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Lattice structures nowadays have gained a peak in research. Inspired by the honeycomb structure and fishbone, this study investigated lattice structures that can provide auxetic behavior and store maximum energy absorption during deformation mode. From that, the study involved designing and producing different modified lattices based on the honeycomb’s structure and the fishbone’s perspective. The specimens were 3D printed within fused filament fabrication techniques within the additive manufacturing platform of Euromed University of Fes. The conception, production, mechanical testing, and simulation have been employed to get optimum data analysis of the mechanical properties of the designed structures. The results observed under quasi-dynamic compression did not show significant densification behavior; but, the auxetic behavior was seen in all structures, while some suddenly collapsed. The experimental and numerical analysis demonstrated similar deformation behavior and strong agreement in their respective results. Nevertheless, some discrepancies in mechanical values were observed, with a relative percentage error of approximately 1% for both methods. Consequently, owing to the enhanced energy absorption observed in the V2 and V3 structures, it is evident that these modifications hold promise for optimizing the performance of these metamaterials in various practical applications.

It is known that copolymers are critical in modifying interfaces of multilayered polymeric products. However, not much is known about the influence of the macromolecular architecture of copolymers on the interfacial morphology evolution, viscoelasticity, and processability of layered systems. Therefore, we demonstrate the role of macromolecular architecture of copolymers at layer–layer interfaces of multilayered polymers from the equilibrium to flow conditions, based on a combined morphological and rheological investigation. Intriguingly, in comparison to a pure grafting case, the formation of interfacial copolymers of a complex grafting architecture of a branching and cross-linking mixture substantially increases the overall viscosity. With a higher grafting density of copolymers of such an architecture, layer–layer interfaces become more corrugated upon reaction. Particularly, under real coextrusion processing flows, with these copolymers, interfacial roughness and irregularities are further amplified in the die exit as compared to that in the feedblock because of the accelerated reaction kinetics by the compressive flow field. Besides, the configuration of copolymers containing a mixture of branched and cross-linked chains at the interface significantly hinders the structural stress relaxation process and resists the interfacial slip. Under fast extensional flows, multilayered films display an unexpected strain-hardening behavior with a strong dependence on the number of layers, arising from the interfacial stitching and elastic network formed with copolymers of the complex architecture. These findings will enable the better understanding of copolymer architectures in the control of interfaces of multilayered films with improved flow stability and macroscopic properties.

To better understand the processing and final properties of multilayer films obtained by layer forced assembly in coextrusion as well as their structure morphology, the present study focuses on model films with LDPE as the base polymer. More specifically, the layer confinement of LDPE by a glassy amorphous polymer (here, PC or PS) was investigated. First, the viscosity and elasticity ratios of the different neat polymers were measured by rheological tests to simulate the processing conditions in the feedblock and multipliers during coextrusion. These results together with the observation of film transparency at the macroscopic scale and the layer breakup phenomena between layers at the microscopic scale enabled us to build a comprehensive stability map rationalizing the conditions required for a well-controlled multinanolayer architecture. Second, the morphology of the coextruded films was analyzed by SEM and TEM. The onset of the layer breakup in the LDPE/PS system was determined at 2048 layers with a layer thickness of 95 nm, while in the LDPE/PC system, it was at 256 layers with a layer thickness of 980 nm. The layer breakup happened at a fewer number of layers for the LDPE/PC system due to the viscoelastic mismatched properties between the base polymers. Interestingly, we have demonstrated that it is nonetheless possible to prepare some nanolayer structures with 16,380 layers of the PS/LDPE system with some defects but still maintain an overall property improvement despite their high mismatched viscoelastic properties. Finally, the orientation and crystalline structure of the coextruded films were characterized by 2D-WAXS and DSC, and the ultimate properties of the films were determined through tensile testing. The geometrical confinement of the LDPE nanolayer did not affect the thermal crystalline properties of LDPE chains, but it affected the crystalline morphologies as well as the final mechanical response of the obtained multilayer films.

It is known that the macroscopic properties of multilayer polymer films are largely dominated by the diffuse interphase formed via interfacial diffusion between neighboring layers. However, not much is known about the origin of this effect. In this work, we reveal the role of interfacial diffusion and the diffuse interphase development in multilayer polymer films, based on a compatible poly(vinylidene fluoride)/poly(methyl methacrylate) system fabricated by forced-assembly micro-/nanolayer coextrusion. Interestingly, the layer morphology is found to prevail in all investigated multilayer films, even for the nanolayered system where the interdiffusion is substantial. It is also demonstrated that, in the presence of macromolecular and geometrical confinements, interfacial diffusion significantly alters the crystalline morphology and microstructure of the resulting micro-/nanolayered films, which leads to quantitatively different dielectric and rheological properties. More importantly, the combination of dielectric relaxation spectroscopy and energy-dispersive X-ray analysis further reveals that multiple diffuse interphases with various length scales exist in the multilayer structures. The presence of these multiple interphases is explained in terms of a proposed physical picture for the interdiffusion of fast-mode mechanism occurring in the coextrusion process, and their length scales (i.e., interphase thicknesses) are further mapped quantitatively. These findings provide new insights into the effects of interfacial diffusion and diffuse interphases toward tailoring interfaces/interphases in micro-/nanolayered polymer structures and for their advanced applications.

Interfacial rheology is crucial in dictating morphology and ultimate properties of particle-stabilized polymer blends, but is challenging to be determined. In this study, a fully polymeric dumbbell-shaped Janus nanoparticle (JNP) of polymethyl methacrylate (PMMA) and polystyrene (PS) spheres with equal sizes (∼80 nm) was prepared and used as an efficient compatibilizer for PMMA/PS blends. The JNPs were preferentially localized at the PMMA/PS interface, thereby reducing the interfacial tension and refining the morphology in both droplet-matrix and co-continuous type blends, whereby a JNP concentration ∼2.5 wt % is sufficient to reach a saturation in droplet size reduction due to compatibilization. Based on the linear viscoelastic moduli and corresponding relaxation spectra (H(τ)*τ) of JNP-compatibilized droplet-matrix blends, besides the droplet shape relaxation time (τF), a longer relaxation time (τβ), typically related to interfacial viscoelasticity, was readily identified. The dependence of τβon the JNP concentration (WJNPs) was significantly dominated by the droplet size reduction induced by the JNP compatibilization, with τβdecreasing with increasing WJNPs. The viscoelastic properties extracted from τβtypically originate from a combination of gradients in interfacial tension due to the particle redistribution at the droplet interface (Marangoni stresses) and the deviatoric stresses of intrinsic rheological origin. The latter originate from the intrinsic viscoelasticity of the particle-laden interface, which is enhanced by particle jamming and particle–polymer interactions, such as entanglements between chains from the polymeric spheres and those penetrating from the bulk into the spheres. To address the challenge of isolating these contributions, a JNP-sandwiched PMMA/PS multilayer structure was designed to exclude the effect of Marangoni stresses and droplet curvature, thus having no τFbut a new relaxation (τ′β), which characterizes the contribution of intrinsic interfacial viscoelasticity. The τ′βwas observed to increase with JNP coverage (Σ) following the Vogel–Fulcher–Tammann model that is typically used to describe the divergent behavior of the “cage” effect in classical colloidal glasses. Moreover, a multimode Maxwell model fitting allows to split the interfacial relaxation into the confined diffusion of JNPs within their cage and the entanglements between the JNPs and the bulk.

Several polymers can be combined in one multilayer structure by reactive coextrusion. Tie-layers are often used to compatibilize adjacent layers and may reduce or suppress interfacial instabilities and defects in multilayer coextrusion flow. However, a new additional defect defined as “grainy” defect can be observed. In our best of knowledge, no study in literature has been dedicated to understand its origin. The phenomena are quite complex due to the coupling of the effects of flow and the physico-chemical mechanisms at the interface. The aim of this work is to understand the relationship between the instabilities and defects encountered in multilayer coextruded films and the role of the copolymer formed in-situ between tie and barrier layers. Polyamide 6 (PA6) and ethylene-vinyl alcohol copolymer (EVOH) were used as barrier layers sandwiched in polypropylene (PP) with or without tie-layer based on polypropylene grafted maleic anhydride (PP-g-MA). Influence of process parameters and nature of the polymer pair on the generation of “grainy” defect has been assessed and related to the rheological and the physico-chemical properties of layers. These experiments showed that this defect appeared mainly in the compatibilized EVOH system and could be distinguished from the usual coextrusion instabilities. Interfacial properties between tie and barrier layers have been investigated. Shear stress relaxation experiments have been carried out on reactive tie/barrier bilayers. Due to the interphase generated in-situ, the relaxation behavior was altered by extending the relaxation time. Investigation of interfacial morphology highlighted that the copolymer architecture significantly affected the interface/interphase development and interface roughness. Hence, relationships between relaxation process, interfacial morphology and copolymer structure were correlated with the generation of grainy defects in coextrusion.

The poly (lactic acid) (PLA), through its organic origin and its biodegradation properties, can be a good alternative to petroleum-based polymers. To this end, the forming process as well blown extrusion and foaming of PLA was investigated in this study as an alternative for the production of food packaging. Through this work, we present some promising routes to enhance its processing ability which presents several challenges mainly due to the poor shear and elongation properties of this biopolymer. To our knowledge, there is no paper dedicated to the investigation of foaming and/or blown extrusion of PLA that involves structural, rheological and thermo-mechanical properties. To achieve this objective, various formulations of PLA with multifunctionalized epoxy, nucleants and plasticizer were prepared and characterized on the basis of their linear viscoelasticity and extensional properties. The balance of chain extension and branching has been also investigated using solution viscosimetry, Steric exclusion chromatography (SEC) and rheology (relaxation spectrum, Van Gurp Palmen curves….). We pushed further by characterizing both the structure and thermo-mechanical properties of PLA formulations. On one hand, a batch foaming assisted with supercritical CO2 was achieved following a full characterization in physicochemical, rheological and thermal domain, The influence of the foaming parameters, the extent of chain modification as well as the contribution of crystallization on cell morphology was evaluated. Based on these parameters, structures ranging from micro to macro-cellular-cell were obtained. On the other hand, the stability maps of blown processing for neat and modified PLA were established at different die temperatures. We have achieved a great enhancement of the blown processing windows of PLA with high BUR (Blow Up Ratio) and TUR (Take Up Ratio) attained. We were able to demonstrate that a higher kinetic of crystallization can also be reached for chain-extended and branched PLA formulated with adequate amounts of nucleants and plasticizers. Induced crystallization during process was also demonstrated. Through this work, blown films with interesting thermo-mechanical and mechanical properties have been produced using an optimal formulation for PLA. References [1] A. Maazouz, K. Lamnawar, B. Mallet, Patent: C08L67/00; C08J5/10. FR2941702 (A1). (2010) [2] Y.-M. Corre, A. Maazouz, J. Duchet, J. Reignier, Batch foaming of chain extended PLA with supercritical CO2: Influence of the rheological properties and the process parameters on the cellular structure. J. of Supercritical Fluids,58 (2011) 177-188 [3] B. Mallet, K. Lamnawar, A. Maazouz, Compounding and processing of biodegradable materials based on PLA for packaging applications: In greening the 21st century material’s world, Frontiers in Science and Engineering, 1-2(2011) 1-44 [4] B. Mallet, K. Lamnawar, A. Maazouz, Improvement of blown extrusion processing of PLA: structure-processing-properties relashionships. Polymer engineering and Science (To appear in 2013).

This work aims to highlight the importance of interphase triggered from interdiffusion at neighboring layers on controlling the interfacial flow instability of multilayer coextrusion based on a compatible bilayer system consist of poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride) (PVDF) melt streams. A fundamental rheological measurement on the bilayer structures provides a good strategy to probe the mutual diffusion process occurred at neighboring layers and to quantify the rheology and thickness of the interphase generated thereof. By implementing steady shear measurements on the multilayer’s, subtle interfacial slippage can be observed at a condition of short welding time and rather high shear rate due to the disentanglement of chains at the interphase. Pre-shear at an early stage on the multilayer was found to greatly promote the homogenizing process by inducing branched structures and hence increasing interfacial area. In coextrusion, some key classical decisive parameters concerning the interfacial instability phenomena such as viscosity ratio, thickness ratio and elasticity ratio, etc. were highlighted. These key factors that are significant in controlling the interfacial stability of coextrusion in an incompatible system seem not that important in a compatible system. In comparison to the severe flow instability observed in the coextrusion of PMMA/PE incompatible bilayer, the coextrusion of PMMA/PVDF compatible bilayer appears to be smooth without apparent interfacial flow instability due to the presence of the interphase. Interdiffusion can reduce (even eliminate) the interfacial flow instability of coextrusion despite of the very high viscosity ratio of PVDF versus PMMA at low temperatures. Indeed, in the coextrusion process, on one hand, the interdiffusion should be studied by taking into account of the effect of polymer chain orientation which was demonstrated to decelerate the diffusion coefficient. On the other hand, the interfacial shear stress was able to promote mixing and homogenizing process at the interface, which favours the development of the interphase and guarantees the stable interfacial flow. The degree of the interphase is related to a lot of parameters like contact time, processing temperature, interfacial shear stress and compatibility of the polymers, etc. Therefore, apart from the classical mechanical parameters, the interphase created from the interdiffusion should be taken into consideration as an important factor on determining the interfacial instability phenomena. References [1] H. Zhang, K. Lamnawar, A. Maazouz, Rheological modeling of the diffusion process and the interphase of symmetrical bilayers based on PVDF and PMMA with varying molecular weights. Rheol. Acta 51 (2012) 691-711 [2] H. Zhang, K. Lamnawar, A. Maazouz, Rheological modeling of the mutual diffusion and the interphase development for an asymmetrical bilayer based on PMMA and PVDF model compatible polymers, Macromolecules (2012), Doi: http://dx.doi.org/10.1021/ma301620a [3] H. Zhang, K. Lamnawar, A. Maazouz, Role of the interphase in the interfacial flow stability of multilayer coextrusion based on PMMA and PVDF compatible polymers, to be submitted. [4] K. Lamnawar, A. Maazouz, Role of the interphase in the flow stability of reactive coextruded multilayer polymers, Polymer Engineering & Science, 49, (2009), 727 - 739 [5] K. Lamnawar, H. Zhang, A. Maazouz, one chapter” State of the art in co-extrusion of multilayer polymers: experimental and fundamental approaches” in Encyclopedia of Polymer Science and Technology (wiley library) (feature article)

Lignocellulosic fibers from date palm trees were employed to reinforce an epoxy matrix. Two fiber sizes were used, with the length and diameter in the range of 20–30 and 1.5–3 mm, respectively, for the socalled long fibers, and in the range of 5–15 and 0.25–0.75 mm, respectively, for the socalled short fibers. The morphologies of the resulting composites, as well as their thermal, mechanical, and water sorption properties were evaluated. Strong interactions between both components and etherification reactions may occur between the hydroxyl groups of the fibers and the epoxy groups of the epoxyamine reactive mixture. These effects are emphasized when decreasing the size of the fibers.

Rheological behavior in molten state of multilayered polymers was investigated by dynamic mechanical measurements. The competition between polymer/polymer interdiffusion and interfacial reaction of functionalized polymers in a sandwich structure was followed by oscillatory mode under small amplitudes of deformation. The systems chosen for study were polyethylene (PE) grafted with glycidyl methacrylate/polyamide (PA) 6 as a reactive system and PE/PA6 as nonreactive one. Moreover, the interphase thickness was estimated by using thermodynamical models. Experimental results of bilayer systems were compared to existing models of multiphase systems. An expression of storage modulus as a function of welding time was also suggested. Thus, the fit between this one and the experimental data was satisfactory with the different appearing phenomena.Rheological behavior in molten state of multilayered polymers was investigated by dynamic mechanical measurements. The competition between polymer/polymer interdiffusion and interfacial reaction of functionalized polymers in a sandwich structure was followed by oscillatory mode under small amplitudes of deformation. The systems chosen for study were polyethylene (PE) grafted with glycidyl methacrylate/polyamide (PA) 6 as a reactive system and PE/PA6 as nonreactive one. Moreover, the interphase thickness was estimated by using thermodynamical models. Experimental results of bilayer systems were compared to existing models of multiphase systems. An expression of storage modulus as a function of welding time was also suggested. Thus, the fit between this one and the experimental data was satisfactory with the different appearing phenomena.

The effect of the elastomer structure on toughening highly crosslinked epoxy systems in a resin transfer moulding process (RTM) was investigated. Two kinds of elastomers containing carboxyl functionalized groups were used: (1) a reactive liquid elastomer based on carboxyl-terminated butadiene-acrylonitrile copolymer (CTBN), (2) a preformed core-shell rubber (CSR). The introduction of CTBN rubber caused the modification in the glass transition temperature due to the miscibility in the epoxy matrix, whereas CSR particles did not. During cure, these elastomers affected the morphological, rheological and dielectric behaviour of epoxy/amine systems. A blend of 5% CTBN and 5% CSR exhibited a bimodal distribution of rubber particle sizes (analyzed by transmission electron microscopy) whereas scanning electron microscopy showed the glass fibre-matrix cohesion in fracture surfaces. A semi-empirical model was used (developed by Castro-Macosko for describing chemorheological behaviour of epoxy/amine systems for the RTM process). The increase in viscosity and the reduction in ion conductivity were the two key parameters to monitor the cure process. The presence of rubber affected the rheological behaviour involving initial viscosity and gel point. The investigation of temperatures, pressures and ionic conductivities in various glass fibre layers was conducted to control the front flow filling and the cure reaction. The introduction of rubber modified the inflexion area of the cured rubber–epoxy blends by changing the cure rate. Copyright © 2004 Society of Chemical Industry

In this work, temperature modulated DSC is used to measure the heat flow evolved during the cure reaction of a dicyanate ester resin. This technique enables the heat capacity contribution to be separated from the heat source term (from the kinetic behavior) in nonisothermal conditions. At any given moment, therefore, the true reaction rate can be calculated without any assumptions about the shape of the baseline of the thermogram. Resulting accurate data are used for the characterization of cure kinetics. The isoconversional analysis shows that the apparent activation energy varies with conversion degree, so that a Kamal & Sourour kinetic model is proposed. Its kinetic parameters are obtained by an inverse method, and such a model is successfully used to simulate nonisothermal, isothermal and multistep cure experiments.

Hairy poly(butyl acrylate) (PBuA) core-shell particles with a crosslinked shell were prepared by soap-free emulsion polymerization. The incorporation of the hairy structure was obtained either by surface polymerization of a methacrylate (MMA) terminated poly(ethylene oxide) (PEO), or by physical adsorption of poly(ethylene oxide)-poly(propylene oxide) (PPO)-poly(ethylene oxide) triblock copolymers. The particle shell was crosslinked during the synthesis so as to keep the integrity and morphology of the particle upon curing the epoxy network. Particle sizes and size distributions were determined both by quasi-elastic light scattering and transmission electron microscopy. Particle morphology was investigated by electron and atomic force microscopies. The presence of the poly(ethylene oxide) layer was evidenced by direct analysis of the latexes by means of ¹H NMR spectroscopy. Mixing of the core shell rubber particles with the reactive epoxy and processing of the toughened-epoxy networks are described. The influence of the hairy layer (with regards to density and PEO chain length) on particle dispersion within the epoxy network, the resulting rheological behaviour of the core-shell (CS)/prepolymer epoxy blends, and mechanical properties of the modified epoxy were examined and discussed.

The interesting mechanical properties of polyether ether ketone give the material a place among the foremost competitors when it comes to replacing metal. Fused deposition modeling has been recognized as an alternative method to process polyether ether ketone parts. In this study, the effect of different process parameters such as nozzle, bed, and radiant temperatures as well as printing speed and layer thickness on the tensile properties of three-dimensional printed polyether ether ketone was investigated. The optimization of the tensile properties of PEEK were studied by performing a reduced number of experiments, using the experimental design method based on the Taguchi approach which limits the number of experiments to 8 instead of 32. Results showed that a decent Young’s modulus was found by setting the nozzle temperature, print speed, and bed temperatures to their high levels and by setting the layer thickness and radiant temperature to their low level. Using these parameters, a Young’s modulus of 3.5 GPa was obtained, which represents 87.5% of the value indicated in the technical sheet. With these settings, we also found a tensile strength of 45.5 MPa, which corresponds to 46.4% of the value given by the studied polyether ether ketone material. A scanning electron microscopic investigation of the porosity and interlayer adhesion, confirmed that a higher bed temperature also tended to promote adhesion between layers.