Polyamide from lactams by reactive rotational molding via anionic ring-opening polymerization: Optimization of processing parameters

A reactive rotational molding (RRM) process was developed to obtain a PA6 by activated anionic ring-opening polymerization of epsilon-caprolactam (APA6). Sodium caprolactamate (C10) and caprolactam magnesium bromide (C1) were employed as catalysts, and difunctional hexamethylene-1,6-dicarbamoylcaprolactam (C20) was used as an activator. The kinetics of the anionic polymerization of !-caprolactam into polyamide 6 was monitored through dynamic rheology and differential scanning calorimetry measurements. The effect of the processing parameters, such as the polymerization temperature, different catalyst/activator combinations and concentrations, on the kinetics of polymerization is discussed. A temperature of 150°C was demonstrated to be the most appropriate. It was also found that crystallization may occur during PA6 polymerization and that the combination C1/C20 was well suited as it permitted a suitable induction time. Isoviscosity curves were drawn in order to determine the available processing window for RRM. The properties of the obtained APA6 were compared with those of a conventionally rotomolded PA6. Results pointed at lower cycle times and increased tensile properties at weak deformation

Elucidating the crystal-chemistry of Jbel Rhassoul stevensite (Morocco) by advanced analytical techniques

The composition of Rhassoul clay is controversial regarding the nature of the puremineral clay fraction which is claimed to be stevensite rather than saponite. In this study, the raw and mineral fractions were characterized using various techniques including Fourier transform infrared spectroscopy and magic angle spinning nuclear magnetic resonance (MAS NMR). The isolated fine clay mineral fraction contained a larger amount of Al (>1 wt.%) than that reported for other stevensite occurrences. The 27Al MAS NMR technique confirmed that the mineral is stevensite in which the Al is equally split between the tetrahedral and octahedral coordination sites. The 29Si NMR spectrum showed a single unresolved resonance indicating little or no short-range ordering of silicon. The chemical composition of the stevensite from Jbel Rhassoul was determined to be ((Na0.25K0.20 (Mg5.04Al0.37Fe0.20&0.21)5.61(Si7.76Al0.24)8O20(OH)4). This formula differs from previous compositions described from this locality and shows it to be an Al-bearing lacustrine clay mineral

Accelerated hardening of nanotextured 3D-plotted self-setting calcium phosphate inks

Direct ink writing (DIW) techniques open up new possibilities for the fabrication of patient-specific bone grafts. Self-setting calcium phosphate inks, which harden at low temperature, allow obtaining nanostructured scaffolds with biomimetic properties and enhanced bioactivity. However, the slow hardening kinetics hampers the translation to the clinics. Different hydrothermal treatments for the consolidation of DIW scaffolds fabricated with an a-tricalcium phosphate /pluronic F127 ink were explored, comparing them with a biomimetic treatment. Three different scaffold architectures were analysed. The hardening process, associated to the conversion of a-tricalcium phosphate to hydroxyapatite was drastically accelerated by the hydrothermal treatments, reducing the time for complete reaction from 7¿days to 30 minutes, while preserving the scaffold architectural integrity and retaining the nanostructured features. ß-tricalcium phosphate was formed as a secondary phase, and a change of morphology from plate-like to needle-like crystals in the hydroxyapatite phase was observed. The binder was largely released during the treatment. The hydrothermal treatment resulted in a 30% reduction of the compressive strength, associated to the residual presence of ß-tricalcium phosphate. Biomimetic and hydrothermally treated scaffolds supported the adhesion and proliferation of rat mesenchymal stem cells, indicating a good suitability for bone tissue engineering applications. Statement of Significance 3D plotting has opened up new perspectives in the bone regeneration field allowing the customisation of synthetic bone grafts able to fit patient-specific bone defects. Moreover, this technique allows the control of the scaffolds’ architecture and porosity. The present work introduces a new method to harden biomimetic hydroxyapatite 3D-plotted scaffolds which avoids high-temperature sintering. It has two main advantages: i) it is fast and simple, reducing the whole fabrication process from the several days required for the biomimetic processing to a few hours; and ii) it retains the nanostructured character of biomimetic hydroxyapatite and allows controlling the porosity from the nano- to the macroscale. Moreover, the good in vitro cytocompatibility results support its suitability for cell-based bone regeneration therapiesPeer ReviewedPostprint (author's final draft

Rhéologie aux interfaces des matériaux multicouches à base de polymères fonctionnels: application au procédé rotomoulage

Le procédé de rotomoulage prend un nouvel essor grâce aux possibilités de mettre en forme des matériaux multicouches à haute valeur ajoutée. Une étude générique a été menée pour une meilleure maîtrise de ce procédé. Ce travail a pour objectif l'étude des interactions matériau/procédé en vue d'optimiser le rotomoulage des multicouches qui demeure assez complexe. Le comportement rhéologique à l'état fondu des multicouches a été étudié par spectrométrie mécanique dynamique. La compétition entre l'interdiffusion polymère/polymère et la réaction interfaciale dans une structure sandwich a été ainsi évaluée. Les propriétés structurales des matériaux ont été reliées aux comportements rhéologiques qui permettent de prédire les conditions de mise en œuvre. L'influence de différents paramètres liés au procédé (température, temps de contact, cisaillement, temps de séjour, aire interfaciale...) a été étudiée. En outre, la détermination expérimentale de la tension interfaciale a permis d'estimer, via des modèles thermodynamiques, l'épaisseur de l'interphase ainsi créée. L'épaisseur de cette même interphase est reliée à son tour aux propriétés adhésives du système bicouche. Les résultats expérimentaux ont été confrontés aux modèles décrivant le comportement rhéologique des systèmes multiphasiques. Ainsi, nous proposons l'utilisation d'une expression de l'évolution du module de conservation élastique en fonction du temps de contact. Les manifestations observées et les résultats trouvés ont été analysés en se basant sur les mécanismes physico-chimiques mis en jeu. Outre son aspect fondamental, cette étude a permis également l'optimisation des conditions de mise en œuvre en relation avec les propriétés finales des systèmes multicouches réactifs

Relation structure/procédé/propriétés finales de matériaux élaborés par rotomoulage

L'objectif de ce travail est d'établir des relations entre la structure du polymère, les paramètres du procédé et les propriétés finales. Tout d'abord, une caractérisation approfondie du matériau nous a permis de relier sa structure moléculaire avec ses propriétés rhéologiques. Ensuite, le phénomène de coalescence a été modélisé en utilisant une méthode originale pour mesurer l'énergie de surface du polymère à l'état fondu. Enfin, les défauts et propriétés des pièces rotomoulées avec la machine de laboratoire ont été analysés (bulles, vagues, porosités, propriétés mécaniques) et mis en relation avec les propriétés du matériau et la cinétique de coalescence

Design of Artificial Neural Network-Based pH Estimator

Taking into consideration the cost, size and drawbacks might be found with real hardware instrument for measuring pH values such that the complications of the wiring, installing, calibrating and troubleshooting the system, would make a person look for a cheaper, accurate, and alternative choice to perform the measuring operation, Where’s hereby, a feedforward artificial neural network-based pH estimator has to be proposed. The proposed estimator has been designed with multi- layer perceptrons. One input which is a measured base stream and two outputs represent pH values at strong base and strong/weak acids for a titration process. The created data base has been obtained with consideration of temperature variation. The final numerical results ensure the effectiveness and robustness of the design neural network-based pH estimator

Chemo-rheological studies and monitoring of high-Tg reactive polyphtalamides towards a fast innovative RTM processing of fiber-reinforced thermoplastic composites

International audienc

Revealing the dynamic heterogeneity of PMMA/PVDF blends: From microscopic dynamics to macroscopic properties

An effort was made to demonstrate the dynamic heterogeneity of poly(methyl methacrylate) (PMMA)/poly(vinylidene fluoride) (PVDF) blends, where its composition dependence and the role of interphase were probed. Firstly, the composition dependence of thermorheological complexity of PMMA/PVDF blends in the melt was revealed. The molecular entanglement state involving intra- and interchain entanglements was found to govern the scenario of thermorheological complexity. Intriguingly, local heterogeneity was further demonstrated to exist in the melt-state blends with intermediate compositions, and its origin was depicted to be the interphase. The interphase, coupled with unfavourable interchain entanglements in those blends, could explain the reduced viscosity and speed-up relaxations, contributing to the overall thermorheological complexity. Besides, two experimental glass transition temperatures of blends were resolved in view of segment motions in the miscible phase and the crystal-amorphous interphase, and further assessed via the "self-concentration" concept. The presence of a crystal-amorphous interphase, likely leading to three distinct dynamics of segments in blends, was supposed to contribute to the dynamic heterogeneity in segment relaxations for PMMA/PVDF blends in the solid state. Lastly, effects of dynamic heterogeneity on dynamic mechanical properties were also evaluated

A thermodynamic approach to surface modification of calcium phosphate implants by phosphate evaporation and condensation

It has been reported in the literature that thermal treatment of calcium phosphate ceramics chemically alters the surface composition by phosphate evaporation. To predict the compositional changes, we have developed a thermodynamic model for the evaporation of phosphorous species from CPP, TCP, HA, and TetCP. In an open atmosphere, the model predicts the formation of a surface layer consisting of a sequence of increasingly phosphate-depleted phases. In a closed system, the atmosphere reaches equilibrium with a single-phase surface layer. To verify our model, we performed a series of experiments which confirmed the predicted formation of phosphate-depleted surface layers. These experiments further demonstrated that controlled supersaturation of the atmosphere led to formation of a phosphate-enriched surface layer as a result of phosphate condensation. In conclusion, our thermodynamic model is capable of predicting the surface modification by phosphate evaporation and condensation of calcium phosphate phases during high-temperature processing in different environments