ASSOCIATION-INDUCED POLYMER BRIDGING - NEW INSIGHTS INTO THE RETENTION OF FILLERS WITH PEO

Ever since polyethyleneoxide (PEO) was introduced as a retention aid i n newsprint and groundwood specialty papermaking, controversy has surr ounded the mechanism by which it acts. Initially proposed as a neutral bridging macromolecule, shown efficiency varied from mill to mill and that a second component was often required for it to work property. C ofactors containing phenolic groups, such as kraft lignin and phenolic resins, were found to be effective. Subsequent laboratory studies sho wed that the dual component retention aid system works even for system s in which neither the PEO nor the cofactor absorbs onto fibres and fi llers, thus apparently refuting the polymer bridging mechanism. Instea d it was proposed that PEO and phenolics form a network in water in wh ich fillers are captured and subsequently swept up by the fibres. The fact that smaller particles were retained less than larger ones was ex plained by the size of the holes in the network. In this paper, we arg ue that the network hypothesis is incorrect and show evidence that the fillers are retained instead by a mechanism of associations-induced p olymer bridging. The more efficient retention of large particles is no t restricted to the PEO retention aid system, but is a universal effec t arising from hydrodynamic fibre-filler interactions.