Lumen loading magnetic paper II: mechanism and kinetics

Magnetic cellulose fibres have been successfully produced by the lumen-loading process. Lumen loading allows filler particles to be introduced exclusively into the lumens of wood fibres while leaving the external surfaces free of filler. The filler is protected by the cell wall from dislodgement during papermaking and the particles do not interfere with inter-fiber bonding. This leads to a lumen-loaded fibre with high resistance to unloading during papermaking and result in papers with a higher strength than those conventionally loaded. Kenaf and black spruce pulp have been loaded with magnetite (Fe3O4). To improve the lumen loading degree, polymeric retention aids have been introduced. Polyethylenimine (PEI) as retention aid in the preparation of lumen-loaded fibre has been found beneficial in the preparation of magnetic cellulose fibres. The maximum lumen loading degree 0.235 g/g pulp was achieved. The factors, which affect the lumen loading degree, included dosage of PEI, pulp drying history, impregnation time and speed. The characteristics of the magnetite surface and its behaviour in water solution in the presence of PEI and aluminum sulfate, the mechanism of adsorption and the kinetics of lumen loading are fully elucidated. Electrophoretic mobility of magnetite is positive in acidic solution and becomes more negative with increasing pH. pHpzc is about 5.5. The magnetite particles are negatively charged without any addition of PEI. The particles reach the point of zero charge when ∼0.15 mg/g pigment of PEI is added and become positively charged with further addition of PEI.