RAFT Grafting Modification Of Cellulose And Its Application In The Papermaking

In recent years, higher quality of paper products is required with the rapid growthof the national economy and people’s living standard. On the contrary, the utilization ofhigh yield pulps of fast-growing wood, secondary fibers, and paper fillers is increasingyear by year due to the lack of papermaking raw materials, which will reduce thequalities of paper, especially their strength properties. The main method to solve thisproblem is to add strength additives in the process of papermaking. However, with thedepletion of non-renewable resources such as oil and coal and the increasingly seriousenvironmental problems to produce petrochemical products, the development andutilization of biomass resources have been paid more and more attention all over theworld. Cellulose, the most abundant natural polymer, is a kind of renewable andinexhaustible source in the world. Using the new chemical synthesis technology ofcontrollable grafting modification to produce special functional materials is animportant way to expand the application area of cellulose.Cellulose-based disulfide acid ester RAFT chain transfer agent was synthesizedsuccessfully by using cellulose as raw material and green environment friendly solventionic liquids as solvents. Then the cellulose-based water-soluble cationic polymer,Cell-g-DMC was synthesized through reversible addition fragmentation chain transferradical polymerization (RAFT). The application of Cell-g-DMC as the strength agentsof pulp was studied.Firstly, dissolving pulp was dissolved in ionic liquids (1-butyl-3-methyl imidazolechloride salt) and the cellulose-based macro-initiator (Cell-BiB) was prepared byreacting the dissolved cellulose with2-bromide butyl acyl bromine (BiBBr). Then thedithiobenzoate cellulose-based RAFT chain transfer agent, Cell-CTA was synthesizedin homogeneous by the reaction of dithiobenzoic acid (DTBA) and Cell-BiB. TheCell-BiB and Cell-CTA was characterized by FT-IR,1H NMR, and13C NMR analysis.The results showed that the groups of disulfide acid ester mainly grafted onto the C6hydroxyl groups of anhydroglucose units.The cellulose based water-soluble cationic polymer (Cell-g-DMC) wassynthesized through RAFT polymerization by using Cell-CTA as chain transfer agent,AIBN as the initiator, and DMC as cationic monomer in the DMF. The effect ofpolymerization conditions such as the molar ratio of DMC to Cell-CTA and AIBN to Cell-CTA, reaction time, and reaction temperature on the intrinsic viscosity, graftingefficiency, zeta potential, and the positive charge density of Cell-g-DMC was studied.The structure of the Cell-g-DMC was characterized by FT-IR and1H NMRmeasurement. The optimum condition for synthesis of Cell-g-DMC was as follows:reaction temperature was60℃, the reaction time was24h, and the molar ratio ofAIBN to Cell-CTA was0.5:1.The influence of grafting chain length, dosage, reaction time, pH value of pulpslurry, temperature, and the shearing on the application effect of Cell-g-DMC wasstudied. The results showed that the Cell-g-DMC can significantly improve tensileindex, tear index, and the bonding strength of the fibers, but has little effect on the fibrestrength. The longer of grafting chain of Cell-g-DMC, the better strengthening effecton the pulp. With the prolonging of reaction time and the enhancement of the shearing,the strength properties of paper first increased and then slightly decreased, but theCell-g-DMC has the ability of resistance to high shearing. The high temperature ofpulp slurry is beneficial to the application effect of the Cell-g-DMC. Besides,Cell-g-DMC has good performance in a wide pH value range and suitable forneutral/alkaline wet end system of papermaking. The optimum application condition ofCell-g-DMC was as follows: the intrinsic viscosity is215ml/g, the dosage ofCell-g-DMC is0.5%, the reaction is15minutes and the temperature is40℃.The crystallinity of the recycled fiber form the paper that used the Cell-g-DMC asstrength aids was lower than that of the paper without Cell-g-DMC. The addition ofCell-g-DMC can inhibit the hornification of fiber during the process of papermaking,which will facilitate the recycling of waste paper.