Synthesis Of Dendrimer-star Cationic Polymer And Its Application In The Papermaking Wet-end

Nowadays, in order to conserve water in paper mill, white water closed system isused in producing newspaper by the means of reduction of sewage discharge and freshwater injection. The white water system contains a large quantity of dissolved andcolloidal substance released from the process of pulping and bleaching, which includelipophilic extractives, lignin, neutral and charged polysaccharides, and proteins. Theyusually accumulate in the white water system due to the recirculation of water in theprocess. The increase of DCS concentration can lead to several operational problems,such as increased corrosion, scaling and foaming problems, slime and biological growth,deposits of extractive materials on the wires and felts, higher probability of paper breaks,and also increase the consumption of cationic chemicals in wet-end, decrease the sheetstrength, burst and breaking length.The aims of the present work are to design and synthesis two kinds ofdendrimer-star cationic polymers, called fixing agent, to handle the problem regardingthe dissolved and colloidal substance released from deinked pulp. The fixing agent withlow molecular and high charge density can be used to fix DCS onto fibers by electricalneutrality/patch mechanism, also can reduce the cationic charge demand in fibersuspension and improve the efficiency of chemicals in the wet-end.The4-ester terminated dendrimer was obtained by the Michael addition reaction ofethylenediamine and methyl acrylate in methanol solvent, and then amidated withtris(tri-hydroxymethyl aminomethane) to obtain hydroxy terminated dendrimer, whichwas subsequently acylated with2-bromoisobutyryl bromide to produce12armsmacroinitiator of atom transfer radical polymerization (ATRP), and finally a range ofpoly(PAMAM-g-DAC) were obtained using PAMAM-Br, DAC, CuBr,2,2’-bipyridineas macroinitiator, monomer, catalyst and ligand, respectively. All the resultedcompounds were characterized by FT-IR and1H NMR and the polymeric charge densitywere titrated by standard PVSK at different pH value. The results showed that thecharge density remained almost the same in different pH, which meaned thatpoly(PAMAM-g-DAC) were pH-insensitive.The photographs of flocs of pulp furnish were obtained by microscope. Withoutretention aids, there was no fillers and DCS flocculating or adsorbing onto the fiber surface. When0.5%of poly(PAMAM-g-DAC) was added, flocculation of the furnishoccurred at once and more fillers and DCS were adsorbed on the fibers. And whenpoly(PAMAM-g-DAC)/CPAM dual-component system was used, the furnishflocculated more than the single system, indicating the good synergetic effect ofpoly(PAMAM-g-DAC) with CPAM. The turbidity and cationic demand of the DCSdecreased rapidly with the dosage of fixing agent increased, the turbidity can be reducedby88.7%when0.2%of poly(PAMAM-g-DAC) was added, and the cationic demandcan be reduced below5ueq/L. As the poly(PAMAM-g-DAC) dosage increased in singlesystem, it showed good effect on the first pass retention and drainage, and also thehigher charge density polymer performed better. The performance of thedual-component system was excellent in different pH value pulp slurry and also couldresist higher shearing.A range of novel cationic starlike polymers poly(pen-g-MeDMA) were synthesizedthrough ATRP by core-first method. The tetrafunctional initiator (pen-Br) was preparedby esterification of pentaerythritol with2-bromoisobutyryl bromide. MeDMA waspolymerized in H2O/EtOH medium using pen-Br, Cu(I)Br,2,2-dipyridine as an initiator,catalyst, and ligand, respectively. The obtained compounds were characterized by FT-IRand1H NMR, and the charge density of the polymers was measured by titration atdifferent pH value. The results indicated that the cationic charge density of the resultedpoly(pen-g-MeDMA) were high and pH-insensitive.The turbidity and cationic demand of the water phase decreased rapidly with thedosage of the poly(pen-g-MeDMA) increased. The turbidity was reduced by87.3%andthe cationic demand was reduced almostly to20ueq/L when0.2%of the polymer wasused. This indicated that the high cationic charge density could induce DCS toflocculate and cling to fibre surface by the meaning of neutralizing and patchmechanism. The combination of poly(pen-g-MeDMA) and CPAM could significantlyimprove the retention efficiency of the DIP, and also, the dual system can be used inacid or alkaline condition, even can resist the high speed shear. It has also beenobserved that the poly(pen-g-MeDMA) had a good synergetic effect with bentonite asmicroparticle retention aid system, which can be used in acid or alkaline condition andhigh speed shear.