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Cellulose nanofibrils (CNFs) produced through processes involving oxidation (e.g. TEMPO oxidation) present reactive groups that allow for straightforward modification in aqueous suspension. CNFs fabricated through mechanical refinement alone can be challenging to modify for subsequent reactions due to only having hydroxyl groups present on the surface. To address these issues, CNFs with only hydroxyl groups present were functionalized with norbornene groups in their native aqueous suspension to achieve up to 10% functionalization per anhydroglucose unit. Since quantification of surface functionalizationof CNFs is challenging through most methods, a degradation and subsequent nuclear magnetic resonance analysis method was developed to quantify norbornene functionalization. The norbornene functionalized CNFs (nCNFs) were crosslinked through UV and thermally initiated thiol-eneclick reactions to create robust CNF hydrogels. By varying the reaction conditions, hydrogels made from nCNFs and a dithiol cross-linker could achieve compression modulus values up to 25 kPa. The materials were stable in aqueous suspensions and the cross-linked hydrogels still exhibited shear thinning behavior with high recovery, which demonstrated that even though effective cross-links were formed, a complete network was not. Through this study, thiolnorbornene crosslinking of CNFs could create robust hydrogels and improve aqueous stability that could have applications in sustainable materials and biomaterials.
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Base-free trifluoroacetylation: From methyl glucopyranoside to cellulose nanofibers
Trifluoroacetic anhydride (TFAA) reacts smoothly with low molecular weight carbohydrates and cellulose nanofibers (CNFs) under base-free conditions. Methyl α- and β-D-glucopyranoside were used as model compounds to optimize reaction conditions, which were then applied to lyophilized CNFs for surface modification. ATR-IR spectroscopy and powder X-ray diffraction were employed to characterize the modified CNFs. Trifluoroacetylation for 4 h yields a degree of substitution (DS) of 0.4 acyl groups per anhydroglucose unit while maintaining a crystallinity index near 50 %. DS values were quantified by gravimetry, acid–base titration after saponification, and a novel approach utilizing solution 19F NMR spectroscopy which offers greater accuracy than the other techniques. This study presents an efficient, base-free method for derivatizing carbohydrates as well as surface functionalization of CNFs with trifluoroacetyl groups, potentially expanding their application in fiber-reinforced thermoplastic composites.
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- Award ID(s):
- 2204206
- PAR ID:
- 10612653
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Carbohydrate Research
- Volume:
- 545
- Issue:
- C
- ISSN:
- 0008-6215
- Page Range / eLocation ID:
- 109282
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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