Colloids and Surfaces A: Physicochem. Eng. Aspects 251 (2004) 1–4
Lumen loading magnetic paper I: flocculation S. Zakariaa,∗ , B.H Onga , T.G.M. van de Venb a
Materials Science Program, School of Applied Physics, Faculty of Science and Technology, 43600, UKM Bangi, Selangor, Malaysia b Pulp and Paper Research Centre, McGill University, Montreal, Quebec, Canada H3A 2A7 Received 20 October 2003; accepted 25 June 2004
Abstract Magnetic paper lumen via loading process was prepared from never-dried and dried kraft kenaf pulp. PEI was used as retention aid during the inter-stage treatment. The paper produced from the magnetic pulp showed an increase of magnetic properties as the loading increased. The physical properties of the paper such as tensile index, burst index, tear and folding endurance showed a reduction in the strength value as the loading capacity increased. The flocculation study shows that the magnetic colloid exists in multi particles aggregates form in water solution, which caused by magneto-dipole interaction. © 2004 Elsevier B.V. All rights reserved. Keywords: Colloid; Flocculation; Lumen loaded; Pulp; Retention aid
1. Introduction The introduction of filler particle within the lumen of pulp fibre has advantages such as the filler is protected by the cell wall from dislongement during paper making and the absence of filler at the outer surface of fibre resulted better interfibre bonding and thus created the formation of higher strength of paper . The process involved two stages that are impregnation and washing stages. Paper making process involves colloidal materials such as fibre, filler and retention aid. The chemistry of papermaking is based upon physical chemistry and colloid chemistry. Understanding of the chemistry of papermaking is essential to gain well control of the paper making system. These include formation, flocculation, retention of fillers and fines, dispersion of additives, treatment of water affluent and waste gases, foam, sizing and preventing pitch deposits. The aqueous solution is extremely complex and many interrelated variables affect the nature of these colloids. For technical application one attempts to stabilise or destabilise dispersion by mutual repulsion or attraction of particles through adsorption of charged ions, using as guides floccu∗
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lation indexes, sedimentation values, zeta potential measurements or related descriptive test methods. Flocculation refers to the successful collisions that occur when the hydraulic shear forces drive destabilization particles toward each other in the rapid mix and flocculation basins [2,3]. Flocculation can be caused in any of the following environment that re double layer compression, charge neutralization, bridging and colloid entrapment .
2. Methods Unbleached Kenaf pulp (hibiscus cannabinus) was used through out the experiment. The unbleached pulp was prepared using 14% alkali active, 25% sulfidity, having 19.3 kappa number and with pulping yield 46.4%. Magnetic pigment magnetite Fe3 O4 (<5 m, 98%) and retention aid polyethylenimine (PEI; mass average Mw 800 and 750,000) were purchased from Aldrich Chemicals. Filler suspension was prepared by dispersing 30 g of pigment in 250 ml of distilled water containing 0–0.1 g/L alum with a laboratory mechanical stirrer. Separately, 15 g dry weight of kenaf pulp was disintegrated in 1250 ml of distilled water containing 0–0.1 g/L alum. Disintegration was carried out for 5 min,
S. Zakaria et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 251 (2004) 1–4 Table 1 Effect of impregnation time and condition of pulp for lumen loading Sample Impregnation time PEI (mg/g pulp) Pulp condition Loading capacity (g/g pulp)
Fig. 1. Experimental arrangement for flocculation testing.
later mixed with pulp at 1% consistency. Subsequently, the mixture of pigment and the pulp was stirred at the standard rotor speed of 3000 rpm for 30 min. Polyethylenimine was used during the inter-stage treatment and stirred (600 rpm) for 4 h. After treatment, the pigment on the fibre surface was removed by washing with tap water in a self-designed fibre classifier, containing a filter screen (45 m) for 30–60 min. This lumen loading pulp was used to produce magnetic paper sheet and tested in accordance with the standard methods of the Technical Association of the Pulp and Paper Industry (TAPPI). Handsheets were prepared from the clean pulp and tested according to TAPPI standard methods. The filler content were determined by igniting the dry pulp (dried at 105 ◦ C overnight) at 900 ◦ C for 4 h. The hysteresis loops were measured using a computerized Vibrating Sample Magnetometer (VSM) for weighted (10–15 mg) pulp samples. The samples vibrate vertically and the dipole field of the samples induced an AFC signal in a pair of coils, which is proportional to the magnetization of the samples. Flocculation investigation was performed using Photometric Dispersion Analyser (PDA 2000). Stock dispersion of magnetite was diluted to 0.2 g/L solid content in distilled water. A range of PEI dosage was added and the ratio (rms/dc) output was monitored. The experimental arrangement is shown in Fig. 1
3. Result and discussions The condition of pulp (whether they are dried or wet) plays an important role during the loading process. The lumen of dried pulp (dried) was observed collapse and the pits were observed shrink compared to the never dried pulp (wet). Although the dried pulp is soaked in water for 24 h before loading process, the size and shape of the lumen and pits did not return as normal (as in the never dry pulp). The loading capacities of wet (never dry) and dry pulp (Table 1) showed a great
10 Wet 0.2261
10 Wet 0.2353
10 Dried 0.0703
10 Dried 0.0484
reduction of 69 and 79% for 30 min (samples 1 and 3) and 60 min (samples 2 and 4) impregnation time, respectively. It seems that 60 min impregnation time did not change much on loading capacity for the wet pulp. Only a slight increased by 4% is observed after another extra 30 min is added to the impregnation time (samples 1 and 2 for wet pulp). The physical properties of paper loaded with magnetic powder were decreased as the loading capacities increased (Table 2). For example, the tensile index from 81 N/mg (the lowest loading capacities 0.048 g/g pulp sample 5) decreased tremendously to 68 N/mg (the highest loading capacities 0.164 g/g pulp sample 7). The reduction by 16% on tensile strength is probably due to the unclean fibre surface affecting the fibre to fibre bonding. There is a possibility that the magnetic filler remain on the fibre surface even after the washing process is completed. The same phenomenon is observed for other physical properties such as burst, fold and tear. The magnetic properties of paper such as specific magnetization at saturation, Ms , the remanent magnetization, Mr , and the coercive force, Hc , which are reported in Table 2 are calculated from their hysteresis loops obtained for each samples using a vibrating samples magnetometer. The hysteresis loop is corresponding to the degree of the lumen loading, where as Ms and Mr are dependent on the quantity of pigment loaded in the fibres. The Ms and Mr value increased with loading. 3.1. Flocculation of magnetite particles Flocculation investigation was performed using Photometric Dispersion Analyser (PDA 2000). The experimental arrangement is shown in Fig. 1. It is observed that the magnetite particles do not flocculate although PEI dosage at point of zero charge was added. No matter how much dosage of PEI, the magnetite particles give the same ratio output as shown Table 2 Physical, optical and magnetic properties of lumen loaded paper Sample Brightness (unit) Tensile index (Nm/g) Burst index (kPa m2 /g) Tear index (mN m2 /g) Fold (number) Filler content (g/g pulp) Ms (emu/g) Mr (emu/g) Hc (Oe)
5 97 81 4.4 4.8 700 0.048 2.0 0.3 155
6 94 76 4.1 4.2 410 0.162 9.3 1.7 198
7 96 68 3.5 4.3 280 0.164 9.4 1.8 215
8 95 80 4.3 4.6. 570 0.093 5.3 1.0 197
S. Zakaria et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 251 (2004) 1–4
Fig. 2. A schematic representation of the response from the ratio output for magnetite suspension (0.2 g/L) with addition of PEI.
in Fig. 2. Further investigation was carried out with the application of ultrasound to the magnetite suspension. Fig. 3 shows the ratio output of magnetite measured as a function of time following the application of ultrasound without any addition of PEI. It is found that the value of ratio output decreased (point A), indicating that smaller particle has been detected. The magnetite particles ‘dispersed’ during sonication process. After a set time (∼30 s), the ratio output reached a plateau. The particles ‘flocculated’ during the absence of sonication process (point B), showing an increase in the value of ratio output. Once again, it reached another plateau, which gave a similar output to the reading before the sonication process. The magnetite showed the same behaviour when further sonication was on and off. The same trend is observed by changing the shear rate (Fig. 4). It is concluded that magnetite particles exist as multiparticle aggregates in water solution resulting from the magnetodipole interparticle interactions. Since magnetite particles failed to disperse ‘chemically’ by adding PEI, increasing the shear rate (‘mechanically’) of lumen loading process is es-
sential. During lumen loading, magnetite particles enter the lumen as smaller aggregates. High shear is essential, since at low shear the aggregates are too large to enter the lumen through the pit holes. Fig. 5 shows the behaviour of magnetite aggregates suspended in water with addition of PEI and ultrasound treatment. PEI was added to the magnetite suspension and gently stirred. When the aggregate is fully covered with PEI (point A), it became positively charged. However, with the application of ultrasound or increased stirring speed, the aggregates breakup either to individual particles or smaller aggregates. When the ultrasound treatment is stopped or no shear is applied, the magnetite particles formed aggregates similar the one before the sonication process. This is suggesting that the magnetite entered the lumen of the fibre through the pit holes as single particles or smaller aggregates and the aggregates growed bigger inside the fibre lumen where no shear existed. It was also observed that the electrophoretic mobility of magnetite aggregate before sonication (point A) is higher than that after sonication (point C) process.
Fig. 3. A schematic representation of the response from the ratio output for magnetite suspension (0.2 g/L) with application of ultrasound.
S. Zakaria et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 251 (2004) 1–4
Fig. 4. A schematic representation of the response from the ratio output for magnetite suspension (0.2 g/L) for difference shear rates.
Fig. 5. Magnetite aggregates with addition of PEI and ultrasound treatment.
4. Conclusion Never dried kenaf pulp offered the greater loading for filler absorption in the lumen. The physical properties of paper decreased as the filler content increased. The ratio output by magnetite from PDA 2000 showed that the magnetite colloids exist in multi particles aggregates form in water solution, resulting from the magneto-dipole interaction.
Acknowledgments IRPA grant 09-02-0143 and National Science Fellowship (Malaysia) are acknowledged. We also would like to thank
CIDA for travelling grant, Pulp and Paper Research Centre, McGill University for facilities to study the colloid and flocculation.
References  S.R. Middleton, A.M. Scallan, Colloid Surf. 16 (1985) 309– 322.  T.G.M. van de Ven, Adv. Colloid Interf. Sci. 48 (1994) 121– 140.  T.G.M. van de Ven, Nordic Pulp Paper Res. J. 15 (5) (2000) 494– 501.  J. Petliki, T.G.M. van de Ven, J. Pulp Paper Sci. 20 (12) (1994) 375–382.