Marrakesh, Mar. 21 (Maroc-Actu) –
A new method of making carbon fiber could convert refinery by-products into high-value, lightweight structural materials for automobiles, aircraft and spacecraft.
The researchers of Massachusetts Institute of Technology (MIT), of the Western Research Institute and the Oak Ridge National Laboratory, all located in the United States, have found a way to make these light fibers from a very cheap raw material: the heavy and sticky waste from oil refining, that refineries today supply for low-value applications, such as asphalt, or end up processing as waste.
The new carbon fiber is not only cheap to manufacture, but it offers advantages over traditional carbon fiber materials as it can have resistance to compression, which means it could be used for carrier applications. Featured in Science Advances.
The research began about four years ago in response to a request from the Department of Energy, which was looking for ways to make cars more efficient and reduce fuel consumption by lowering their overall weight. “If you look at the same car model today, compared to 30 years ago, it is significantly heavier,” he notes. in a statement Nicola Ferralis, researcher at MIT… The weight of cars has increased by more than 15% in the same category.
A heavier car requires a bigger engine, more powerful brakes, etc., so reducing the weight of bodywork or other components has a ripple effect that results in further weight savings.
Carbon fiber composites aren’t a new idea, but so far they’ve only been used in a few very expensive models. The new research aims to change that by providing inexpensive starting material and relatively simple processing methods.
Automotive-grade carbon fiber currently costs $10 to $12 a pound (€9 to 11 for half a kilo), Ferralis points out, and automotive-grade carbon fiber cars cost 10 to 12 dollars per pound (9 to 11 euros for half a kilo). “they can be much more”, up to hundreds of dollars per pound for specialty applications such as spacecraft components.
These fibers are generally made from polymers (such as polyacrylonitrile) derived from petroleum, but using an expensive intermediate stage of polymerization of carbon compounds. The cost of the polymer can represent more than 60% of the total cost of the final fiber.said Ferralis.
Instead of using a refined, processed petroleum product to start with, the team’s new approach uses what is essentially the slag left over after the refining process, a material known as petroleum pitch. ” This is sometimes called the bottom of the barrel. »he remembers.
“The tar is incredibly dirty,” he says, because it’s a jumble of heavy hydrocarbons mixed together, and “that’s what makes it beautiful in a way, because there’s a lot of chemistry that can be exploited”. This makes it a fascinating material to start with”.
It is useless for combustion because, although it can burn, it is too dirty a fuel to be practical, and this is especially true with tightening environmental regulations. “There are so many that the intrinsic value of these products is very low, so they often end up in landfills. » he adds.
Another source of pitch the team also tested is coal tar, a similar material that is a by-product of coking coal, used for example in steel production. This process yields 80% coke and 20% coal tar, “which is basically wasteful,” he explains.
Working with researchers at Oak Ridge National Laboratory, who have experience manufacturing carbon fiber under a variety of conditions, from lab scale to pilot plant, the team sought to find ways to predict performance in order to guide the choice of conditions for these manufacturing experiments.
“The process required to make carbon fiber from pitch is really minimal, both in terms of energy requirements and in terms of the actual treatment to be carried out.“, says Ferralis.
Graduate student Asmita Jana, author of the study, explains that pitch is “composed of a heterogeneous set of molecules, whose properties change drastically if their shape or size is changed”, whereas an industrial material must have very constant properties.
By carefully modeling how bonds and crosslinks form between constituent molecules, Jana was able to develop a way to predict how a given set of processing conditions would affect the properties of the resulting fiber.
“We were able to reproduce the results with amazing accuracy, to the point that companies could take these graphs and be able to make predictions. » characteristics such as fiber density and modulus of elasticity.he adds.
The work yielded results showing that by adjusting the starting conditions, it was possible to make carbon fibers not only resistant to traction, like most fibers of this type, but also to compression, which means that they could be used in carrier applications. This opens up entirely new possibilities in terms of the utility of these materials, they declare.
“The new path that we are developing is not just a cost effect,” emphasizes Mr. Ferralis. “It could open up new applications, and it’s not necessarily about vehicles.
Making composites from conventional fibers is complicated by the fact that the fibers must be formed into a fabric and arranged in precise, detailed patterns. The reason is, he says, that “is to compensate for the lack of compressive strength”. It’s a matter of engineering to overcome the deficiencies of the material, but with the new process, all that extra complexity wouldn’t be necessary.