J. Petlicki et Tgm. Vandeven, ADSORPTION OF POLYETHYLENIMINE ONTO CELLULOSE FIBERS, Colloids and surfaces. A, Physicochemical and engineering aspects, 83(1), 1994, pp. 9-23
The adsorption of a low and a high molecular weight polyethylenimine (
PEI) onto pulp fibers has been investigated. These two cases represent
two extreme modes of behavior: low molecular weight PEI can penetrate
into the porous wall of the fibers, while for high molecular weight P
EI adsorption in pores is negligible. From both equilibrium isotherms
and the kinetics of adsorption it can be concluded that PEI molecules
adsorbed on the surface maintain their identity as individual molecule
s and do not form a uniform adsorption layer. The final coverage depen
ds on the size of a PEI molecule in solution, which, besides the molec
ular weight, is determined by the ionic strength, pH and PEI concentra
tion. The kinetics of high molecular weight PEI adsorption closely fol
low Smoluchowski and Langmuir kinetics, similar to the deposition of c
olloidal particles. Adsorption on the wall of the lumen (hollow space
inside the fiber) is determined by diffusion through pit apertures and
cut ends of the fibers. The kinetics of low molecular weight PEI are
mainly governed by the rate at which molecules can diffuse into the po
res of the fiber wall. After a few days, a pseudo-equilibrium is estab
lished in which the rate of adsorption equals the rate of desorption.
The rate of PEI rearrangement is much slower than the rate of desorpti
on. The implications of these findings to papermaking are discussed.