Epoxy Resin Resists Flames, Reduces Waste
Emergency Management Planning and Assistance researchers have reportedly begun developing an epoxy resin that can be repaired and recycled, in addition to being flame-retardant and mechanically strong.
According to the release from EMPA, the potential applications for the new epoxy resin can range from coating for wooden flooring to composites in aerospace and railways.
About the Research
The report details how epoxy resins can be tough, versatile polymers that can be used to build aircrafts, cars, trains, ships and wind turbines. These epoxies reportedly have excellent mechanical and thermal properties and are much lighter than metal. The report states that their only weakness is that they are not recyclable.
Now EMPA researchers, led by Sabyasachi Gaan at Empa's Advanced Fibers laboratory, have reportedly developed an epoxy resin-based plastic that is fully recyclable, repairable and flame retardant. Additionally, all of this was reportedly done while retaining the thermomechanical properties of epoxy resins. The team has also published their findings in the Chemical Engineering Journal.
According to the release, these plastics are known as thermosets. In this type of polymer, the polymer chains are reportedly closely crosslinked, which can make melting impossible. Once the plastic has hardened, it can no longer be reshaped.
However, this is reportedly not the case for thermoplasts like PET or polyolefins. According to the researchers, their polymer chains lie closer together, though are not chemically linked to each other. When heated, the polymers can reportedly be melted and formed into new shapes.
Additionally, due to the lack of crosslinks, the mechanical properties at elevated temperatures are generally not as good as those of thermosets.
The epoxy resin that the EMPA researchers developed in collaboration with national and international partners is technically a thermoset, though unlike other thermosets it can be reshaped like a thermoplast. According to the report, the main component is the addition of a very special functional molecule from the class of phosphonate esters into the new resin matrix.
"We originally synthesized this molecule as a flame retardant," said co-inventor of this technology and Empa scientist Wenyu Wu Klingler.
The bond the molecule forms with the polymer chains of the epoxy resin, however, is reportedly dynamic and can be broken under certain conditions. This can apparently loosen the crosslinking of the polymer chains so that they can be melted and reshaped.
These materials, also reportedly referred to as vitrimers, have only been known for about ten years and are considered to be somewhat promising. "Today, fiber-reinforced composites are not recyclable at all, except under very harsh conditions, which damage the recovered fibers," explained Wu Klingler. "Once they have reached the end of their service life, they are incinerated or disposed of in landfills. With our plastic, it would be possible for the first time to bring them back into circulation again."
"Our vision for the future is a composite material, in which both the fibers and the plastic matrix can be completely separated and reused,” added Gaan
"The production of carbon fibers requires a lot of energy and releases an enormous amount of CO2. If we could recycle them, their environmental footprint would be a lot better – and the price a lot lower."
Additionally, the recovery of valuable elements like phosphorus connected to the matrix polymer would reportedly be possible.
The release says that fiber-reinforced composites may not be the only application for the new polymer. As an example, the report adds that it could be used to coat wooden floors, as a transparent, resistant layer that has good flame-retardant properties and where scratches and dents can be "healed" with a little pressure and heat.
"We didn't develop a single material for a specific purpose, but rather a toolbox," Gaan stated. "Flame retardancy, recyclability and repairability are a given. We can optimize all other properties depending on the intended use."
As an example, Gaan said that flow characteristics are important for the production of fiber-reinforced plastics, while exterior wood coatings should also be weather-resistant.
To pursue these and other applications of the material, the researchers are now reportedly looking for industrial partners. In addition to all its other advantageous properties, the modified epoxy polymer is also reportedly inexpensive and simple to manufacture.
More Epoxy News
In April, a team of researchers from Spain were studying the use of microparticles recovered from worn-out batteries as fillers for epoxy resins in an effort to recycle the material. According to the study, zinc alkaline batteries are one of the most popular sources of portable electrical energy, with more than 300,000 tons being consumed every year.
The research team noted that recycling batteries is an important challenge today, adding that it was first identified by the European Commission on the Strategic Action Plan on Batteries: Building a Strategic Battery Value in Europe, in April 2019. In finding more effective recycling processes, recycled products should be used for the production of new batters or other applications.
An alkaline battery reportedly includes several valuable ingredients, including zinc oxide (ZnO), which can be used in many applications, such as electronics, solar cells, photocatalysis and sensors. However, according to the study, since ZnO particles are expensive to make, the recycling of these microparticles from waste can provide a sustainable and long-term solution.
Using an epoxy thermosetting resin from Huntsman International LLC. (Houston), which was based on diglycidyl ether of bisphenol A and cured at 140 C (284 F) for 8 hours, the researchers created samples by pouring the epoxy into a two millimeter (0.08 inch) mold and cut into different specimens. Alongside the recycled ZnO battery microparticles, two other commercial ceramic oxide nanoparticles were tested: ZnO and TiO2.
Using Field Emission Gun Scanning Electron Microscopy (FEG-SEM) and Fourier Transform Infrared Spectroscopy (FTIR), the scientists looked at potential benefits of recycled ZnO as an epoxy resin filled compared to its commercial counterparts.
Researchers found that each of these microparticles have a different morphology and size. The geometry of the recycled ZnO was described by the team as similar to “desert roses,” which each petal acted as a nanosheet, whereas commercial ZnO rectangular parallelepipeds nanoparticles and commercial TiO2 are smaller spherical nanoparticles.
After testing, it was shown that the addition of ceramic fillers did not impact the thermoset’s thermal strength and mechanical stiffness. The recycled ZnO composite also had the same hydrothermal resilience as the original epoxy thermoset.
However, because of its roughness due to its flowerlike microparticles, the addition of the recycled battery filler exhibited hydrophilic properties. The water angle contact increased about 12% with the presence of ceramic particles, but the epoxy resin reinforced with the recycled ZnO microparticles exhibited the highest hydrophobicity at 35%.
When etched with acid stearic and acetic acid corrosion of the ZnO on the surface was induced, also enhancing the growth of the surface roughness. The presence of desert rose ZnO particles also enhances the lotus effect.