Littérature scientifique sur le sujet « Poly(vinyl acetate)–borate aqueous dispersion »

Gel-like, highly viscous polymeric dispersions from borate-crosslinked polyols can be prepared entirely with organic liquids and have viscoelastic properties similar to the equivalent materials prepared in aqueous or organo-aqueous solutions.

Abstract Emulsion nanoparticles of polyaniline (PANI) were synthesized in the aqueous media by using hydroxylpropylcellulose (HPC) as a stabilizer and ammonium persulfate as an oxidant in the presence of TiO2 with nanometer size. New poly(vinyl acetate) (PVAc) coating over carbon steel was prepared by addition of emulsion nanoparticles in different concentrations (1%, 2% and 1.5%) in PVAc as the major matrix. The Tafel plot records were used for the definition of potential and corrosion current (Icorr). Nanoparticles were characterized and compared by X-ray diffraction (XRD), thermal gravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). By adding TiO2, the thermal stability of the nanocomposite increased. A small size of colloidal particles prevented the precipitation of conducting polymer particles and led to better dispersion of nanocomposites in the matrix of the PVAc binder; therefore, the paint was homogeneous and anticorrosion properties of the coating increased. According to the results, 1.5% of PANI-TiO2 nanocomposite in PVAc has a much lower Icorr in NaCl aqueous solution and 2% of PANI-TiO2 nanocomposite in PVAc has the best corrosion protection in HCl.

Objectives : Levels of organic contaminants in excess of the standard minimum have been detected in many commercial and residential sites, and the severity of soil and groundwater pollution is increasing. In particular, non-aqueous phase liquids (NAPLs) are hydrophobic organic pollutants that do not mix with water and are difficult to remove with existing soil remediation technology. These pollutants slowly dissolve into the groundwater over long periods of time, thus contaminating the groundwater. With the increasing need to remove NAPLs for soil and groundwater remediation, widespread interest has focused on the use of nanoscale zero valent iron (nZVI). However, nZVI has the disadvantage of reduced subsurface mobility. Hence, in the present study, the nZVI surface is modified with poly(1-vinylpyrrolidone-co-vinyl acetate) (PVP/VA), which has both hydrophilic and hydrophobic groups, to improve the mobility and selectivity of nZVI for the removal of NAPL.Methods : The PVP/VA modified nZVI is synthesized through the reaction of FeSO4･7H2O and NaBH4 in the presence of PVP/VA. To confirm the dispersibility of the prepared material, a precipitation experiment is performed using a visible light spectrometer, and the mobility through a sand-filled column is evaluated. In addition, the variation in particle size and characteristics according to the presence of PVP/VA is examined via transmission electron microscopy. The nitrate reduction ability of nZVI with PVP/VA is also evaluated to reveal changes in reactivity depending upon the degree of dispersion. To confirm the selective mobility towards NAPL, trichloroethylene and dodecane are used to evaluate the mobility with and without PVP/VA. Finally, the ratio of nZVI passing through the sponge layer absorbing dodecane is evaluated to determine the selective mobility towards NAPL in the porous medium.Results and Discussion : Although the dispersibility of the PVP/VA-nZVI is not significantly changed, the particle size is significantly decreased. Both the mobility in porous media and the nitrate reduction rate are improved via PVP/VA modification. The affinity for hydrophobic contaminants and the selective migration of PVP/VA-nZVI towards the NAPL layer are also improved. The high affinity for the NAPL was also shown by the column with NAPL layer.Conclusions : Surface-modification with PVP/VA, which has both hydrophilic and hydrophobic ends, enabled the synthesis of nZVI with a smaller and more uniform particle size, thus providing high mobility in porous media and high reactivity towards contaminants. The combined hydrophilicity and hydrophobicity of PVP/VA is shown to increase the affinity of nZVI towards NAPL and, thus, promote its migration to the NAPL layer. Thus, it is anticipated that the efficiency of soil remediation can be improved by promoting the movement of nZVI towards the target NAPL layer.

In a modern society that is always more and more sensitive to the respect and the preservation of the environment and its living beings, and where the research of sustainable resources and ecological solutions is continuous, also in the field of the Cultural Heritage conservation, in the last decades, the developing of innovative technologies has been inspired by those principles. It’s in this context that in the laboratories of the chemistry department of the University of Florence and CSGI Consortium, a new family of Highly Viscous Polymeric Dispersions (HVPDs) for the cleaning of artistic, fragile surfaces was formulated and studied. They are 95% aqueous systems obtained from poly(vinyl alcohol) (PVA) or poly(vinyl acetate)s (PVAc) via complexation and crosslinking between the side-chain hydroxyl groups of the polymer and borate ions. Due to the low toxicity of the formulations these HVPDs are very attractive eco-friendly cleaning tools for the conservation of painted surfaces. They can incorporate a wide range of organic liquids, with particular reference to the less toxic ones, and thank to their high viscosity and thickness, the significant retention of the solvent reduces the potential damages to the original materials of the work of art but also the intoxication risk for the operators and the environmental impact. Their cleaning action is effective, confined to the desired area, controllable and gradual, parameters that are greatly appreciated by restorers. Their viscoelastic properties ensure a good adhesion onto the surface (even the molded, irregular or vertical ones) and easiness of removal in one piece through lifting with tweezers; thereby, the potential for residues is minimized and the clearance step with neat solvents often is not necessary.