3. Results and discussion
Dispersed cellulose fibers were initially isolated from printed
paper wastes via pretreatment with sodium hydroxide solution
(12 wt%) for the removal of residual lignin and ink particles, as
well as maceration of tightly packed cellulose bundles. Well dispersed
cellulose fibers were subsequently dissolved in an ionic
liquid, 1-allyl-3-methylimidozoium chloride (AMIMCl) to form a
homogeneous cellulose solution. In this study, a cellulose solution
of 4 wt% was used since cellulose solution of higher concentration
would be very viscous and hence difficult to be extruded directly
into the coagulation bath. Besides, cellulose solution of too low
concentration was found to be undesirable due to the formation of
cellulose beads which would collapse readily upon drying.
Through combined gravity force and appropriately applied pressure,
uniform droplets of cellulose solution were being extruded
through syringe needle nozzles of varying diameters. Larger but
uniform droplet sizes were obtained with increased diameter of
syringe needle nozzles under constant applied pressure. Spherical
cellulose beads were formed instantly as droplets of cellulose were
being introduced into the coagulation bath. The formation of cellulose
beads was governed by the relative rates of diffusion of nonsolvent
and cellulose molecules into the gelling zone [11]. Syringe
needles of different nozzle diameters were used in order to prepare
cellulose beads of mean diameters which varied within the
range of 0.4–2.2 mm (Fig. 1). The mean diameters of cellulose
beads as prepared by using syringe needle nozzles of diameter
0.50 mm, 0.80 mm and 1.20 mm were 0.4170.03 mm,
0.8370.11 mm, and 2.1470.08 mm, respectively. The mean masses of cellulose beads were observed to increase with their
mean diameters at 4.72, 9.30, and 27.8 mg/per bead, respectively
(Fig. 1(d)).
Fig. 2 shows the cross-sectional SEM micrographs of cellulose
beads with different mean diameters. These micrographs showed
the presence of 3D nanofibrillar networks which constituted the
highly porous microstructure of cellulose beads. Intermolecular
hydrogen bonds formed within the crystalline regions of cellulose
fibers could have served as physical cross-linkers during the coagulation
process which led to the formation of 3D nanofibrillar
network microstructure [12]. Cellulose beads were highly porous
in nature as evidenced by their substantially high specific surface
areas which ranged between 107 m2
/g and 498 m2
/g depending
on their mean sizes. The specific surface areas of cellulose beads
were observed to vary inversely proportional to their mean diameters
of 0.4170.03 mm, 0.8370.11 mm, and 2.1470.08 mm at
498 m2
/g, 324 m2
/g, and 107 m2
/g, respectively (Fig. 3). The lower
specific surface area of larger cellulose beads could be attributed to
higher packing density of their 3D nanofibrillar networks microstructure.
Being non-toxic, biocompatible, biodegradable, abundance
and cheap, the potential utility of cellulose beads with optimized
microstructure as drug delivery carriers or absorbent
materials is therefore envisaged
3. Results and discussionDispersed cellulose fibers were initially isolated from printedpaper wastes via pretreatment with sodium hydroxide solution(12 wt%) for the removal of residual lignin and ink particles, aswell as maceration of tightly packed cellulose bundles. Well dispersedcellulose fibers were subsequently dissolved in an ionicliquid, 1-allyl-3-methylimidozoium chloride (AMIMCl) to form ahomogeneous cellulose solution. In this study, a cellulose solutionof 4 wt% was used since cellulose solution of higher concentrationwould be very viscous and hence difficult to be extruded directlyinto the coagulation bath. Besides, cellulose solution of too lowconcentration was found to be undesirable due to the formation ofcellulose beads which would collapse readily upon drying.Through combined gravity force and appropriately applied pressure,uniform droplets of cellulose solution were being extrudedthrough syringe needle nozzles of varying diameters. Larger butuniform droplet sizes were obtained with increased diameter ofsyringe needle nozzles under constant applied pressure. Sphericalcellulose beads were formed instantly as droplets of cellulose werebeing introduced into the coagulation bath. The formation of cellulosebeads was governed by the relative rates of diffusion of nonsolventand cellulose molecules into the gelling zone [11]. Syringeneedles of different nozzle diameters were used in order to preparecellulose beads of mean diameters which varied within therange of 0.4–2.2 mm (Fig. 1). The mean diameters of cellulosebeads as prepared by using syringe needle nozzles of diameter0.50 mm, 0.80 mm and 1.20 mm were 0.4170.03 mm,0.8370.11 mm, and 2.1470.08 mm, respectively. The mean masses of cellulose beads were observed to increase with theirmean diameters at 4.72, 9.30, and 27.8 mg/per bead, respectively(Fig. 1(d)).Fig. 2 shows the cross-sectional SEM micrographs of cellulosebeads with different mean diameters. These micrographs showedthe presence of 3D nanofibrillar networks which constituted thehighly porous microstructure of cellulose beads. Intermolecularhydrogen bonds formed within the crystalline regions of cellulosefibers could have served as physical cross-linkers during the coagulationprocess which led to the formation of 3D nanofibrillarnetwork microstructure [12]. Cellulose beads were highly porousin nature as evidenced by their substantially high specific surfaceareas which ranged between 107 m2/g and 498 m2/g dependingon their mean sizes. The specific surface areas of cellulose beadswere observed to vary inversely proportional to their mean diametersof 0.4170.03 mm, 0.8370.11 mm, and 2.1470.08 mm at498 m2/g, 324 m2/g, and 107 m2/g, respectively (Fig. 3). The lowerspecific surface area of larger cellulose beads could be attributed tohigher packing density of their 3D nanofibrillar networks microstructure.Being non-toxic, biocompatible, biodegradable, abundanceand cheap, the potential utility of cellulose beads with optimizedmicrostructure as drug delivery carriers or absorbentmaterials is therefore envisaged
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