Biobased Carbon Fibers and Thermosetting Resins for Use in DOD Composites Applications

Using biological resources to make advanced fibers and high-performance thermosetting resins will help reduce the dependence of military composites on the volatile cost of petroleum, resulting in significant technological gains and reducing the toxicity of composite materials.

Various weapons platforms that use composite materials including the Apache helicopter, the high-mobility multipurpose wheeled vehicle, Stiletto, F-22, and USS Radford.

The goal of this research was to use renewable resources derived from plants and other sources to prepare high-performance carbon fiber and thermosetting matrix resins with high strength and high thermal resistance. The scientific objectives were to 1) develop methods for breaking down, modifying, and processing renewable resources to make epoxy resins, vinyl resins, and carbon fibers, and 2) determine structure-property relationships for these novel materials.

Numerous scientific and engineering advancements were developed in this project. Bacteria can successfully decompose lignin into useable structures for the formation of small filaments that might be possible to convert into carbon fibers. Approximately 300 strains of bacteria that decompose lignin were identified, and some have the potential to make lignin into fiber-forming oligomers, including newly identified species of Serratia. However, scale-up of this process proved problematic and unfeasible for completion in this project.

Lignin was chemically fractionated to alter its molecular weight distribution and its usefulness for separating chemically modified lignin. Various chemical modifications of lignin have been used successfully in carbon fiber development. These methods include acetylation and methacrylation, and separation strategies were developed to produce carbon fiber precursors. Both melt- and solution-spinnable lignin-based fibers were produced. Thermo-oxidation and UV curing were successful stabilization methods for these fibers.

Carbon fibers were produced from a few types of lignin and chemically modified lignin. The resulting mechanical properties were relatively poor, but there are obvious steps that need to be taken to improve these properties. Electrical conductivity of these fibers ranged from moderately conductive, similar to that of polyacrylonitrile (PAN)-based fibers, to highly conductive, indicating a significant graphitic content. The highest mechanical properties were achieved for lignin-based carbon fibers by stretching the fibers during processing, resulting in modulus of 35 GPa, strength of 1 GPa, and elongation to failure of 3 percent, significantly exceeding the state of the art in lignin-based fibers. However, life cycle analysis of the lignin-based carbon fibers is not favorable due to the recent reduction in cost of PAN-based carbon fibers.

Numerous biobased resins were developed, including epoxies, vinyl esters (VEs), unsaturated polyesters (UPEs), and polyurethanes, many with excellent properties that can be used in high-performance polymers, composites, and coatings applications. Lignin-based cross-linkers have been prepared that have performance similar to that of bisphenol A cross-linkers while having significantly reduced toxicity. For example, Isosorbide methacrylate was developed with the highest ever transition temperature of greater than 250 °C for a VE system. This work has also produced numerous reactive diluents and viscosity reducers for VE and UPE technology based on fatty acids, lignin, and isosorbide that will maintain or increase polymer performance while reducing hazardous emissions.

Biobased lignin-derived resins with high-bioatomic efficiency that are good for the lower end of high-performance composites and most coatings applications were identified. Furan epoxies are very promising with good thermomechanical properties and very high toughness, making them excellent candidates for composites and coatings applications. Higher-performing UPE resins using isosorbide as an additive or component were developed, but the feasibility for scale-up is low due to the long reaction times required.

This work was performed by John J. La Scala, Joshua Sadler, Faye R. Toulan, Anh-Phuong Lam, Christopher Annunziato, Amod Ogale, Meng Zhang, Annel Greene, Steven Chambers, Joseph Stanzione III, Kaleigh Reno, Richard Wool, Fengshuo Hu, Eric Hernandez, Donghun Koo, and Giuseppe Palmese for the Army Research Laboratory. For more information, download the Technical Support Package (free white paper) below.

This Brief includes a Technical Support Package (TSP).
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Biobased Carbon Fibers and Thermosetting Resins for Use in DOD Composites Applications

(reference ARL-0252) is currently available for download from the TSP library.

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