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

Obtenção e caracterização de compósito sanduíche de poliamida 11 e fibra de juta

Aliando boas propriedades mecânicas e de isolação térmica. Para isso, a poliamida 11 (PA 11) foi utilizada como matriz e a fibra de juta, como reforço. A PA 11 é um polímero termoplástico de origem renovável, fabricado a partir de óleo de mamona, conhecida por suas propriedades contra agentes químicos. A fibra de juta é a segunda fibra natural mais cultivada no mundo e é igualmente barata. O material compósito sanduíche foi criado a partir de uma termoprensa. A malha de juta foi utilizada pré-impregnada de PA 11 em alguns casos. Diversos compósitos foram criados, variando-se a pressão, tempo e temperatura. Após a caracterização, notou-se um aumento do módulo em flexão, tensão em flexão e módulo de Young de todos os compósitos em relação à uma referência, a pré-impregnação da juta também resultou em maior rigidez dos compósitos. O compósito sanduíche apresentou ganhos de no mínimo 3 vezes em tensão na flexão máxima em comparação à referência, e módulo em flexão teve também um aumento dessa proporção, mostrando que o compósito é promissor

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

Mise en forme de composites carbone/PEEK dans le domaine caoutchoutique

Les matériaux composites à matrices thermoplastiques renforcées de fibres longues sont étudiés de manière intensive pour leur introduction dans les prochaines générations de pièces structurales aéronautiques. Par ses performances thermomécaniques, l’unidirectionnel carbone/PEEK apparait comme un candidat possible, toutefois les procédés actuels de formage ne semblent pas en mesure de réaliser des pièces épaisses avec ce matériau. Ce travail a pour objectif de proposer un procédé innovant capable de réaliser des pièces composites carbone/PEEK épaisses de types cornières structurales en L ou en U. Le coeur du concept est la réalisation de l’étape de mise en forme dans le domaine caoutchoutique pour favoriser le glissement inter-plis et éviter ainsi la formation de défaut de type plissement quelle que soit l’épaisseur. Dans un premier temps, la fenêtre de processabilité adaptée à l’obtention d’une préforme a été définie en se basant sur les propriétés physiques de la matrice PEEK. Puis, la santé matière et les performances des pièces réalisées par ce nouveau procédé ont été mesurées, la comparaison à des pièces obtenues par un procédé conventionnel de formage valide le procédé proposé

Effect of interfacial crystalline growth on autohesion of PEEK

This work aims to clarify the role of the crystalline growth on the autohesion strength of amorphous PEEK below its melting temperature. The self-bonding strength versus temperature, pressure and time has been measured by lap shear test on 250-micron thick amorphous PEEK assembled at various conditions. The effect of the crystalline growth on the adhesion strength has been established at 155°C, 200°C and 250°C. Autohesion is temperature dependent, whereas pressure at less than 1 MPa and time up to 3 h, have less impact on the adhesion strength. Nevertheless, the evolution of the crystalline morphology with time results in increasing the interfacial strength: a gain of 40% is noticed between 1 and 3 h at 250 °C to reach 0.9 MPa. The degree of crystallinity is higher at the interface than elsewhere in the material, the interface acting as nucleating agent. The evolution of the crystalline morphology at the interface with time shows the refinement of the primary lattice when the temperature is higher than or equal to the previous crystallization temperature, corresponding to the highest temperature seen by the polymeric material. The crystalline growth has an ambivalent effect on the autohesion of PEEK: it reduces the mobility of the macromolecular chains and thus their interdiffusion through the interface and at the same time, it is observed that the improvement of its crystal lattice reinforces the interfacial strength

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

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

Laser transmission welding as an assembling process for high temperature electronic packaging.

Higher efficiency, power density, reliability and longer lifetime of power electronic devices would stem from progresses in material science. In this work, we propose to use a high performance thermoplastic polymer PAEK as packaging box to extend the operating temperature above 200°C. More, the laser transmission welding process has been applied to PAEK to join the two-part module. In order to validate this assembling process, the temperature distribution inside the specimens was measured during laser transmission welding. The assembly consists of a quasi-amorphous sample as the upper part and a semi-crystalline sample as the lower part. The temperature fields were measured by infrared thermography with the camera sensor perpendicular to the welded interface. With an energy beam of 28 J.mm-2 and irradiation time of 15 s, we have noticed that the maximum temperature inside the sample is kept far from the PAEK degradation one. Moreover, the temperature at the interface reaches the melting temperature thus assuring enough mobility for polymeric chains to get adhesion at the interface. The location and size of the heat-affected zone has been determined. Finally, some frames were machined and successfully welded

Friction, acoustic emission, and wear mechanisms of a PEKK polymer

The tribological behavior of a steel/PEKK ball-on-flat contact was studied regarding the load, the velocity and the sliding distance in reciprocating or unidirectional motion. The friction measurements were synchronized with an acoustic emission (AE) device. The results show a behavior change associated with an adiabatic effect on the polymer when the mechanical energy input increases. Two interfacial mechanisms are also characterized: Schallamarch ridges and longitudinal ploughings. These mechanisms are related to two AE frequencies of 0.2 MHz and 1 MHz. The discussion on these two AE populations brings a stronger analysis and completes the friction and the wear mechanisms results