Energy harvesting performance of BaTiO3/poly(vinylidene fluoride-trifluoroethylene) spin coated nanocomposites

The energy harvesting efficiency of poly(vinylidene fluoride-trifluoroethylene) spin coated films and its nanocomposites with piezoelectric BaTiO3 have been investigated as a function of ceramic filler size and content. It is found that the best energy harvesting performance of ~0.28 W is obtained for the nanocomposite samples with 20% filler content of 10 nm size particles and for 5% filler content for the 100 and 500 nm size fillers. For the larger filler average sizes, the power decreases for filler contents above 5% due to increase of the mechanical stiffness of the samples. Due to the similar dielectric characteristics of the samples, the performance is mainly governed by the mechanical response. The obtained power values, easy processing and the low cost and robustness of the polymer, allow the implementation of the material for micro and nanogenerator applications.

Magnetoelectric CoFe2O4/polyvinylidene fluoride electrospun nanofibres

Magnetoelectric 0-1 composites comprising CoFe2O4 (CFO) nanoparticles in polyvinylidene fluoride (PVDF) polymerfibre matrix have been prepared by electrospinning. The average diameter of the electrospun composite fibres D is ~ 325 nm, independently of nanoparticle content, and the amount of crystalline polar β phase is strongly enhanced when compared to pure PVDF polymer fibres. The piezoelectric response of these electroactive nanofibres is modified by an applied magnetic field, thus evidencing the magnetoelectric character of the CFO/PVDF 0-1 composites.

Effect of ionic liquid anion type in the performance of solid polymer electrolytes based on Poly(Vinylidene fluoride-trifluoroethylene)

The effect of different anions within the ionic liquid in the characteristics of solid polymer electrolytes (SPEs) based on P(VDF-TrFE) has been investigated. 1-ethyl-3-methylimidazolium acetate, [C2mim][OAc], 1-ethyl-3-methylimidazolium triflate, [C2mim][(CF3SO3)3], 1-ethyl-3-methylimidazolium lactate, [C2mim][Lactate], 1-ethyl-3-methylimidazolium thiocyanate, [C2mim][SNC] and 1-ethyl-3-methylimidazolium hydrogen sulphate [C2mim][HSO4] have been used in SPE prepared by thermally induced phase separation (TIPS). The polymer phase, thermal and electrochemical properties of the SPE have been determined. The thermal and electrical properties of the SPEs strongly depend on the selected IL, as determined by their different interactions with the polymer matrix. The room temperature ionic conductivity increases in the following way for the different anions: [SNC] > [CF3SO3)3] > [HSO4] > [Lactate] > [OAc], which is mainly dependent on the viscosity of the ionic liquid.

Effect of butadiene/styrene ratio, block structure and carbon nanotube content on the mechanical and electrical properties of thermoplastic elastomers after UV ageing

Thermoplastic elastomers based on a triblock copolymer styrene-butadiene-styrene (SBS) with different butadiene/styrene ratios, block structure and carbon nanotube (CNT) content were submitted to accelerated weathering in a Xenontest set up, in order to evaluate their stability to UV ageing. It was concluded that ageing mainly depends on butadiene/styrene ratio and block structure, with radial block structures exhibiting a faster ageing than linear block structures. Moreover, the presence of carbon nanotubes in the SBS copolymer slows down the ageing of the copolymer. The evaluation of the influence of ageing on the mechanical and electrical properties demonstrates that the mechanical degradation is higher for the C401 sample, which is the SBS sample with the largest butadiene content and a radial block structure. On the other hand, a copolymer derivate from SBS, the styrene-ethylene/butadiene-styrene (SEBS) sample, retains a maximum deformation of ~1000% after 80 h of accelerated ageing. The hydrophobicity of the samples decreases with increasing ageing time, the effect being larger for the samples with higher butadiene content. It is also verified that cytotoxicity increases with increasing UV ageing with the exception of SEBS, which remains not cytotoxic up to 80 h of accelerated ageing time, demonstrating its potential for applications involving exposition to environmental conditions.

Study of the potential employment of Malvaceae Species in composites materials

The employ of vegetal fibers for textiles and composites represents a great potential in economic and social sustainable development. Some Malvaceae species are considered tropical cosmopolitans, such as from Sida genus. Several species of this genus provide excellent textile bast fibers, which are very similar in qualities to the jute textile fiber. The objective of the present study is present the physicochemical characterization of six Brazilian vegetal fibers: Sida rhombifolia L.; Sida carpinifolia L. f.; Sidastrum paniculatum (L.) Fryxell; Sida cordifolia L.; Malvastrum coromandelianum (L.) Gurck; Wissadula subpeltata (Kuntze) R.E.Fries. Respectively the two first species are from Brazilian Atlantic Forest biome and the four remaining from Brazilian Cerrado biome, despite of present in other regions of the planet. The stems of these species were retted in water at 37oC for 20 days. The fibers were tested in order to determine tensile rupture strength, tenacity, elongation, Young’s modulus, cross microscopic structure, Scanning Electronic Microscopy (SEM), regain, combustion, acid, alkali, organic solvent and cellulase effects, pH of the aqueous extract, Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). The obtained values were compared with those from fibers of recognized applicability in the textile industry including hemp. The results are promising in terms of their employment in thermoset and thermoplastic medium resistance composites.

Microstructure and mechanical properties of carbon nanotube reinforced cementitious composites developed using a novel dispersion technique

The authors also acknowledge Centre for Textile Science and Technology (University of Minho) and FIBRENAMICS PLATFORMfor providing required conditions for this research. Sincere thanks are also due to Mr. Pedro Samuel Leite and Mr. Carlos Jesus for their kind help in sample preparation and testing.

Mechanical performance of natural fiber-reinforced composites for the strengthening of masonry

The growing concerns regarding the environmental impact generated by the use of inorganic materials in different fields of application increased the interest towards products based on materials with low environmental impact. In recent years, researchers have turned their attention towards the development of materials obtained from renewable sources, easily recoverable or biodegradable at the end of use. In the field of civil structures, a few attempts have been done to replace the most common composites (e.g. carbon and glass fibers) by materials less harmful to the environment, as natural fibers. This work presents a comprehensive experimental research on the mechanical performance of natural fibers for the strengthening of masonry constructions. Flax, hemp, jute, sisal and coir fibers have been investigated both from physical and mechanical points of view. The fibers with better performance were tested together with three different matrices (two of organic nature) in order to produce composites. These experimental results represent a useful database for understanding the potentialities of natural fibers as strengthening systems.

Development of ductile cementitiuos composites using carbon nanotubes

Concrete is the primary construction material for civil infrastructures and generally consists of cement, coarse aggregates, sand, admixtures and water. Cementitious materials are characterized by quasi-brittle behaviour and susceptible to cracking [1]. The cracking process within concrete begins with isolated nano-cracks, which then conjoin to form micro-cracks and in turn macro-cracks. Formation and growth of cracks lead to loss of mechanical performance with time and also make concrete accessible to water and other degrading agents such as CO2, chlorides, sulfates, etc. leading to strength loss and corrosion of steel rebars. To improve brittleness of concrete, reinforcements such as polymeric as well as glass and carbon fibers have been used and microfibers improved the mechanical properties significantly by delaying (but could not stop) the transformation of micro-cracks into macro forms [2]. This fact encouraged the use of nano-sized fillers in concrete to prevent the growth of nano-cracks transforming in to micro and macro forms. Nanoparticles like SiO2, Fe2O3, and TiO2 led to considerable improvement in mechanical performance and moreover, nano-TiO2 helped to remove organic pollutants from concrete surfaces [3].

Green composites for advanced technical applications

This paper provides an overview of properties and application of natural fibre composites. Natural fibre market, merits and demerits, surface treatment techniques, properties of some recently developed natural fibre composites and applications have been discussed.

Poly(2-hydroxyethyl methacrylate): A new star polymer

Multiarm star polymers are attractive materials due to their unusual bulk and solution properties. They are considered analogues of dendrimers with a wide range of applications, such as drug delivery, membranes, coatings and lithography.1 The advent of controlled polymerization made possible the existence of this unique class of organic nanoparticles (ONPs).2 Two major synthetic strategies are usually employed in the preparation of star polymers, the core-first and arm-first approaches. The core-first approach involves a controlled living polymerization using a multiarm initiator core while the arm-first methodology is based in the quenching of living polymers with multifunctional coupling agent or bifunctional vinyl compounds. Herein, we present the synthesis and characterization of a new star polymer, the multiarm star poly(2-hydroxyethyl methacrylate). The tetra-armed star polymer was prepared by reversible addition fragmentation chain-transfer (RAFT) polymerization using the core-first approach. The RAFT chain-transfer agent (RAFT CTA) pentaerythritol tetrakis[2-(dodecylthiocarbonothioylthio)-2-methylpropionate] was used as multiarm initiator core were 2-hydroxyethyl methacrylate (HEMA) was polymerized using AIBN as radical initiator. Structural characterization was performed by 1H NMR and FTIR. The new polymer is able to uptake large quantities of organic solvents, forming gels. The rheological behavior of these gels was also investigated.

Solid polymer electrolytes based on chitosan and europium triflate

Solid polymer electrolytes (SPEs) were obtained from chitosan plasticized with glycerol and contained europium (III) trifluoromethanesulfonate salt. The transparent samples were characterized by thermal analysis (DSC and TGA), impedance spectroscopy and electron paramagnetic resonance (EPR). The sample with 55.34 wt.% of europium triflate showed the best ionic conductivity of 1.52 × 10−6 and 7.66 × 10−5 S cm−1 at 30°C and 80°C, respectively. The thermal analysis revealed that the degradation started at around 130–145°C and the weight loss ranged from 20 to 40%. The DSC of the samples showed no Tg, but only a large endothermic peak that was centered between 160 and 200 °C. The EPR analysis showed a broadening of the EPR resonance lines with increasing europium contents in the chitosan membranes due to the magnetic dipole–dipole coupling and spin–spin exchange between the Eu2+ ions. Moreover, the electrolytes based on chitosan and europium triflate presented good flexibility, homogeneity, and transparency.

Polymer electrolyte based on DNA and N,N,N-trimethyl-N-(2-hydroxyethyl)ammonium bis(trifluoromethylsulfonyl)imide

Combining ionic liquids (ILs) with polymers offers the prospect of new applications, where they surpass the performance of conventional media, such as organic solvents, giving advantages in terms of improved safety and a higher operating temperature range. In this work we have investigated the morphology, thermal and electrochemical properties of polymer electrolytes prepared through the addition of con- trolled quantities of the cholinium based IL N,N,N-trimethyl-N-(2-hydroxyethyl)ammonium bis(trifluo- romethylsulfonyl)imide ([N1 1 1 2(OH)] [NTf2]) to a deoxyribonucleic acid (DNA) host network. These novel IL-based electrolytes have been analyzed aiming at applications in electrochemical devices. An optimized sample showed good thermal stability up to 155 °C and a wide electrochemical window of ~3.5 V. The highest conductivity was registered for the DNA[N1 1 1 2(OH)][NTf2] (1:1) (2.82 × 10-5 and 1.09 × 10-3 S cm-1 at 30 and 100 °C, respectively).

Effect of the alkyl chain length of the ionic liquid anion on polymer electrolytes properties

New polymer electrolytes (PEs) based on chitosan and three ionic liquid (IL) families ([C2mim][CnSO3], [C2mim][CnSO4] and [C2mim][diCnPO4]) were synthesized by the solvent casting method. The effect of the length of the alkyl chain of the IL anion on the thermal, morphological and electrochemical properties of the PEs was studied. The solid polymer electrolytes (SPE) membranes were analyzed by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), polarized optical microscopy (POM), atomic force microscopy (AFM), complex impedance spectroscopy (ionic conductivity) and cyclic voltammetry (CV). The obtained results evidenced an influence of the alkyl chain length of the IL anion on the temperature of degradation, birefringence, surface roughness and ionic conductivity of the membranes. The DSC, XRD and CV results showed independency from the length of the IL-anion-alkyl chain. The PEs displayed an predominantly amorphous morphology, a minimum temperature of degradation of 135 °C, a room temperature (T = 25 °C) ionic conductivity of 7.78 × 10−4 S cm−1 and a wide electrochemical window of ∼ 4.0 V.

Polymer electrolytes for electrochromic devices

Polymer electrolytes are currently the focus of much attention as potential electrolytes in electrochemical devices such as batteries, display devices and sensors. Generically, solid polymer electrolytes (SPEs) are mixtures of salts with soft polar polymers. SPEs have many advantages including high energy density, no risk of leakage, no issues related to the presence of solvent, wide electrochemical stability windows, simplified processability and light weight. With the goal of developing a new family of environmentally friendly multifunctional biohybrid materials displaying high ionic conductivity we have produced in the present work, flexible films based on different polymers or hybrids incorporating different salts. The polymer electrolytes studied here have been characterized by means of Differential Scanning Calorimetry, Thermogravimetric Analysis, X-ray diffraction, Polarized Optical Microscopy, complex impedance spectroscopy and cyclic voltammetry. An evaluation of the performance of the sample with the highest conductivity as electrolyte in all solid-state ECDs was performed.

Evaluation of natural fibers from brazilian malvaceae family and its potential as reinforced composites

This study compares the physicochemical characteristics of six species from Brazilian Malvaceae family with natural fibers of recognized applicability in the industry. The objective of the present study is present the physicochemical characterization of six Brazilian vegetal fibers: Sida rhombifolia L.; Sida carpinifolia L. f.; Sidastrum paniculatum (L.) Fryxell; Sida cordifolia L.; Malvastrum coromandelianum (L.) Gurck; Wissadula subpeltata (Kuntze) R.E.Fries. Respectively the two first species are from Brazilian Atlantic Forest biome and the four remaining from Brazilian Cerrado biome, despite of present in other regions of the plane