Printable, castable, nanocrystalline cellulose-epoxy composites exhibiting hierarchical nacre-like toughening

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 w...

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Bibliographic Details
Published in:Cellulose (London) 2022-03, Vol.29 (4), p.2387-2398
Main Authors: Rao, Abhinav, Divoux, Thibaut, Owens, Crystal E., Hart, A. John
Format: Article
Language:English
Subjects:
Aggregates
aluminum
Aluminum base alloys
Bioorganic Chemistry
brittleness
Castability
Cellulose
Ceramics
Chemical properties
Chemistry
Chemistry and Materials Science
Composites
Crosslinking
Fracture toughness
gelation
gels
Glass
Hardness
Lamellar structure
Machining
microstructure
Multiscale analysis
Nacre
Nanocomposites
Nanocrystals
Natural Materials
Organic Chemistry
Original Research
Physical Chemistry
Polymer matrix composites
Polymer Sciences
Polymers
Sustainable Development
Three dimensional composites
wood
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Summary: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. Graphical Abstract
ISSN:0969-0239
1572-882X
DOI:10.1007/s10570-021-04384-7