Grafting of a polyol polyether chain onto TEMPO nanocellulose Jaka Levanič, mag. inž. Les. Ida Poljanšek, doc. dr. Primož Oven, prof. dr. SP Technical Research Institute of Sweden, Borås, Sweden 13th – 14th April 2016 Conference and Joint Working Group Meeting: Cellulosic material properties and industrial potential

Introduction & aim Cellulose is an abundant natural polymer Widely available from numerous lignocellulosic as well as some microbial and animal sources Cellulose nanofibers have exceptional mechanical properties Desire to produce a cast able resin where cellulose nanofibers would act as part of the resin matrix (chemical bonds instead of physical interactions) Grafting of a polyol polyether chain with an unsaturated C – C bond which would allow crosslinking Moon in sod., 2011. Chem. Soc. Rev. 40: 391-3994

Goals Using the TEMPO reagent to oxidize the hydroxyl group on the surface of cellulose fibers to carboxyl groups Using a combination of mechanical procedures to prepare TEMPO oxidized cellulose nanofibers Graft a polyol polyether chain via the „grafting to“ approach onto the surface of TEMPO oxidized cellulose nanofibers Roy in sod., 2009. Chem. Soc. Rev. 38, 7: 1825 - 2148

Materials and methods Grinding and pre – swelling of the dried cellulose fibers TEMPO oxidation of the cellulose fibers Mechanical disintegration of the oxidized cellulose fibers using a high shear mixer and ultrasound Grafting of the polyol polyether chain onto the TEMPO oxidized cellulose nanofibers using a modified Steiglich esterification process (Moore and Stupp, 1990) Characterization of the products (SEM, FTIR, NMR, conductometric titration, TGA and DSC)

TEMPO oxidation Standard procedure according to Isogai et. al (2010) using TEMPO, NaClO and NaBr Selective oxidation takes place on the 6th carbon atom which is the most reactive one ← (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl aka. TEMPO Biliuta in sod., 2013, Carb. Poly. 91: 502 - 507

TEMPO oxidation pH was maintained at 10,0 +/- 0,1 using 0,5M NaOH Reaction was carried out until the pH remain unchanged for a set amount of time The oxidation process was stopped by lowering the pH to 7,0 using 0,5M HCl Fibers were filtered and washed with distilled water

Mechanical treatment of the oxidized fibers TEMPO oxidized cellulose fiber suspension in water (2%) Mechanical processing was done with a combination of high shear mixing (UltraTurrax) and sonication Cycles were kept short to prevent overheating and discoloration of the suspension The goal was to break the TEMPO oxidized fibers into individual nanofibers

Results – Fiber morphology Fiber comparison at 40 times magnification A 2% fiber suspension in water Fibers during different steps of processing Each step has an effect on the fiber dimensions and suspension behavior Raw cellulose ↑ TEMPO Celllulose ↑ TEMPO cel. w/ HSM ↑ TEMPO cel w/ HSM and US ↑

Results – Nanofiber morphology The mechanically treated fiber suspension was diluted and centrifuged to remove the larger particles The top layer from the centrifuging process was removed and saved for analysis on FE – SEM Average diameter was 5 – 10 nm

Results – Nuclear magnetic resonance (CP – MAS)* A comparison between raw cellulose and TEMPO oxidized cellulose fibers An additional signal has been observed at 174,5 ppm and is typical for the carbon atom belonging to carboxyl groups *Cross Polarization Magic Angle Spinning (CP-MAS)

Results – Conductometric titration Raw cellulose has no functional groups that could be titrated with NaOH NaOH consumption is determined graphically between equivalent points A and B and the carboxyl content calculated (Besbes et. al, 2011) TEMPO oxidized cellulose samples had a carboxyl content of 1,3 mmol/g

Results – Grafting Grafting was performed with a modified Steiglich esterification process in dichloromethane (DCM) To promote grafting, DPTS* and DCC* were used The reaction was carried under normal pressure and temperature Only mild agitation was used All samples were reacted for 24 hours Final product was filtered and washed with cold DCM to remove unreacted reagents Samples were then dried under vacuum and room temperature *DPTS = 4-(dimethylamino) pyridinium 4-toluene sulfonate *DCC = N,N'-Dicyclohexylcarbodiimide

Results – FTIR Differences between the TEMPO oxidized cellulose and the grafted product are minimal, observable only at the carboxyl band A reduction in peak height was noted at 1605 cm-1 and a new peak appeared at 1645 cm-1. This is assumed to mean a reduction in –COOH concentration and an ester bond formation.

Results – Thermal analysis (TGA and DSC) The most obvious difference was in the temperature of decomposition Raw cellulose decomposes in a narrow temperature range in two steps TEMPO cellulose and the grafted TEMPO cellulose decompose in a wider temperature range and the two step decomposition is not as pronounced Sample Decomposition temperature Cellulose 290°C TEMPO cell. 210°C Grafted TEMPO cell 200°C

Conclusions Hydroxyl groups were successfully oxidized to carboxyl groups with the use of TEMPO The concentration of carboxyl groups was in accordance with the published articles, around 1,3 mmol/g Average nanofiber diameter for TEMPO oxidized nanocellulose was between 5 and 10nm The polyol polyether chain was successfully grafted to the TEMPO nanocellulose backbone The decomposition temperature of TEMPO nanocellulose and the grafted TEMPO nanocellulose are significantly lower than the raw cellulose

Acknowledgement The authors wish to gratefully acknowledge the Ministry of Higher Education, Science and Technology of the Republic of Slovenia, within the Program P4-0015 COST Action FP1205: Innovative applications of regenerated wood cellulose fibers for making it possible for me to attend this meeting