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The adsorption of four cationic surfactants with different alkyl chain lengths on cellulose substrates was investigated. Cellulose fibers were used as model substrates, and primary alcohol groups of cellulose glycosyl units were oxidized into carboxylic groups to obtain substrates with different surface charges. The amount of surfactant adsorbed on the fiber surface, the fiber zeta-potential, and the amount of surfactant counterions (Cl(-)) released into solution were measured as a function of the surfactant bulk concentration, its molecular structure, the substrate surface charge, and the ionic strength. The contribution of each of these parameters to the shape of the adsorption isotherms was used to verify if surfactant adsorption and self-assembly models usually used to describe the behavior of surfactant/oxide systems can be applied, and with which limitations, to describe cationic surfactant adsorption onto oppositely charged cellulose substrates.

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Polypyrrole was polymerized on the surface of cellulose fibres using a sequence of fibre impregnation in FeCl 3 solutions, thickening and re-dispersion in a pyrrole solution. f-Potential and adsorption isotherms of the FeCl 3 -cellulose systems showed that the adsorption of iron III was associated with the formation of free Fe 3+ cations in the impregnation liquor. Moreover, under the test conditions applied, the amount of adsorbed iron III was not sufficient to promote the polymerization of a adequate amount of pyrrole on the fibre surface. Optimization of the polymerization reaction required that the FeCl 3 concentration in the impregnation liquor be increased to approximately 1 mol/l with a subsequent decrease of pH to approximately1.8. Based on scanning electron (SEM) micrographs and the low cellulose polymerization degree measured after pyrrole polymerization, we concluded that the decrease in the electric resistance of bulky polypyrrole/cellulose compounds was associated with a not negligible degradation of the cellulose fibres due to acid hydrolysis and the subsequent impossibility to prepare hand sheets with modified fibres due to the insufficient strength of the wet fibre network. The results of this investigation bring into question the use of FeCl 3 -pyrrole-cellulose systems for the elaboration of conducting paper sheets with good and stable mechanical properties.

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