To wood or not to wood, that’s been the question! Ever since oil-based plastics burst onto the manufacturing scene, cost, sustainability, and performance have defined the ongoing woods vs. plastics war. In many applications, plastics tend to dominate in cost efficiency and durability, while wood retains a clear edge in sustainability.
Researchers at the University of Oulu, Finland, may be tipping that balance in wood’s favor – at least in certain applications. The researchers have invented wood-derived alternatives to two of industry’s most widely used resins: polyester and epoxy.
High-performance composite materials are indispensable in the marine, renewable energy, sports, transportation, and construction industries, where material durability and performance are critical. Polyester resins are everywhere, forming the matrix in glass-fiber composites used in everything from boat hulls and automotive body panels to roofing sheets and sanitary fixtures. Epoxy resins, meanwhile, serve as structural adhesives and protective coatings, and act as the primary matrix in carbon fiber components for wind turbine blades, aircraft structures, high-end sporting goods, and civil engineering reinforcements.
However, these materials come with significant sustainability challenges. Both polyester and epoxy resins are primarily derived from fossil fuels, making them energy-intensive and carbon-heavy to produce. The composites they form are also notoriously difficult to recycle. The cured resins form tightly cross-linked networks that cannot simply be melted down. Plus, separating them from embedded glass or carbon fibers is like taking candy from a dragon. Recycling is possible, but it usually involves specialized, expensive processes that only some facilities can handle at scale.
In an effort to address the dilemma of performance vs. sustainability, the researchers have developed bio-based resins that not only address sustainability concerns but also deliver on performance.
The science magic behind these materials is as follows. Conventional epoxy resin, widely used in high-performance composites, is made from diglycidyl ether of bisphenol A (DGEBA), a petroleum-derived resin. In the new materials, the researchers replace this fossil-based backbone with furfural-derived diepoxides produced from agricultural and wood residues, thereby creating a plant-based epoxy system that can be cured. The researchers produced the essential building block, furfural, from lignocellulosic biomass.
The results are resins that are not only sustainable but also outperform their fossil-based counterparts! During testing, the glass fiber-reinforced composites with a variant of the plant-based resin exhibited improved toughness and significantly higher tensile and flexural strengths and toughness than DGEBA resins. These results represent a big win for sustainable composite alternatives.
“The biomass-based polyester resin we developed shows up to 76% higher tensile strength than a commercial fossil-based polyester resin,” says Mikko Salonen, doctoral researcher.
Derived from sustainable agricultural and forestry sidestreams such as sawdust and straw, the resins address a significant part of the sustainability challenge. But that’s not all in the sustainability column. Due to the furfural-based diepoxy’s degradable chemical structure, the composites can be chemically broken down, and the components extracted as raw materials.
For the first time, we have high-performing bioresins that can be chemically recycled, creating a closed-loop circular manufacturing system for composites. There may be other bio-based epoxies, but this is the first reported combination that achieves high mechanical performance and chemical recyclability in these composites.
Another significant benefit of the biomass-based furan resins is their potential commercial viability. The production process of these new materials is compatible with existing chemical production lines, eliminating the need to overhaul factories to adopt the new technology.
“Bio-based resins will not have a significant price difference compared to fossil resins,” said research team member Juha Heiskanen. “Once bio-based platform chemicals are produced, they can be processed using existing chemical industry production lines.”
By utilizing byproducts of an existing industry, the research also opens the door to new value chains in the bioeconomy.
“Upgrading bio-based raw materials into high-performance materials and products offers a significant opportunity to expand the bioeconomy,” noted Heiskanen.
According to the press release, the use of bio-based materials is also strategically important for Europe, which has less than 2% of global oil reserves. It not only supports material self-sufficiency but also aligns with the EU’s sustainability and circular economy goals.
So, what’s next for this exciting new research? For now, it remains in the experimentation and validation stage. While it has great potential, it may be a while before we see yachts and turbines made from renewable, recyclable composites. The research team has three patents covering its work and is currently seeking industrial partners to move into pilot-scale production.
A paper covering the comprehensive research was published in the journal Composites Part B: Engineering.
Source: University of Oulu