Synthesis Of Star Cationic Polyacrylamide And Its Application In The Papermaking

In recent years, along with the papermaking wet operation system changing fromacidic to neutral/alkaline and the increasingly improvement of white water closedcirculation degree, the traditional papermaking additives without the capacity ofresistance to high shear force were suffered greatly interference. Besides, the currentsituation has a significant effect on the physical properties of paper, such as theretention rate, water filtration performance, breaking strength and tearing strength.Therefore, one of the important research works is to develop an efficient, environmentfriendly, and multi-functional aids for the complicated papermaking wet-end system.Compared to the linear polymers with the same molecular weight, the starpolymers can overcome the deficiency of the linear polymers, what is more, they have aserious of characters including higher surface faculties degree, the lower viscosity ofsolution and smaller hydrodynamics radius. For this reason, star polymers probablybecome good additives for papermaking wet-end system.The multi-arm star cationic polyacrylamide (S-PAM) was synthesized throughreversible addition-fragmentation chain transfer (RAFT) polymerization by the methodof “core-first”. It was investigated as retention and drainage aid and strength agent inthe papermaking.Firstly, the ester-terminated half-generation polyamidoamine dendrimer wasamidated by using tris (tri-hydroxymethylaminomethane) to obtain hydroxy-terminateddendrimer PAMAM-OH which was subsequently acylated to produce macroinitiatorPAMAM-Cl by using chloroacetyl chloride. The nucleophilic reaction between sodiumdithiobenzoate and chloromethyl groups in PAMAM-Cl was then used to obtain thedesired product, i.e. multi-functional group RAFT chain transfer agent(PAMAM-DTBA). The structures of resulting products were characterized by FT-IRand1H-NMR spectra. The star cationic polyacrylamide (S-CPAM) was synthesizedthrough reversible addition-fragmentation chain transfer (RAFT) polymerization byusing PAMAM-DTBA as multi-functional group chain transfer agent, AIBN as theinitiator, acrylamide (AM) and methacryloyloxyethyltrimethyl ammonium chloride(DMC) as monomer in the THF. The structure of the S-PAM was characterized byFT-IR, intrinsic viscosity measurement and cationic degree. The effect ofpolymerization reaction system and process conditions on product quality was studied, and the optimun conditions of synthsis of S-CPAM were as follows: reactiontemperature60℃, reaction time24h, the initiator concentration was0.15%(based onthe total monomer mass), the molar ratio of chain transfer agent to initiator was0.417and the cationic monomer concentration was65%(based on the total monomer mass).The performance of S-CPAM as retention and drainage aids for the retention systemof aspen APMP was studied. The results showed that the larger relative molecularweight and higher cationic charge density of S-CPAM had better effect on the FPR anddrainage rate. Along with the increasing dosage of S-CPAM, the FPR and drainage rateof the pulp were improved, and the optimum dosage of S-CPAM was0.5%(based ondry pulp). With the enhancement of the shearing, the prolonging of action time and theincreasing of pH value, the performance of S-CPAM displays a trend of declining.However, the high branched structure of S-CPAM has a resistance to the high shearing,and it has relatively insensitive to shearing and pH value.The strengthening effect of S-CPAM on aspen APMP and the optimum applicationcondition were studied in this paper. The results indicated that the strengthening effectof S-CPAM to aspen APMP was best under the following conditions: the dosage ofS-CPAM is0.3%, the reaction is2.5minutes, and the pH value of the system is8.Compared to the control sample, the burst, tearing and tensile index of the paper usedS-CPAM increased by41.7%,11.7%and30.2%, respectively. The SEM image of thehandpaper used S-CPAM displayed that the fibers combined stronger and there wasmore point junction. In addition, it was also found that fillers could reduce thestrengthening effects of S-CPAM.