#thermosets

Laser-assisted 3D printing can fabricate free-standing thermoset-based electronics in seconds

Thermosets, such as epoxy and silicon rubbers, are a class of polymer (i.e., plastic) materials that harden permanently when they undergo a specific chemical reaction, known as "crosslinking." These materials are highly durable, heat-resistant with excellent electrical insulation in various applications such as in adhesives, coatings, and automotive parts. Thermosets are also widely used to fabricate electronic components, including switches, circuit breakers and other core circuit components. So far, thermoset-based free-standing devices have proved difficult to construct by using conventional 3D printing processes. One key reason for this is that the materials need to be provisionally supported by other supporting objects until they become solid, which adds more steps to the printing process.

Durable plastic gets a sustainability makeover in novel polymerization process

Car tires, replacement hip joints, bowling balls—these and other items are made from a class of plastics called thermosets, known for extreme durability. Their "crosslinked polymer" chemical structure guarantees longevity but also makes these petrochemical-based materials—which comprise 15%–20% of all polymers produced—impossible to recycle. "Currently, zero percent of the world's thermoset materials are recycled—they're either incinerated or thrown in landfills," said Brett Fors, professor of chemistry and chemical biology in the College of Arts and Sciences. The Fors lab has addressed that environmental challenge by creating an alternative made from a bio-sourced material that has crosslinked thermosets' durability and malleability but can be easily recycled and degraded.

Recycling the non-recyclable: New epoxy resin resists flames and reduces waste

Empa researchers have developed an epoxy resin that can be repaired and recycled, in addition to being flame-retardant and mechanically strong. Potential applications range from coating for wooden flooring to composites in aerospace and railways. Epoxy resins are tough and versatile polymers. In combination with glass or carbon fibers, they are used, for example, to manufacture components for aircraft, cars, trains, ships and wind turbines. Such epoxy-based fiber-reinforced polymers have excellent mechanical and thermal properties and are much lighter than metal. Their weakness: They are not recyclable—at least not yet. Now Empa researchers led by Sabyasachi Gaan at Empa's Advanced Fibers laboratory have developed an epoxy resin-based plastic that is fully recyclable, repairable and also flame retardant—all while retaining the favorable thermomechanical properties of epoxy resins. They have published their findings in the Chemical Engineering Journal.

Lightweight reinforced resin composite materials using clay particles

An international team of researchers, led by Dr. Umar Abdul Hanan (Universiti Teknologi Malaysia (UTM)) has successfully developed a method that uses montmorillonite (clay) particles to reinforce resin composites.

Unsaturated polyester (UP) resin is a low cost thermoset with excellent processing ability and mechanical properties that finds applications in fiber-reinforced polymer (FRP) materials. It also crosslinks readily in the presence of a catalyst such ketone peroxide, forming an even stronger and stiffer resin.

Unfortunately, this also leads to lower fracture toughness. Several methods to enhance the toughness of the cross-linked resin have been proposed; one such method involved blending with nano-fillers made from rubber but this reduces the strength and stiffness of the resin.

Here, for the first time, the team has demonstrated that nano-clay composite made from unsaturated polyester (UP) blended with montmorillonite (MMT) clay nanoparticles of high compressive strength, stiffness and toughness could be achieved by optimizing the filler content.

Simple chemistry overcomes long-standing barriers to recycling about a quarter of today's plastics

Despite research and policy efforts, recycling initiatives have skidded on more complex materials like tires and mattresses, filling dumps and natural land across the country.

Now, Northwestern University researchers have used simple chemistry to address long- standing barriers associated with recycling about a quarter of today's plastics—materials that Northwestern's John Torkelson say hold a tremendous amount of embedded energy.

Torkelson, a professor of chemical and biological engineering and of materials science and engineering in the McCormick School of Engineering at Northwestern, will present on seven novel techniques to transform tires and other similar thermoset polymers into recyclable materials at the American Physical Society (APS) on March 14. His lab's breakthrough research builds on excitement in the sustainability field and will help mitigate fires, pollution and the lost economic value associated with synthetic polymer waste.

"This is our case of looking at a class of materials that were considered hopeless in terms of recycling," Torkelson said. "And using one- or two-step chemistry to transform them into recyclable material with full recovery of properties to see how that can really help address some major issues with regard to sustainability."

Eco-friendly foam can insulate buildings without warming the globe

Rigid foam boards used to insulate buildings can prevent energy loss, making homes more efficient at keeping warm or cool. The advantages in energy efficiency, however, are undercut by environmental concerns over polystyrene products. Blowing agents used in foam production, such as hydrocarbons and hydrofluoroolefins, end up in the atmosphere and contribute to global warming.

Scientists at Oak Ridge National Laboratory developed a competitive, eco-friendly alternative made without harmful blowing agents. The nontoxic thermoplastic foam is made using hollow glass spheres and expandable polymer microspheres.

"The combination of these two sources allows us to tailor formulations to maintain the material's thermal performance across a limited range of densities" said ORNL's Meghan Lamm. "We are also working with thermoset materials, which offer high-temperature stability, for improved flame resistance."

Novel self-healing materials developed for testing on the International Space Station

Some materials used in aerospace applications such as polymers can degrade and erode with prolonged exposure to atomic oxygen, ultraviolet radiation, and extreme temperature cycling in the outer space. Also, because orbiting spacecraft such as the International Space Station travel at approximately 18,000 miles per hour, micrometeoroids and other space debris pose serious threats to the integrity of lightweight space structures comprised of polymers and their composites.

Introducing self-healing materials that incorporate specially designed nanoparticles and microparticles could provide a more durable solution for space structures. Several labs at the University of Illinois Urbana-Champaign worked together to meet this challenge, and for the first time, sent self-healing materials into orbit for testing at the ISS National Laboratory.

"The materials we use are novel nanocomposites, based on thermosetting polydicyclopentadiene (pDCPD)-matrix mixed with self-healing components, which can be cured in a matter of minutes to hours compared to traditional thermosetting polymers that take days to cure inside an autoclave. Also, these novel pDCPD-based materials are amenable to additive manufacturing techniques with the potential for rapid fabrication or repair of parts right where they are in space," said Debashish Das, a postdoctoral scholar in the Department of Aerospace Engineering at UIUC.

New strategy for promoting the reuse of carbon fiber reinforced plastics

Epoxy resin is a type of thermoset resin commonly used in glue, paint and composite materials. NIMS and ISMA have developed a new thermoset plastic recycling system capable of easily decomposing epoxy resins in an aqueous solution of a naturally derived peptide. The use of this system may promote the reuse and recycling of plastics, including carbon fiber reinforced plastics (CFRP)—carbon fibers combined with an epoxy resin matrix—by a wide range of industries.

Environmental pollution caused by plastics—particularly in the marine environment—has raised global concern about urgent need to promote plastic waste recycling. Some recycling methods have already been developed to decompose thermoplastic resins used in containers and packaging through thermal and chemical processes, and efforts are underway to put recycling plants into practical use. On the other hand, a method for recycling thermoset resins, including epoxy resins, has yet to be developed due to their poor thermal degradability and low solubility in available solvents.