Cellulose Microfibril-Water Interaction as Characterized by Isothermal Thermogravimetric Analysis and Scanning Electron Microscopy

Abstract

Microfibrillated celluloses, liberated from macroscopic lignocellulosic fibers by mechanical means, are sub-fiber elements with lengths in the micron scale and diameters ranging from 10 to a few hundred nanometers. These materials have shown strong water interactions. This article describes an investigation and quantification of the 'hard-toremove (HR) water content' in cellulose fibers and microfibrillated structures prepared from fully bleached softwood pulp (BSW). The fiber/fibril structure was altered by using an extended beating process (up to 300 minutes), and water interactions were determined with isothermal thermogravimetric analysis (TGA). Isothermal TGA is shown to be a convenient and insightful characterization method for fiber-water interactions for fibers and microfibrils at small sample size. In addition, scanning electron microscopic (SEM) images depict the differences between fibers and microfibrils with respect to beating time in the dried consolidated structures. Highly refined pulps with microfibrils were determined to have two critical drying points, i.e., two minima in the second derivative of weight versus time, not before reported in the literature. Also in this study, hard-to-remove (HR) water content is related to the area above the first derivative curve in the constant rate and falling rate drying zones. This measure of HR water correlates with a previous measurement method of HR water but is less ambiguous for materials that lack a constant drying rate zone. Blends of unbeaten fibers and microfibril containing samples were prepared and show potential as composite materials.

Dewatering Behavior of a Wood-Cellulose Nanofibril Particulate System

“…In another work, Sen et al . 36 used another method to calculate the HR water for pulp fibers by integrating the area above the 1st derivative curve in the constant and falling rate zones, and compared this method with the method used by Park et al . The authors refined cellulose fibers to liberate microfibrils with different sizes ranging from several microns down to hundreds of nanometers.…”

Enhanced Absorbent Products Incorporating Cellulose and Its Derivatives: A Review

“…In support of this statement, a strong exotherm has been observed accompanying the first increment of water uptake onto completely dry cellulose (Kocherbitov et al 2008). Water that is strongly bound to cellulose has also been characterized as "hard to remove water" as measured by thermogravimetric analysis or as freezing or non-freezing bound water as measured using differential scanning calorimetry (Park et al 2006(Park et al , 2007Sen et al 2012).…”

Microcrystalline cellulose property–structure effects in high-pressure fluidization: microfibril characteristics

“…This seems logical as the amount of hard-toremove water is linked to the cellulose-air interfacial area [74]. Spence et al [75] used a similar method to determine the HR-water content of a heavily homogenized (20 passes) bleached kraft pulp MFC.…”