Sustainable Design for the Direct Fabrication and Highly Versatile Functionalization of Nanocelluloses

Abstract This study describes a novel sustainable concept for the scalable direct fabrication and functionalization of nanocellulose from wood pulp with reduced energy consumption. A central concept is the use of metal‐free small organic molecules as mediators and catalysts for the production and subsequent versatile surface engineering of the cellulosic nanomaterials via organocatalysis and click chemistry. Here, “organoclick” chemistry enables the selective functionalization of nanocelluloses with different organic molecules as well as the binding of palladium ions or nanoparticles. The nanocellulosic material is also shown to function as a sustainable support for heterogeneous catalysis in modern organic synthesis (e.g., Suzuki cross‐coupling transformations in water). The reported strategy not only addresses obstacles and challenges for the future utilization of nanocellulose (e.g., low moisture resistance, the need for green chemistry, and energy‐intensive production) but also enables new applications for nanocellulosic materials in different areas.

Next, sulphite softwood dissolving pulp (66.7 g, 15% consistency, 10 g dry mass of pulp) was added and the mixture was heated to the temperature stated in Table S1.
After stirring the suspension with a mechanical IKA RW 20 digital stirrer (2,400 rpm) for 24h, the reaction temperature was decreased to room temperature and next ultra sonicated in a bath for 1h using a BANDELIN SONOREX DIGITEC. Next, the reaction mixture was diluted with water (800 mL) and neutralized to pH = 7 by NaOH (aq. 1 M). Afterwards the suspension was centrifuged with EBA 21 Hettich ZENTRIFUGEN with 6,000 rpm for 10 min and the supernatant was decanted away.
The heterogeneous precipitate was further washed by water and subsequent centrifugation; this procedure was repeated three times. The material was further homogenized with IKA T 25 ULTRA TURRAX High Speed Homogenizer (15,000) rpm for 90 min. The material was then put in a beaker and placed in liquid nitrogen at temperature less than -198 o C before freeze-drying. Liquid nitrogen was preferred as opposed the normal freezer, as it is a fast-freezing method and this method helps in preserving the pore size distribution of the 3D-structure. The yields of dry NFC foam (Table S1) were generally >97% based on the initial amount of sulphite softwood dissolving pulp (Table S1).    HCl (1 M)). Afterwards the suspensions were centrifuged with 6,000 rpm for 10 min and the supernatant was decanted away. The precipitates were further washed by deionized water following centrifugation; this procedure was repeated three times.
The purified materials were combined and homogenized with IKA T 25 ULTRA TURRAX High Speed Homogenizer (15,000 rpm) for 90 min. The average Mw was determined by SEC (M w = 112 360 Da, PDI = 6.8) All of this material was subsequently freeze-dried as described above giving a 3D-foam material.

Typical procedure for the recycling of formic acid
To a round bottom flask (500 mL) was poured concentrated formic acid (200 mL).
Next, sulphite softwood dissolving pulp (66.7 g, 15% consistency, 10 g dry mass of pulp) was added and the mixture was heated to 90 o C. After stirring the suspension with a mechanical IKA RW 20 digital stirrer (2,400 rpm) for 24h, the reaction temp.
was decreased to room temperature and next ultra sonicated in a bath for 1h using a BANDELIN SONOREX DIGITEC. Subsequently, the reaction mixture was centrifuged with 6,000 rpm for 10 min and the formic acid was decanted. This formic acid (200 mL) was next reused for a second round of NFC fabrication. The precipitates from the above sequences were washed using deionized water (800 mL) and then neutralized to pH = 7 by NaOH (aq. 1M). (Alternatively NaOH (1 M, 50 mL/g percipitate) was added to reach a pH between 13-14. After stirring for 1h, the suspension was neutralized (pH = 7) with HCl (1 M). Next, the reaction mixture was centrifuged with 6,000 rpm for 10 min and the water was decanted. The precipitate was further diluted with water and centrifuged; this procedure was repeated three times with IKA T 25 ULTRA TURRAX High Speed Homogenizer (15,000 rpm) for 90 min. After this, the resulting NFC material was freeze-dried to a foam material as described above.
General procedure for the NFC processing using TEMPO-NaClO-oxidation-

homogenization method
The processing of wood pulp-derived nanofibrillated cellulose (NFC) using 2, 2, 6, 6tetramethypiperidine-1-oxyl (TEMPO)-NaClO-oxidation method combined with mechanical shearing of pulp. TEMPO/NaClO-oxidation was done on cellulose sulphite softwood dissolving pulp according to the method described by Saito et al. 2 Here the pulp was suspended in deionized water (100 mL/g pulp) containing TEMPO  Freeze-drying of the NFC-gel 25 g, 50 g, or 100 g of TEMPO-oxidized NFC-gel were put in beakers and placed in liquid nitrogen at temperature less than -198 o C before freeze-drying. Liquid nitrogen was preferred as opposed the normal freezer, as it is a fast-freezing method and this method helps in preserving the pore size distribution of the 3D-structure ( Figure S4). To a round bottom flask (500 mL) charged with formic acid derived NFC foam or material, was added a NaOH (1 M, 50 mL/g NFC-foam or solid)) at room temperature. After stirring for 1h, the suspension was neutralized (pH = 7) with HCl (1 M). Centrifugation of this suspension at 6,000 rpm for 10 min was followed by decantation of the supernatant. The precipitate was further washed with deionized water to give the NFC in quantitative yield. This material was freeze-dried (lyophilized) according to the above procedure to provide NFC foam in quantitative yield. IR-analysis determined that all formic ester groups were gone.
The washed NFC was further treated by Soxhlet extraction using CH 2 Cl 2 . After Soxhlet extraction for 24h, the modified NFC was dried under reduced pressure.    Table S3a. Elemental analysis of "click" reacted 1a-1c modified NFC.

S BET a (m 2 g -1 ) Material P BJH b (Å) V BJH c (cm 3 g -1 )
NFC Typical procedure 2 for the silylation of NFC with 1a and 1c.
Next, the solution was added to a solution of cold methanol and the alcohol initiated poly(e-caprolactone) (PCL) precipitated. After filtration, a white solid was isolated and dried under reduced pressure providing the corresponding alcohol-initiated PCL. 1 H NMR and MALDI-TOF analysis of the isolated 6-mercaptohexan-1-ol initiated PCL (0.95 g) revealed that only the alcohol group had been esterified and that the thiol was intact.

Typical procedure for the (S)-tartaric acid-catalyzed synthesis of alcoholinitiated poly(d-valerolactone) (PVL)
To an oven dried vial (24 mL) containing d-valerolactone (VL) (0.75 g, 7.5 mmol, 1.0 equiv.) were added 6-mercaptohexan-1-ol (40 mg, 0.3 mmol, 4 mol%), (S)-tartaric acid (60 mg, 0.4 mmol, 5 mol%) and the reaction was heated to 110 o C. 6 After stirring for 1h, the temperature was decreased; the reaction mixture was dissolved in CH 2 Cl 2 and filtered. Next, the solution was added to a cold methanol (-20 o C) and a white precipitate was formed. After filtration and drying under reduced pressure, a white solid was formed. 1 H NMR and MALDI-TOF analysis of the isolated 6mercaptohexan-1-ol-initiated PVL (0.69 g) revealed that only the alcohol group had been esterified and that the thiol was intact.  After stirring for 16h, the reaction allowed to reach room temperature, CH 2 Cl 2 was added and the Novozyme 435 particles was removed by filtration using celite. The filtrate was added to a cold methanol solution and a white precipitate was formed.
Next, filtration and drying of the white solids under reduced pressure gave the corresponding nonanoic acid-terminated PCLs as white solids. 1 H NMR analysis of the isolated nonanoic acid-terminated 6-mercaptohexan-1-ol-initiated PCL revealed that only the alcohol end-group had been esterified and that the thiol was intact. 5

Procedure for the thiol-ene 'click' reaction between allyl-1c-NFC and 1octanethiol
To a scintillation vial (20 mL) containing 1c-NFC (30 mg) and octanethiol (293 mg, 2.0 mmol) was added DMPA (3 mg) and the reaction mixture was irradiated with an UV-lamp (UV-B bulb, TL20W/12, 20 W) for 24h. Next, the UV treated NFC material was removed and extracted with a Soxhlet extractor with acetone for 16h. The extracted NFC foam material was subsequently dried overnight under reduced pressure.

pentene-1-ol-initiated PCL
To a scintillation vial (20 mL) containing TPSi-1a-NFC foam material (30 mg) and PCL or PVL with a free terminal olefin-end-group (30 mg), was added THF (0.5 mL) and DMPA (3 mg). Next, the reaction was irradiated for 24h using an UV-lamp (UV-B bulb, TL20W/12, 20 W). The UV-treated NFC material was removed and next extracted using a Soxhlet extractor and acetone as the solvent for 17h. The extracted NFC foam material was subsequently dried overnight under reduced pressure.
Next, the mixture was neutralized to pH 6-7 using HCl (1N). Afterwards the material was washed with water and acetone by centrifugation and then dried under vacuum.
The washed NFC foam material was subsequently dried overnight under reduced pressure. The cinchona-alkaloid-modified NFC exhibits high UV-activity and was fluorescent ( Figures S5, S6 and S7). Performing the same procedure with NFC without addition of DMPA did not give a NFC material with UV activity (Blank). Table S6. Elemental analysis of Quinidine-TPSi-1a-NFC.  Step 1.
The aminofunctionalized Amp-1e-NFC (AmP-NFC) (200 mg) was suspended in a pH = 9 adjusted deionized water solution (10 mL). Li  a pH = 9 adjusted deionized water (6 ml) solution and then added to the AmP-NFC suspension. The reaction was stirred at r.t for 24 h. The reaction mixture was washed with water and acetone (3 times) and dried under vacuum, giving the product AmP-NFC-Pd(II) as brown powder (0.34 mg).
The AmP-NFC-Pd(II) (200 mg) was suspended in water (8 mL) and a solution of NaBH 4 (135 mg) in water (5 ml) was added slowly. The reaction was stirred at r.t for 30 min and then washed with water and acetone (3 times), followed by drying under vacuum over night, giving the product AmP-NFC-Pd(0) as grew powder (170 mg).
The elemental analysis showed that the Pd content on the AmP-NFC-Pd(0) is 7.77 wt.%.

Reac0on)0me)(h)) acid)effect)for)the)silyla0on)of)3:phenylpropionalcohol)with)silane)1a)
Tartaric$acid$ General procedure for the acid screening of silylated filter paper: To a flask containing filter paper (500 mg, 1 equiv.), was added acid (10 wt.%, 50 mg) and toluene (7 mL). Next, silane 1a (8.1 mmol, 2.9 equiv.) in toluene (3 mL) was added and the flask was heated to 70 o C in an oil-bath. After stirring, for the time stated in Table S9, the paper was washed with CH 2 Cl 2 (50 mL) and subsequently Soxhlet extracted using CH 2 Cl 2 for 17h. Then the paper was dried overnight under vacuum. Table S8. Acid screening for the silylation of filter paper with silane 1a.
a The reaction was run for 24 h.
General procedure for the silylation on filter paper: To a flask containing filter paper (500 mg, 1 equiv), was added acid (10 wt.%, 50 mg), toluene (7 mL), followed by addition of silane 1 (8.1 mmol, 2.9 equiv.) in toluene (3 mL  General procedure for the thiol-ene 'click' reaction between modified filter paper and alkene or thiol: To a mixture of silylated filter paper (around 30 mg) and thiol or alkene (2.0 mmol) was added DMPA (1 wt.%, 4.5 mg). Then the reaction was irradiated with UV-lamp (UV-B bulb, TL20W/12, 20 W) for 1 h. Afterwards the filter paper was extracted (Soxhlet) with CH 2 Cl 2 . Then the paper was dried overnight under vacuum. General procedure for the thiol-ene 'click' reaction between modified filter paper and polymer: To a mixture of silylated filter paper (around 30 mg) and polymer (60 mg) in minimum amount of DMF was added DMPA (1 wt.%, 4.5 mg). Then the reaction was irradiated with UV-lamp (UV-B bulb, TL20W/12, 20 W) for 1 h. Afterwards the filter paper was extracted (Soxhlet) with dichloromethane. Then the paper was dried overnight under vacuum.     Figure S8. A water droplet on a hydrophobized filter paper with C-16 hexadecene Procedure for the thiol-ene 'click' reaction between TPSi-1a-modified-filter paper and Quinidine or Quinine To a scintillation vial (20 mL) containing TPSi-1a-filter paper (30-32 mg) and Quinidine or Quinine (30 mg, 0.1 mmol) in DMF (0.5 mL) was added DMPA (2 mol%). Next, the reaction was irradiated for 24h using an UV-lamp (UV-B bulb, TL20W/12, 20 W). The UV-treated filter paper was removed and next extracted using a Soxhlet extractor and acetone as the solvent for 17h. The extracted was filter paper was subsequently dried overnight under reduced pressure. The cinchona-alkaloidmodified NFC exhibit high UV-activity and was fluorescent ( Figure S9 and S10). From left: Unmodified filter paper, modified filter paper with (3-mercaptopropyl)trimethoxysilane, filter paper after click reaction with Quinidine, filter paper after click reaction with Quinine. Figure S10. UV-activity of modified filter paper (long wave): From left: Unmodified filter paper, modified filter paper with (3-mercaptopropyl)trimethoxysilane, filter paper after click reaction with Quinidine, filter paper after click reaction with Quinine.