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Nowadays, the world requires more sustainable and eco-friendly materials to replace or limit the usage of synthetic materials. Moreover, several researchers focused their attention on the use of agricultural sources as reinforcement for biocomposites since they are abundant, cost-effective and environmentally favorable sources. In such a context, purpose of the present paper is the evaluation of lemongrass plant (Cymbopogon flexuosus) as possible source of natural reinforcement for biocomposites. To this aim, natural fibers were obtained from the leaf and the stem of lemongrass and their main properties were compared for the first time. To this scope, mechanical and thermal characterizations, chemical investigation, Fourier-transform infrared spectroscopy, X-Ray diffraction and scanning electron microscope analysis were carried out. The experimental campaign showed that, despite having similar chemical composition (i.e., cellulose, hemicellulose and lignin contents equal to 44–45%, 28–29% and 17%, respectively), leaf fibers possess higher mechanical properties (i.e., + 55% and + 76% in the tensile strength and modulus, respectively) than stem ones. This result can be ascribed to different factors such as larger amount of absorbed water (i.e., + 4%) and ash content (+ 2%) shown by stem fibers in addition to a more compact structure evidenced by leaf fibers which also present higher density (i.e., 1.139 g/cm3 versus 1.019 g/cm3).

Despite natural fibers gaining significant attention in recent decades, their limited performance and poor durability under humid environments cannot allow them to fully replace their synthetic counterparts as reinforcement for structural composites. In such a context, this paper aims to investigate how exposure to a humid/dry cycle affects the mechanical response of epoxy laminates reinforced with flax and glass fibers. In particular, the main goal is to assess the performance evolution of a glass–flax hybridized stacking sequence in comparison with the full glass and flax fiber reinforced composites. To this end, the investigated composites were first exposed to salt-fog for 15 or 30 days and then to dry conditions (i.e., 50% R.H. and 23 °C) for up to 21 days. The presence of glass fibers in the stacking sequence significantly stabilizes the mechanical performance of composites during the humid/dry cycle. Indeed, hybridization of inner flax laminae with outer glass ones, acting as a protective shield, hinders the composite degradation due to the humid phase also promoting performance recovery during the dry phase. Hence, this work showed that a tailored hybridization of natural fibers with glass fibers represents a suitable approach to extend the service-life of natural fiber reinforced composites exposed to discontinuous humid conditions, thus allowing their employment in practical indoor and outdoor applications. Finally, a simplified theoretical pseudo-second-order model that aimed to forecast the performance recovery shown by composites was proposed and experimentally validated, highlighting good agreement with the experimental data.

Despite their scarce resistance to humid or wet conditions, natural fiber reinforced composites (NFRCs) seem to be able to partially recover their performances under discontinuous exposition to marine environment. To investigate this peculiarity, flax fiber reinforced composite was at first subjected to salt-fog spray condition at 35 °C for 15 and 30 days, respectively, and then stored in ‘‘dry” condition (i.e., 50% R.H. and 22 °C) between 0 and 21 days. The performances evolution was evaluated through flexural tests, water uptake and contact angle measurements. Moreover, the morphology of fractured mechanical samples was examined by using 3D optical microscope and scanning electron microscope (SEM). Flax fiber reinforced composite experienced phenomena of both reversible and irreversible degradation during the wet phase thus evidencing a relevant mechanical recovery thanks to the drying. Quite interestingly, the laminate showed an almost complete recovery of the flexural strength, meaning that this property is more strictly related to mainly reversible aging phenomena whereas the greater stiffness loss is more probably due to irreversible ones.

This paper aims to investigate the ability of an eco-friendly and cheap treatment based on sodium acetate solutions to improve the mechanical properties of flax fiber-reinforced composites. Flax fibers were treated for 5 days (i.e., 120 h) at 25 °C with mildly alkaline solutions at 5%, 10% and 20% weight content of the sodium salt. Quasi-static tensile and flexural tests, Charpy impact tests and dynamical mechanical thermal (DMTA) tests were carried out to evaluate the mechanical properties of the resulting composites. Fourier transform infrared analysis (FTIR) was used to evaluate the chemical modification on the fibers surface due to the proposed treatment, whereas scanning electron microscope (SEM) and helium pycnometry were used to get useful information about the morphology of composites. It was found that the treatment with 5% solution of sodium acetate leads to the best mechanical performance and morphology of flax fiber-reinforced composites. SEM analysis confirmed these findings highlighting that composites reinforced with flax fibers treated in 5% sodium acetate solution show an improved morphology compared to the untreated ones. On the contrary, detrimental effects on the morphology as well as on the mechanical performance of composites were achieved by increasing the salt concentration of the treating solution.

The goal of this paper is to evaluate the effectiveness of a cost-effective and eco-friendly treatment based on the use of sodium citrate (Na3C6H5O7) on the mechanical properties of flax fiber reinforced composites. To this scope, flax fibers were soaked in mildly alkaline solutions of the sodium salt at different weight concentration (i.e., 5%, 10% and 20%) for 120 h at 25 °C. The modifications on fibers surface induced by the proposed treatment were evaluated through Fourier transform infrared analysis (FTIR), whereas scanning electron microscope (SEM) and helium pycnometer were used to obtain useful information about composites morphology. The effect of the concentration of the treating solution on the mechanical response of composites was determined through quasi-static tensile and flexural tests, Charpy impact tests and dynamical mechanical thermal (DMTA) tests. The results revealed that composites reinforced with flax fibers treated in 10% solution exhibit the best mechanical performances as well as the lowest void contents. SEM analysis supported these findings showing that, by treating fibers in solutions with concentration up to 10%, composites having better morphology can be manufactured, in comparison to untreated ones. Conversely, higher Na3C6H5O7 concentrations negatively affect both the morphology and the mechanical properties of composites.

This paper aims to propose and characterize a sustainable hydraulic mortar entirely obtained by the reuse of waste materials, with marble slurry coming from quarries in the north-western Sicily and glass powder coming from a waste collection plant in Marsala (Province of Trapani). The first was used as raw material to produce the mortar binder by a kilning and slaking process, while the second was used as a pozzolanic additive. The chemical and morphological characterization of the marble slurry was done by XRD, FTIR, STA and SEM analyses. Glass powder was analyzed through particle size distribution measurements, XRD and standard pozzolanic tests. Hydraulic mortars constituted by slaked lime from kilned marble slurry and waste glass powder (LGS) were prepared beside commercial Natural Hydraulic Lime (NHL) based mortars (NGS) and air-hardening lime (LSS)-based mortars. Mechanical and absorption properties of the mortars were investigated as a function of the grain size of the glass powder by means of three-point bending and compressive strength tests, capillary uptake, helium pycnometry and simultaneous thermal analysis. The results demonstrated that the formulation LGS exhibits significantly improved mechanical and absorption properties compared to air-hardening mortars (LSS). It confirms the possibility of producing a more sustainable hydraulic mortar exclusively from waste materials for civil engineering.

Nowadays sustainability is one of the main concept in building construction, both considering energy saving buildings and life cycle assessment of building materials. According to these considerations, in this work the use of recycled and waste materials to produce a binder and the use of a natural fiber as reinforcement are investigated to obtain a sustainable mortar. Particularly, lime is obtained by kilning waste marble slurry from marbles quarries in western Sicily; pozzolanic aggregate is obtained by grinding glass powder from urban waste collection; natural fibers come from a widespread grass: Ampelodesmos Mauritanicus also known as diss. Scanning electron microscopy and helium picnometry have been performed to characterize diss fibers. Samples with different fibers volume percentage have been prepared and subjected to three-point bending and compression tests, in order to verify the modification of resistance related to the presence of fibers; moreover, capillary uptake and thermal conductivity have been evaluated.The results show a great influence of fibers’ percentage on both mechanical and environmental properties of mortars, resulting in lowering of mechanical resistance and thermal conductivity.

Cork is a unique material, characterized by small closed cell structures, high insulating properties, very low density, high fire resistance and a very good durability after simple thermal treatment. The main use of cork in the production of stopper and insulating panels obtained with cork grains and a polymeric resin. Usually cork grains used in panel production have a grainsize around 1-2 mm. In this work cork grains have been used as aggregates for natural hydraulic lime mortars by reducing grainsize distribution. Cork grainsize has been reduced by means of a knife mill and divided in three different distributions, i.e. 1, 0.5 and 0.25mm. Mortars have been prepared according to NHL to cork to natural sand volume ratio equal to 2:3:2. Three point bending and compression tests showed that reducing cork grainsize leads to a slight increase in mechanical performance. On the other hand thermal conductivity showed to be independent from cork grainsize. Scanning electron microscope investigation was also performed to better understand these results.

Over the last decades, natural fiber-reinforced polymer composites (NFRPs) gained great attention in several engineering fields thanks to the reduction of the environmental impact and the end-of-life cost disposal. Unfortunately, the use of NFRPs is limited, mainly due to their weak resistance against humid environments. Since limited literature is available about the evolution of the dynamic mechanical response of NFRPs under aggressive environments, this paper aims to investigate the damping properties of flax, jute and flax/jute epoxy composites exposed to salt-fog up to 60 days. Furthermore, sodium bicarbonate fiber treatment was performed to improve the composites&rsquo, durability. The effectiveness of treatment was evidenced for full flax-reinforced composites, whereas no beneficial effect was found for jute composites. Moreover, treated hybrid laminates having outer laminae reinforced with flax showed better damping behavior than their hybrid counterparts during the whole aging campaign.

The use of natural fibers in cement composites is a widening research field as their application can enhance the mechanical and thermal behavior of cement mortars and limit their carbon footprint. In this paper, two different wild grasses, i.e., Ampelodesmos mauritanicus, also called diss, and Pennisetum setaceum, also known as crimson fountaingrass, are used as a source of natural aggregates for cement mortars. The main purpose is to assess the possibility of using the more invasive crimson fountaingrass in place of diss in cement-based vegetable concrete. The two plant fibers have been characterized by means of scanning electron microscopy (SEM), helium picnometry and thermogravimetric analysis. Moreover, the thermal conductivity of fiber panels has been measured. Mortars samples have been prepared using untreated, boiled and Polyethylene glycol 4000 (PEG) treated fibers. The mechanical characterization has been performed by means of three point bending and compression tests. Thermal conductivity and porosity have been measured to characterize physical modification induced by fibers’ treatments. The results showed better thermal and mechanical properties of diss fiber composites than fountaingrass one and that fiber treatments lead to a reduction of the thermal insulation properties.

Insulated Gate Bipolar Transistor (IGBT) is the reference design for power semiconductor switches in the range of the medium-high power applications. Different designs were proposed along the development story of this device, but the actual trend is leaded by the Field-Stop IGBT (FS-IGBT) concept. One of the main advantages of this design is the great accuracy in defining the Emitter injection efficiency of the vertical PNP. However a careful design of the Collector side has to be carried out to avoid unwanted effects such as a negative temperature coefficient for the Von of the device. In this work we present the two main cause of the aforementioned effect, with a detailed analysis of the effect of the arising of a Schottky Barrier (SB) at the Collector contact for low doping concentrations.

An optimized electro-thermal IGBT SPICE model based on the Kraus model was developed to allow reliable simulation at application level. A particular emphasis to the temperature dependence of physical parameters was given for both the on-state and breakdown conditions. The model was experimentally validated in steady state and transient operation on a Field-Stop trench-gate 30 A-600 V commercial IGBT device. The effectiveness of the convergence-accuracy aspects was proved for the proposed model. The application to the short-circuit protection circuit design for a hard switched fault in an inverter motor-drive application was also analysed. The ability of the proposed IGBT model was experimentally verified with a simplified-equivalent circuit where a short condition was forced on the load, enabling the desaturation protection by the IGBT driver. The results show an accurate prediction of the device electro-thermal behaviour under short-circuit conditions, with a possible optimal design of the desaturation circuit parameters when the device experiences hard-switched-fault or fault-under-load events. © 2015 Elsevier Ltd.

In this paper, an innovative process flow developed to improve the thermal resistance of power ICs was presented. In this field, one of the major device failure mechanisms is related to the high temperatures reached during the working cycles due to the extremely critical electrical current densities. Therefore, heat transfer and dissipation are crucial aspects that need continuous improvements. Usual approaches to face this issue deal with package heat sinks design, solder selection, and wafer thinning. In this paper, a novel technological approach was settled, in which heat sinks microstructures were successfully integrated at wafer level stage on standard p-i-n diodes. To this aim, the bulk Si on the backside was partially replaced with Cu, a material characterized by a higher thermal conductivity material. Moreover, the well microstructures filled by Cu provide the advantage of wafer self-support, without requiring dedicated and more expensive thinning and handling technologies. An extensive characterization of the final devices was also carried out to evaluate the process and the thermal and electrical improvements. Finally, a failure analysis on selected devices was performed to identify any critical issue with the standard packaging process.

With the increasing interest in electro-thermal simulation of multi-cellular IGBT structure, the use of PSpice device compact models becomes very attractive because they ensure a good trade-off between accuracy and speed. However, the evaluation of model parameters can be difficult if model doesn't actually reflect the device physics: hence a calibration of parameters is needed to match the static and dynamic device electrical characteristics. We present a calibration procedure for IGBT PSpice model parameters, tested on the PSpice NIGBT model of a 18A-600V PT-planar device: the obtained model is compared with PSpice library one based on physics measured and extracted parameters. Both models are used in a DC-DC buck converter simulation to verify the abilities of calibrated model to better describe the IGBT losses and circuit efficiency in accordance with experimental measurements.

We derive an efficient and accurate computer-aided-design-based design methodology for the optimization of floating field-limiting ring terminations. The proposed approach is based on an iterative optimization of the ring-to-ring spacings starting from the outermost ring and proceeding back toward the main junction. Physics-based simulations show that each optimization step does not impair the previous one, thus allowing to easily identify the minimum number of rings needed to achieve the desired termination efficiency yet minimizing the number of simulation steps. The accuracy of the method is thoroughly discussed on the basis of comparisons against either literature results or experimental data.

Nowadays, the attention about the building sustainability is increasingly emerging, because of the major responsibility of the building field on the environmental degradation: both in terms of energy consumption from non-renewable sources and the raw materials impoverishment. In addition, the level of comfort required by users is growing and the thermal insulation of buildings becomes the key element for the reduction of energy consumption and CO2 emissions, both in the case of new construction and of the existing ones. The heat load of a building depends on the presence of insulating material which defines the performance of the building envelope. The main purpose of this work is both to introduce the production technology of a new ecofriendly Thermo-plaster and to evaluate its thermal insulation performances, also comparing amongst the most diffused insulation materials available in the market. This new technology, on the contrary of other competitor materials, is completely natural and doesn’t use any plastic matters. This new plaster is produced by using a mix of mortar, recycled and natural materials. Amongst the recycled ones we can recall the sawing mud and the glass, among the natural ones we used the Ampelodesmos Mauritanicus (also called diss), which is a perennial plant of the Gramineae family. Increasing the diss fibres percentage improves the thermal benefit. The Proposed plasters have shown thermal performances that can be considered satisfying and competitive compared to other commercially available plasters, analysed through the evaluation of the thermal and dynamics characteristics of four different possible stratigraphic configurations of vertical external walls.