Supplementary information

Hydrophobic cellulose nanopaper through a mild esterification procedure

Houssine Sehaqui, Tanja Zimmermann, and Philippe Tingaut

S1: degree of substitution (DS) calculation

The carbon weight content of the esterified CNF nanopapers was corrected with respect to the theoretical value of pure cellulose using the formula:

%C is to the corrected weight percentage of carbon in the esterified nanopapers, %Cexp is the experimental weight percentage of carbon in the modified nanopapers as determined by elemental analysis, 44.44 is the theoretical carbon weight percentage of cellulose, 41.95 is the experimental weight percentage of carbon in unmodified CNF nanopaper as determined by elemental analysis.

After the chemical modification of cellulose, the molecular formula could be written as:

C6+Cg.DSH10+(Hg-1).DSO5+Og.DS with Cg, Hg and Og being the number of carbon, hydrogen and oxygen in the grafted entity, and DS the degree of substitution.

The weight content of carbon is then:

(1)

This gives a DS of:

(2)

For different anhydrides we have:

Acetic anhydride: Cell-OHàCell-O-CO-CH3 (Cg=2 , Og=1 , Hg=3)

Butyric anhydride: Cell-OHàCell-O-CO-C3H7 (Cg=4 , Og=1 , Hg=7)

Hexanoic anhydride: Cell-OHàCell-O-CO-C5H11 (Cg=6 , Og=1 , Hg=11)

2- dodecen-1-yl-succinnic anhydride: Cell-OHàCell-O-CO-CH-C12H23 (Cg=16 ,

Og=3 , Hg=27)

This leads to the DS values presented in Table 1

Table 1: DS of esterified nanopapers according to Eq. 2

sample / %Cexp / %Ccorr. / DS
CNF / 41.95 / 44.44 / -
CNF -2 / 43.03 / 45.58 / 0.38
CNF -4 / 44.13 / 46.75 / 0.24
CNF -6 / 44.81 / 47.47 / 0.19
CNF -16 / 45.77 / 48.49 / 0.10

S2. XPS raw data of reference and esterified CNF nanopapers

Figure 2: XPS low resolution spectra of reference and esterified CNF nanopapers.

Table 2: Atomic composition of O and C in the nanopapers’ surface as obtained by XPS

CNF / CNF-2 / CNF-4 / CNF-6 / CNF-16
Atomic % (O) / 44.54 / 43.47 / 42.91 / 41.45 / 37.22
Atomic % (C) / 55.46 / 56.53 / 57.09 / 58.55 / 62.78
O/C / 0.8 / 0.77 / 0.75 / 0.71 / 0.59

S3. FTIR in transmission for the grinded reference and esterified nanopapers

In order to assess the reaction in the bulk of the nanopapers, ca 3 % w/w of grinded nanopaper in powder form was dispersed in a matrix of potassium bromide and pressed to form pellets. Infrared absorption spectra in transmission of grinded treated and unmodified nanopapers were obtained using a Perkin-Elmer Paragon 1000 PC FT-IR spectrometer with a HLLT detector, at a resolution of 4 cm-1 (50 scans). Spectra are presented in Figure 1. All signals previously attributed to the grafted groups with the ATR mode were also detected for the esterified grinded nanopaper in transmission, therefore suggesting that the reaction was not only limited to the surface but also occurred in the nanopaper bulk.

Figure 2: FTIR spectra in transmission of reference and esterified CNF nanopapers (CNF-2 and CNF-16).

S4. Sorption isotherms of reference and esterified CNF nanopapers

Nitrogen sorption isotherms for reference and esterified CNF nanopapers are shown in Figure 2. According to the IUPAC classification, all the sorption isotherms are of type IV which involves adsorption on mesoporous adsorbents with strong adsorbate–adsorbent interaction.

Figure 3: Sorption isotherms of reference and esterified CNF nanopapers

S5. Evolution of the tensile modulus at 50%RH (a) and in the wet state (b) for reference and esterified nanopapers.

Figure 4: a. Evolution of the tensile modulus at 50%RH with the density of reference and esterified CNF nanopapers. b. Tensile modulus in the wet state for reference and modified nanopapers as a function of number of carbons in the graft.