Abstract
Due to their exceptional mechanical and chemical properties and their natural abundance, cellulose nanocrystals (CNCs) are promising building blocks of sustainable polymer composites. However, the rapid gelation of CNC dispersions has generally limited CNC-based composites to low CNC fractions, in which polymer remains the dominant phase. Here we report on the formulation and processing of crosslinked CNC-epoxy composites with a CNC fraction exceeding 50 wt%. The microstructure comprises sub-micrometer aggregates of CNCs crosslinked to polymer, which is analogous to the lamellar structure of nacre and promotes toughening mechanisms associated with bulk ductility, despite the brittle behavior of the aggregates at the nanoscale. At 63 wt% CNCs, the composites exhibit a hardness of 0.66 GPa and a fracture toughness of 5.2 MPa m\(^{1/2}\). The hardness of this all-organic material is comparable to aluminum alloys, and the fracture toughness at the centimeter scale is comparable to that of wood cell walls. We show that 3D CNC-epoxy composite objects can be shaped from the gel precursors by direct-write printing, casting, and machining. The formulation, processing route, and insights on toughening mechanisms gained from our multiscale approach can be applied broadly to highly loaded nanocomposites.
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Acknowledgments
The authors thank Sooraj Narayan and Prof. Lallit Anand for assistance with the finite element model. Financial support was provided by the Procter and Gamble Corporation, and we thank Neville Sonnenberg for discussions related to the project. C.E.O. was supported by the United States Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program.
Funding
Financial support was provided by the Procter and Gamble Corporation. C.E.O. was supported by the United States Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program.
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AR and AJH conceived and designed the project, AR designed and performed the experiments and interpreted the data, TD supported the experiments and contributed to data interpretation, CEO designed the tooth model and performed the micromilling experiments. AJH supervised the research. AR, TD and AJH wrote the manuscript. All authors discussed the results and reviewed the manuscript.
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Rao, A., Divoux, T., Owens, C.E. et al. Printable, castable, nanocrystalline cellulose-epoxy composites exhibiting hierarchical nacre-like toughening. Cellulose 29, 2387–2398 (2022). https://doi.org/10.1007/s10570-021-04384-7
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DOI: https://doi.org/10.1007/s10570-021-04384-7
Keywords
- Cellulose
- Composites
- Nacre
- Wood
- Structural materials
- Mechanics
- Additive manufacturing
- Sustainable