Effect of modified layering treatment on the properties of papers made from recycled fibers

Nanotechnology methods like layer-by-layer technique has shown large potential for modifying the cellulose fibers characteristics and improving its quality. In this technique, cellulosic fibers and counter-ionic particles are placed in an interaction media. During the interaction, ionic particles are absorbed by fibers surface mainly via electrostatic absorption. There is rinsing step between consecutive layering in order to remove physically and loosely absorbed of particles on the fiber surface. Application of different steps of rinsing in this technique has made difficult its practical use. Therefore in current research, effect of using a modified layer-by-layer system (without rinsing stages) on enhancing the strength of papers made from recycled fibers has been examined.
The experiments were conducted to form 1 to 3 successive layers of cationic and anionic starches on recycled fibers prepared from old corrugated container. For each layering stage, 500 ml pulp suspension having 0.48 consistency with was mixed with starch solutions using a laboratory mixer at constant mixing of 750 rpm for 10 minutes. Then, the physical properties (thickness and apparent density) and strengths characteristics (tensile index, burst index and TEA) of handsheets with 60±3 g/m2 basis weight prepared from treated and untreated fibers were compared.
The results have revealed that by treatment of recycled fibers with modified system of layer-by-layer technique, unlike apparent density the thickness of paper decrease. Moreover, this system had considerable impact on development of paper strengths. For example, by layering of three layers of ionic starches, tensile index of papers increased from 15.9 N.m/g to 47.29 N.m/g, burst index improved from 1.05 kPa.m2/g to 2.15 kPa.m2/g and tensile energy absorption increased from 2.42 J/m2 to 10.28 J/m2. Furthermore, SEM micrographs have shown a different appearance in treated fibers compared to the untreated fibers; indicated an increase in gelatinization of treated fiber surface due to an increase in cationic starch absorption.
Layering of cationic starch and anionic starch in modified system of layer-by-layer lead to increase electrostatic absorption of cationic starch onto the recycled fibers. This phenomena with enhancing the bonds between fibers resulted in improving the strengths of papers made from recycled fibers.