Preparation of Microfibrillated Cellulose from Wood Pulp through Carbamate Modification and Colloid Milling

Abstract

This paper studies a new convenient method to prepare microfibrillated cellulose from a bleached eucalyptus kraft pulp. First, the wood pulp was reacted with urea to produce cellulose carbamate (CC), and then the CC was treated with colloid mill in an acidic medium. A feasible preparation process for CC was to soak the pulp with the urea solution, and then the cellulose pulp was dewatered, dried, and reacted with urea at high temperatures above the melting point of urea. The Kjeldahl method, infrared spectroscopy, and solid 13C NMR were used to confirm the effectiveness of the reaction. On the basis of CC with the degree of substitution, DS = 0.123, the aqueous suspension with 2% content of CC at pH values of 1, 3, or 7 was severally ground by a colloid milling. After centrifugation, the nanocellulose carbamate fiber (CCNF) in the supernatant was obtained. X-ray diffraction showed that CC and CCNF had the same crystal form as the cellulose pulp, but the crystallinity decreased successively. The nanometer diameter of the CCNF fiber was observed with scanning electron microscopy. Results showed that when the pH value of the CC suspension decreased during the colloid milling, the crystallinity of the CCNF decreased along with the decrease of fiber diameter, and the zeta potential of the supernatant increased. This indicated that carbamate side groups of CC were protonated at low pHs and the cation repulsion between cellulose molecular chains enhanced the driving force of the pulp separation to CCNF. Interestingly, the thermal stability of CCNF is comparable to that of the original cellulose, and the enhancement effect of CCNF on starch can be clearly observed even at a relatively low loading of CCNF.

Graft onto approaches for nanocellulose-based advanced functional materials

“…Under acidic conditions, these modified cellulose fibres turn cationic thereby easing the mechanical disintegration by exerting electrostatic repulsion forces. 159…”

A post-sulfonated one-pot synthesized magnetic cellulose nanocomposite for Knoevenagel and Thorpe–Ziegler reactions

“…44,59,66 The thermal decomposition of urea produced ammonia and isocyanic acid, which converted the FeCl 3 and FeCl 2 into Fe 3 O 4 and cellulose into cellulose carbamate, entitled as MCCNCs. [67][68][69] Under higher temperatures, the presence of excess ammonia would facilitate the cellulose regeneration from the cellulose carbamate producing MCNCs, which could explain the absence of FTIR adsorption bands that could be assigned to n(C]O) at >1700 cm −1 . 45,70 The post-sulfonation of the synthesized composite using ClSO 3 H would functionalize the surface of both the CNCs and Fe 3 O 4 by SO 3 H, as indicated by the XPS S 2p spectrum, EDX-mapping of sulfur and decrease of thermal stability.…”

Cellulose carbamates via transcarbamoylation/transurethanization of methyl carbamates in superbase–acid conjugate ionic liquids

“…Further, several reaction media have been applied, starting from alkaline water/urea mixtures and known cellulose solvents to ionic liquids (ILs) and deep eutectic solvents, or even supercritical carbon dioxide. 5,8,9,19,24,[26][27][28][29][30][31][32][33] The direct approach for the preparation of CC, commonly known as the 'CarbaCell' process, involves reaction of alkali treated cellulose with urea at temperatures above urea's pyrolysis point (Scheme 1a 'CarbaCell' process). 14,34 The reaction is initiated when urea is heated and releases isocyanic acid, which acts as the reactive intermediate.…”

“…Further, several reaction media have been applied, starting from alkaline water/urea mixtures and known cellulose solvents to ionic liquids (ILs) and deep eutectic solvents, or even supercritical carbon dioxide. 5,8,9,19,24,26–33…”