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International audience; Thermoset (TS) epoxy resins can be toughened with a thermoplastic (TP) for high‐performance applications. The final structure morphology has to be controlled to achieve high mechanical properties and high impact resistance. Four polyethersulfone‐modified epoxy resins are considered. They consist of different epoxy monomer structure (TGAP, triglycidyl‐p‐aminophenol and TGDDM, tetraglycidyl diaminodiphenylmethane) and a fixed amount of thermoplastic, and they are cured with two different amounts of curing agent. A reaction‐induced phase separation occurs for all formulations generating morphologies, different in shapes and scales. The aim is to control the final morphology and in particular its dominant length scale. This morphology depends on the phase separation process, from the initiation to its final stage. The initiation relies on the relative miscibility of the components and on the stoichiometry between epoxy and curing agent. The kinetics depends on the viscosity of the systems. The different morphologies are characterized by electron microscopy or neutron scattering. Dynamic mechanical analysis allows confirming the presence of a phase separation even when it is not observable by electron microscopy. Vermicular morphologies with few hundreds nanometer width are obtained for the systems containing the TGAP as epoxy monomer. Systems formulated with TGDDM presents morphologies on much smaller scale of order a few tens of nanometers. We interpret the different sizes of the morphologies as a consequence of a larger viscosity for the TGDDM systems as compared to the TGAP ones rather than by a latter initiation of phase separation

The viscoelastic behaviour of cellulose acetate with a degree of substitution (DS) of 245 plasticized by triacetin was studied at short times by dynamic oscillatory measurements. Two distinct regimes and unexpected scaling behaviour according to plasticizer content were highlighted. The dynamics of chains and their structural organization are not modified up to 35 wt% of triacetin. The rheological behaviour is led by a constant correlation length corresponding to the distance between strong intermolecular interactions subsisting in the melt state at high temperature even in the presence of plasticizer. This particular structure involves the apparition of strain hardening effects during uniaxial extensional flow tests and an important elasticity corresponding to the apparition of a Weissenberg effect at really low shear rates during shear sweeps. Intramolecular hydrogen bonds are responsible of the high rigidity of cellulose acetate chains. Plasticized cellulose acetate in the melt state belongs to the class of associating polymers and its rheological behaviour is mainly led by stickers.

We consider the microscopic mechanisms of damaging in plasticized cellulose acetate under tensile stress. We show how they appear and develop during the course of deformation until failure. By usin...

The mechanical properties of injection molded plasticized cellulose acetate polymers processed with two different plasticizers (Triacetine and Diethyl phthalate) and various weight fractions comprised between 15 and 30 wt % have been investigated. Plasticized cellulose acetate exhibit a brittle-to-ductile transition from a low impact strength to a high impact strength of order 40 kJ/m². Obtaining a high impact resistance at room temperature requires plasticizer content larger than 25 wt.%. An important strain hardening is obtained for samples with both plasticizers during tensile experiment. At 15 wt.% plasticizer content, the measured strain hardening modulus is around 148 MPa at 60 °C. Different parameters influencing the strain hardening behavior have been identified: the tensile direction as compared to that of the injection flow, the temperature and the plasticizer, consistent with studies on pre-strained samples of synthetic amorphous polymers.

The interaction between cellulosic material and benzophenone was studied by molecular modeling. A model of the crystalline part of a native microfibril was built from previously published coordinates of the Iβ allomorph. This model presents three faces, namely (200), (110), and (110), of about the same surface area. The energetical and geometrical characteristics of the benzophenone adsorption onto this microfibril were studied with a Monte Carlo protocol. It was shown that the interaction does occur on the three faces and was stabilized by both van der Waals and electrostatic forces. On the hydrophobic (200) face, a large number of interacting sites without specific geometry were sampled by the adsorbing molecule. The hydrophilic surfaces, (110) and (110), also have many interaction sites, but in contrast, the orientation of the adsorbed molecules is more strict. These two hydrophilic surfaces display equivalent behavior. Three surfaces (crystalline (110) and (200) and amorphous) subjected to periodic...

The binary blend compatibility of polyamide 6 (PA6) with poly(vinyl alcohol) (PVOH), poly(vinyl acetate) (PVAC), and partially hydrolyzed PVAC was studied for a wide range of compositions, by atomistic and mesoscopic modeling. The Flory−Huggins interaction parameter χ, calculated for these mixtures by atomistic modeling, showed that favorable interactions develop for PVAC with a low hydrolysis degree for a specific composition and also for compositions rich in either component. The effect of the PVAC hydrolysis degree on the mixture compatibility was explained in terms of the reduced ability of the acetylated chains to form hydrogen bonds, which in turn, may result in weaker intramolecular interactions. Such an effect may also be due to the more extended conformations assumed by these chains because of the bulky side groups. Calculations at high temperature gave small negative χ parameters, in good agreement with results reported by others. The χ and other structure-dependent parameters, derived from the ...

Due to its biodegradability and renewability, a great interest has been devoted to investigating cellulose acetate in order to expand its potential applications. In addition, secondary cellulose acetate (CDA) could also be considered as a model system for strongly polar polymer system. The dynamical behavior of CDA is supposed to be governed by H-bonding and dipolar interaction network. Due to their high glass transition temperature, cellulose acetate-based systems are processed when blended with plasticizers. It is thus of utmost importance to study the miscibility and plasticizing effects of various molecules. We prepared CDA films via solvent casting method with diethyl phthalate as the plasticizer. Miscibility diagrams were established by calorimetry and thermo-mechanical (DMTA) experiments. Dynamical properties were analyzed by DMTA and broadband dielectric spectroscopy. We could identify the α-relaxation of these CDA-plasticizer systems in the frequency range from 0.06 Hz to 10 6 Hz, which allowed for describing the dynamics in the so-called Williams-Landel-Ferry/Vogel-Fulcher-Tammann regime.

Solution and interfacial properties of water-soluble hybrid linear−dendritic polyether copolymers are investigated by static and dynamic surface tension measurements and adsorption experiments on polymeric substrates. The results obtained show that the block copolymers are able to form mono- and multimolecular aggregates in water. Contacting a solid polymeric substrate with an aqueous solution of hybrid block copolymer increases the hydrophilicity of the substrate. Adsorption on the hydrophobic surface of poly(ethylene terephthalate) proceeds only through the dendritic blocks of the hybrid macromolecule. For more hydrophilic substrates such as regenerated cellulose, both the poly(ethylene glycol) tail and the poly(benzyl ether) dendrons adsorb on the surface, increasing its hydrophilicity.