Preparation and characterization of hyper-crosslinked resins and nanocomposites

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

Microporous Hyper-Crosslinked Polystyrenes and Nanocomposites with High Adsorption Properties: A Review

Hyper-crosslinked (HCL) polystyrenes show outstanding properties, such as high specific surface area and adsorption capability. Several researches have been recently focused on tailoring their performance for specific applications, such as gas adsorption and separation, energy storage, air and water purification processes, and catalysis. In this review, main strategies for the realization of HCL polystyrene-based materials with advanced properties are reported, including a summary of the synthetic routes that are adopted for their realization and the chemical modification approaches that are used to impart them specific functionalities. Moreover, the most up to date results on the synthesis of HCL polystyrene-based nanocomposites that are realized by embedding these high surface area polymers with metal, metal oxide, and carbon-based nanofillers are discussed in detail, underlining the high potential applicability of these systems in different fields

Mesoporous silica nanoparticles as carriers of active agents for smart anticorrosive organic coatings: a critical review

Mesoporous silica nanoparticles with properly designed textural properties and tailored release of corrosion inhibitors are highly efficient smart carriers for advanced anticorrosive nanocomposite coatings

Role of polymer network and gelation kinetics on the mechanical properties and adsorption capacity of chitosan hydrogels for dye removal

Chitosan (CS) hydrogels are receiving growing attention as adsorbents for water purification purposes. The conditions of preparation of this class of materials play a crucial in the determination of their performances; however, this aspect is often neglected in the literature. In this study, we deal with this issue, focusing on the structure-property relationships of CS hydrogels obtained by phase inversion method. We show that the concentration of the starting solution determines the density and strength of intermolecular interactions, and that the gelation kinetics dictates the hydrogel structure at the microscale. Consequently, even subtle changes in the preparation protocol can cause significant differences in the performances of CS hydrogels in terms of mechanical properties and dye adsorption capacity. The observed trends are often neither trivial nor monotonic. Nonetheless, we demonstrate that they can be interpreted looking at the CS network structure, which can be inferred by rheological measurements

Sustainable and Green Production of Nanostructured Cellulose by a 2-Step Mechano-Enzymatic Process

Nanostructured cellulose (NC) represents an emerging sustainable biomaterial for diverse biotechnological applications; however, its production requires hazardous chemicals that render the process ecologically unfriendly. Using commercial plant-derived cellulose, an innovative strategy for NC production based on the combination of mechanical and enzymatic approaches was proposed as a sustainable alternative to conventional chemical procedures. After ball milling, the average length of the fibers was reduced by one order of magnitude (down to 10–20 μm) and the crystallinity index decreased from 0.54 to 0.07–0.18. Moreover, a 60 min ball milling pre-treatment followed by 3 h Cellic Ctec2 enzymatic hydrolysis led to NC production (15% yield). Analysis of the structural features of NC obtained by the mechano-enzymatic process revealed that the diameters of the obtained cellulose fibrils and particles were in the range of 200–500 nm and approximately 50 nm, respectively. Interestingly, the film-forming property on polyethylene (coating ≅ 2 μm thickness) was successfully demonstrated and a significant reduction (18%) of the oxygen transmission rate was obtained. Altogether, these findings demonstrated that nanostructured cellulose could be successfully produced using a novel, cheap, and rapid 2-step physico-enzymatic process that provides a potential green and sustainable route that could be exploitable in future biorefineries

Layer-by-Layer-Coated Cellulose Fibers Enable the Production of Porous, Flame-Retardant, and Lightweight Materials

New sustainable materialsproduced by green processing routes arerequired in order to meet the concepts of circular economy. The replacementof insulating materials comprising flammable synthetic polymers bybio-based materials represents a potential opportunity to achievethis task. In this paper, low-density and flame-retardant (FR) porousfiber networks are prepared by assembling Layer-by-Layer (LbL)-functionalizedcellulose fibers by means of freeze-drying. The LbL coating, encompassingchitosan and sodium hexametaphosphate, enables the formation of aself-sustained porous structure by enhancing fiber-fiber interactionsduring the freeze-drying process. Fiber networks prepared from 3 Bi-Layer(BL)-coated fibers contain 80% wt of cellulose and can easily self-extinguishthe flame during flammability tests in vertical configuration whiledisplaying extremely low combustion rates in forced combustion tests.Smoke release is 1 order of magnitude lower than that of commerciallyavailable polyurethane foams. Such high FR efficiency is ascribedto the homogeneity of the deposited assembly, which produces a protectiveexoskeleton at the air/cellulose interface. The results reported inthis paper represent an excellent opportunity for the developmentof fire-safe materials, encompassing natural components where sustainabilityand performance are maximized

Reusable melanin-based biosorbents for efficient methylene blue removal: the new frontier of fungi-inspired allomelanin coatings for sustainable water remediation processes

The impact of water pollution caused by industrial wastes on our society prompted the urgent search for efficient remediation processes. Moved by the increasing interest in this research field, we report herein on the design and fabrication of an innovative water filtering device based on a nylon membrane coated with a synthetic melanin polymer inspired by fungal allomelanins and generated via the oxidative polymerization of 1,8-dihydroxynaphthalene. The melanin coating, obtained via the straightforward and low-cost ammonia induced solid state polymerization technique, proved to be highly stable with no evidence of debonding phenomena, did not alter the porous structure of the nylon filter and its flow rate and induced a slight but appreciable improvement of its tensile properties. The adsorbing performances of the melanin coated membrane were tested toward the azo dye methylene blue both in batch and in-flow conditions and compared with those of the synthetic melanin polymer as a bulk. The data revealed that the adsorption process: a) fits quite well with the Langmuir isotherm model, suggesting a monolayer adsorption on a surface with homogeneous sites, with a maximum adsorption capacity of 262 mg/g; b) is a favourable, exothermic and spontaneous process; c) is governed by a pseudo-second order kinetics. The in-flow experiments revealed the high efficiency of the filtering membrane in removing MB up to 99%; moreover, tests carried out to assess the regeneration and reuse of the membrane showed that the methylene blue removal efficiency was not affected up to seven adsorbing/desorbing cycles

Cellulose Isolation from Tomato Pomace: Part II-Integrating High-Pressure Homogenization in a Cascade Hydrolysis Process for the Recovery of Nanostructured Cellulose and Bioactive Molecules

: This work proposes a biorefinery approach for utilizing tomato pomace (TP) through a top-down deconstructing strategy, combining mild chemical hydrolysis with high-pressure homogenization (HPH). The objective of the study is to isolate cellulose pulp using different combinations of chemical and physical processes: (i) direct HPH treatment of the raw material, (ii) HPH treatment following acid hydrolysis, and (iii) HPH treatment following alkaline hydrolysis. The results demonstrate that these isolation routes enable the production of cellulose with tailored morphological properties from TP with higher yields (up to +21% when HPH was applied before hydrolysis and approximately +6% when applied after acid or after alkaline hydrolysis). Additionally, the side streams generated by this cascade process show a four-fold increase in phenolic compounds when HPH is integrated after acid hydrolysis compared to untreated sample, and they also contain nanoparticles composed of hemicellulose and lignin, as shown by FT-IR and SEM. Notably, the further application of HPH treatment enables the production of nanostructured cellulose from cellulose pulp derived from TP, offering tunable properties. This approach presents a sustainable pathway for the extraction of cellulose and nanocellulose, as well as the valorization of value-added compounds found in residual biomass in the form of side streams

Microporous Hyper-Crosslinked Polystyrenes and Nanocomposites with High Adsorption Properties: A Review

Hyper-crosslinked (HCL) polystyrenes show outstanding properties, such as high specific surface area and adsorption capability. Several researches have been recently focused on tailoring their performance for specific applications, such as gas adsorption and separation, energy storage, air and water purification processes, and catalysis. In this review, main strategies for the realization of HCL polystyrene-based materials with advanced properties are reported, including a summary of the synthetic routes that are adopted for their realization and the chemical modification approaches that are used to impart them specific functionalities. Moreover, the most up to date results on the synthesis of HCL polystyrene-based nanocomposites that are realized by embedding these high surface area polymers with metal, metal oxide, and carbon-based nanofillers are discussed in detail, underlining the high potential applicability of these systems in different fields

PolyHIPEs Containing Hyper-Cross-Linked Resins: Hierarchical Porosity with Broad and Versatile Sorption Properties

Polymers templated within high internal phase emulsions (polyHIPEs) are characterized by a highly interconnected macroporous structure and exhibit remarkable absorption properties. Hyper-cross-linked resins (HCLRs) are micro/mesoporous polymers with high adsorption capacities toward organic molecules. Here, polyHIPEs based on styrene (ST) and divinylbenzene (DVB) and containing unmodified and amino-functionalized HLCRs based on vinylbenzyl chloride (VBC) and DVB are realized using two different approaches, one based on the post-HIPE addition and the other based on the in-HIPE addition of the HCLRs. The amino-functionalization of the HCLRs was used to induce their localization on the polyHIPE’s surface. PolyHIPEs containing the amino-functionalized HCLRs exhibited significantly enhanced specific surface areas and sorption capacities for polar volatile organic compounds (VOCs) and CO2, and the addition of HCLRs does not negatively affect the high uptake of organic solvents by the polyHIPEs. The polyHIPEs containing the HCLRs exhibited regenerability above 99% in five sorption cycles. Nitrogen adsorption analysis and sorption tests demonstrated that the polyHIPEs with HCLRs synergistically combine the adsorption of the micro/mesoporous HCLRs with the absorption capacities of the polyHIPEs to generate advanced sorbent systems