Multifunctional Cellulosic Scaffolds from Modified Cellulose Nanocrystals. Eldho Abraham and Oded Shoseyov Hebrew University of Jerusalem, Israel

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1 Multifunctional Cellulosic Scaffolds from Modified Cellulose Nanocrystals Eldho Abraham and ded Shoseyov Hebrew University of Jerusalem, Israel 1

2 Structure of a plant fibre 2

3 Functionalisation of CNC Chlorosilanes create an oligomeric silylated layer Halogenated acetic acids create carboxymethyl surfaces Sulfuric acid treatment provides sulfate esters Carboxylic acid halides create ester linkages TEMP mediated hypochlorite oxidation creates carboxylic acids Acid anhydrides create ester linkages Isocyanates create urethane linkages Epoxides create ether linkages 3

4 Esterification of CNC by acetic anhydride and iodine CNC esterification (a) iodine catalyzed reaction mechanism by nucleophilic substitution (esterification) (b) and the structure of a highly esterified Ac-CNC crystal (c). Abraham et. al; ACS Appl. Mater. Interfaces 2016, 8, and ACS Appl. Mater. Interfaces 2017, 9 (3),

5 AFM and TEM of ACNC AFM TEM Abraham et. al; ACS Appl. Mater. Interfaces 2016, 8,

6 Structure analysis of ACNC TEM of Ac-CNC Abraham et. al; ACS Appl. Mater. Interfaces 2016, 8, FTIR (a) and Solid 13 C NMR (b) ACNC crystals

7 ptical polarized images of dried ACNC films TGA SEM of ACNC films cross sections XRD 7

8 Hydrophobicity and transparency Contact angle e (a) Dispersity (2 wt.%) of CNC and ACNC in different solvents (b) water swelling analysis of CNC and ACNC coated mung bean seeds with time (e) water contact angle on the top of ACNC film d (c) highly hydrophobic behaviour of water precipitated spongy ACNC Abraham et. al; ACS Sustainable Chem. Eng, (2016) 4 (3), ). (d) transparency and smoothness of dried ACNC film ACS Appl. Mater. Interfaces 2016, 8,

9 Scheme for the synthesis of ACNC aerogels CNC Cellulose I I H I I I + H Cellulose H -I 2 Ac-CNC Cellulose CH 3 Freeze drying ACNC precipitated in water HR-SEM of ACNC aerogel (scale 50 μm) ACNC aerogel (0.4 wt%) Ultralightweight scaffold on the top of a dandelion without bending the flower s seed heads.

10 Mechanism of the aerogel formation (a) Schematic of the structure of acetylated cellulose nanocrystals (ACNC). (b) ACNC/ethanol stored syringe. (c) ACNC dispersed in water. (d) Dispersed ACNC particles and growing ice crystals during freezing. (e) Ice templating of ACNC crystals in between the channels of ice crystals. (f) Internal SEM of the aerogel. (g) Schematic of the aerogel structure with protruded ester pendants. 10

11 Structure of the aerogel Abraham et. al; ACS Appl. Mater. Interfaces 2017, 9 (3), (a) ACNC Aerogel made in falcon tube. (b) aerogel made in a freezing chamber. (c) aerogel with a density of 7.5 kg m 3 can sustain a 300 g weight. SEM of the: (d, e) outer top, (f, g) inner core, and (h, i) middle part. 11

12 (a, b) TEM images of ACNC crystals; and SEM images of the inner layers of the aerogels with (c) 0.4 wt.%, (d) 0.6 wt.%, (e) 0. 8 wt.%, and (f) 1 wt.% starting ACNC concentrations (scale bars of the scaffolds are 100 μm). 12

13 FTIR (a) and Solid 13 C NMR (b) ACNC aerogel Compressive stress strain of the aerogel Abraham et. al; ACS Appl. Mater. Interfaces 2017, 9 (3),

14 Absorption capacities (C m ) ACNC aerogel (0.5 wt%) for a collection of organic solvents and oils Lipophilicity leophilicity Hydrophobicity 14

15 Lipophilicity of the aerogel Abraham et. al; ACS Appl. Mater. Interfaces 2017, 9 (3), Peptide carbonyl binding-site is present in this cleft cavity of lactoglobulin which possibly makes suitable interaction with the 15 carbonyl carbon of the ACNC molecules

16 Movie 1: Flexibility of the aerogel Movie 2: Ultra-lightweightness of the aerogel 16

17 Flame retardant cellulosic aerogels I II III H H H H R R = 6 R R or H n H H (-) B H H R R IV - B R FTIR of ACNC, ACNC/BTCA, and Boric acid/acnc/btca aerogels I= BTCA (1, 2, 3, 4 Butanetetracarboxylic Acid) II= ACNC with DS<2 III= Boric acid IV= Structure of cross-linked BTCA/BA/ACNC Cross-linked flame retardant hydrophobic aerogel 1570 cm -1 = boron-ester bond 17

18 Before heating at 300 o TGA After heating at 300 o

19 Conclusions CNC could be successfully esterified with acid anhydrides where iodine as catalyst by single step modification The acetate esterified CNC (ACNC) is highly hydrophobic in nature with crystalline behavior ACNC films are good candidate for transparent hydrophobic nanocoating ACNC forms flexible ultra lightweight aerogels upon water precipitation followed by freeze drying ACNC aerogels possess oleophilicity, hydrophobicity and lipophilicity with potential applications ACNC aerogels holds enhanced thermal stability together with good mechanical properties ACNC aerogels with boric acid and BTCA shows flame retardant properties. 19

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