Physical Shearing Strengthening Cationic Pretreatment To Promote Fiber Fibrillation

Cationic cellulose filaments(CCF)can be used as a good flocculant in wastewater treatment because of its high specific surface area and positive surface charge.At the same time,the bonding performance with pulp fiber can not only improve the retention of fine fibers and fillers,and cut consumption of fiber raw materials,but also improve the mechanical properties of paper and composites.However,the direct and efficient production of highly substituted cationic cellulose filaments remains a challenges.In this paper,regular cationic fiber(RCF)was prepared by a conventional cationization pretreatment method without shearing,and the KRK cationic fiber(KCF)was obtained by the KRK high-concentration mill,then both of these were treated by high pressure homogenization to prepare the regular cationic cellulose filaments(RCCF)and KRK cationic cellulose filaments(KCCF)respectively.The structure and morphology of RCF and KCF were compared by different characterization methods,and the effect of high shearing combined with cationization on performances and structure of fiber was investigated.The optimum conditions for preparation of CF were as follows:etherification temperature 50℃,etherification time 2.5 h,the ratio of NaOH to etherification was 2.0,the dosage of EPTMAC and anhydroglucose units in cellulose molar ratio of 1.5.FT-IR and NMR results showed the evidence of introducing of-N+(CH3)Cl-onto the fiber surface,and EDS analysis showed that the nitrogen substituents in KCF were more uniformly distributed and denser.Meanwhile,the maximum substitution degrees of KCF and RCF prepared under the same optimal conditions were 0.28 and 0.14 respectively,and the time was 90 and 150 minutes,respectively,which indicated that the efficiency and rate of etherification reaction under shearing action were greatly improved.The substitution degree of KCF reached the maximum when the plates gap of KRK refiner is 2 mm.The results of optical microscopy and scanning electron microscopy(SEM)showed that the shearing lead to fiber cell wall surface layer falling off,which would be beneficial for the reagent to enter fibers.BET analysis shows that the specific surface area of raw pulp fiber,RCF and KCF is 1.8 m2/g,2.2 m2/g and 3.7 m2/g respectively,which indicates that the cationic treatment slightly increases the specific surface area of the fiber,and the shear effect increases obviously the specific surface area of the fiber.XRD analysis showed that cationic treatment changed the crystalline type of cellulose,and the crystallinity was reduced from 73.6%of the original pulp fiber to 50.3%.There is only one dispersion diffraction peak in the X-ray diffraction diagram of KCF,which indicates that the main amorphous components in the sample and the disorderly arrangement of cellulose macromolecules increase,which shows that the cationic reaction of the fiber under shear stress has great influence on the crystallization area,so the etherification efficiency is greatly improved.Water retention performance test found that the change of fiber water retention performance was consistent with the change of specific surface area,which showed that fiber water retention was mainly affected by fiber surface area and the permeability of reagent.Finally,the macroscopic morphological analysis found that the RCCF is white and emulsified,and flocculation precipitation can occur when standing still while KCCF can disperse stably with transparent and gelatinous,and there is obvious Tyndall effect.SEM observed that diameter of RCCF is from a few hundred nanometers to several microns.The diameter of KCCF in 100-200 nm,length in 100～200μm,has a high long diameter ratio and good dispersion.Due to the surface of the KCCF distributes high positive charges,leading to the separated of cellulose filaments from each other by electrostatic repulsion,and the dissociation can be completed by simple homogenization.