Contact interactions cellulose fibers

Because protein and cellulosic fibers are buried in contact with copper metal objects, a chemical microsystem is established whereby the degradation of the fiber and the corrosion of the metal interact physically and chemically. As the corrosion solution impregnates and swells the fibers, polymer molecules in amorphous areas are spread apart but are prevented from complete dissolution by the resistant crystalline segments. Copper ion from the corrosion solution is bound to the polymers (Figure 5). As the fiber degrades and more end groups are formed, more copper is bound. Polymers expand further apart as interchain forces are reduced. 

Attractive Forces. Attractive forces, collectively called van der Waal s forces, exist between two oil droplets. Simplistically, these forces may be thought of as the attraction between oil molecules at the o/w interfaces that have lower energy when in contact with each other than when in contact with water. Several phenomena are involved hydrophobic interactions and London dispersion forces are most commonly considered. These are effective as (roughly) the fourth power of the distance between the surfaces and are unaffected by ionic strength. The attraction due to van der Waal s forces is shown in Figure 6. Suspensions of solids (cellulose fibers, finely divided CaCOa, etc.) are stabilized in the same way. Ionic surfactants are used that selectively adsorb to the solid surface, generating a v[/ potential and making possible a stable suspension. 

While we will continue to address the subject of using surfactants to control contact interactions in Chapters 3 and 4, we would like to devote the remainder of this chapter to a discussion of the cohesive forces between anisometric particles—specifically, between the cellulose fibers. This study conducted by the authors and their colleagues is of importance in papermaking applications. 

The results of the contact force measurements, p, between cellulosic fibers in the presence of PEI are shown in Figure 2.23. The observed trends are similar to those shown in Figure 2.21 for the friction coefficient measurements and are also in good agreanent with the patch model of flocculation by the PEI, and the previously mentioned electrokinetic studies, as reflected by the maximum in the cohesive force at low concentrations of PEI. As expected, after reaching the maximum, the cohesive forces decrease with a further increase in the PEI concentration. This corresponds to the decrease in the fraction of available negatively charged patches for interaction with PEI and the increase in the electrostatic repulsion due to a continued adsorption of PEI. 

Amelina, E. A., Videnskiy, 1. V., Ivanova, N. 1. et al. 2001. Contact interactions between the individual fibers of cellulose and its derivatives Mechanism of action of the cationic surfactants. Kolloidnyi Zh. 63 581-585. 

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