Preparation Of Spherical Polyelectrolyte Brushes And Their Application In Wet-end Papermaking

As the criterion such as energy saving and emission reduction, environment protection, etc. become higher, and with the development of Wet-end Papermaking, Improving the retention of fines and fillers is an effective way to reduce the environment pollution and to save resources, then the finding of better retention-aid is still make sense. Based on the basic theory of Wet-end Papermaking and the application of retention-aid on papermaking, it is concluded that Spherical polyelectrolyte brushes (SPB) take the advantage of both charged particles and polyelectrolyte. Charged particles take an ionization surface and three-dimensional nano-structure while polyelectrolyte possesses controllable molecular weight and charge densities. The spherical or spherocyte-like structure of SPB has the ability of shear resistance. So SPB would be easier to induce the flocs flocculation by bridging which making the flocs stronger in turbulence. And SPB will be an effective retention-aid for the papermaking. Herein, SPB was prepared and evaluate, then SPB was investigated as flocculation and retention-aids for Wet-end papermaking. The interaction between SPB and fibers or fillers was investigated, and the retention-aid properties of SPB were also studied. The mainly mechanism for SPB on flocculation of pulp was got by studied the process of flocculation and the properties of flocs. The results were shown as follows:Firstly, the cationic spherical polyelectrolyte brushes (CSPB), with different molecular weight and cationic charge densities were prepared by "grafting from" method, and using colloidal silica particles as template. Anionic spherical polyelectrolyte brushes (ASPB) was also prepared with sodium styrene sulphonate as monomer, and spherical polyelectrolyte brushes with hydroxy (HSPB) was also prepared by copolymerization between 2-(Acryloyloxy) ethyl trimethyl ammonium chloride and hydroxyethyl acrylate, then HSPB with fluorescence was got by modifying the polyelectrolyte with fluorescein isothiocyanate. The SPB was characterized by fourier-transform infrared spectrometry, thermo gravimetric analysis, colloid titration, gel permeation chromatography, transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy methods. The TEM and FE-SEM results showed that the as-obtained SPB samples retain a spherical structure form with a diameter of about 70 nm. The results show that CSPB with different surface grafting density and charge density was successfully fabricated. It was also found out that surface grafting density and charge density of ASPB was 0.84×10-3 mmol/g and 33.3×10-3 eq/g respectively. While HSPB was successfully fabricated with 0.42×10-3 mmol/g surface grafting density and 53.3×10-3 Jeq/g charge density. The zeta-potential and thickness of SPB in a function of different aqueous salt solutions and different type and concentrations was studied. It shows that the magnitude of thickness decrease with increasing salt concentration. Among then CSPB was sensitive to SO42- while ASPB was sensitive to Ca2+. What’s more the adsorption ability of SPB was different as the change of charge.Then CSPB with different molecular weight and cationic charge densities was investigated as flocculation and retention-aids for Wet-end papermaking. Relative turbidity, zeta potential, focused beam reflectance measurement (FBRM) and FE-SEM methods was used to study the flocculation properties of bleached eucalyptus kraft pulp and reed pulp. The results showed that flocculation property was related to the types and concentrations of salt solution. In our experimental data range, high concentration of salt, Na2SO4 and base take a restrain effect on the flocculation of pulp, while CaCl2 and acid was helpful to flocculation. The morphology and structure of the flocs were investigated by microscope, FE-SEM and fluorescence microscope. It reveals that the flocs flocculate by CSPB was denser than by line polyelectrolyte, and the interaction between fiber and CSPB was mainly on fiber surface. Based on the relative turbidity, zeta potential and size change, it was found out that bridging flocculation model may be the mainly mechanism for CSPB on flocculation of kaolin/pulp. This may due to the high charge densities and three-dimensional nano-structure adding the thickness of adsorbed layer, then it is useful for bridging flocculation. Then dynamic drainage jar (DDJ) was used to evaluate retention. In our experimental data range, the dosage of cationic monomer need keep a suitable range, while in the copolymerization between DMC and AM, the higher ratio of DMC was benefit to flocculation. The first-pass retention (FPR) of Precipitated calcium carbonate (PCC) with different retention aids was displayed. The results show that in the reed pulp/PCC, the FPR of PCC was improved from 30.9% to 77.5% after CSPB was used, while in the kraft pulp/PCC, the FPR of PCC was improved from 17.3% to 67.9%. CSPB showed better retention efficiency than line polyelectrolyte and cationic starch under different turbulent conditions.Then CSPB act as flocculation for kaolin, with relative turbidity, zeta potential, laser particle size analyzer and FBRM. The morphology and structure of the flocs were investigated by microscope, FE-SEM and fluorescence microscope. The results showed that to get well flocculation efficiency, molecular weight and cationic charge densities should in a proper range. The flocs flocculate by CSPB was denser and larger than by line polyelectrolyte, these denser and larger flocs were benefit to flocculation. Based on the relative turbidity, zeta potential and size change during flocculation, it was found out that patch flocculation model may be the mainly mechanism for CSPB on flocculation of kaolin.At last, both CSPB and ASPB act as one component for microparticle systems, the retention was test by DDJ. The morphology and size change of the flocs were investigated. And then, the paper was made and its mechanical property was evaluated. In our experimental data range, the results show that in the reed pulp/PCC, the FPR of PCC retained by CSPB/APAM and CPAM/ASPB were improved to 89.9% and 86.4% respectively, while in the kraft pulp/PCC, the FPR of PCC was improved to 93.7% and 90.2% respectively. SPB showed better flocculation and retention efficiency than PDMC/APAM, cationic starch/APAM and PDMC/SiO2 under different turbulent conditions. It was also found that increase of shear intensity led to a decrease in retention efficiency, while SPB still showed better retention efficiency. Based on the relative turbidity, zeta potential and size change, it was found out that patch-bridging flocculation model may be the mainly mechanism for both CSPB/APAM and CPAM/ASPB on flocculation of kaolin/pulp. This may due to the high charge densities and three-dimensional nano-structure adding the thickness of adsorbed layer, then it is useful for bridging or patch flocculation. The high retention of CSPB/APAM and CPAM/ASPB on kaolin led to the decrease of the tensile index and tear index of paper sheet, but not obvious. Compare to PDMC/APAM and PDMC/SiO2, it concludes that SPB was more promising papermaking.