| Aim to explore the conductive paper with superior properties, polypyrrole has many good features, such as non-toxic under low temperature, easy synthesis, good film-forming performance and conductive stability, therefore, in the article, polypyrrole/wood fibers conductive paper(CF) were successfully prepared through in-situ chemical oxidation polymerization, the oxidant and dopant were FeCl3 and a novel series of self-made cationic polyacrylate surfactants(CPS). The CPS were synthesized through radical polymerization, the lipophilic monomers were styrene(St) and butyl acrylate(BA), N,N-dimethylaminoethyl methacrylate(DMAM) as the hydrophilic monomers. As the structure of CPS was controllable, the obtained polymeric surfactant exhibited higher surface activity, the long chain could be twisted and fixed on the composites conductive fibers as dopant in the polymerization process, the conductive stability and mechanical property could be improved. In addition, as a result of the good dispersibility of CPS, the flocculation problem of conductive fibers in the pulp suspension was solved.The structure of CPS was demonstrated by Fourier transform infrared spectroscopy(FT-IR) and Nuclear magnetic resonance spectroscopy(1H-NMR). The solution properties and aggregation behaviors of CPS were investigated by Gel permeation chromatography(GPC), Surface tension analysis, Fluorescence spectroscopy(FLD), Transmission electron microscopy(TEM) and Dynamic light scattering(DLS). In addition, colloid titration test was used to study the adsorption situation of CPS on fibers. The structure, micromorphology and chemical composition of conductive paper were demonstrated through Fourier transform infrared spectroscopy(FT-IR), Scanning electron microscopy(SEM), Atomic force microscope(AFM), X-ray photoelectron(XPS). Thermogravimetric(TG) anylysis was used to investigate the thermal stability of conductive paper. And the conductive stability and mechanical properties of conductive paper were measured using a four-probe ohmmeter and zero distance tensile strength tester. The study shows that:The CPS have similar weight-average molecular weights on the order of 104 and the polydispersity increased with increasing the content of hydrophilic monomer. When the content of hydrophilic groups was lower, the surface tension of CPS1 solution decreased to 39.11 mN/m, and the critical micelle concentration was 2.20 g/L. The surface tension and critical micelle concentration increased with increasing the content of hydrophilic groups. With increasing concentration CPS, the fluorescence intensity gradually increased, I1/I3 values were decreased, the characteristic absorption peak of pyrene probe(0,0) shifted from 334 nm to 338 nm, I338/I334 values increased from 0.53 to 1.42. The above-mentioned results certified that the hydrophobic groups tended to aggregate and form hydrophobic microdomains, pyrene molecules transferred from the aqueous polar phase to micellar interphase. It became more difficult for molecules to aggregate to form micelles with increasing the content of hydrophilic groups, and the formation velocity of micelles was also decreased. Surface tension and Fluorescence spectroscopy results displayed the similar critical micelle concentration. CPS aggregate micelles displayed as core-shell spheres, and the thickness of hydrophilic layer on the surface of CPS micelles increased with increasing the content of hydrophilic groups. The micelle size and dispersion index also increased with increasing the CPS solution concentration. In the same solution concentration, the micelle size increased with increasing the content of hydrophilic groups. In addition, the micelle size measured by TEM was smaller than DLS test.The adsorption amount of higher Mw(higher charge density) polymer on the surface of fibers was comparatively lower than that of lower Mw(lower charge density) polymer. PPy not only formed aggregations on the surface of fibers but also penetrated into the fiber wall, it displayed indistinctly spherical structure, and the oxidation of PPy tended to occur on the surface of conductive paper; The surface morphology of modified fiber was coarser than natural fiber, and the close degree of conductive paper fibers was improved, the gaps between fibers and fibers were filled, single paper fiber exhibited flat structure; The amount of PPy increased as the hydrophilic monomer(DMAM) increases and then comes to a lower amount, the highest amount and density of PPy particles were obtained at the DMAM content of 40%; Compared with the natural wood fiber, conductive fibers have lower degradation temperature, and the degradation rates were reduced, the residue char was increased; The optimal conditions of this experiment: reaction temperature was 0°C, synthesis time was 120 min, pH in this system was 2, the content of PPy was 12% of the dry natural fibers, n(Py)/n(FeCl3)=1:2. With the increase of DMAM content in CPS, the resistivity of conductive papers first decreased, then they increased, the resistivity was decreased from 460 K?·cm of CF1 to 30 K?·cm of CF5, then increased to 86 K?·cm of CF9; When the conductive fibers stored at 5°C, the storage time had little effect on the conductivity. The conductive paper stored in air was electrically unstable, and the resistivity also increased with increasing the storage time and temperature, the conductivity decay at elevated temperature occurred quicker than that at lower temperature. The conductivity of conductive paper in vacuo was higher than that in air at same temperature; The tensile index was decreased from 33.5 KN·m·kg-1 of unmodified paper to 22.8 KN·m·kg-1 of CF5, it can be ascribed to the acid hydrolysis, oxidative degradation and the binding force between fiber effected on the mechanical property of conductive paper. It was also worth to mention that the tensile index of CF5 was increased from 22.8 KN·m·kg-1 to 36.8 KN·m·kg-1 after the conductive fiber was treated with polyacrylamide strengthening agent at a dosage of 2%, and the conductivity was not affected. |
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