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Glutamate glucan-xylan complexes as dry-strength agents for bonding of cellulosic fibers
Complexes of glutamate glucan (a derivative of chitosan) in interaction with beech wood xylans (Fagus sp.) were formed by ionotropic gelation to be used as dry-strength agents for paper by increasing the relative bonded area. Glutamate glucan (GG) was subjected to a reductive amination reaction with α-ketoglutaric acid and sodium cyanoborohydride in order to render a water-soluble chitosan derivative. GG was characterized by FTIR, 13C-NMR and potentiometric titration, regarding to its degree of substitution (26%). Complexes of glutamate glucan–xylan were prepared by ionotropic gelation, varying pH, ionic strength of the liquid medium and mass percentage of xylan. Conditions were carefully selected to minimize the particle size of the complexes and maximize the Z potential with the purpose to facilitate the adsorption of these complexes on cellulosic fibers. Glutamate glucan–xylan complexes (GG-Xil) were firstly adsorbed on bleached pine kraft fiber, and the loaded fibers were used to prepare paper samples. The content of (GG-Xil) was quantified determining the percentage of nitrogen in the fibers by elemental analysis on the surface of the fibers with energy dispersive X-ray spectroscopy (EDS). The effect of GG-Xyl on the dry-tensile strength, as well as the relative bonded area (RBA) were determined. The addition of the complexes improved the tension index by 10.4% and RBA by 21.2%, which indicated that these complexes effectively improved the interaction between the cellulosic fibers. Comparison of these results with those observed by the use of GG and xylan individually, it was concluded that the improvement in strength is mainly due to the contribution of the xylan concentration in the complexes.