Colloids and Surfaces A: Physicochem. Eng. Aspects 251 (2004) 31–36 Lumen loading magnetic paper II: mechanism and kinetics S. Zakaria a,∗ , B.H. Ong a , T.G.M. van de Ven b a Materials Science Program, School of Applied Physics, Faculty of Science and Technology, University Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia b Pulp and Paper Research Centre, McGill University, Montreal, Que., Canada H3A 2A7 Received 20 October 2003; accepted 25 June 2004 Abstract 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 (Fe 3 O 4 ). 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 0.235g/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. pH pzc 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. © 2004 Elsevier B.V. All rights reserved. Keywords: Lumen loading; Magnetite; Retention aid; Electrophoretic mobility; Magnetic pulp 1. Introduction The preparation of paper involves a study of colloidal ma- terials and retention aid. The utilisation of filler in the wet end chemistry and retention aid during the papermaking re- quires a certain amount of understanding in the chemistry of papermaking. This will lead to a better paper formation and retain as much as filler if used during paper making. Filler has been used for more than two centuries as an addi- tive to improve paper qualities, such as brightness, opacity, smoothness, and printability and at the same time to reduce the production cost. Most common fillers are clay, calcium carbonate, and titanium dioxide. The utilization of fillers has ∗ Corresponding author. E-mail address: sarani@pkrisc.cc.ukm.my (S. Zakaria). progressively grown in modern times. However, two major problems are associated with the addition of fillers. Firstly, the presence of the filler particles on the fibre surfaces pre- vents good fibre-to-fibre contact during sheet consolidation, thus weakening the inter-fibre bonds. The other one is the poor retention of the filler particles in the sheet during pa- permaking. Drainage forces readily shear the rather tenuous bond between filler particle and fibre surface and a frac- tion of the filler passes through the paper machine wire. This problem is only partially solved by the use of retention aids. Green et al. [1,2] visualized the production of lumen- loading fibres in which the filler is mostly all within the lumens as a multi-stage process. The first stage, which is called the impregnation stage, consisted of mixing fibre to- gether with an excess of filler for a set time. This excess 0927-7757/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2004.06.029