STUDYING THE EFFECT OF CATIONIC STARCH- ANIONIC NANOSILICA SYSTEM ON RETENTION AND DRAINAGE

Nanoparticles are widely used in the papermaking industry as retention/ drainage aids, usually in conjunction with a high mass cationic polyelectrolyte such as cationic starch. However, little convincing knowledge of their role and mechanism in the wet-end system is yet found. This work focused on the role of nanosilica on papermaking wet end system in response to some processing parameters (drainage, retention, and electrostatic force of the whole system). The observations indicated that the nanosilica performance is defined by interactions of nanosilica with the complex aqueous environment of wet end system. The interaction mechanism seems to rely on introduction of nanoparticles into a cationic starch-fines-fibers network, converting the fiber mat on the forming wire into a porous structure that is responsive to retention and drainage

Fundamentals of strength loss in recycled paper

Considerable work has been devoted to the upgrading of recycled chemical (low yield) pulp fibers during the past decade. There is also disagreement on the effectiveness of an upgrading process regardless, whether of chemical or mechanical origin. One serious problem which restricts sustainable progress in the field of fine-paper recycling is the lack of knowledge of the mechanism by which recycling affects the texture and arrangement of the cell wall which ultimately causes inferior properties of the recycled fibers. The deteriorative effect of recycling on fine-paper manifested itself on the loss in potential bonding of recycled fibers. The loss in potential bonding of the recycled fibers translated into hornification (i.e., loss in fiber wet-flexibility) and/or surface deactivation by recycling. The susceptibility of the fibers for hornification rather than surface deactivation during recycling is substantiated with different techniques. It is concluded that the hornification is responsible for inferior properties of recycled fibers. More importantly, observations in the present work suggest that refining/beating does not develop any new surface area. The effect of refining is restricted to a reduction in the rigidity of the lamellae by mechanical fatigue and subsequently, increased swelling and plasticization of the fiber wall. Thus, drying of never-dried fibers (unbeaten or beaten) from water pulls the lamellae toward each other by surface tension forces and binds the lamellae rich in surface by crystallization forces. These forces lead to an increase in the crystallization of the cell wall provided that the condition required for crystallization, is met by the molecular orientation in the cell wall. When these fibers are re-wetted again, the delamination does not reverse completely, and the lamellae remain partially closed. This results in increased rigidity of unraveled lamellae and restricts the internal surfaces of fibers to access by water. The concomitant result is restricted swelling and thus, loss in wet-plasticity of the fibers on recycling. Most of this change takes place in the first cycle. Repeated recycling deteriorates further the wet-plasticity of the fibers. Based on these findings a model is proposed which explains the mechanism by which hornification develops in the fiber wall during recycling. The proposed model also provides new information on the effects of fiber beating or refining.Forestry, Faculty ofGraduat

Biodegradation and recycling potential of barrier coated paperboards

Four commercial barrier coated boards (i.e., internally-sized uncoated board, one-side polyethylene coated board, double-side polyethylene coated board, and multilayer laminated board) were examined for biodegradation using a soil burial approach on a laboratory scale. It was observed that the base-boards were fully biodegradable in a matter of weeks or months, and the degradation process could be accelerated either by sample size modification or enrichment of the soil microbial population. Freezing pretreatment of boards or the fiber directionality of boards had no influence on the rate of degradation. The boards were also found to be recyclable following a simple procedure of re-slushing and screening. The base-boards became almost fully separated from the polyethylene coated material without any special pretreatment.</jats:p

The Effect of Degree of Substitution of Cationic Starch on Multi-layer Formation of Ionic Starches in Recycled Fibers

Layer-by-layer self-assembly technique is a novel method in nanotechnology for modifcation of the surface properties of solid materials. Among these materials cellulosic fbers can undergo surface changes by formation of polyelectrolyte multi-layers (PEM) using layer-by-layer method. In this study, the effect of degree of substitution of cationic starch on multi-layer build up of cationic and anionic starches and on the bonding ability of the waste corrugated container (OCC) recycled fber with layer-by-layer  technique was  investigated. Experiments were  conducted  at pH≈7.5 and 750 rpm stirring rate in a dynamic drainage jar (DDJ) for 10 min deposition time to  construct 1  to 8  consecutive  layers. The handsheets  at 60 g/m2 on weight basis were made with untreated and  layer-by-layer  treated fbers and  their strengths have been evaluated. The results showed that the interbonding ability indices of fbers such as  tensile  index and  internal bonding  improved signifcantly with multi-layering of cationic starch. However, there was no meaningful change in quality of the specimens formed. Compared to the untreated fbers, the tensile index of cationic starch increased by 129% at 7th layer with DS≈0.045 and internal bonding increased by 400% at the 5th  layer. Moreover, with  regard  to  different  degrees  of  substitution  of  starch,  the increasing  trend  in properties was observed;  in which DS≈0.018  for  lower number of layers and DS≈0.045 for higher number of layers. In the frst case, more starch of lower DS was needed to neutralize the charge of the fber surface but in the second case greater charge balance of two polymers resulted in further adsorption and greater stability of cationic starch layer, and consequently higher strength has been achieved for the obtained paper

Photocatalytic paper using zinc oxide nanorods

Zinc oxide (ZnO) nanorods were grown on a paper support prepared from soft wood pulp. The photocatalytic activity of a sheet of paper with ZnO nanorods embedded in its porous matrix has been studied. ZnO nanorods were firmly attached to cellulose fibers and the photocatalytic paper samples were reused several times with nominal decrease in efficiency. Photodegradation of up to 93% was observed for methylene blue in the presence of paper filled with ZnO nanorods upon irradiation with visible light at 963 Wm–2 for 120 min. Under similar conditions, photodegradation of approximately 35% was observed for methyl orange. Antibacterial tests revealed that the photocatalytic paper inhibits the growth of Escherichia coli under room lighting conditions