Effect of sepiolite content on mechanical, thermal and flammability properties of ethylene vinyl acetate nanocomposite

Polymer/clay nanocomposites are a new class of composite materials consisting of a polymer matrix with dispersed clay nanoparticles. Ethylene vinyl acetate (EVA)/Sepiolite and EVA/modified Sepiolite (M-Sepiolite) nanocomposites were prepared by melt extrusion using a counter-rotating twin-screw extruder followed by injection molding in order to examine the mechanical, morphological, thermal and flammability properties of the nanocomposites. Sepiolite was modified with silane treatment (M-Sepiolite). Sepiolite content was various in EVA with 1, 3, 5 and 7 wt%. The mechanical properties of EVA/Sepiolite and EVA/M-sepiolite nanocomposites were studied through tensile. Scanning electron microscopy (SEM) was used to investigate the phase morphology of nanocomposites. The thermal properties were determined using Thermogravimetric analysis (TGA) and flame retardancy of nanocomposites was conducted by characterization for limiting oxygen index. The mechanical, thermal and flame retardancy properties of EVA / Sepiolite nanocomposite increased with the increase sepiolite content due to good dispersion and well interface interaction between Sepiolite and EVA. The mechanical, thermal and flame retardancy properties the EVA/M-Sepiolite nanocomposite was better than the mechanical, thermal and flame retardancy properties of EVA/Sepiolite nanocomposite, where the modification of Sepiolite caused extremely good interface interaction, as well as good dispersion and better adhesion between Sepiolite and polymer matrix

Electrical, mechanical and electromechanical properties of graphene-thermoset polymer composites produced using acetone-DMF solvents

Recently, graphene-polymer composites gained a central role in advanced stress and strain sensing. A fundamental step in the production of epoxy-composites filled with graphene nanoplatelets (GNPs) consists in the exfoliation and dispersion of expanded graphite in a proper solvent, in the mixing of the resulting GNP suspension with the polymer matrix, and in the final removal of the solvent from the composite before curing through evaporation. The effects of traces of residual solvent on polymer curing process are usually overlooked, even if it has been found that even a small amount of residual solvent can affect the mechanical properties of the final composite. In this paper, we show that residual traces of N,N′-Dimethylformamide (DMF) in vinylester epoxy composites can induce relevant variations of the electrical, mechanical and electromechanical properties of the cured GNP-composite. To this purpose, a complete analysis of the morphological and structural characteristics of the composite samples produced using different solvent mixtures (combining acetone and DMF) is performed. Moreover, electrical, mechanical and electromechanical properties of the produced composites are assessed. In particular, the effect on the piezoresistive response of the use of DMF in the solvent mixture is analyzed using an experimental strain dependent percolation law to fit the measured electromechanical data. It is shown that the composites realized using a higher amount of DMF are characterized by a higher electrical conductivity and by a strong reduction of Young’s Modulus

Large Scale Production of Porous and Non-Porous PVDF/GNPs Nanocomposites for Electrical and Electromechanical Applications

In this thesis work, PVDF/GNP nanocomposites have been investigated, focusing on electrical, electromechanical, and electromagnetic applications. PVDF/GNP nanocomposites comprise a new generation of multifunctional materials that combine the properties of PVDF and of GNPs. In particular, different nanocomposites made of PVDF filled with different weight concentrations of GNPs were fabricated, without any chemical modification or functionalization, either on GNPs or on polymer chains. Thus, this work can open new perspectives in the use of graphene-based nanofillers in polymer composites, since no chemical modification or functionalization of graphene is needed. Furthermore, the effect of GNPs on morphology, electrical, electromagnetic, mechanical, and electromechanical properties of PVDF/GNP nanocomposites have been studied. This thesis is organized into two parts. The first one consists of five chapters and deals with the PVDF/GNP nanocomposite film production and characterization. In the first Chapter, short overviews of GNPs and PVDF are provided, focusing on their structure, main properties, and synthesis techniques. In Chapter 2 the best time-temperature combination in the PVDF-film preparation process is discussed. This combination is very important for the PVDF film structure. Then, GNP/PVDF nanocomposites were fabricated via the solution mixing method. It was found that the addition of GNP in PVDF has a strong effect on the conductivity of the nanocomposite. In particular, when 2wt % GNP is added in the PVDF polymer matrix, the electrical conductivity of nanocomposites is around 16 orders of magnitude greater than the one of pure PVDF. In Chapter 3, the nucleation effect of unmodified GNPs on PVDF/GNP composite films was investigated. To the best of our knowledge, this is the first study focused on the use of GNPs without any chemical modification or functionalization as nucleation agents for β-phase formation enhancement. Furthermore, the morphological, electrical, mechanical and electromechanical properties of film nanocomposites were significantly affected by the nucleation effect of GNPs on polymer chains. Chapter 4 deals with the evaluation of the piezo-resistive properties of PVDF composite films filled with GNPs. The samples have thickness in the range of 20-30 µm and they are characterized by high flexibility and stability, and by remarkable chemical and physical resistances. The piezo-resistive behavior of the PVDF/GNP composite films filled at 1.5% and 2% wt has been studied under quasi static and cyclic flexural loadings. In both cases, the produced films show a stable and repeatable response to the applied flexural strain. In particular, the computed sensitivity at a strain of 1.5% is nearly 15 for the PVDF/GNP film loaded at 1.5% wt. On the other hand, Chapter 5 deals with the piezoelectric response, measured through the piezoresponse force microscopy (PFM). PFM investigations have been adopted to assess the piezoelectric properties of the PVDF/GNP nanocomposites at the nanoscale. The piezoelectric responses of the different samples were compared: neat PVDF, PVDF nanocomposite filled with GNP at 0.3 wt%, 0.5 wt% and 0.7 wt%. The enhancement of the piezoelectric response of the PVDF / GNP nanocomposite can be explained assuming that GNPs induce the formation of the β-phase in PVDF, as shown elsewhere. The results show a qualitative correlation between induced β-phase, as assessed through FT-IR measurements, and intensity of the measured piezoelectric response, resulting from the PFM analysis. The second part of the thesis consists of two chapters and is focused on PVDF/GNP nanocomposites for electromagnetic and power generation applications. Chapter 6 deals with the synthesis and characterization of 3D porous graphene nanocomposite aerogels for electromagnetic applications. The produced nanocomposites are morphologically and electrically characterized, and their relative complex permittivity is measured in the frequency range of 8-18 GHz. Finally, in Chapter 8, a novel flexible and washable membrane for renewable energy production is investigated. In particular, an aluminum-PVDF/GNP membrane saline battery is designed, fabricated, and characterized. It is noticed that the voltage generated is quite stable with the time since voltage variations are visible only at the beginning of the measurements. An almost constant voltage of 0.8 V was measured in the matching condition, i.e. when the cell is loaded on a 470 kΩ resistance

Flammability and thermal properties of ethylenevinyl acetate filled treated and untreated sepiolite nanocomposites

Flame retardant ethylene-vinyl acetate (EVA)/ Sepiolite nanocomposites were prepared by melt blending using twin screw extruder and injection molding machine at various Sepiolite content. Modification process of sepiolite was carried out by using 3-aminopropyltrimethoxysilane (3-APTMS) in water/ethanol medium. Thermal and flame retardancy properties of the prepared nanocomposites were evaluated. By the addition of unmodified sepiolite, both flame retardancy and thermal stability characteristics improved. Silane modified sepiolite has further improved these properties. It was also found that Sepiolite has increased the thermal degradation temperature of EVA

Transition behavior, surface characteristics and film formation of functionalized poly(methyl methacrylate-co-butyl acrylate) particles

Carboxylic functionalized poly(methyl methacrylate-co-butyl acrylate) particles were synthesized by soap free emulsion polymerization using sodium salts of itaconic acid and acrylic acid. Transition behaviors of these latexes in terms of glass transition of matrix and cluster were found to be completely different from those synthesized by solution polymerization. This disparity was attributed to the difference between co-monomers sequence distribution along the chains. Distribution of functional groups in the latexes was determined by conductometric titration. Film formation process of the latexes was also examined and interpreted based on the density of surface functional groups, transition behaviors, and particle size. AFM images revealed that, as the amount of these ionic co-monomers increases, more ordered films are obtained, while the particle inter-diffusion is greatly retarded. A dimensionless parameter indicating relative roughness of the films further supported the aforementioned findings. (C) 2014 Elsevier B.V. All rights reserved

Transition behavior, surface characteristics and film formation of functionalized poly (methyl methacrylate-co-butyl acrylate) particles

Carboxylic functionalized poly(methyl methacrylate-co-butyl acrylate) particles were synthesized by soap free emulsion polymerization using sodium salts of itaconic acid and acrylic acid. Transition behaviors of these latexes in terms of glass transition of matrix and cluster were found to be completely different from those synthesized by solution polymerization. This disparity was attributed to the difference between co-monomers sequence distribution along the chains. Distribution of functional groups in the latexes was determined by conductometric titration. Film formation process of the latexes was also examined and interpreted based on the density of surface functional groups, transition behaviors, and particle size. AFM images revealed that, as the amount of these ionic co-monomers increases, more ordered films are obtained, while the particle inter-diffusion is greatly retarded. A dimensionless parameter indicating relative roughness of the films further supported the aforementioned findings. (C) 2014 Elsevier B.V. All rights reserved

Development of ethylene-vinyl acetate composites reinforced with graphene platelets

Composites of ethylene-vinyl acetate (EVA) reinforced with graphene platelets are fabricated. Morphological, thermal, mechanical, electrical properties as well as moisture absorption of the composites are characterized. Transmission electron microscopy shows a good dispersion of graphene platelets in the matrix. The unidirectional orientation of graphene platelets parallel to the surface of the composites is revealed by field emission scanning electron microscopy and is validated using the Halpin–Tsai model. Tensile strength and elongation of the composites are respectively improved by 109 and 83%, after the addition of 3 wt% graphene platelets. The incorporation of 5 wt% graphene platelets enhances the char residue of the composites from 0.544% for pure EVA to 6.63% for the composites. The electrical conductivity of the composite with 3 wt% graphene platelets is two orders of magnitude higher than that of pure EVA with 10−13 S cm–1 electrical conductivity. (Figure presented.)

Gas permeability and permselectivity properties of ethylene vinyl acetate/sepiolite mixed matrix membranes

Ethylene vinyl acetate (EVA) mixed matrix membranes (MMMs) were prepared by incorporating fibrous sepiolite modified by 3-aminopropyltrimethoxysilane (3-APTMS). Gas transport through the prepared MMMs was investigated in detail. Permeabilities of O2, CO2, CH4, and N2, gases were significantly increased by the addition of 3 wt.% of sepiolite. At the same sepiolite loading, the CO2/CH4 and CO2/N2 selectivity of the MMMs at 5 bar were respectively enhanced by 9% and 28.2%, while the O2/N2 selectivity did not notably change and their values remained nearly constant around 2.5-3. The enhanced permeation was attributed to the decreased crystallinity percentage, confirmed by X-ray diffractometry (XRD) and differential scanning calorimetry (DSC). Moreover, XRD results and microscopic images demonstrated that sepiolite fibers were uniformly dispersed in the EVA matrix due to the presence of hydrogen bonding between amino groups of modified sepiolite and carbonyl groups of EVA. Also, upon the incorporation of 3 wt.% sepiolite, the tensile strength and elongation at break were simultaneously enhanced by 46% and 76%, respectivel