the high structural properties of the material, larger spans can be achieved with fewer supports. Other suggested applications include partition walls on ships, decks and railings on ship balconies, and fire shutter doors. He said that future applications can be extended to the automotive and aerospace industries. Fi:resist won the 2016 JEC Architecture and Infrastructure Innovation Award.

Nanoclay is another important development area, showing the potential to obtain high flame retardant properties at low cost. They promote the formation of carbon, and because of their very small particle size and ability to disperse at the sub-micron level, a smaller amount of nanoclay is required compared to macro-scale additives. When uniformly dispersed in the resin system, 5-10% (weight) of nanoclay content can reduce the peak exotherm by 70%. Initial work on graphene nanosheets (GNP) and carbon nanotubes (CNT) also showed positive results.

Although EU-funded development programs such as MAT4RAIL and FIBRESHIP have achieved important milestones in new flame-retardant materials and improved composite performance, there are many other high-potential initiatives. E.g:

(For more details, please refer to the online sidebar "Measuring and improving the fire resistance of composite materials")

SAERTEX’s Bünker said: “Our goal is that by providing a variety of high-performance materials, flame retardancy is no longer a major issue for customers, and they can focus on meeting the overall needs of the project.” In fact, the composites industry as a whole Is moving towards this goal.

"Flame Retardant Polymer Composites" by Mahadev Bar, R. Alagirusamy and Apurba Das, Department of Textile Technology, Indian Institute of Technology, New Delhi, India. Fibers and Polymers 2015, Volume 16, Issue 4, Pages 705-717.

"TR 18001-Literature Review on Fire Performance of Natural Fiber Composite Materials" by Asanka Basnayake, Juan Hidalgo, Luigi Vandi and Michael Heitzmann of the University of Queensland Composites Group at the University of Queensland, Australia. April 2018.

"Composite Materials and Fire Protection: The Development and New Trends of Flame Retardant Additives", by Belén Redondo, AIMPLAS Composites Department, Plastics Technology Center, Valencia, Spain.

The CompositesWorld webinar "Using advanced nonwovens to enhance composite fire protection" was held by TFP on January 31, 2018.

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