| Cationic starch has widespread applications in paper manufacturing industry because of its advantages such as low cost, biodegradation and strong combinative capabilities with fiber and filler. The studies on the preparation of cationic starch are always the concerned focus of paper chemicals. In this work, the effects of types and preparation technology of cationic starches on the mechanical properties of paper were studied in detailed. Briefly, twenty-eight kinds of cationic starch samples were prepared based on corn starch, cassava starch and potato starch by water-wet-process, deep eutectic solvent based process and extrusion process respectively. Twenty-six samples were analyzed by FT-IR. Twenty-two samples were analyzed by XRD and SEM. Testing of the substitution degree of twenty-eight samples was also done. Ten of the prepared cationic starch samples were applied practically to the 100% LBKP paper in order to evaluate the strength-enhancing abilities of different cationic starch products. The obtained results and conclusions were shown as following.(1) Three kinds of cationic starches were produced using different raw starches including corn starch, cassava starch and potato starch under the same water-wet-process and their properties were studied respectively. It was found that the morphologies and crystal structures of cationic starch particles and the raw starch particles were almost the same because the reactions occurred mainly on the surface of starch particles. On the other hand, the potato cationic starch particles showed obvious differences in the XRD results and SEM images from the raw potato starch particles, which was attributed to the high permeability and high substitution degree of potato cationic starch particles. The rank of the starch cationization reaction efficiency of the three kinds of raw starches is:potato starch (80.5%)>corn starch (67.8%)>cassava starch (62.3%) under twenty-four-hour reaction condition. The rank of the strength-enhancing effects to the 100% LBKP paper of the three kinds of cationic starches is:corn starch>cassava starch>patato starch. Generally, the cationic corn starch with moderate substitution degree and molecular weight showed superior enhancement effects.(2) Three kinds of cationic starches were produced using different raw starches including corn starch, cassava starch and potato starch under the same deep eutectic solvent based process and their properties were studied respectively. It was found that the morphology of cationic starch particles was changed, which was different remarkably with the water-wet-process. The morphologies of cationic starches particles including corn starch, cassava starch and potato starch did not show obvious differences. The rank of the starch cationization reaction efficiency of the three kinds of raw starches is:potato starch (90.4%)>corn starch (86.2%)>cassava starch (76.6%). The rank of the strength-enhancing effects to the 100% LBKP paper of the three kinds of cationic starches is:corn starch>cassava starch>patato starch. Comparing with the cationic starches produced by the conventional water-wet-process method and ionic liquid based process, the cationic starches produced by deep eutectic solvent based process showed better results in the reaction efficiency, strength-enhancing effects to the 100% LBKP paper as well as eco-friendly property.(3) Three kinds of cationic starches were produced using different raw starches including corn starch, cassava starch and potato starch under the extrusion process and their properties were studied respectively. The effects of extrusion temperature and additive amount of base on the properties of three kinds of cationic starches were also studied. It was found that the morphologies and crystal structures of starch particles were changed clearly during the extrusion reaction process, which led to the increasing of amorphous region and the formation of clay-like starch bulks and gel structures. This phenomenon was different obviously with the case of cationic starch prepared by water-wet-process and normal semi-dry method. Three kinds of cationic starches were characterized by FT-IR and showed the similar results. The cationic corn starch was synthesized under the condition using small amount of the base, under which the molar ratio of base and etherifying agent was kept at 1:1 at 70 ℃, showing crystal peak at diffraction angle 21° in the XRD data which was related to the high crystal degree of corn starch. The SEM images of potato starches showed obvious gelatinization structures on the surface of starch particles, which was attributed to their low gelatinization temperature and low crystal degree. The rank of the starch cationization reaction efficiency of the three kinds of raw starches is:corn starch (85.6%)> potato starch (83.6%)> cassava starch (76.3%) under the reaction condition of 90℃ and the molar ratio of base and etherifying agent kept at 2:1. The mechanical strength enhancement effects of prepared cationic starch to the 100% LBKP paper were distinguished. The tendency of the effects to the three mechanical strength parameters was not the same. As to the effects of the tensile index and those of the folding strength, the rank was:potato starch>corn starch> cassava starch; as to the inter-bonding force enhancing, the rank was:corn starch> cassava starch>potato starch. Comparing with the cationic starches produced by the conventional water-wet-process, the cationic starches produced by extrusion process showed better results in the substitution degree, the reaction efficiency, and the strength enhancement effects to the 100% LBKP paper. |
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