Studies On Surface Engineering Of Pulp Fibers Based On The Layer-by-layer(LBL) Deposition Technique

The layer-by-layer deposition technique is one of molecular self-assemble techniques, which has greatly been developed in the past decade.Its applications to papermaking had become an important study field and attracted the attention of many scientists.The adsorption behaviors of polyelectrolytes onto cellulose fiber and the effects of polyelectrolytes multilayer on paper sheet properties have been studied in the paper.The potential applications of the techniques to papermaking were explored in the meantime.At the beginning,Polyelectrolyte titration and Zeta potential measurement were used to investigate the influence factors in the cationic polyelectrolytes and anionic polyelectrolytes deposition process respectively,including beating degree of pulp,pulp fraction,dosage of cationic polyelectrolytes,species of anionic polyelectrolytes,pulp slurry pH,and so on.The results showed that the beating degree of pulp influenced the saturated adsorptive value of polyelectrolytes.The adsorptive value of polyelectrolytes on the fine was more than that of fibers.The desorption of cationic polyelectrolytes from fibers surface arose from the decline of pulp slurry's pH.Then,the effects of layer-by-layer deposition of PA-PAA and PA-Aluminium silicate on the paper properties were studied.After the layer-by-layer deposition of PA-PAA,the mechanical properties of paper increased significantly except for tearing index of paper. The breaking length of handsheets was increased by 70%,and bursting index were doubled, whereas tearing index decreased.These results indicated that the fibers inter-bonding improved.After deposition of PA-Aluminium silicate,brightness of paper fell off and opacity of paper rose,but the properties of paper didn't significantly decline,otherwise absorbability of paper declined wavily,and the value of odd layers was higher than that of even layers.Laser Scanning Confocal Microscope(LSCM) was used to observe the distribution of polyelectrolytes on fiber surface after layer-by-layer deposition of polyelectrolytes.The LSCM images showed that there were polyelectrolytes depositing on fiber surface to form a certain thickness film.At last,PAE/SA and PAE-CMC dual polymeric strengthening system based on the theory of layer-by-layer deposition technique were investigated to apply to bleached kraft soft pulp and old corrugated container pulp accordingly.It can be seen from results that the treatment of fibers with PAE and SA consecutively had better effects on sheet strength properties than that with any of them separately.The tensile strength had increase by 77.9%. The folding strength was ten times more than that of control.And bursting index was as much again as that of control.The increased extent of strength was different for the pulps with different beating degree.The PAE-CMC dual strengthening system which was added by different strategies has strengthening effect on the OCC pulp.The strategies were:PAE and CMC were added consecutively,PAE and CMC were added synchronously,the polyelectrolytes complexes(PECs) compounded by PAE and CMC was add.But the density of paper didn't change remarkably through these two strengthening systems.In conclusion,the bonding strength between fibers could be improved by the layer-by-layer deposition of polyelectrolytes.As a result,the mechanical properties of paper can be improved greatly,and it was correlated with the fiber surface change after layer-by-layer deposition of polyelectrolytes.