| Currently,straw,reed and recycled fiber are largely used for paper making raw materials.Papermaking process and paper quality are seriously affected by short fibers,high content of parenchyma cell and the high water retention value etc.Paper strength agent is widely used as one of papermaking additives.Paper wet-strength aids includes five kinds:a) UF and modified UF;b) MF and modified MF;c) PAE/PPE;d)polyethylene mine(PEI);e) others species.PEI is a kind of polymer with highly branched chains,primary amine, secondary amine and tertiary amine groups.Crosslinking network is formed between PEI and hydroxyl group on fibers.So it can be used for wet-strength aids and retention agent.Non-modified PEI is mainly applied in papermaking field.Bringing structural performance into full play,PEI was effectively modified. The cationic strength agents of paper were prepared through modification of PEI with ECH,bisphenol A epoxy resin emulsion and water-soluble glycerine epoxy resin respectively.The influence of composition,additive amount and retention aid of cationic polyamide on paper strength is discussed.Secondly,improving adhesive strength between PEI and fibers,The effect of adding order of PEI and CPAM on paper strength is studied,and the rheological properties,pulp potential, molecular structure,thermal stability and paper microstructure were characterized by Zeta potential instrument,rheoviscometer,FTIR,TG and SEM, respectively.The main results show as follows:(1) Under the optimum conditions of w(modified PEI)1.0%,w(CMC)1.0% and m(PEI):m(ECH) 1:1,the wet-tensile index was enhanceed from 3.23 N·m·g-1 to 6.49 N·m·g-1,and the wet strength was increased from 14.26%to 26.48%. (2) Under the optimum conditions of w(modified PEI)1.0%,w(CPAM)= 0.2‰,and m(PEI):m(BAE) 1:1.5,the wet strength was enhanced from 14.46%to 21.65%and the ring crush index improves by 40.54%.Zeta potential analysis showed that the electric charge of slurry system tended to zero when m (PEI):m(BAE) was 1:1.5,w(modified PEI) was 1%,and w(CPAM) was 0.2‰.(3) Under the optimum conditions of w(modified PEI)1.0%,w(modified eEI)17%,and w(CPAM)0.2‰,wet strength was 22.84%and folding endurance was increased over 10%.Zeta potential analysis showed that the electric charge of slurry system tended to zero when w(GE) was 17%,w(modified PEI) was 1%,(4) When it was filled earlierly than the modification,CPAM affected the retention rate of the modification of PEI and produced different drgee of resin obstacle,which decreased paper properties.(5) FT-IR analysis indicates that quaternary ammonium groups are found in the modified PEI/ECH molecular structure.The vibration absorption peak of benzene ring framework and characteristic absorption peak of benzene ring are found in the modified PEI/BAE molecular structure.The vibration absorption peaks of hydroxy,ether bond,methyl and epoxy group are found in the modified PEI/GE molecular structure.(6) Thermograbimetry analysis shows that decompositions temperature of PEI,the modified PEI/ECH,the modified PEI/BAE and the modified PEI/GE respectively start at more than 197℃,270℃,287℃,271℃,Which proved that the heat resistances of the modified PEI were improved obviously.(7) SEM analysis indicates that paper fracture is caused by fiber breakage, which provides basis for the fact that the modified PEI can increase interfiber-bonding strength.
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