Synthesis Of Water-based Polyurethane And Applications As Paper Strength Agent

Because of the shortage of traditional wet strength agents, a lot of new environment-friend wet strength agents are developed as paper chemicals. Water-based polyurethane(WPU) as one of environment-friend water-based polyurethane resins with water as solvent, is non-polluting, non-toxic, safe, reliable, excellent mechanical properties, compatibility and easy modification with incomparable advantages that the traditional wet-strength resins are not, is applied in paper industry as a research hotspot recently.Based on the reaction mechanism of -NCO group and -OH on the fiber, blocked WPU was synthesized on the basis. Because the effect of blocked WPU was affected by temperature in the application, the deblocked temperature was studied. In this paper, according to hand sheets making from bleached softwood pulp, WPU was added to the pulp, the effect on sheet tensile strength of wet strength agents with synthesized WPU and sharing of WPU and CPAM was systematically analyzed. The water-based polyurethane was synthesized. According to the performance of thesynthesized polyurethane, the reaction time became longer relatively with increased blocked agent. In accordance with the dosage of blocked agent and the stability of emulsion, the dosage of the hydrophilic chain extender was 2% of the quality of the two monomers 2,4-TDI and PEG1000. When the degree of neutralization was 0.9-1.1, the storage stability of WPU emulsion increased significantly. Stirring intensity, solvent, temperature and the ways of adding water were discussed on the emulsification effect. Experimental results showed that room temperature, stirred by strong shear stress in a suitable solvent condition, slowly adding water during the final rapid accession to help emulsifying success.The synthesized products were characterized by IR and the deblocked temperature was studied. The results showed that absorption peak of the -NCO group of the blocked PU products near 2250-2280cm-1 had weakened significantly, indicating that blocked reaction was successful. After chain extender, N-H had a clear absorption peak near 3300cm-1, indicating that introduction of the hydrophilic group was successful. The result of deblocked temperature showed that blocked products at 100℃, 110℃and 120℃heating had absorption peak near 2250cm-1, indicating that the blocked product could be deblocked with high temperature, and the prolonged heated time was in favor of -NCO group deblocked. TG curve confirmed further the results of FTIR test.The application of the water-based polyurethane in the paper was studied. The synthetic WPU emulsion containing different dosage of blocked agent was added to the pulp, and the results showed that when the dosage of blocked agent was 0.1mol, the application performance of emulsion was the best. According to discussing the application condition of WPU emulsion, drying temperature of the sheets was 100℃; the condition of high temperature curing was 40min at 110℃,the UV curing time was 2.5min. Comparing the methods of UV curing, UV+high temperature curing and high temperature curing, the high temperature curing was the best method. According to discussing the effects of zeta potential of pulp and paper tensile strength were affected by the amount of WPU at different pH, the results showed that the prepared WPU was electropositive which could absorb directly with the pulp; and the synthesized WPU emulsion could be applied better under neutral and acidic conditions. When the amount of emulsion was 3.0%, paper wet-strength retention rate in the neutral condition reached 19.45%; when the amount of emulsion was 2.5%, paper wet-strength retention rate in the acidic condition reached 20.70%. Through CPAM and WPU sharing, the results showed that CPAM and WPU used together and added CPAM after WPU could improve wet strength. When adding the order of 2.0% WPU + 0.2% CPAM, the paper wet strength increased 16.01%, comparing with a single WPU added, increased 12.7 times, and comparing with blank samples, paper wet-strength retention rate reached 18.99%, increased 9.9 times. When adding the order of 3.0% WPU + 0.2% CPAM, the paper wet strength increased 12.62%, comparing with a single WPU added, increased 15 times, comparing with blank samples, paper wet-strength retention rate reached 21.29%, increased 11 times.