Tempo-Mediated Oxidation Of Tunicate Cellulose

The research of 2,2,6,6-tetramethyl-piperidine-l-oxyl free radical (TEMPO)-NaBr-NaClO oxidation on cellulose is currently known for preparing nanofibers (NFs). The reaction condition of TEMPO-mediated oxidation is moderate, which can make C6 primary hydroxyl onto the surface of the cellulose crystalline region into a primary carboxyl. Therefore TEMPO-mediated oxidation was not only a method of producing cellulose nanofibers but also the effective method of chemical modification on the cellulose crystalline surface. The products prepared by this method of oxidation have wide application values in the fields of packaging, food, electronic displays, sensors and so on.In the thesis, tunicate cellulose microcrystals (t-MCs) and plant cellulose microcrystals (Whatman CF11, p-MCs) were oxidized by using TEMPO-NaBr-NaClO through addition of a buffer solution into the TEMPO-mediated oxidation system instead of dropping the NaOH solution to maintain pH 10 value of the reaction system. This is a simpler and more effective controlling way for preparation of cellulose nanofibers. Optimal process conditions and oxidation degree (DO) of t-MCs and p-MCs were also discussed.The morphologies of TEMPO-mediated oxidized tunicate cellulose nanofibers (t-TONFs) and TEMPO-mediated oxidized plant cellulose nanowhiskers (p-TONWs) were characterized by polarizing optical microscopy (POM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The DOs of t-TONFs and p-TONWs were characterized by Fourier transform infrared spectrometry (FT-IR) and conductimetric titration (CT). Crystalline forms of tTONFs and p-TONWs were characterized by X-ray diffractometry (XRD).The results showed that the widths of t-TONFs and p-TONWs were about 25 nm and 20nm respectively, their lengths were about several micrometers. When the reaction temperature was 50℃ and the reaction time was 9h, the DO of t-TONFs and p-TONWs reached the highest value of 0.16 (the carboxyl contents of 0.98mmol/g) and 0.22 (the carboxyl contents of 1.36mmol/g), respectively. XRD results showed that the crystalline type of t-TONFs and p-TONWs were still I, which indicated the oxidation process occurred only onto the surface of the crystalline and amorphous region.In order to improve the yield of p-TONWs, plant cellulose nanowhiskers (p-NWs) were prepared by hydrochloric acid hydrolysis of p-NCs at first, then p-NWs were oxidized by TEMPO-mediated oxidation system and the yield of p-TONWs was improved from 19 wt% to 25 wt%.In this thesis, lyotropic chiral nematic liquid crystals (N*-LCs) behavior of the sulphuric acid hydrolysis product of p-NWs was also discussed. Fingerprint texture was observed and the pitch of N*-LCs was about 6.5μm at a concentration of 5.8wt%. After p-NWs treated with TEMPO-mediated oxidation, the pitch of N*-LCs remained 6.9μm at the same concentration of 5.8wt%. FT-IR. result showed that the surface of p-TONWs produced by sulfuric acid hydrolysis with TEMPO-mediated oxidation occurred carboxylation of C6 hydroxyl.