The shift towards efficient as well as sustainable systems when it comes to energy and transportation infrastructure goes on to demand stronger and lighter materials. Often, engineers get compelled to shift away from traditional homogeneous components in favor of composites.
According to R&D associate staff member at the Department of Energy’s Manufacturing Demonstration Facility- MDF, Oak Ridge National Laboratory- ORNL, Dr. Matthew Korey, fiber-reinforced composites have gone on to revolutionize a range of application spaces, and in numerous cases, they are not just a more efficient material; they are actually required.
Korey explains that one example pertaining to this is large-scale additive manufacturing. As one scales the technology up, one begins introducing thermal gradients in the print, and some regions, thereby, will go on to cool faster than others. The fact is that one cannot do it with just resin and needs fiber reinforcement so as to help with thermal management.
This performance happens to come at a cost, since composites can go on to be energy-intensive to manufacture and challenging in order to recycle. The scale of the expected need when it comes to composite materials, in the case of lighter vehicles, larger wind turbines, durable infrastructure, etc., enhances the challenge to national importance and has gone on to make the advancement when it comes to sustainable composite manufacturing a pretty significant area of research.
Dr. Soydan Ozcan, who leads the Sustainable Manufacturing Technologies Group, goes on to conduct R&D on bio-composites as well as recycling practices for composites and polymers at the MDF. The group’s objective of the work is to de-risk the adoption and scale-up of advanced manufacturing so as to enable circular economies, having one eye on sustainability and the other on the commercial viability.
The Breakdown of Tough Composites
The very traits which go on to make the composites valuable in terms of applications like wind energy, automotive, as well as aerospace can also make them pretty challenging from a sustainability point of view. Wind turbine blades, for example, happen to be too large to get within the building and too tough so as to cut with a saw. However, it is indeed possible to recycle the materials, and, in some scenarios, the resulting feedstock happens to be both sustainable as well as cost-effective.
In order to refine the size reduction of composites at scale, researchers have gone on to collaborate with Cumberland in order to run a distinct shredder and granulator having a capacity of 4,000 lb/hr. that is capable of accepting parts of almost 4 × 4 ft. The line has been outfitted along with a sensor suite in order to capture the throughput, power draw, as well as vibration, thereby enabling real-time life cycle as well as techno-economic analysis. By way of controlling the ram pressure, the technique can go on to be optimized for the material being processed.
One of the major concerns that the shredder operation has, specifically in terms of working with tough composite materials, happens to be uptime. By way of correlating wear with the output through the sensors, researchers went on to discover that they could make use of the vibration of the machine so as to reliably indicate tooth wear. Rather than periodically shutting the machine down as well as opening it up so as to physically measure the knife blades, operators can go on to run the machine up until the time the vibration data indicates that the service is required. Cumberland happens to be now offering the sensor suite as a choice to its customers.
It is well to be noted that the output from the granulator can be used the way it is in some applications, but in others, the size variation can be an issue. Significantly, the granulator goes on to screen out most larger pieces; however, it can create 7-10% dust, which can be a challenge for downstream processes, like vacuum-fed 3D printing. A Leistritz twin screw extruder as well as a Bay Plastics Machinery pelletizer go on to further process materials into pellets that can be made use so as to make homogenous parts. Additives as well as biomaterials can also be added at the extrusion step. Planned research will hence apply the sensor suite possibility to extrusion processes, thereby looking for opportunities to lessen the cost and at the same time enhance sustainability.
Although the extrusion process goes on to create a high-quality, uniform pellet, it also happens to be energy- and labor-intensive, thereby exposing polymer molecules to shear stresses as well as heat that can go on to degrade their properties. Another approach is to seek a cleaner, more uniform granule while at the same time skipping the extrusion and pelletization steps. Significantly, the researchers look to integrate a Witte classifier table into their size reduction line in order to sort out oversized as well as undersized granules. As a separate product, dust can very well go from being a major contaminant to a valuable output.
In the case of some applications like fluidized bed pyrolysis, they actually require the dust, says Dr. Korey, and hence they are indeed interested in seeing if one can run this process so as to produce as much dust as there can be, and how much energy is that going to take?
Biology as a Sustainable Feedstock
One more active area of research at the MDF happens to be looking at the other end of composite material life cycles, thereby looking to replace carbon-intensive feed materials with bio-derived materials.
Even if one makes use of a petroleum-based polymer matrix, one can indeed offset 30% of that with natural fiber, which will go on to give a more favorable life cycle evaluation on the back end, says R&D associate staff member with the MDF, Dr. Amber Hubbard.
It is worth noting that the natural fiber choices include cellulose nanofibrils, wood flour, flax, as well as hemp. These can go on to offer tensile strength, thereby enhancing the mechanical properties, apart from displacing petrochemicals. Although the temperature limitations as well as compatibility issues go on to mean that bio-derived materials may not always be a drop-in replacement in terms of traditional resins, they happen to be compatible with matrix materials like PP and PLA, which are also recyclable.
The traits of some bio-based composites can go on to be retained or even enhanced by recycling processes. Research goes on to suggest that it might be because of the way that the natural fibers go on to deform if shredded and ground. While, on the other hand, carbon fibers just break, natural fibers can bend as well as fibrillate. Fibrillation could be offering better penetration as well as adhesion to the polymer matrix.
The SM2ART program, which is a collaboration between ORNL, the University of Maine, as well as industrial partners, has gone on to show that bio-fiber-reinforced composites can scale up for applications when it comes to construction that have insulation and even structures themselves. In 2023, an entire 600-square-foot home got printed from bio-based materials at the University of Maine Advanced Structures and Composites Center and even received the Combined Strength Award at CAMX.
Bringing Advanced Manufacturing Into the Field
The entire goal of the MDF is to get manufacturing solutions right from the lab and into the field, wherein industry collaborators can go on to get benefitted as well as advance the state of the art. The MDF apparently collaborates with manufacturers primarily through two methods: a larger research proposal or a smaller technical collaboration. Notably, the large projects happen to go through a competitive process in which manufacturers go on to submit a proposal in response to the announcement, like the DOE-funding opportunity announcement- FOA. All these can go on to take 6-12 months in order to acquire, as well as carry the risk of the project being awarded to someone else.
It is well to be noted that more frequently, the industry partners happen to work along with MDF directly on certain specific manufacturing problems by way of entering into a collaborative research and development agreement- CRADA under which research can begin sooner, thereby helping the industry partners to begin getting the data they require so as to commercialize a product or even justify a larger-scale research project. Companies that are looking to work on a sustainability challenge in manufacturing may as well directly contact the Sustainable Manufacturing Technologies Group.