Synthesis Of Dendrimer-star Cationic Polyacrylamide By RAFT And Its Application In The Papermaking

With the global scarcity of fiber resources and the increase of dissolved andcolloidal substances (DCS) concentration，papermakers pay more attention to thesynthesis of new multi-functional aids for the complicated papermaking wet-endsystem. Dendrimer-star polymer with small interaction between molecules, lowerviscosity of solution, and higher surface functional degree is a kind of excellentadditive for papermaking wet-end system. At present, only a few synthesis methods areused to synthesize dendrimer-star polymer, including reversible addition fragmentationchain transfer (RAFT), atom transfer radical polymerization (ATRP), and nitrogenoxygen free radical polymerization (NMP). In present work, the dendrimer-starcationic polyacrylamide was prepared through RAFT polymerization by core-firstmethod, and was used as strength agent and anionic trash fixing agent in thepapermaking process.Firstly, the G0.5PAMAM was modified using tris(hydroxymethyl) aminomethane(TRIS), chloroacetyl chloride (CAC) and dithiobenzoate (DTBA) to obtain a newreversible addition-fragmentation chain transfer (RAFT) agent PAMAM-DTB with12dithiobenzoate terminal groups in a dendrimer core. Then, dendrimer-star cationicpolyacrylamide (DS-CPAM) was synthesized through RAFT polymerization usingPMAM-DTB as chain transfer agent (CTA), azodiisobutyronitrile (AIBN) as theinitiator, and methacryloyloxyethyltrimethyl ammonium chloride (DMC) andacrylamide (AM) as monomer in the N, N-dimethyl formamide (DMF) andtetrahydrofuran (THF). The structure of resultant polymers was characterized by FT-IR,1H NMR spectra. And the intrinsic viscosity, cationic density, and zeta potential werealso evaluated. The results demonstrated that the optimum conditions of synthsis ofDS-CPAM were as follows: the molar ratio of chain transfer agent, initiator, andmonomer of1:2.4:2400, reaction temperature of60℃, the cationic monomerconcentration of75%, reaction time of27h.The study found that DS-CPAM could increase the physical properties of aspenBCTMP through hydrogen bond or intermolecular forces, enhancing the combinationbetween the fibers. The best strengthening effect of synthetic product could beobtained when the application conditions were the pH of7.6, dosage of DS-CPAM of0.5%, reaction time with BCTMP of5min, stirring speed of200rpm. The structure properties of the DS-CPAM had great influence on their strengthening effect. TheDS-CPAM with intrinsic viscosity of122.76mL/g and cationic density of3.379meq/ghad the best properties to enhance the paper strength. The XRD analysis showed thatadding DS-CPAM did not cause the crystallinity of cellulose changed, which wasbenefit to reusing the secondary fibers. The SEM showed that the cross-linked networkmembrane formed between fibers after adding the DS-CPAM.The DS-CPAM could control anionic trash in the slurry system by formingcomposite flocculant and fixing on fiber through the mechanism of chargeneutralization/patch flocculation. The results indicated that the optimum conditions toremove the anionic trash were: dosage of DS-CPAM of0.7%, intrinsic viscosity of116.47mL/g, cationic charge density of4.37meq/g. The analysis showed that fibersurface was covered with a large number of fibrils and colloidal substance when the0.5%DS-CPAM was added. The SEM images showed that a lot of particles were fixedon the fiber surface after adding the DS-CPAM compared with the control sample. Thisstudy indicated that the DS-CPAM could be used as excellent anionic trash catcher inthe papermaking industry.