Shape Memory Polymers Charged with Modified Carbon-Based Nanoparticles

In this thesis, shape memory nanocomposites were prepared and characterized. The polymer matrix consisted in an epoxy-based liquid crystalline elastomer (LCE). Multi-walled carbon nanotubes (MWCNT) and graphite nanoplatelets (GNP) were selected as fillers. The influence of different contents of nanofillers on mechanical, thermal and shape memory properties was evaluated. In order to disperse and homogeneously distribute the nanofillers within the polymer matrix an in-depth evaluation on the optimal conditions to synthesize the materials was carried out. These conditions had a substantial influence on the final distribution of the nanofillers within the epoxy-based matrix, which was analyzed from a macroscopic and microscopic point of view. The best results were obtained through a chemical surface modification of the nanoparticles. The chemical modification of MWCNTs consisted in grafting the selected epoxy monomers on the surface. The obtained adducts were characterized in terms of chemical, thermal and morphological features. Concerning GNP, a similar protocol based on surface modification was carried out. In this case, a preliminary oxidation process was performed in order to promote the exfoliation of graphene sheets, in form of graphene oxide (GO), and to favour their dispersion within the polymer matrix. Different degrees of oxidation were attempted. GO nanoparticles were successively modified with epoxy monomers. Also in this case, chemical, morphological, structural and thermal characterization was carried out. Surface modified carbonaceous nanoparticles were then dispersed in varying amounts in the organic matrix. The obtained nanocomposite systems were characterized in their chemical-physical and morphological properties. The adopted compatibilization strategies used for both MWCNTs and GNP were found to be extremely effective to get homogeneous samples and to enable a dramatic enhancement of the actuation extent at low nanofiller content. Moreover, the stress threshold required to trigger the reversible thermomechanical actuation was significantly decreased. The effect of nanoparticles on thermomechanical properties of the materials was correlated to the microstructure and the phase behavior of the host system. Results demonstrated that the incorporation of carbon nanofillers amplified the soft-elastic response of the liquid crystalline phase to external stimuli. Tunable thermomechanical properties of these systems make them suitable for a variety of potential advanced applications ranging to robotics, sensing and actuation, and artificial muscles

Upgrading Sustainable Polyurethane Foam Based on Greener Polyols: Succinic-Based Polyol and Mannich-Based Polyol

It is well known that the traditional synthetic polymers, such as Polyurethane foams, require raw materials that are not fully sustainable and are based on oil-feedstocks. For this reason, renewable resources such as biomass, polysaccharides and proteins are still recognized as one of the most promising approaches for substituting oil-based raw materials (mainly polyols). However, polyurethanes from renewable sources exhibit poor physical and functional performances. For this reason, the best technological solution is the production of polyurethane materials obtained through a partial replacement of the oil-based polyurethane precursors. This approach enables a good balance between the need to improve the sustainability of the polymer and the need to achieve suitable performances, to fulfill the technological requirements for specific applications. In this paper, a succinic-based polyol sample (obtained from biomass source) was synthesized, characterized and blended with cardanol-based polyol (Mannich-based polyol) to produce sustainable rigid polyurethane foams in which the oil-based polyol is totally replaced. A suitable amount of catalysts and surfactant, water as blowing reagent and poly-methylene diphenyl di-isocyanate as isocyanate source were used for the polyurethane synthesis. The resulting foams were characterized by means of infrared spectroscopy (FTIR) to control the cross-linking reactions, scanning electron microscopy (SEM) to evaluate the morphological structure and thermal gravimetric analysis (TGA) and thermal conductivity to evaluate thermal degradation behavior and thermal insulation properties

Greener Nanocomposite Polyurethane Foam Based on Sustainable Polyol and Natural Fillers: Investigation of Chemico-Physical and Mechanical Properties

Nowadays, the chemical industry is looking for sustainable chemicals to synthesize nanocomposite bio-based polyurethane foams, PUs, with the aim to replace the conventional petrochemical precursors. Some possibilities to increase the environmental sustainability in the synthesis of nanocomposite PUs include the use of chemicals and additives derived from renewable sources (such as vegetable oils or biomass wastes), which comprise increasingly wider base raw materials. Generally, sustainable PUs exhibit chemico-physical, mechanical and functional properties, which are not comparable with those of PUs produced from petrochemical precursors. In order to enhance the performances, as well as the bio-based aspect, the addition in the polyurethane formulation of renewable or natural fillers can be considered. Among these, walnut shells and cellulose are very popular wood-based waste, and due to their chemical composition, carbohydrate, protein and/or fatty acid, can be used as reactive fillers in the synthesis of Pus. Diatomite, as a natural inorganic nanoporous filler, can also be evaluated to improve mechanical and thermal insulation properties of rigid PUs. In this respect, sustainable nanocomposite rigid PU foams are synthesized by using a cardanol-based Mannich polyol, MDI (Methylene diphenyl isocyanate) as an isocyanate source, catalysts and surfactant to regulate the polymerization and blowing reactions, H2O as a sustainable blowing agent and a suitable amount (5 wt%) of ultramilled walnut shell, cellulose and diatomite as filler. The effect of these fillers on the chemico-physical, morphological, mechanical and functional performances on PU foams has been analyze

Flow resistance in open channels colonized by Phragmites australis: field experiments and modeling

The analysis and the prediction of the effects of the hydrodynamic interaction between water flow and riparian vegetation in natural and manmade vegetated water bodies are the main objectives of Ecohydraulics. Riparian vegetation has a paramount impact on both flow resistance and water quality in vegetated open channels. Defining the most appropriate management practice of riparian vegetation inside both natural and manmade water bodies is crucial for assuring a balance between a satisfactory level of hydraulic conveyance and a high environmental value of water. The presence of riparian vegetation significantly affects both mean and turbulent water flow fields, with important implications on oxygen production and transport of nutrients within vegetated open channels. Experimental analysis and modeling were performed in this thesis, to provide additional understanding of the hydrodynamic interaction between riparian vegetation and water flow at field scale in an abandoned reclamation channel colonized by rigid and emergent plants of Phragmites australis (Cav.) Trin. ex Steud., also known as Common reed. Different riparian vegetation management scenarios were evaluated: undisturbed conditions, partial riparian vegetation cover and total riparian vegetation removal. Field hydraulic tests were carried out for investigating the experimental cross sectional distributions of streamwise velocity and main turbulence features (Reynolds stresses and Turbulent Kinetic Energy). The outcomes of the experimental activities were employed for modeling the flow resistance of the examined vegetated reclamation channel by employing both 1D numerical simulations and literature models, which accuracies were assessed by comparing experimental and modeled vegetative global water flow resistance coefficients. In the case of partial riparian vegetation cover, a methodology based on the detailed analysis of the experimental cross sectional streamwise velocity distribution was proposed. This methodology provides estimates of global water flow resistance with prediction errors smaller than the direct application of the examined models. In the last part of the doctoral research program, the feasibility of Digital Hemispherical Photography (DHP) technology was evaluated for assessing Leaf Area Index (LAI) of mature Common reed plants to be exploited for flow resistance modeling of vegetated streams. The uncertainty of DHP-derived LAI was evaluated from a functional perspective, by estimating its impact on the uniform water flow velocity predicted with Västilä & Järvelä model. DHP proved to be a reliable technology for ecohydraulic modeling at field scale

On the Indirect Estimation of Wind Wave Heights over the Southern Coasts of Caspian Sea: A Comparative Analysis

The prediction of ocean waves is a highly challenging task in coastal and water engineering in general due to their very high randomness. In the present case study, an analysis of wind, sea flow features, and wave height in the southern coasts of the Caspian Sea, especially in the off-coast sea waters of Mazandaran Province in Northern Iran, was performed. Satellite altimetry-based significant wave heights associated with the period of observation in 2016 were validated based on those measured at a buoy station in the same year. The comparative analysis between them showed that satellite-based wave heights are highly correlated to buoy data, as testified by a high coefficient of correlation r (0.87), low Bias (0.063 m), and root-mean-squared error (0.071 m). It was possible to assess that the dominant wave direction in the study area was northwest. Considering the main factors affecting wind-induced waves, the atmospheric framework in the examined sea region with high pressure was identified as the main factor to be taken into account in the formation of waves. The outcomes of the present research provide an interesting methodological tool for obtaining and processing accurate wave height estimations in such an intricate flow playground as the southern coasts of the Caspian Sea

Effects of reed beds management on the hydrodynamic behaviour of vegetated open channels

This work presents the results of experimental activities carried out during a 3-years research program, to assess the effects of infesting reed beds on the mean and turbulent hydrodynamic features of vegetated reclamation channels at field scale. The devices and methodologies employed in the experiments represent an innovation in the study of vegetative flow resistance directly at field. Different management scenarios of the vegetated cover were evaluated, with the aim to assess the optimal strategy for balancing the need for an effective hydraulic conveyance and the need to preserve the environmental quality of the vegetated water bodies

Effect of nanotubes on shape memory effect in liquid-crystalline epoxy-based elastomers

In this work, shape memory nanocomposites were prepared and characterized. The polymer matrix consisted in an epoxy-based liquid crystalline elastomer (LCE). Multi-walled carbon nanotubes (MWCNT) and graphite nanoplatelets (GNP) were selected as fillers. The influence of different contents of nanofillers on mechanical, thermal and shape memory properties was evaluated. In order to disperse and homogeneously distribute the nanofillers within the polymer matrix an in-depth evaluation on the optimal conditions to synthesize the materials was carried out. These conditions had a substantial influence on the final distribution of the nanofillers within the epoxy-based matrix, which was analyzed from a macroscopic and microscopic morphological point of view. The best results were obtained through a chemical surface modification of the nanoparticles. The chemical modification of MWCNTs consisted in grafting the selected epoxy monomers on the surface. The obtained adducts were characterized in terms of chemical, thermal and morphological features. Concerning GNP, a similar protocol based on surface modification was carried out. In this case, a preliminary oxidation process was performed in order to promote the exfoliation of graphene sheets, in form of graphene oxide (GO), and to favour their dispersion within the polymer matrix. Different degrees of oxidation were attempted. GO nanoparticles were successively modified with epoxy monomers. Also in this case chemical, morphological, structural and thermal characterization was carried out. Surface modified carbonaceous nanoparticles were then dispersed in varying amounts in the organic matrix. The obtained nanocomposite systems were characterized in their chemical-physical and morphological properties. The adopted compatibilization strategies used for both MWCNTs and GNP were found to be extremely effective to get homogeneous and to enable a dramatic enhancement of the actuation extent at low nanofiller content. Moreover, the stress threshold required to trigger the reversible thermomechanical actuation was significantly decreased. The effect of nanoparticles on thermomechanical properties of the materials was correlated to the microstructure and the phase behavior of the host system. Results demonstrated that the incorporation of carbon nanofillers amplified the soft-elastic response of the liquid crystalline phase to external stimuli. Tunable thermomechanical properties of these systems make them suitable for a variety of potential advanced applications ranging to robotics, sensing and actuation, and artificial muscles

Controlled Actuation of a Carbon Nanotube/Epoxy Shape-Memory Liquid Crystalline Elastomer

Thermally induced shape-memory polymers are materials based on exploiting one or more phase transitions, such as glass, melting, or clearing transition, to trigger a shape-memory effect. Among shape-memory polymers, liquid crystalline elastomers are considered as very interesting candidates, thanks to the synergistic effect of the ordered liquid crystalline phase and the polymeric network on their programming and recovering behavior. Here, the synthesis of new shape-memory smectic epoxy-based elastomers incorporating multiwalled carbon nanotubes is reported. The realized materials show two types of shape-memory behavior that can be selectively actuated by choosing the appropriate thermal recovery conditions. The surface modification of the nanotubes enables a dramatic enhancement of the actuation extent at low nanofiller content. Moreover, the stress threshold required to trigger the reversible thermomechanical actuation is significantly decreased. The effect of nanotubes on thermomechanical properties of the materials is elucidated and correlated to the microstructure and phase behavior of the host system. Results demonstrate that the incorporation of multiwalled carbon nanotubes amplifies the soft-elastic response of the liquid crystalline phase to external stimuli. Tunable thermomechanical properties of these systems make them potentially suitable for a variety of applications ranging to robotics, sensing and actuation, and artificial muscles

Shape memory actuation in liquid-crystalline epoxies and their nanocomposites

Thermally triggered shape-memory polymers are materials based on exploiting one or more phase transitions, such as glass, melting, or clearing transition, to give shape-memory effect. Among shape-memory polymers, liquid crystalline elastomers (LCEs) are good candidates due to the synergistic effect of the ordered liquid crystalline phase and the lightly cross-linked polymeric structure, responsible for their programming and recovering behavior. Herein, the synthesis and characterization of shape-memory epoxy-based LCEs incorporating compatibilized carbon nanoparticles is presented. The general thermal, morphological and viscoelastic properties of the realized nanocomposite films are reported and discussed, with a particular concern on the thermo-mechanical actuation. Results demonstrate that the soft-elastic response, and consequently, the thermal actuation of the LCE-based nanocomposites is improved by the presence of nanofillers, and strictly related to the microstructure generated. Tunable thermomechanical properties of these systems make them potentially suitable for a variety of applications ranging to robotics, sensing and actuation, and artificial muscles