Khalid Lamnawar

Rheological, Morphological and Mechanical Studies of Sustainably Sourced Polymer Blends Based on Poly(Lactic Acid) and Polyamide 11

The objective of this study was to gain a deep understanding of composition and compatibilization effects on the properties of entirely sustainably sourced polymer blends based on polylactide (PLA) and polyamide 11 (PA11). Generally, PLA cannot challenge regular commodity polymers due to its weak thermo-mechanical properties and its poor elongation properties. With this work, however, we present a promising route to overcome these drawbacks in order to enhance the processability of PLA: blending the polymer with various compositions of other ductile biopolymers such as PA11, as well as mixing PLA/PA11 blends with various amounts of a chain extender, Joncryl ADR®-4368, containing reactive epoxy functions, in a laboratory-scale twin-screw extruder. The effects on the rheological, morphological and mechanical properties were investigated. Results showed that a “self compatibilization” between PLA and PA11 chains can occur but it was found to be insufficient, contrary to recent work reported in the literature. The role of Joncryl as a compatibilizer for the PLA/PA11 system has been demonstrated by the significant decrease of particle size and interfacial tension as well as the improvement of ductile properties. Moreover, a new relaxation peak appeared in the relaxation spectrum, indicating the generation of a copolymer at the polymer-polymer interface.

A nonlinear shear and elongation rheological study of interfacial failure in compatible bilayer systems

This work aims to examine whether or not interfacial failure can occur in a compatible polymer bilayer system under large shear and elongation deformations, as well as to probe the sensitivity of nonlinear transient rheology to the presence of interface/interphase at neighboring layers. For this, stress relaxation after a step strain and fast startup in simple shear and uniaxial extension experiments have been performed on healed and coextruded poly(methyl methacrylate)/poly(vinylidene fluoride) bilayers with the presence of a robust diffuse interphase as evaluated by energy dispersive X ray. For unhealed bilayers, interfacial failure occurred in shear flows at intermediate deformations, while for healed bilayers the interphase greatly delayed the onset of interfacial failure to larger deformation steps and to a higher deformation rate in the startup shear. Extensional rheology demonstrated that the presence of an interphase in the bilayers greatly enhanced the transient extensional viscosity ηE+(t) as we...

Rheology at the Interface and the Role of the Interphase in Reactive Functionalized Multilayer Polymers in Coextrusion Process

Coextrusion technologies are commonly used to produce multilayered composite sheets or films for a large range of applications from food packaging to optics. The contrast of rheological properties between layers can lead to interfacial instabilities during flow. Important theoretical and experimental advances regarding the stability of compatible and incompatible polymers have, during the last decades, been made using a mechanical approach. However, few research efforts have been dedicated to the physicochemical affinity between the neighboring layers. The present study deals with the influence of this affinity on interfacial instabilities for functionalized incompatible polymers. Polyamide (PA6)/polyethylene grafted with glycidyl methacrylate (PE‐GMA) was used as a reactive system and PE/PA6 as a non reactive one. Two grades of polyamide (PA6) were used in order to change the viscosity and elasticity ratios between PE (or PE‐GMA) and PA6. It was experimentally confirmed, in this case, that weak disturban...

Reactive Functionalized Multilayer Polymers in Coextrusion Process

Coextrusion technologies are commonly used to produce multilayered composite sheets or films with a large range of applications. The contrast of rheological properties between layers can lead to interfacial instabilities during flow. Important theoretical and experimental advances have been made during the last decades on the stability of compatible and incompatible polymers using a mechanical approach. The present study deals with the influence of this affinity on interfacial instabilities for functionalized incompatible polymers between the neighboring layers. Polyamide (PA6)/Polyethylene‐grafted (GMA) or pure PE were studied with different viscosity and elasticity ratios. We have experimentally confirmed, in this case, that the weak disturbance can be predicted by considering an interphase of non‐zero thickness (corresponding to interdiffusion/reaction zone) instead of a purely geometrical interface between the two reactive layers. As a first step, rheological behavior of multilayer coextruded cast fil...

Hybrid RTM process: Monitoring and processing of composites based on reactive thermoplastic systems

In this work, hybrid process coupling “Reactive Extrusion” and “Resin Transfer Molding” machine (T-ERTM) equipped with an instrumented mold was designed and developed. Polyamides model matrix according to two kinds of polymerizations were studied as well anionic and chain extension reactions. For the former, different ratios of catalyst and activator were investigated. For the latter, various formulations of prepolymer with chain extender (CA) were studied at different stoichiometry ratios and temperatures. Since that both reaction kinetics are very fast to be monitored at short times by usual technics, the chemo-rheological evolutions were firstly studied ex-situ by coupling rheology with FTIR and dielectric spectroscopy (DRS). Secondly, the T-ERTM process with an “instrumented mold” was developed with specific dielectric sensors in order to in-situ track viscosity and reaction evolution. The in-situ results corroborate the ex-situ ones aforementioned. Overall, a processing window was obtained for each r...

Rheokinetic studies for in-situ monitoring of T-RTM process: Rheology coupled to dielectric analysis and FTIR spectroscopy

The goal of this work is to develop study and characterize the structural evolution of thermoplastic matrix during the thermoplastic Resin Transfer Molding process. To attain this objective, the reaction kinetic and its properties for forming process of PA-matrix were investigated as an alternative for the production of thermoset systems. Through this work, various formulations of PA with anionic polymerization from caprolactam were studied. Reaction kinetic were determined depending on processing parameters and chemistry. Besides, we present some promising routes to in-situ monitor the process of thermoplastic composites with tailored mechanical and physical properties. The dielectric analysis technique and FTIR spectroscopy was coupled to rheology and used to monitor the reaction versus time, temperature and the type of catalyst. Indeed we characterize both the structure and chemorheological properties of PA formulations. Based on the obtained results, the T-RTM cycle processing window for good impregnation of the fiber reinforcement were purposed as well the injection time, the reaction temperature and composition.The goal of this work is to develop study and characterize the structural evolution of thermoplastic matrix during the thermoplastic Resin Transfer Molding process. To attain this objective, the reaction kinetic and its properties for forming process of PA-matrix were investigated as an alternative for the production of thermoset systems. Through this work, various formulations of PA with anionic polymerization from caprolactam were studied. Reaction kinetic were determined depending on processing parameters and chemistry. Besides, we present some promising routes to in-situ monitor the process of thermoplastic composites with tailored mechanical and physical properties. The dielectric analysis technique and FTIR spectroscopy was coupled to rheology and used to monitor the reaction versus time, temperature and the type of catalyst. Indeed we characterize both the structure and chemorheological properties of PA formulations. Based on the obtained results, the T-RTM cycle processing window for good impregna...

Fundamental studies of interfacial rheology at multilayered model polymers for coextrusion process

Fundamental studies have been devoted to the interfacial phenomena at multilayered systems based on two model compatible polymers of PVDF and PMMA with varying molar masses. Linear and nonlinear rheology are demonstrated to be sensitive to the presence of diffuse interphase triggered at polymer/polymer interface. Firstly, the interdiffusion kinetics as well as the interphase development have been investigated using SAOS measurements with results analyzed under Doi-Edwards theory. The PMMA/PVDF mixture, has been examined to own close component monomeric friction coefficients. Based on this physics, a new rheological model was developed to quantify the interdiffusion coefficients. Thereby, rheological and geometrical properties of the interphase have been quantified, as validated by SEM-EDX. Secondly, step strain, shear and uniaxial extension startup were carried out to investigate their sensitivity to the diffuse interphase. An original model was proposed for the stress relaxation of multilayer and that of...