Effect of cationic polyelectrolyte and surfactant on cohesion and friction in contacts between cellulose fibers

The methodics and devices are presented for quantitative study of the characteristics of interaction in contact between individual fibers: friction force F in shear test, and cohesion force, i.e. contact strength p in rupture test. In experiments with cellulose fibers in various liquid media, the friction coefficient mu has been estimated, and the molecular component of friction force related only to attraction of fibers, in the absence of any external normal load has been found. The specific free energy of interaction U has been evaluated in measurements using model samples with the nature of surface similar to that of cellulose fibers. The effects of cationic polyelectrolyte and surfactant: polyethyleneimin and tetrabuthylammonium iodid on these parameters have been quantitatively determined. Complicated, non-monotonic (with several extrema) dependence have been estimated between values F, mu, p, U and surfactant concentration C. Comparison of these data with the zeta-potential measurements of cellulose fibers in the same surfactant solutions allows one to propose an explanation of the mechanisms of these polyelectrolyte and surfactant influence on fiber interactions. (C) 2000 Elsevier Science B.V. All rights reserved.