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The purpose of hybridization is to obtain a new material preserving advantages from all of its constituents. Hybridization offers intermediate properties respect to the original materials, by creating a balance effect within the fibres incorporated in the composite materials and leading to a composite with more tailored behaviour The increasing need to mitigate the environmental impact of synthetic fibres and polymers is promoting the use and application of natural materials orienting the research toward the development of biodegradable systems. In this framework, hybrid reinforced laminates with flax and basalt twill layers alternatively stacked, were manufactured by resin infusion fabrication technology and impacted at low velocity to investigate their dynamic behaviour, in an attempt to couple the impact resistance of basalt fibres with the environmentally friendly nature of flax fibres. For comparison purposes, the same experimental characterization has been performed on laminates reinforced with only basalt or flax fibres. The experimental results confirmed the positive role played by fibre hybridization in terms of damage. The Electronic Speckle Pattern Interferometry technique was adopted to analyze the internal damage and to provide information on the shape and the extent of the delamination, that was found concentrated under the impactor-material contact point for the basalt and flax/basalt laminates.

In an attempt to increase the low-velocity impact response of natural fiber composites, a new hybrid intraply woven fabric based on flax and basalt fibers has been used to manufacture laminates with both thermoplastic and thermoset matrices. The matrix type (epoxy or polypropylene (PP) with or without a maleated coupling agent) significantly affected the absorbed energy and the damage mechanisms. The absorbed energy at perforation for PP-based composites was 90% and 50% higher than that of epoxy and compatibilized PP composites, respectively. The hybrid fiber architecture counteracted the influence of low transverse strength of flax fibers on impact response, irrespective of the matrix type. In thermoplastic laminates, the matrix plasticization delayed the onset of major damage during impact and allowed a better balance of quasi-static properties, energy absorption, peak force, and perforation energy compared to epoxy-based composites.

Hydrophobic surfaces are highly desired for several applications due to their exceptional properties such as self-cleaning, anti-icing, anti-friction and others. Such surfaces can be prepared via numerous methods including plasma technology, a dry technique with low environmental impact. In this paper, the effect of a one-step sulfur hexafluoride (SF6) plasma treatment upon the low velocity impact behavior of basalt/epoxy composites has been investigated by using several characterization techniques. A capacitive coupled radiofrequency plasma system was used for the plasma surface treatment of basalt/epoxy composites, and suitable surface treatment conditions were experimentally investigated with respect to gas flow rate, chamber pressure, power intensity, and surface treatment time by measuring the water droplet contact angle of treated specimens. The contact angle measurements showed that treating with SF6 plasma would increase the hydrophobicity of basalt/epoxy composites, moreover, the impact results obtained on reinforced epoxy basalt fiber showed damage in a confined area and higher impact resistance for plasma-treated basalt systems.

Basalt-epoxy laminates are establishing gradually in engineering sectors due to increasing attention toward environmental matters. Some properties should be improved to extend their applications and the cold spray (CS) metallization provides a potential solution. Unfortunately, the fragile nature of thermosetting polymers makes it difficult the CS coating formation and grow-up. Therefore, this research work aims to study an innovative solution able to enhance the adhesion mechanisms between the cold sprayed metal particles and the thermosetting polymer-based substrates. For this purpose, an original manufacturing method that provides the surface PLA treatment for thermosetting samples was developed. AlSi10Mg particles were cold sprayed on the treated surface, and the low-velocity impact behaviour of the metallised hybrid structures was analysed in details. The outcomes prove the effectiveness of the method proposed on the deposition process and the beneficial effects of metallization on impact damage mechanisms.

Metal nanoparticles (NPs) were prepared from acrylamide complex of iron and nickel nitrates by controlled thermolysis at constant temperature in a self-generated atmosphere and used to fabricate epoxy resin nanocomposites. X-ray diffraction performed on the nanoparticles revealed a metal core/polymeric shell structure for the nanoparticles thermolysed at higher temperature as also confirmed by cross analysis of thermo-gravimetrical and vibrating magnetometer data. Optical microscopy was used to investigate the achieved dispersion of the nanoparticles within the uncured resin and transmission electronic microscopy was used to analyse the morphology and the average dimensions of the nanoparticles. Thermal stability of manufactured nanocomposites was studied by thermo-gravimetric analysis in inert and oxidative conditions, reporting that negligible variations are induced by the presence of nanofillers. A complete thermo-mechanical and fracture characterization was carried out to assess the effect of nanoparticles on final nanocomposite system. A slight increase of the modulus is recorded at room temperature whereas a significant variation is induced for higher temperature. The presence of nanoparticles induces a global increase in the fracture energy of nanocomposite associated to different failure mechanisms. Magnetic data indicate that iron particles based nanocomposites display room-temperature ferromagnetic behaviour with saturation magnetization and coercivity depending on the diameter of the metal core.

Confinement and surface effects provided by nanoparticles have been shown to produce changes in polymer molecules affecting their macroscopic viscosity. Nanoparticles may induce rearrangements in polymer conformation with an increase in free volume significantly lowering the viscosity. This phenomenon is generally attributed to the selective adsorption of the polymer high molar mass fraction onto nanoparticles surface when the polymer radius of gyration is comparable to the nanoparticles characteristic dimensions. Carbon nanotubes seem to be the ideal candidate to induce viscosity reduction of polymer due to both their high surface-to-volume ratio and their nanometric sizes, comparable to the gyration radius of polymer chains. However, the amount of nanotube in a polymer system is limited by the percolation threshold as, above this limit, the formation of a nanotubes network hinders the viscosity reduction effect. Based on these findings, we have used multiwalled carbon nanotubes MWCNT "aggregates" as viscosity reducers. Our results reveal both that the use of nanotube clusters reduce significantly the viscosity of the final system and strongly increase the nanotube limiting concentration for viscosity hindering. By using hydroxyl and carboxyl functionalized nanotubes, this effect has been rather maximized likely due to the hydrogen bridged stabilization of nanotube aggregates.

SUMMARY The fire behavior and the smoke emission of an unsaturated polyester resin modified by the addition of three phosphorus-based fire-retardant materials (ammonium polyphosphate (APP), silane-coated APP, and melamine pyrophosphate) at two concentration levels (20% w/w, 35% w/w) have been investigated. Scanning electron microscopy, Fourier transform infrared spectroscopy and optical microscopy analysis have been performed to verify the dispersion and the action mechanism of additives within the resin. Results from cone calorimetric tests demonstrated that the incorporation of the fire retardants at 35% w/w has a strong effect on flammability and smoke suppressant properties with respect to both the neat resin and the loaded systems at 20% (w/w). In particular, the smoke formation and smoke parameters are reduced by 50% and 80%, respectively, leading to the conclusion that APP can be used single-handedly without combination with specific smoke suppressors. Copyright © 2011 John Wiley & Sons, Ltd.

Shape memory alloy (SMA) elements embedded in a structure allow to control the structural properties, thanks to their coupled thermo-mechanical behavior. In this study, the manufacturing and the shape control abilities of glass fiber/polyester resin SMA hybrid composites (SMAHCs) were experimentally investigated. Mechanical and calorimetric characterizations of SMA were carried out and correlated to the thermo-mechanical behavior of the SMAHC. The SMAHC was manufactured by the Vacuum Infusion Process that uses dry fibers and liquid matrix for the composite production. A polyester resin having a curing temperature lower than the SMA Austenite transition temperature was chosen as matrix, so a blocking system for the SMA wires was not needed during the cure. The thermo-mechanical behavior of the SMAHC was investigated by monitoring the shape change of the plate during heating of the embedded wires. The results give some indications on the appropriate characterization and choice of materials for SMAHC manufacturing.

Smoke is considered to be the main hazard of fires involving epoxy resins but its production depends on many variables, principally the chemical character and the burning rate of the polymer plus the availability of oxygen. The work reported aimed to study the smoke suppressant effect and flammability performance of zinc-based compounds (FR system) in epoxy matrix composites used in the aerospace and aeronautical industry. The flammability performance of neat and FR-loaded systems was screened using microcombustion calorimetry, while smoke generation, in terms of carbon monoxide (CO) and carbon dioxide (CO2) production, was analysed under dynamic conditions using cone calorimetry. Final results indicate that the dispersion of zinc borate and zinc hydroxystannate (ZHS) into epoxy matrices leads to a significant variation in flame retardant properties reducing both total heat release by about 25 and 30%, respectively, and heat release capacity by about 30 and 50%, respectively. The system containing ZHS shows an enhancement in all smoke suppressant properties; both tin compounds (zinc stannate (ZS) and ZHS) give a reduction of CO2/CO ratio from 41 to 25 for ZS and from 41 to 36 for ZHS compared to neat matrix. Copyright © 2010 Society of Chemical Industry

Flame behaviour is a fundamental requirement for advanced aerospace composites. In this work, a commercial, low-viscosity epoxy system, typically used in liquid infusion composite processes, and its mixtures with three different zinc-based flame retardants (ZB, ZS, ZHS) at different weight percentages has been investigated by cone calorimetry and thermogravimetric analysis. Cone calorimetry has been performed to verify the flame retardancy effects induced by each filler composition. Nevertheless manufacturability issues require the evaluation of the rheological changes induced by filler on the unloaded matrix system. Rheological tests have been, therefore, performed to identify the maximum concentration of filler. Based on these results thermogravimetric tests have been performed to investigate thermal degradation kinetics of selected systems. The feasibility of Kissinger and Flynn-Wall-Ozawa method for the determination of characteristic degradation kinetics parameters has been evaluated and results were analysed. A simplified decomposition model was assumed to analyse epoxy degradation behaviour; it was found that this model gives appreciable matching with experimental TGA curve trend for neat epoxy whereas for the filled compounds additional stages were assume to occur.

The consolidation of a polymer-based composite part is usually accompanied by the build-up of the stresses and deformations that are caused mainly by the polymer matrix shrinkage, the resin rheological and mechanical properties changes associated with the advancement of the cure reaction and by the material properties mismatch of the system constituents, mold, fibers reinforcement, and thermoset resin. These process-induced residual stresses and strains are obviously undesired phenomena that should be avoided leading to low performance, shape distortions, warpage, matrix cracks, and delaminations. Therefore, the optimization of the manufacturing cycle coupled to the capability to predict and measure the processing residual stress and strains represent important issues to be addressed. In this work, after a preliminary introduction on the most relevant mechanisms inducing the formation of stresses and strains in polymer-based composite parts, the most recent advances both in the modeling of the cu...

As-received and pre-treated sepiolite/epoxy systems, characterised by an inorganic content from 2 to 10 wt.%, were investigated in order to assess induced-filler effect on degradation and fire behaviour. Thermogravimetrical results show that the thermal stability of the hosting epoxy, is slightly affected by the presence of sepiolite for both typologies; whereas, changes induced in char morphology by the pre-treated clay will significantly affect the fire behaviour of the final nanocomposite. Modelling of thermo-gravimetrical results in air atmosphere, by means of Kissinger procedure, shows a noteworthy reduction of activation energies associated with each degradation steps, especially at highest sepiolite content either by using as-received and pre-treated inorganic filler. This substantially indicates that the presence of sepiolite shorten the whole degradation process on the temperature scale. On the other hand, the different morphology of the char layer during the burning process can have relevant flame retardant effects acting on both condensate and vapour phase. Analysing the cone calorimetric data, a reduction of about 27% of the peak of heat release rate for the highest sepiolite percentage is measured and the burning total period is increased thus confirming that sepiolite when pre-treated represents a valid fire retardant inorganic filler for such a system.

The cure kinetics of an epoxy–amine commercial thermoset system have been investigated with the isothermal differential scanning calorimetry technique. In particular, a kinetic study has been performed in the glass–transition zone, in which diffusion phenomena compete with the chemical transformations and the overall reaction rate is partially slowed by the reduced segmental chain mobility. A generalized form of the Vogel equation has been formulated to account for the effect of the increasing glass–transition temperature on the chain mobility and, therefore, on the overall reaction rate. The kinetic model has been expressed with two factors representing the chemical reaction rate and the segmental mobility reduction. As the main result, the activation energy relative to the diffusion phenomena has been found to be very low, having a value of 42.5 K ≈ 0.356 kJ/mol, which is compatible only with the small-angle rotation of the reactive unit. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3757–3770, 2002

In resin transfer molding (RTM) process, a polymer composite part is fabricated by injecting a thermoset resin into a fiber preform placed in a closed mold cavity. After the infiltration of the resin into the empty spaces in the mold, the manufacturing process is characterized by a curing reaction, which is an exothermic resin polymerization phenomenon that cross-links the resin and results in a solid structure. In most cases, the resin cure is initiated by heating the mold. The heat released during the reaction can cause temperature gradients in the composite, which leads to residual stresses in the part. Residual stresses are undesirable as they can cause shrinkage and warpage. By controlling the temperature of the mold walls, one can control the cure reaction and reduce the thermal gradients through the composite part. In this paper, we present a methodology based on scaling analysis of the energy balance equation to manage the heat generated by the cure reaction that minimizes the temperature gradients before the resin solidifies. The method capability is demonstrated with a highly reactive polyester resin infiltrated into different types of glass fiber preforms in a rectangular mold.

Summary An high resolution optical technique based on the film fiber optic refractometer has been used to investigate the effect of the thickness on the glass transition dynamic of Atactic Polystyrene films in the range 20–120 nm. The thermo-optic behavior of a set of layers dip coated onto the fiber has been analyzed upon cooling from long term equilibrated melt state. The glassy transition temperature is observed to be thickness-independent as did both the width and the lower and upper bounds of the transition itself. At lowering the thickness of the film the relevant effect is the reduction of the “contrast” between the melt equilibrium phase and the glassy state. A double layers model where a surface soft layer (3.9 nm at 418 K) do not contribute to the glass dynamic retaining liquid features even at temperature well below the glass transition, while the core layer shows a bulk glass transition, is able to quantitatively reproduce reflectance experimental data.

Despite the use of toxic and not environmentally-friendly chemicals, some proteins derived from animal or microbial sources have been investigated as novel green flame retardants for cotton fabrics. In particular, phosphorus- and sulphur-rich proteins (i.e. caseins and hydrophobins) have been homogeneously deposited on cotton fabrics starting from protein aqueous suspensions/solutions. These surface treatments, based on the use of species able to favour the dehydration of cellulose instead of its depolymerization, have strongly enhanced the production of a thermally stable carbonaceous structure (char), hence significantly enhancing the flame retardancy of the fabrics, as assessed by thermogravimetry and flammability tests. (C) 2013 Elsevier Ltd. All rights reserved.

Sepiolite/epoxy systems, characterised by an inorganic content from 2% to 10% by weight, were tested by using different experimental techniques in order to assess the effects thermo-mechanical and fracture behaviour. It was found that filler dispersion is independent on the type of sepiolite used, i.e. hydrated and de-hydrated, whereas the addition of hydrated sepiolite strongly increases the viscosity of the final suspension. Mechanical properties have been investigated and discussed. The conservative modulus of the sepiolite/epoxy system increases as much as 21% and 94% respectively, at 35 °C and 200 °C respect to the unfilled polymer, with the incorporation of 10 wt% of sepiolite, both hydrated and dehydrated, with a slightly increasing of the corresponding glass transition temperature. The effect of sepiolite on the coefficient of thermal expansion lead to a variation in both glassy and rubbery region, respectively of about 7–8% and 9%. Fracture toughness analysis revealed that the critical stress intensity factor negligibly changes by increasing the sepiolite content, whereas the critical strain energy release rate (GIC) reaches an noteworthy value around 30% higher than neat epoxy.

Polymer nano-composite matrix could be the ideal solution for a new generation of composite materials. The continuous demand for new high performance polymer composite for various applications, in different industrial sectors, has lead many researchers to investigate the potential use of the carbon nanotubes (CNTs) as nano-reinforcements of polymer matrix for the manufacturing of traditional laminate composite. CNTs have attracted considerable attention due to their unique mechanical, surface, multifunctional properties and strong interactions with the hosting matrix mainly associated to their nano-scale features. CNTs’ impressive mechanical properties, with stiffness and strength values falling within the range of 100-1000 GPa and 2.5-3.5 GPa, respectively, make them ideal candidates to develop novel composites characterized by advanced polymer matrices (Treacy, 1996). Despite the enormous amount of experimental data available in literature (Coleman et al. 2006, Thosterston et al., 2003), there are still controversial results concerning elastic property, strength and fracture toughness; moreover, due to inherent difficulties in processing these unconventional nanostructure as nano-fillers in polymer system, a reliable theoretical correlation of the experimental data is still in shadow. Different approaches to build an appropriate theory for predicting reinforcement efficiency of CNTs within an hosting matrix have been presented in the literature.Indeed, the reinforcement capability of carbon nanotubes in a polymeric matrix will depend on their amount, but, undoubtedly, their arrangement within the hosting medium plays a fundamental role in the load transfer mechanism. For this reason, the state and level of dispersion need to be accounted in any attempt for predicting the mechanical behaviour of the final nano-composite system. In literature the enhancing reinforcement of CNT loading for the Young’s modulus is commonly reported. However, at the same time, discrepancy among the different data is highlighted. Therefore, an important issue for modelling purpose is the lack of a reliable database for this property. Characterization and structure-properties of nano-mechanics modelling research have shown that enhancement in mechanical properties of nano-composites are strongly

A hybrid configuration at the micromechanical level is presented and described as a suitable approach to enhance the damping features of advanced polymer composites. A micro-level hybridization was achieved on dry preform reinforcements by embedding visco-elastic fibres within standard carbon tows. Unidirectional composites with two viscoelastic volume fractions (2.5% and 5% vol/vol) were manufactured by a vacuum infusion process and later tested by dynamic mechanical analysis along the principal directions. Final results reveal a significant enhancement (+80% and +56%) of the damping properties, respectively, for the longitudinal and the transverse directions in the case of the highest viscoelastic fibre content. In turn, the elastic properties of the final composite were greatly reduced (−37% and −35%) with respect to the standard composite. Final results support further work in the direction of micromechanical hybridization looking at the potential exploitation of standard textile configurations with different viscoelastic fibre content to enhance damping properties.

Composites of carbon nanotubes (CNT) in polymeric matrices have attracted considerable attention in the research communities due to their good electrical conductivity, high stiffness and high strength at relatively low CNT contents. Effective utilization of CNT in composites depends primarily on the ability to disperse them homogeneously throughout the polymer matrix, avoiding the formation of bundles due to van der Waals interactions existing between the nanotubes. In this work composites of polystyrene at various percentages of SWNT were fabricated using Latex Technology technique, a polymer type-independent method based on using a surfactant as a dispersing agent. An electrical characterization of SWNT composites was performed both in DC and AC modes. From the analysis of DC data a percolative behavior was found for the conductivity as function of SWNT content. The innovative contribution of this work consists in the modeling of the composite material upon its electrical properties. AC measurements and the analysis of impedance as function of angular frequency lead to the formulation of an equivalent circuit able to model the composite material in correspondence of the percolative threshold. Copyright © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.

Gas and water vapour transport properties are of main concern in evaluating the suitability of a polymeric material to be used as a protective for monuments. In this work, oxygen, carbon dioxide and water vapour transport properties have been investigated for a new class of polymers, fluorinated polyurethanes, which have been recently proposed as a protective material for stone monuments. They consist of block copolymers made of hydrophilic polyurethane and hydrophobic perfluoropolyether blocks. The properties of these copolymers are expected to be strongly related to the relative amounts of these two blocks.