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A comprehensive collection of news and information about composites.

Posted by: Ginger Gardiner

8. December 2016

RECYCLAMINE epoxy hardener enables cleavage of cross-links
leaving a thermoplastic epoxy polymer.
SOURCE: Fig. 1,
“Recyclable HP-RTM molding epoxy systems and their composite properties”, CAMX 2016.

Most of you know about Connora Technologies' (Hayward, CA, US) RECYCLAMINE hardener for epoxy resins that enables recycling of thermoset composites without pyrolysis. (If not, read my blog "Connora makes epoxy truly recyclable".) This is achieved by designing the thermoset cross-links to be broken, which converts the epoxy into long polymer strands, a.k.a. thermoplastic epoxy. Thus, not only can the fibers be captured without chopping or shredding, the resin is also recovered for reuse.

SOURCE: Connora Technologies.


Great. But does it really work? According to work published by two separate groups in 2016: Yes.
Connora had already presented work in 2013 and 2014 ("Recyclable by Design: A Chemical Approach to Recyclable Epoxy Composites," CAMX 2014) that explored how RECYCLAMINE works in composites and post-recycled fiber performance. Though RECYCLAMINE can be used in a variety of processes (infusion, filament winding, etc.), the 2016 presentations mainly demonstrated RECYCLAMINE in high-pressure resin transfer molding (HP-RTM) and characterized laminates made from virgin and recycled materials.


Recycling process for RECYCLAMINE 301-SuperSap300 epoxy/8-ply T300 carbon fiber twill fabric laminate. SOURCE: Fig. 2, “Recycling treatment of carbon fibre/epoxy composites …,”
Composites Part B 104 (2016) 17-25, by
Gianluca Cicala, S.D. La Rosa, A. Latteri, R. Banatao, S. Pastine.

The Recycling Process
RECYCLAMINE hardeners feature amino end groups connected by a central group, which is where cleavage of the cured epoxy cross-links is achieved with temperature (70-100°C) and pH (acidic). The composite laminate is placed into hot vinegar, and after 1-3 hours (time depends upon temp.), the resin is dissolved away from the fiber, maintaining the original architecture without degradation or loss of fiber length. The fiber is dried and ready for reuse, while the epoxy is collected as a thermoplastic material akin to a stiff polyamide but with reportedly exceptional adhesive properties.
 

HP-RTM, Recycle, HP-RTM
The project completed by Fraunhofer Project Center for Composites Research (FPC, London, Ontario, Canada) and the Dept. of Polymer Engineering at the Fraunhofer Institute for Chemical Technology (ICT, Pfinztal, Germany) aimed to demonstrate cradle-to-cradle recycling of a thermoset composite made using HP-RTM.

A series of 0.5 m2 panels were fabricated using RECYCLAMINE 101 hardener with Entropy Resin’s (Hayward, CA, US) SuperSap 300 bio-epoxy. Unidirectional carbon fiber preforms supplied by SGL (Wiesbaden, Germany) were placed into a heated mold, resin was injected and cured, and parts were demolded for testing.

SOURCE: Fig. 2 and 3, “Recyclable HP-RTM molding epoxy systems and their composite properties”, CAMX 2016.

Mechanical testing of the panels made with virgin and recycled preforms showed all moduli values (tension, compression, flexure) to be nominally the same and no significant difference in 0º panel properties. There was a 10-20% decrease in 90º panel strength and corresponding failure strain, which is believed to be due to sample handling during recycling. 


SOURCE: “Recyclable HP-RTM molding epoxy systems and their composite properties”, CAMX 2016.


Italian HP-RTM Studies
The second set of projects was conducted by the University of Catania (Catania, Italy), Dept. of Civil Engineering and Architecture (DICAR) with findings published in Volume 104 of the journal Composites Part B.  

HP-RTM panels were made with eight plies of a 190 gsm twill fabric from T300 carbon fiber supplied by Prochima (Calcinelli di Saltara, Italy) in a biaxial layup [0/90]8 and SuperSap 300 epoxy resin with RECYCLAMINE 301 hardener. They were molded using HP-RTM technology developed by Cannon-Afros (Saronno, Italy).

The composite laminates were tested with the following results:

  • DSC characterization: Tg of 100°C
  • DMA characterization:
    Tg of 88°C after 5-min cure at 120°C
    Tg of 102°C after 1hr- post-cure at 120°C
  • Tensile strength:  580 MPa
  • Modulus: 23 GPa
  • Elongation to break: 3.33%

Composite laminate samples were recycled in a 25 vol % acetic acid solution at 80°C for 1.5 hours. Scanning electron microscope (SEM) analysis showed no significant difference between virgin and recycled fibers and that chemical treatment does produce clean fibers with no damage.

The thermoplastic polymer recovered is described as a poly-hydroxyamino ether (PHAE) with a Tg of 79.5°C obtained via DSC and a tensile strength of 55 MPa and modulus of 2.4 GPa obtained from testing per ASTM D638.

The virgin and recycled materials were determined to be suitable for automotive structural applications and processed well using HP-RTM. A baseline life cycle analysis (LCA) was established with the next step to incorporate results from recovery and re-use of the epoxy thermoplastic. Once this is complete, the LCA will be updated and a life cycle cost (LCC) analysis of the recycling process will be carried out.

Hybrid Carbon and Natural Fiber Composites
Further work demonstrating RECYCLAMINE with hybrid laminates of carbon and natural fibers was presented at CAMX 2016. The same resin and carbon fabrics from above were combined with a Biotex 400 gsm twill flax fiber fabric from Composites Evolution (Chesterfield, UK). Panels were fabricated using HP-RTM and vacuum-assisted resin transfer molding (VARTM) and then tested. VARTM panels were cured at room temperature for 6 hours with a 1-hr post-cure at 120°C.

Test results, omega-shaped HP-RTM mold and hybrid sample composition.
SOURCE: “The use of recyclable epoxy and hybrid lay up for biocomposites: technical and LCA evaluation,” by Gianluca Cicala, A.D.La Rosa, A.Latteri, R.Banatao, S.Pastine, CAMX 2016.

Cured laminates were then soaked in acetic acid at 80°C for 3 hours until matrix was fully dissolved and fibers were clean. Both natural and carbon fiber reinforcements were recovered and analyzed with no detected degradation. Thermoplastic epoxy recovered tested per ASTM D790 showed a tensile strength of 42.3 MPa and modulus of 2.85 GPa.

IPCC GWP indicator analysis for different end of life options for 8-ply carbon fiber laminates.

SOURCE: Fig. 11, “The use of recyclable epoxy and hybrid lay up for biocomposites: technical and LCA evaluation,” by Gianluca Cicala, A.D.La Rosa, A.Latteri, R.Banatao, S.Pastine, CAMX 2016.

An LCA was performed with the 8-ply all-carbon laminates having the most environmental impact. Compared to landfill (yellow) and incineration (red), the RECYCLAMINE-enabled chemical recycling method demonstrated (green) offers a 60% improvement in global warming potential (GWP) using the carbon dioxide equivalents (CO2e) established by the Intergovernmental Panel on Climate Change (IPCC) in 2014.

Connora will continue this work in its Phase II SBIR awarded October 2016, specifically analyzing the performance of RECYCLAMINE composites in HP-RTM. Stay tuned for future updates.

Posted by: Jeff Sloan

8. December 2016

Underbody braces for the Corvette C7, made via pultrusion and overwrapped carbon fiber fabric.

On a vehicle already famous for having a long history of composites use, finding a new part on which to apply the material is a challenge, but PolyOne’s Advanced Composites Glasforms unit managed to do just that with the underbody braces designed for the C7 generation Corvette, manufactured by General Motors (GM).

Ben Hochman, director of marketing at Glasforms, says he and his team had been meeting with GM engineers and discussing material and technical challenges on the Corvette. The topic of underbody braces came up. GM wanted to get away from the steel braces traditionally used and had developed an aluminum alternative that, unfortunately, was somewhat lacking in flexural stiffness. The result, says Hochman, was a less-than-optimal driving experience.

GM then turned to composites, but the challenge was developing the mechanical properties in all directions that the company required. And that’s where Glasforms stepped in.

There are four underbody braces on the Corvette — one associated with each wheel. Each brace is about 2 ft long, 1.25 inches wide, 0.375 inch thick, and notched at each end to accommodate metallic fasteners. The braces are designed to reduce chassis sway and confer greater stability in vehicle handling, giving a tighter “feel” to the driving experience. Basically, as underbody brace stiffness increases, so does handling stiffness. The “feel” of the Corvette has been highly developed by GM, and is expected by drivers. A composite underbody brace must, therefore, allow the Corvette to continue to meet that expectation.

Underside of Corvette. The braces are the black, narrow, diagonally oriented rods running from the outside edge of the vehicle toward the yellow wheel suspension system.

Hochman says Glasforms settled on an underbody brace design that would use a carbon fiber/epoxy composite manufactured via pultrusion. Pultrusion offers a constant cross-section, high stiffness and good longitudinal fiber alignment. What a pultruded part lacks, however, is good transverse strength. To manage that, says Hochman, “We developed three design scenarios for the brace, mixing and matching torsion and flexural stiffness.”

  1. A unidirectional, hybrid carbon and glass fiber profile
  2. A unidirectional carbon fiber profile
  3. A profile made with a unidirectional carbon fiber and a transverse engineered fabric, which had the advantage of minimizing potential cracks from propagating.

Testing at Wichita State University showed that the first option was an estimated 33% lighter than the aluminum part, with a 36% increase in flexural stiffness. The second option was estimated to be 41% lighter than the aluminum part, with a 100% increase in flexural stiffness, but a large reduction in torsional rigidity. The third profile was also 41% lighter than aluminum, with a 50% increase in flexural stiffness, and maintained torsional rigidity slightly better than that of aluminum.

GM engineers chose this third option because it met all of the technical requirements and had the best combination of properties.

The resulting brace assemblies, ultimately 17% lighter than their aluminum competitors, were delivered to GM for vehicle shake and road testing. They were validated and now are an upgrade option on the C7 Corvette.

Glasforms does all carbon fiber underbody brace manufacturing and has, says Hochman, “seen an increase in interest since the product’s release. The discerning buyer is very intrigued by the performance properties of these braces.”

Looking ahead, Hochman believes the braces have application on other vehicle platforms. He thinks Glasforms’ knowledge on composite design and manufacture will allow the company to adapt easily to other structural applications in automotive composites.

Posted by: Sara Black

7. December 2016

A new supersonic passenger aircraft is being developed in Denver, CO, US.

Boom Technology (Denver, CO, US), a 2014 start-up aircraft developer, is in the process of building the XB-1, a flying 1/3-scale demonstrator of its supersonic (faster than sound) commercial aircraft. A mockup of the demonstrator was recently on display at the company’s hangar at Centennial Airport near Denver. XB-1 is intended to demonstrate in flight the key technologies for practical supersonic travel, says the company.

Boom Technology’s founder is CEO Blake Scholl, a pilot with a background at Amazon and the founder of Kima Labs. Co-founder and chief engineer is Joe Wilding, who has played leadership roles on multiple aircraft certification programs, including the Adam A700 light jet. Co-founder and chief technology officer Josh Krall, with a background in physics simulation, has developed multi-disciplinary optimization algorithms and design software for the program. At the November open house, the three described the ideas behind the endeavor.

They believe they have a viable business case for the airlines, one that bests the previous longest-flying supersonic transport, the Concorde, jointly developed and built by Aerospatiale and British Aircraft Corp. (BAC) and ultimately retired in 2003.  A typical round-trip ticket on the Concorde cost about $20,000 and fuel burn was 6,800 gallons per hour, but the trip between New York and London took about 3.5 hours; the Concorde was retired due to declining sales and rising costs, an accident and the overall post-9/11-caused aviation downturn. According to Boom, their 45-seat jet will be 2.6 times faster than conventional passenger jets, yet cost flyers about $5000 per seat, round trip, in line with today’s business class tickets. Bulky lay-flat seats aren’t needed, since overwater flights will take less than half the time of current flights (thus, little to no jet lag). The group’s preliminary design goal is a speed of Mach 2.2 (faster than the Concorde’s Mach 2) with a 9,000 nautical mile range. Sir Richard Branson of Virgin has already publicized his intention to buy 10 of the craft. The company has an impressive Advisory Board, including Frank Cappuccio, former executive vice president and general manager of Lockheed Martin Skunk Works, Tom Hartmann, another Lockheed Martin Skunk Works director, who was in charge of LM’s Quiet Supersonic Transport program, and Scott Bledsoe, formerly with Gulfstream’s supersonic program and now president of Blue Force Technologies. Astronaut and test pilot Capt. Mark Kelly is also on the board.

So how will Boom bring profitable supersonic air travel? According to the company’s web site, passengers want to get to their destinations faster. But, the viability of supersonic flight depends on reducing operating costs sufficiently (i.e., lower fuel burn) coupled with reasonable fares travelers are willing to pay for the speed; according to Boom, this requires just a 30% efficiency improvement over Concorde’s airframe and engines, with composite materials playing a role, says the company. With more than 1,000 simulated wind tunnel tests already done, three major innovations include an “area ruled fuselage” (the aft cabin will be tapered to reduce cross-section), a chine or wing extension towards the nose for balance and control at supersonic speeds, and a refined delta wing with a swept trailing edge that reduces supersonic drag and quiets the sonic boom.

Carbon fiber composites will be used throughout the airframe, for lighter weight and to counteract the significant growth and expansion that the Concorde’s aluminum design experienced in flight. The XB-1 demonstrator will be powered by three General Electric turbojet engines with shaped variable geometry inlets. Acknowledging that a ban on supersonic flights still exists over the US, the company says the jet will begin with overwater routes, such as New York to London or San Francisco to Tokyo. The sonic boom from a Boom jet will reportedly be much quieter than the Concorde’s. Boom Technology says that its XB-1 will begin test flights in late 2017, starting in Colorado, then moving to Edwards AFB in California. Watch the video explaining the company’s vision here:  http://boomsupersonic.com/, and a behind-the-scenes look at the XB-1 here: http://boomsupersonic.com/xb-1/

Posted by: Heather Caliendo

7. December 2016

A cutaway section of a carbon fiber rocket nozzle from NASA’s Marshall Space Flight Center reveals the layers of material. Photo credit: Michael Mercier/UAH. 

I came across a new patent that I thought would be of interest to you all. The process, developed by a University of Alabama in Huntsville (UAH) professor, produces carbon fiber that forms ablative rocket nozzles and heat shields. The university claims that the new process could be of interest to NASA, which has a dwindling stockpile of cellulose rayon fiber that dates back to the late 1990s.

"This is a green process, so it is environmentally clean," says William Kaukler, an associate research professor at UAH’s Rotorcraft Systems Engineering and Simulation Center and a NASA contractor for 35 years in a news release from the university. "We recycle all the byproducts."

Kaukler developed the new ionic process at UAH’s Reliability and Failure Analysis Laboratory with funding from the U.S. Army’s Aviation and Missile Research, Development and Engineering Center (AMRDEC).

"Other people know about using ionic processes to make fibers but they are not making carbon fibers with them," Kaukler says. "The trick was to make the properties of this fiber match the properties of the North American Rayon Corp. (NARC) fiber."

NARC ceased rayon production in the U.S. after it was unable financially to comply with Environmental Protection Agency regulations for the hazardous wastes created.

To form a solid fuel rocket nozzle, layers of carbon fiber fabric made from carbonized rayon are coated with pitch and wound around a mandrel, and then heat-treated to convert the pitch to solid carbon. The resulting nozzle will be a carbon fiber reinforced-carbon composite. A single large solid rocket motor like that used for shuttle boosters can use up to 35 tons of fiber. The rocket nozzles of Army missiles are made from phenolic resin and this same carbon fiber.

"This carbon fiber is not the same fiber that you’d go out and make aircraft or car parts from," says Kaukler. "This is the only way to make the carbon fiber that is suitable for rocket nozzles, is to start with cellulosic fiber." The more common carbon fiber used in structural applications is made from polyacrylonitrile (PAN) and, while stronger, its thermal conductivity is too high.

Heat created from the rocket’s burning fuel slowly burns away the interior of the nozzle in flight.

"That’s why you have to make the fiber out of cellulose, because it has the lowest rate of thermal conductivity of any fiber," Kaukler says. The low conductivity keeps the propellant’s heat in for more propulsion efficiency and it prevents the nozzle from burning away too quickly in flight, with disastrous consequences.

Scaling up the process to manufacturing dimensions could aid NASA as it moves forward with solid rocket motors in its next-generation Space Launch System, and it could prove useful for heat shields used in re-entry to Earth’s atmosphere or on planetary probes designed for landing, Kaukler says.

"It would be useful for any aero-entry onto a planet," he says. 

Dr. William Kaukler with a display of the results of his work in his lab at the Reliability and Failure Analysis Laboratory in UAH’s Von Braun Research Hall. Photo credit: Michael Mercier/UAH.

Posted by: Ginger Gardiner

6. December 2016

Evonik is a specialty chemicals company based in Essen, Germany. It has a strategic innovation unit, called Creavis, which develops new competencies for Evonik by launching Project Houses — cross-organizational ventures with a specific aim and timeline.

Established in 2013, Evonik’s Composites Project House has developed new materials and system solutions for lightweight construction, mostly aimed at automotive, transportation and energy applications. One example is VESTANAT PP polyurethane prepreg which offers room-temp storage, 2-3 minute cure in a 180°C compression molding press and a reportedly 35% cost savings vs. RTM. Another development is the PulPress automated process which braids fiber reinforcements around ROHOCELL polymethacrylimide (PMI) foam, injects 2-part resin into the preform and cures in mobile press cells to create 3D sandwich structures up to 1.2 m long on a continuous basis at a reported rate of 30 parts/hr.

SOURCE: “Targeting Greater Efficiency”, pp. 10-11, Elements #54, published by Evonik.

 This blog, however, is about the Composites Project House development being launched as “Thermoreversible Crosslinkable Thermoplast-Thermoset Hybrid.” Described as a new class of materials, Evonik’s goal was to combine the mechanical performance of crosslinked thermosets with the fast processing of thermoplastics while resolving the latter’s high-viscosity melt phase which causes fiber impregnation issues.

The solution, developed with the Karlsruhe Institute of Technology (Karlsruhe, Germany), is a special type of Diels-Alder chemical reaction that acts as a thermal switch. With elevated temperature, the crosslinks formed during cure are dissociated for quick reshaping of the composite. Upon cooling, the crosslinks reform, stabilizing the molded shape and ensuring structural properties. The crosslinking that occurs is reversible, and the polymer can reportedly be heated and cooled many times without loss of properties.


SOURCE: “Hybrid Polymers”, pp. 15-16, Elements #54, published by Evonik.

According to the “Hybrid Polymers” article in issue #54 of Evonik’s innovation magazine Elements, this hybrid system can be applied to a variety of polymers. The first to be commercialized is based on an acrylate copolymer. According to a March 2015 press release, this first product is to be released in 2018, and pilot plants in operation since late 2014 at the company’s Marl site have demonstrated that these hybrid polymers save both time and cost in manufacturing composites. Potential customers have already received samples for testing, and a B pillar has been produced with a cycle time of less than 60 seconds.

 
SOURCE: “Hybrid Polymers”, pp. 15-16, Elements #54, published by Evonik.

These pilot plants produce glass- and carbon-fiber prepregs where woven and noncrimp fabrics are coated with the hybrid polymer then briefly heated and cooled. These prepregs are not sticky, and thus require no separation or release film. They are also stable at room temperature for more than two years. For parts production, prepreg is cut and stacked and laminates are heated rapidly — e.g. infrared radiation to 180-200°C — to open all crosslinks, after which parts can be quickly molded. No thermal treatment is needed for curing, because the crosslinks reestablish during the cooling step. Thus, cycle times can be very short. Also, any waste produced can be reused or recycled because crosslinking in the hybrid polymer prepreg is reversible.


SOURCE: Evonik Innovation for Composites brochure.

Properties of the resulting parts, including modulus, tensile strength and water absorption, are on par with epoxies, and thus are superior to thermoplastics like polyamide 6. Performance is consistent up to a service temperature of 100°C

More recent testing has revealed further benefits. According to Marcel Inhestern, now head of the Thermoreversible Crosslinkable Thermo­plast-Thermoset Hybrid project at the Compos­ites Project House, “the material shows excellent alkaline resistance. The chemical resistance is comparable to highly-crosslinked epoxy resins. For example, when stored at pH 13 or higher for several days at higher temperatures the material does not dissolve.” 

For more information contact marcel.mi.inhestern@evonik.com

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