Acid-Free Preparation of Cellulose Nanocrystals by TEMPO Oxidation and Subsequent Cavitation

Abstract

Softwood bleached kraft pulp (SBKP) and microcrystalline cellulose (MCC) were oxidized using a 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated system. The TEMPO-oxidized SBKP prepared with 10 mmol/g NaClO (SBKP-10) had a higher mass recovery ratio and higher carboxylate content than the other prepared celluloses including the TEMPO-oxidized MCCs. The SBKP-10 was then exposed to cavitation-induced forces through sonication in water for 10-120 min to prepare aqueous dispersions of needle-like TEMPO-oxidized cellulose nanocrystals (TEMPO-CNCs) with homogeneous width of 3.5 to 3.6 nm and average lengths of ∼200 nm. The average chain lengths of the cellulose molecules that make up the TEMPO-CNCs were less than half the average lengths of the TEMPO-CNCs. Compared with conventional CNCs prepared by acid hydrolysis, the TEMPO-CNCs prepared by the acid-free and dialysis-free process exhibited higher mass recovery ratios, significantly higher amounts of surface anionic groups, and smaller and more homogeneous widths.

Cellulose Nanocrystals as a Sustainable Raw Material: Cytotoxicity and Applications on Healthcare Technology

“…Pristine cellulose presents limited reactivity due to its functionalities; however, the 3D hierarchical of its crystalline structures (CNCs) open up new opportunities for innovative applications. As a result, several studies have been reported focused on obtaining nanocrystalline cellulose from variable sources using different reaction strategies and various methodologies …”

“…Concerning the renewable sources of raw materials, there are several possible lignocellulosic materials for the isolation of whiskers: vegetable sources, such as cotton, coconut fiber, corn cobs, pineapple leaves, manioc residues, palm fiber, residual biomass from palm oil extraction, banana fibers, hemp, wood pulp, old newspaper and recycled newsprint, microcrystalline cellulose (MCC), bacterial cellulose, the product of which is named bacterial nanocellulose, microbial cellulose or biocellulose, and animal sources, such as tunicates and marine biomass …”

“…Transmission electronic microscopy (TEM) and atomic force microscopy (AFM) analysis are valuable tools to crimp the morphological nanostructure of CNCs: the acicular shape of the crystals and their nanosized characteristics . The relationship between CNC nanosizes and mammalian cell interactions are discussed in Section 3.…”

“…Cellulosic fibers can be subjected to acid hydrolysis and produce cellulose nanocrystals (CNCs) or cellulose nanowhiskers: needle‐shaped nanometric or rod like particles. The use of a diversified CNC extraction process or other manufacturing steps led to different properties, such as average diameter ( D ), length ( L ), aspect ratio ( L / D ), crystallinity index, and thermal stability . In addition, numerous research facilities are producing nanocellulose, and several new labs and pilot plants have been announced…”

Nanocellulose Film Properties Tunable by Controlling Degree of Fibrillation of TEMPO-Oxidized Cellulose

“…containing >0.8 mmol/g sodium carboxylate groups by mechanical disintegration in water under suitable conditions (Isogai et al, 2011(Isogai et al, , 2018Zhou et al, 2018Zhou et al, , 2019. When TEMPOoxidized cellulose nanofibril (TOCN) films are prepared from completely individualized and transparent TOCN/water dispersions by casting on a plate or filtration on a membrane filter and subsequent drying, the films have good flexibilities, high light transparencies, and high mechanical strengths (Zhao et al, 2018), extremely low oxygen permeabilities of <0.2 ml µm m −2 day −1 kPa −1 under dry conditions, and low thermal expansion coefficients of <10 ppm/K (Fukuzumi et al, 2009(Fukuzumi et al, , 2013Zhao et al, 2018).…”