E. Vismara, M. Zarattini, A. Bernardi, D. Nanni, S. Bertini, C. Freire
Politecnico di Milano,
Keywords: nanocellulose, allyl group, cyclodextrin, glycidyl methacrylate
Summary:Advances in the chemical modification of nanocelluloses have been recently reviewed by Youssef Habibi.1 Our work aims to enlarge the number of nanocellulose chemical modifications and broaden the horizon of nanocellulose applications. Oxidized and hydrolyzed nanocelluloses were prepared from short high-grade pure cotton fibers (CFT), too short to be spun. Figure 1a reports the CFT solid-state NMR spectrum (CP Mas), where the cellulose profile confirms the purity and the two C4 signals around 90 ppm integration gives the crystallinity index (IC), left C4 crystalline part, right amorphous part. Oxidized nanocellulose was prepared by TEMPO mediated oxidation.2 Acid hydrolyzed nanocellulose was prepared according to the well-known procedure.3 Both oxidized and hydrolyzed nanocelluloses maintained the CFT crystallinity, as verified by their CP Mas spectra. Allyl and allyl oxidized nanocelluloses were prepared from hydrolyzed nanocellulose and oxidized nanocellulose, respectively. Nanocellulose allylation took inspiration from an efficient method of preparing allyl cellulose.4 CP Mas spectra showed that the hydrolyzed nanocellulose and oxidized nanocellulose were fully allylated. The allylation significantly increases the amorphous part, as shown by Figure 1b. Allyl nanocelluloses were further functionalized by free-radical thiol–ene coupling according to click chemistry methodology.5 Mono[6-deoxy-6-[(mercaptotetramethylene)thio]]- -cyclodextrin prepared according to the methodology described by Wenz 6 was used to functionalize allyl nanocelluloses, to achieve new nanocelluloses that merge nano-properties with cyclodextrin inclusion property. Cyclodextrins are used in food, pharmaceutical,drug delivery, and chemical industries, as well as agriculture and environmental engineering. Figure 2 shows on the left the typical CP Mas spectrum profile of an allyl cyclodextrin nanocellulose, where a part of the allyl group is preserved and a part is functionalized with mono[6-deoxy-6-[(mercaptotetramethylene)thio]]-beta -cyclodextrin. Bacterial cellulose 7 was functionalized by surface radical glycidyl methacrylate (GMA) grafting, transferring the approach used for cellulose textiles to nanocellulose.8 The GMA grafting occurred as confirmed by the IR spectrum reported in Figure 2 on the right. The IR spectrum of GMA bacterial nanocellulose, where GMA structure is reported, shows the glycidyl ester and epoxide group signals. GMA grafting maintained the crystallinity of the starting bacterial cellulose. As GMA bacterial nanocellulose was found capable to adsorb beta naphthol, it can be studied for manufacturing innovative adsorbent nanocellulose for the removal of aromatic compounds from contaminated waters. Similarly, as it was found capable to adsorb amoxicillin, it can be studied for manufacturing innovative nanocellulose for drug delivery.