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The hybrid assembling of thermoplastics with thermosets through controlled interdiffusion is an attractive approach towards integrated structural composite bonding. The fracture toughness of the interphase between the high Tg thermoplastic polyetherimide and the RTM6 epoxy is found to be four times higher than the corresponding RTM6 value under specific curing cycle. The origin of this remarkable cracking resistance is elucidated by analyzing the crack path in relationship with the morphology and local elastoplastic and fracture properties of the interphase. The crack is trapped inside a morphological gradient involving a relatively low PEI concentration. Uniaxial compression and nanoindentation tests on homogenous blends exhibit an unexpected softening in this PEI content window. This efficient crack trapping mechanism originates thus from a synergistic coupling between a lower local strength and higher local fracture toughness. This finding opens to many new options for interface toughening beyond the system addressed in this research.

The evolution upon curing of interdiffusion as well as phase separation is characterized at the interphase between a high T g poly(ether sulfone) thermoplastic (TP) and a high density thermosetting network (TS), both components being initially miscible. We show that the late stages of the diffusion process overlap with the early stages of phase separation, which is contrary to the expectations from the current state of the art. The penetration depth of the TS into the TP is found to increase with decreasing gelation time within the investigated operating window. This is due to the stronger thermal activation of diffusion over reaction at the early stages of curing. A chemometric model is developed based on Raman spectroscopy data in order to further analyze these results. The predictions of the model are compared with the profiles generated by image analysis carried on microtomed sections of fully cured interphases. The concentration profiles of partially cured interphases are predicted as well and used to correlate the degree of curing of the TS with the front velocity for each profile.

The multiple melting peaks of isothermally crystallized poly(ether ether ketone) were investigated by fast-scanning chip calorimetry over a wide range of heating rates from 500 to 60,000 K s −1 . The analysis of heating rate dependence of melting temperatures revealed that there are two crystal populations with distinct melting kinetics for the samples prepared at different crystallization temperatures, 170 °C ≤ T iso ≤ 270 °C. For each T iso , the two melting temperatures of the metastable crystals without prior reorganization or superheating (i.e. zero-entropy-production melting temperatures) were constantly 20 K and 30 K, respectively, higher than T iso . We first discuss this behavior quantitatively based on the Lauritzen-Hoffman nucleation approach. Finally we conclude that these increases in temperature are linked to the number of stems which construct the secondary surface nuclei. The existence of two crystal populations can be caused by differences in the stability of the crystal or “local” differences in the free energy of the surrounding melt.

The local mechanical properties of partially cured epoxy resins based on tetraglycidyl methylene dianiline (TGMDA) are proved to be heterogeneous at the nanoscale with the degree of heterogeneity decreasing when the crosslinking density increases. The fully cured resin can be considered homogeneous on both the nano- and macroscale. These conclusions are supported by a comprehensive statistical analysis of AFM-based local mechanical properties measurements, which reveal changes in the modulus distributions from multimodal to monomodal. Furthermore, the histograms of adhesion force and energy dissipation exhibit decreasing fluctuations with increasing degree of curing. The surface topography of all samples is very flat at the nanoscale, which indicates that the observed features are not the result of surface irregularities. The existence of differently cured domains due to local fluctuations in the curing kinetics is proposed as the origin of the observed properties contrast.

Sorption and diffusion of supercritical carbon dioxide (scCO2) into polycarbonate (PC) nanocomposites loaded with 0, 1 and 2 wt% of multi-walled carbon nanotubes (MWNTs) have been investigated. After determination of the saturation equilibrium, the samples have been saturated with scCO2 to ensure a partial foaming with a density gradient from the surface to the center of the samples and the morphology of the porous materials has been analysed by SEM. The gradient materials were very advantageous for EMI shielding since the foamed structure at the surface had low dielectric constant and limited the reflection of the EM signal while the presence of highly conductive solid in the middle ensured a high absorption of the electromagnetic radiation.

Supercritical carbon dioxide readily induced foaming of various polymers. In that context, supercritical CO2 was applied to carbon nanotubes based polycarbonate nanocomposites to ensure their foaming. Surprisingly, efficient foaming only occurs when low pressure is applied while at high pressure, no expansion of the samples was observed. This is related to the ability of supercritical carbon dioxide to induce crystallization of amorphous polycarbonate. Moreover, this behaviour is amplified by the presence of carbon nanotubes that act as nucleating agents for crystals birth. The thermal behaviour of the composites was analysed by DSC and DMA and was related to the foaming observations. The uniformity of the cellular structure was analyzed by scanning electron microscopy (SEM). By saturating the polycarbonate nanocomposites reinforced with 1 wt% of MWNTs at 100 bar and 100°C during 16h, microcellular foams were generated, with a density of 0.62, a cell size ranging from 0.6 to 4 μm, and a cellular density of 4.1.1011 cells.cm-3. The high ability of these polymeric foams to absorb electromagnetic radiation was demonstrated at low MWNT content as the result of the high affinity of the polycarbonate matrix for MWNTs, and therefore to the good MWNTs dispersion.

Naturally occurring halloysite nanotubes (HNTs) are used to prepare Polypropylene (PP)/HNTs nanocomposites using a novel "one step" water-assisted extrusion process with and without the use of a PP-graft-maleic anhydride (PP-g-MA) as compatibilizer. In order to analyze the influence of PP-g-MA and/or water injection on the HNTs dispersion and therefore on nanocomposite properties, structural analysis (SEM and TEM) is combined with rheological and thermo-mechanical experiments. The best clay dispersion is obtained when compatibilizer and water injection are combined together (synergistic effect). As a consequence, the linear viscoelastic properties and the dynamic storage modulus are dramatically enhanced for this system. A mechanism explaining the interaction between HNTs and PP-g-MA in presence of water is proposed. The thermal stability and flame retardant property are also investigated. Thermal analyses reveal two opposite effects of HNTs on the thermal behaviour of PP. A surface catalytic action of the halloysite speeds up thermal degradation of PP. However, this effect is reduced with improved HNTs dispersion, presumably via an entrapment mechanism of the decomposition products inside the lumens. Finally, cone calorimeter results show that low flammability of nanocomposites is only achieved when combining water injection and PP-g-MA. In view of these results, PP/HNTs nanocomposites prepared using this novel processing route are promising candidates for flame retardant applications.

The present study demonstrates the effect of unfunctionalized MultiWalled Carbon Nanotubes (MWNTs) interfacial confinement on coalescence suppression in an immiscible polymer blend exhibiting a sea-island morphology. The effect of carbon nanotubes on morphological stabilization in polyamide (PA)/ethylene-methyl acrylate random copolymer (EA) blends is studied using electronic microscopy techniques. Owing to their interfacial localization, MWNTs are shown to enhance both phase dispersion and stability of the dispersed phase for long mixing time (at least 60 min) and very low filler content (0.5 wt.-% MWNTs) compared to what was previously observed in literature. MWNTs also produce a more uniform distribution of droplets size. The main stabilization mechanism proposed is the formation of a deformable barrier network providing a mechanical barrier against coalescence. Blends stabilized by solid anisotropic nanoparticles, like MWNTs, could therefore offer an interesting alternative to blends compatibilized by block-copolymers. (C) 2010 Elsevier Ltd. All rights reserved.

The present study demonstrates for the first time the possibility to jam unpurified and unfunctionalized multiwall carbon nanotubes (MWNTs) at the interface of an immiscible blend of polyamide (PA) and ethylene-acrylate (EA) copolymer The confinement appears to be stable The influence of the mixing strategy and of the polyamide type used has been examined When the MWNTs are first dispersed in PA6, most of them migrate to the interface although some of them stay in the PA phase. When the MWNTs are first dispersed in PA12, they remain well dispersed in PA. When the MWNTs are first dispersed in the EA copolymer or when the three components are simultaneously mixed, a large part of the MWNTs migrate to the interface whatever the PA used However, some of the MWNTs remain in the EA phase and when PA12 is used, part of the MWNTs penetrate inside the PA nodules. By a combination of TGA and separation techniques, we show that the first polymer to come in contact with the nanotubes during melt mixing is (at least partially) adsorbed irreversibly, by non-covalent adsorption The resulting modification of interfacial thermodynamics explains the observed confinement. (C) 2010 Elsevier Ltd All rights reserved.

We critically evaluate and compare all major published methods for the experimental determination of the plateau modulus for monodisperse as well as polydisperse polymers with linear architecture. For long-chain monodisperse model systems (M-W/M-n 20-30), the various methods show excellent agreement. within an error margin of 5-10% close to the experimental uncertainty. For low numbers of entanglements, the terminal peak integration method requires a careful extrapolation at the high frequency side. This is best achieved by a simple subtraction of the Rouse relaxation. The universal terminal relaxation concept is validated for long chains. in logical agreement with tube model concepts. We further analyze the extension to polvdisperse polymers of the methods validated for monodisperse systems. Agreement between the methods within a 15% range can be achieved in favorable cases. The preferred method is the terminal peak integration, with the same caveats as for monodisperse samples. Predictions from tube models can nicely complement other approaches but should be used with caution because they are sensitive to errors on the experimentally determined molecular weight and distribution. Methods based on the 'crossover' modulus are only semi-quantitative. A cross-check of all available methods is the best way to achieve maximal accuracy for polydisperse systems. (c) 2006 Elsevier Ltd. All rights reserved.

The conjugated effects of both reactive compatibilization and dynamic vulcanization on the phase inversion behavior of poly(butylene terephthalate) (PBT)/epoxide-containing rubber blends have been studied in detail. Pure ethylene-methyl acrylate random copolymer (E-MA) and ethylene-methyl acrylate-glycidyl methacrylate random terpolymer (E-MA-GMA) were used as non reactive or reactive rubber phase, respectively. Location of the phase inversion region was studied using several techniques, including transmission electron microscopy (TEM) and dynamical mechanical thermal analysis (DMTA). To evaluate the relative influence of the blend compatibilization and the dynamic vulcanization on the phase inversion behavior, the relative kinetics of the two reactions were modified using different PBT and E-MA-GMA grades. The obtained results show unambiguously that the position and the width of the phase inversion region is essentially governed by the kinetic of the dynamic vulcanization process. The effect of the blend compatibilization remains quite limited even in the case of fast interfacial reaction. The crosslinking of the rubber phase induces an important shift of the phase inversion composition to higher rubber content. For blends containing low molecular weight PBT, up to 60 wt% of rubber can be homogeneously dispersed in the PBT matrix at long mixing time. In this case, development of high performance PBT based thermoplastic vulcanisates can be envisioned. (C) 2004 Elsevier Ltd. All rights reserved.

The possibility to generate particle-in-particle morphology by controlling blending sequence has been investigated for reactive processing of poly(butylene terephthalate) (PBT) with ethylene-methyl acrylate-glycidyl methacrylate (E-MA-GMA) random terpolymer. Composite droplet morphology consisting of a PBT matrix, a E-MA-GMA dispersed phase and PBT sub-inclusions is spontaneously formed upon melt mixing due to the coalescence of poorly stabilized E-MA-GMA particles. The development and dimensions of this complex morphology is mainly controlled by the relative kinetics between the coalescence process and the chemical reactions occurring during the melt processing. This can be influenced by an adequate adjustment of various blending parameters such as blend composition, PBT viscosity and rubber phase reactivity. The generation of particle-in-particle morphology can also be forced by using a two-step blending sequence. In this latter case, blend morphology consisting in PBT matrix with PBT/E-MA-GMA core-shell particles can be generated. (C) 2004 Elsevier Ltd. All rights reserved.

Thermally induced chain-scission and redistribution reactions in as-polymerized and fractionated bisphenol-A polycarbonate (PC) materials made by melt-transesterification and interfacial polymerization were studied at temperatures between 200 and 300 degreesC in open systems, where volatile reaction products are continuously removed, and in closed systems, where these products are retained. Under the applied conditions, PC made via interfacial polymerization shows no measurable susceptibility towards redistribution. This is the result of an extremely low concentration of hydroxyl end-groups. Upon similar thermal treatment, PC made by melt-transesterification undergoes fast redistribution which leads to post-condensation in open systems and strong changes of molecular weight distributions (MWDs) for fractions in all cases. Redistribution effects were visualized through changes in the MIND of mixed fractions. The initial stages of redistribution were simulated using a Monte Carlo method based on a random sampling technique. From comparison between experimental and simulation results, it can be concluded that approximately half a percent of all carbonate linkages is involved in a redistribution reaction per minute at 250 degreesC for the studied samples. (C) 2002 Elsevier Science Ltd. All rights reserved.

Bisphenol-A polycarbonate/eugenol-siloxane copolymers were fractionated at the preparative scale by the continuous polymer fractionation (CPF) technique. It is the first example of copolymer fractionation by CPF. The distribution of siloxane species across the fractions was assessed for copolymers differing in initial siloxane concentration and block length. On- and off-line combinations of size exclusion chromatography and infrared spectroscopy were used to analyze chemical composition (CC) of the unfractionated samples across the molecular weight distribution enabling comparison with the fractions. A polycarbonate-siloxane copolymer containing 10 wt% of very short siloxane blocks (dp = 2) was fractionated solely according to molecular weight (MW). By contrast, a copolymer containing 5 wt% siloxane blocks with a larger degree of polymerization (dp = 23) was fractionated according to MW, as well as to CC. This 'chemical drift' effect for the larger siloxane block length can be ascribed to large solubility differences of low MW chains, which drastically vary in composition according to the (small) number of siloxane blocks they contain. (C) 2002 Elsevier Science Ltd. All rights reserved.

Melt-polymerized bisphenol-A polycarbonate materials characterized by a low degree of branching were fractionated according to molecular weight by the continuous polymer fractionation (CPF) method. The distribution of two types of end-groups and in-chain salicylate moieties arising from thermal rearrangement reactions were assessed across the molecular weight distribution by analysis of the fractions. Experimentally determined branching densities of the fractions agreed well with a molecular simulation based on a random sampling polycondensation model. Both simulation and experiments showed that the branching density increases with molecular weight in the experimentally accessible range. (C) 2001 Elsevier Science Ltd. All rights reserved.

This paper deals with the development of a compatibilized polymer blend based on poly(2,6-dimethyl-1,4-phenylene ether) (PPE) and poly(butylene terephtalate) (PBT). Blending of PBT with PPE, with PBT as the continuous phase, could yield materials which are mutually incompatible, and the phase morphologies obtained during blending of these polymers are generally unstable. When PPE is functionalized selectively, in situ compatibilization during processing is feasible. Due to the formation of segmented copolymers, which act as compatibilizing agents, stabilization of the morphology obtained during blending is feasible. Different types of reactive PPE polymers were investigated, e.g. PPE with hydroxyalkyl, carboxylic acid, methyl ester, amino and t-BOC protected amino endgroups. These groups are positioned either in the middle of the chain or as the endgroup. All these reactive PPE polymers result in better compatibilization after mixing with PBT versus unfunctionalized PPE. PPEs with carboxylic acid endgroups proved to be the most efficiently compatibilized with PBT, for the PBT type employed in this study. Promoters, which catalyze or take part in the coupling between PBT and/or functionalized PPEs, such as triphenyl phosphite (TPP), sodium stearate, titanium (IV) isopropoxide and epoxy resins, were used in order to improve compatibilization of the PPE/PBT blends. The use of these promoters proved to give synergetic compatibilization in combination with functionalized PPEs.

In order to assess the reliability of absolute molecular weights of bisphenol-A polycarbonate samples measured by size exclusion chromatography, the results obtained from two experimental systems and two calibration methods are compared with each other as well as with data provided by light scattering determinations. The interest of coupling a light scattering detector to the chromatographic system is discussed.

Two complementary methods were developed to produce sulphonated poly(oxy-1,4-phenylene-oxy-1,4-phenylene-carbonyl-1,4-phenylene) (SPEEK) with random, homogeneous compositions over the range of zero to one sulphonate group per repeat unit. The sodium salts (Na-SPEEK) were prepared from about 5 to 100% sodium sulphonate. They displayed excellent thermal stability. The behaviour of Tg, ΔTg and ΔCp at the glass transition as a function of composition suggested the onset of ionic clustering below 25 to 30% sodium sulphonate—an observation confirmed by preliminary SAXS studies. In particular, Tg increased sigmoidally from about 150°C for 5% Na-SPEEK to 415°C for 100% Na-SPEEK. No evidence of crystallinity was observed by d.s.c. in melted and quenched samples above 9% sodium sulphonate. The equilibrium water content at room temperature and 58% relative humidity was four molecules of water per sodium sulphonate group for all compositions. For immersed films, this value increased from 8 molecules of water per sodium sulphonate group for 38% Na-SPEEK to an indeterminably large number for 100% Na-SPEEK, which slowly dissolved. Upon re-equilibration at 58% relative humidity, the water content of the films decreased to about 5.5 molecules per sodium sulphonate group. A low temperature (−80°C to −60°C) mechanical relaxation peak was present in the films conditioned at 58% relative humidity.