Effect of Clay Amounts on Morphology and Mechanical Performances in Multiscale PET Composites

This work presents an investigation of the properties of poly(ethylene terephthalate)/glass fibers/nanoclay multiscale composites. The aim is to demonstrate the effect of adding various clay amounts on the morphology and mechanical performances of multiscale PET composites. Multiscale composites were prepared by adding 0.5, 1.0, 3.0, and 5.0 wt% of Cloisite 15A montmorrillonite. Initially, a masterbatch of pure PET blended with 10 wt% of Cloisite 15A was obtained in a co-rotating twin screw extruder. The multiscale composites were then blended via mechanical mixing, and injection moulded by adding the masterbatch to the glass fibre reinforced matrix. The morphological and mechanical characterizations of all compounds are discussed. X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that the characteristic (001) peak of the nanocomposite obtained by extrusion (masterbatch) shifted to the lower angle region stating an intercalated structure. However, the subsequent injection moulding process changed the morphological structure of the multiscale nanocomposites reducing the basal distance mostly for small loadings of nanoclay. The addition of nanoclay to PET matrices increases the degree of crystallinity, the clay platelets possibly playing the role of nucleating agent, as revealed by DSC and FTIR. The time relaxation spectra broaden as seen by DMA, as the ratio of clay/polymer interfaces increases. The yield stress of composites with 0.5 and 1 wt% of C15A content are enhanced. For more than 3% of nanoclay, the yield stress decreases. The Young’s modulus is increased when adding nanoclay. Indeed, clay exfoliation was not attained, but the intercalated particle dispersion improved the stiffness properties of PET/glass fibers/nanoclay composites

Toward improvement of the properties of parts manufactured by FFF ( Fused Filament Fabrication) through understanding the influence of temperature and rheological behaviour on the coalescence phenomenon

In this paper, the printing temperature ranges of PLA and PEEK, two semi-crystalline thermoplastics, have been investigated for the Fused Filament Fabrication (FFF) process. The printing range, comprised between the melting temperature and the degradation of each polymer, is 160°C to 190°C for PLA and 350°C to 390°C for PEEK. The complex viscosity has been measured for both polymers within the printing range. The kinetics of coalescence has been registered by measuring the bonding length between two filaments of the same polymer according to the temperature. At 167°C, the filaments of PLA reached the maximum value of bonding length. For PEEK, the filaments reached the maximum value of bonding length at 380°C. For the both materials, the final height of the filament is 80% of the initial diameter. The comparison of the obtained results with experimental study and predictive model shows a good agreement when the polymer is totally in fusion state

Probing wettability alteration of boron nitride surface through rheometry

While the surface of many ceramic particles is covered by positive and negative species, boron nitride displays no charge on the surface. Nevertheless, the interest in boron nitride is rising: Little materials combine electrical insulation and high thermal conductivity; both properties are required for many applications, for instance, in electronic devices and sensors. Hydroxyl (−OH) groups are usually created on the surface to increase the hydrophilicity of particles. In this work, we compare four treatments to select the one that increases most significantly the hydrophilicity of hexagonal boron nitride platelets, that is to say, for which the most −OH groups are grafted on to the surface. The treated particles have been studied by SEM, FTIR, and XPS. Our results show that these techniques are not appropriate to probe slight chemical changes. Indeed, hydroxyl groups are more likely introduced on the edges of the platelets. The highest hydroxyl concentration corresponds to 2.4% of boron atoms functionalized. The settling of low concentrated suspensions has been followed by optical visualization. Multiple light scattering was used for high concentrated suspensions. The rheological behavior of stable suspensions in water and isopropanol has been determined by transient flow and dynamic tests. Measuring the viscosity of suspensions appears as a way to evaluate the surface alterations of boron nitride. The method involving thermal treatment is the most efficient to increase the concentration of hydroxyl groups when the particles are suspended in water. The treatment with nitric acid seems to be the most efficient when the particles are suspended in isopropanol. Moreover, the thermal treatment is more environmentally friendly than using strong acids or bases. Hydroxylated particles can be used either as a starting material for further modification such as covalent functionalization or directly to prepare suspensions or polymeric based composites

Experimental investigation on the effect of nanostructuration on the adherence properties of epoxy adhesives by a probe tack test

In this work, we aimed to characterize the energy of adherence of nanoscale structured epoxy adhesives Diglycidyl ether of bisphenol-A/Methylene–diethylaniline(DGEBA/MDEA)induced by phase separation triblock copolymers Poly(MethacrylatedeMethyl)-b-Poly(ButylAcrylate)-b-Poly(MethylMethacrylate) (PMMA-b-PBA-b-PMMA) at gel state by a probe tack test,which is an original use of this kind of test for thermoset adhesives. For a set of mechanical parameters(probe’s roughness,contacttime,contact pressure and debonding velocity),we measured the energy of adherence for both neat and filled adhesives. The probe tack test was performed at different steps of gelation. We compared the behavior of the adhesives and evaluated the dissipation contribution to the energy of adherence of the adhesives during the test. We finally discussed the nanoparticles'influence on the competition between cavitation and fibrillation. We report that the addition of nanoparticles leads to an overall improvement of the energy of adherence, with a significant increase of the dissipation contribution to the energy measured

Étude et durabilité de solutions de packaging polymère d'un composant diamant pour l'électronique de puissance haute température

Les besoins en électronique de puissance, de plus en plus exigeants, ont motivé des recherches à l'échelle mondiale sur d'autres matériaux tels que le diamant comme remplaçant du silicium. Nos travaux de recherche sont plus spécifiquement axés sur la définition et la qualification de matériaux polymères capables de garantir l'intégrité des fonctions physiques de modules de puissance en environnement sévère. L'étude concerne la durabilité de candidats polymères à retenir pour le boîtier dont l'objectif est de protéger l'interrupteur de l'environnement extérieur. Suite aux choix des différents polymères étudiés, variables dans leur chimie et leur morphologie (amorphe ou semi-cristallin), un premier objectif scientifique est alors de chercher les relations structures/propriétés permettant de contrôler le procédé de mise en forme des polyimides semi-cristallins et d'en déduire les conditions requises à l'obtention de performances optimisées. Un second objectif a concerné la tenue des différents matériaux sélectionnés en vieillissements isothermes thermo-oxydatifs.Requirements in power electronics are more and more demanding about materials behavior in their operating conditions. This has motivated global scale researches about other materials replacing silicon such as diamond. This study is specifically focusing on the definition and qualification of polymer materials which could preserve physical functions of power modules in severe environments. This study focuses on the durability of several polymers used for the case. This later allows to protect the chip from external environment. The choice of different studied polymers which are dissimilar in chemistry and morphology (i.e. amorphous or semicrystalline) has been made in this study. Then, a first scientific goal was to search the structures/properties relations leading to the control of the manufacturing process of semicrystalline polyimides. A second goal concerned the mechanical strength evaluation of selected materials after thermo-oxidative isothermal ageing.TOULOUSE-INP (315552154) / SudocSudocFranceF

Multi-materials assemblies bonded by a copolymer-filled epoxy resin

In order to reduce the weight of embedded systems, we have to achieve innovative materials and new assembly process, such as adhesive bonding between different materials (metals, composites, polymers). The assemblies should ensure a good transfer of stress (thermal, mechanical) over a wide range of temperature. The choice of the adhesive will be the key to succeed. Within this context, we propose to add some copolymers to the adhesive, these latter allowing us to tune the viscoelastic properties of the adhesive. The copolymers also ensure a high thermal and mechanical stability for the adhesive, enabling its use at high temperature without degradation, and low temperature without brittleness. This study will allow us to further the understanding of the mechanisms which modulate adherence at the interface polymers/substrates, which are yet to be understood, as well as their physical and chemical properties

Influence of parameters controlling the extrusion step in fused filament fabrication (FFF) process applied to polymers using numerical simulation

Extrusion is one of the oldest manufacturing processes; it is widely used for manufacturing finished and semi- finished products. Moreover, extrusion is also the main process in additive manufacturing technologies such as Fused Filament Fabrication (FFF). In FFF process, the parts are manufactured layer by layer using thermoplastic material. The latter in form of filament, is melted in the liquefier and then it is extruded and deposited on the previous layer. The mechanical properties of the printed parts rely on the coalescence of each extrudate with another one. The coalescence phenomenon is driven by the flow properties of the melted polymer when it comes out the nozzle just before the deposition step. This study aims to master the quality of the printed parts by controlling the effect of the parameters of the extruder on the flow properties in the FFF process. In the current study, numerical simulation of the polymer coming out of the extruder was carried out using Computational Fluid Dynamics (CFD) and two phase flow (TPF) simulation Level Set (LS) method by 2D axisymmetric module of COMSOL Multiphysics software. In order to pair the heat transfer with the flow simulation, an advection-diffusion equation was used. Advection-diffusion equation was implemented as a Partial Differential Equation (PDE) in the software. In order to define the variation of viscosity of the polymer with temperature, the rheological behaviors of two thermoplastics were measured by extensional rheometer and using a parallel-plate configuration of an oscillatory rheometer. The results highlight the influence of the environment temperature and the cooling rate on the temperature and viscosity of the extrudate exiting from the nozzle. Moreover, the temperature and its corresponding viscosity at different times have been determined using numerical simulation. At highest shear rates, the extrudate undergoes deformation from typical cylindrical shape. These results are required to predict the coalescence of filaments, a step towards understanding the mechanical properties of the printed parts

Influence of the printing parameters on the stability of the deposited beads in fused filament fabrication of poly(lactic) acid

Fused Filament Fabrication (FFF) is one among a wide variety of processes of Additive Manufacturing. Similar to the others, FFF enables freeform fabrication and optimized structures, from. The aim of this work is to optimize the printing conditions in the FFF process based on reliable properties: printing parameters and physical properties of the polymer. The chosen polymer is poly(lactic) acid (PLA), a biodegradable thermoplastic polyester derived from corn starch and, as one of the most common polymers in the FFF process. the maximum inlet velocity of the filament in the liquefier is empirically determined according to process parameters such as the feed rate, the nozzle diameter and the dimensions of the deposited segment. Then, the rheological behavior of poly(lactic) acid including the velocity field, the shear rate and the viscosity distribution in the nozzle are determined by analytical study and numerical simulation. Our results show the variation of the shear rate according to the diameter of the nozzle and the inlet velocity. The shear rate reaches its maximum value for high inlet velocity and smaller diameters, near the internal wall. The distribution of the viscosity is obtained along the radius of the nozzle. For high inlet velocity, some defects appear at the surface of the extrudates. At highest shear rates, the extrudates undergo severe deformation microscopy. These results are valuable for choosing the printing parameters ( in order to improve the quality of the manufactured parts

Étude de l’adhésion fibre/matrice d’un matériau composite expansé lors du moussage

Dans une optique d’allégement des structures, les polymères et matériaux composites à matrice organique expansés font leur apparition dans l’industrie. Cependant, leur optimisation est plus complexe que celle de leurs homologues denses, car il faut obtenir une adéquation entre les réactions de polymérisation du polymère et de moussage de l’agent gonflant. De plus, une bonne adhésion fibre/matrice est nécessaire pour obtenir des structures homogènes en termes de répartition et de diamètre de porosités. Une mauvaise adhésion des fibres peut être responsable d’une nucléation hétérogène du polymère, avec l’apparition de grosses porosités, responsables d’une diminution des propriétés mécaniques du matériau

Boron nitride inclusions within adhesive joints: Optimization of mechanical strength and bonded defects detection

Non Destructive Testing (NDT) by active InfraRed Thermography (IRT) of bonded Carbon Fibers Reinforced Plastic (CFRP) laminates is a very challenging issue. Adding Boron Nitride (BN) particles within the joint material provides an interesting solution to better capture bonding defects. Though increasing additives leads to the improvement of NDT, the validation of this solution requires the mechanical characterization of the new joint material. In this way, the influence of particles on the mechanical properties of the adhesive joint is first investigated via double strap lap shear tests for different BN volume fraction. At the same time, controlled size void inclusions are generated within composite assemblies in order to evaluate the IRT ability to detect bonded defects inside BN-based adhesives. It is demonstrated that thermal data post-processing methods such as Singular Values Decomposition (SVD) and Principal Component Thermography (PCT) help to get the best trade-off be­ tween mechanical performance and defect detection