Abstract
Atomic force microscopy with chemically modified tips was used to evaluate the inter fiber bonding properties of typical wood pulp fibers. Using –OH functionalized AFM tips as a model of cellulosic pulp fiber surfaces, pull-off forces and work of adhesion were measured in aqueous media. Three distinct tip-surface interactions were identified from force-displacement curves, representing three typical surface conditions of wet pulp fiber surfaces: solid, swollen and micro-fibrillated. The work of adhesion calculated shows that van der Waals forces are the major contributing factor on non-swollen solid regions of fiber surfaces. The difference in inter-molecular bond strength of different pulp fibers is relatively small. The inter-fiber bonding properties of pulp fibers are mainly controlled by the surface deformability, which determines the area of molecular contact at fiber-fiber physical interaction points.
Highlights
In a paper sheet, individual fibers are held together by van der Waals forces and hydrogen bonds, providing paper with the essential structural and mechanical strength
In order to further increase the use of high yield pulp fibers (HYP) fibers in high end paper products, it is essential to understand the differences in inter-fiber bond properties between HYP and softwood bleached kraft pulp fibers (SBKP)
The cantilever with 0.42N/m nominal spring constant was used for force measurement of adhesion while others were used for fiber surface imaging
Summary
Individual fibers are held together by van der Waals forces and hydrogen bonds, providing paper with the essential structural and mechanical strength. The adhesion due only to the van der Waals and hydrogen-bonding interactions between the tip and the fiber surfaces were measured (Feldman, Tervoort, Smith, & Spencer, 1998) Most of these studies were performed on fully bleached chemical pulp fibers, which mainly consist of cellulose and hemicelluloses. The cellulosic fiber surface of a fully bleached chemical fiber was simulated by AFM-tips modified with –OH terminated SAMs. Force-distance curve measurements were performed in water under a controlled environment. Rupture force, rupture distance and work of adhesion were measured on some typical commercial wood HYP fibers, in order to study the effects of different pulping methods on the inter-fiber bonding properties of the resulting fibers
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