Castaldo, Rachele
(2017)
Preparation and characterization of hyper-crosslinked resins and nanocomposites.
[Tesi di dottorato]
Abstract
This thesis focuses on the preparation and the adsorption study of innovative hyper-crosslinked (HCL) polymers and nanocomposites.
New microporous nanocomposites were prepared including multi-walled carbon nanotubes (MWCNTs) in styrene/vinylbenzyl chloride/divinylbenzene hyper-crosslinked resins. In order to promote the embedding of the MWCNTs within the gel-type precursor, a proper surface modification strategy was set up, based on the grafting of a poly(vinylbenzyl chloride) (PVBC) resin, able to participate to the hyper-crosslinking step, onto the nanotubes surface. After dispersion of the MWCNTs into the monomer mixture, HCL nanocomposites were prepared by suspension polymerization followed by Friedel-Crafts reaction. Volumetric gas adsorption and adsorption from solution analysis revealed that, by addition of the modified MWCNTs, it was possible to modulate the pore size distribution and the adsorption properties of HCL polymers.
Then, a new synthetic strategy to obtain HCL polymers and nanocomposites was proposed, based on the bulk prepolymerization of a gel type precursor followed by the traditional Friedel-Crafts alkylation step. The obtained HCL materials showed comparable properties with respect to the corresponding resins obtained by suspension prepolymerization. Moreover, the versatility of the proposed process was demonstrated through the realization of two innovative classes of advanced materials: i) HCL microporous organic polymer nanocomposites (MOPNs) and ii) polymer composites containing HCL resins and nanocomposites as fillers.
In particular, MOPNs characterized by different porous structures and adsorption properties were prepared including graphene nanoplatelets (GNP) or surface modified graphene oxide (GO) into a styrene/vinylbenzyl chloride/divinylbenzene matrix. Using surface modified GO grafted with PVBC, microporous nanocomposites based on a styrene/divinylbenzene precursor, i.e. without the chlorinated monomer, were also realized. Their microporosity was only generated during the hyper-crosslinking occurring at the interface between the modified GO nanoplatelets and the styrene based matrix.
HCL resins and nanocomposites were employed as fillers in two type of composites, polysulfone membranes and chitosan hydrogels. The composite polysulfone membranes were tested for phenol adsorption from water solution, demonstrating that the addition of the functional microporous fillers within the polysulfone phase is able to induce significant enhancement of the equilibrium adsorption capacity. Adsorption tests of various dyes on the composite chitosan-based hydrogels proved that it is possible to effectively combine the adsorption performances of the HCL resin with the chitosan matrix for the realization of new functional materials for broad-spectrum water remediation.
Finally, an in-depth study of the effect of the oxidation degree on the self-assembly and the surface area of graphene oxide is reported. Different self-assembly processes were used to prepare bulk and porous 3D GO structures, respectively based on water removal by evaporation at the liquid/air interface and by freeze-drying at the dynamic ice/water interface. Combination of morphological analysis, BET SSA analysis on cast and freeze-dried GO samples and SSA analysis through methylene blue adsorption on GO water suspensions allowed the evaluation of the effect of the oxidation degree on the processability and the adsorption properties of graphene oxide.
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