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The prediction of the morphology of ternary polymer blends requires a good knowledge of the values of the three interfacial tensions. We selected three polymers, either biobased or biodegradable, PA, PBAT and PLA and we accurately measured their interfacial tensions using the retraction method, varying the molar mass or inverting the phases. The following values of interfacial tensions were obtained: = 3.3±0.7mN/m, = 5.6±0.3mN/m and = 3.0±0.4 mN/m. These values were used to calculate the spreading coefficients giving rise to two negative coefficients and one coefficient close to zero. Ternary blends with various compositions, two different levels of viscosity for the PBAT, different processing conditions were prepared. There was a very good agreement between the predictions of the spreading theory, when using the values of interfacial tensions in the right order of magnitude, and the observed morphologies, whatever the polymer serving as a matrix. When the PLA or PBAT was chosen as the matrix, the ternary blend morphology was composed of composite droplets, presenting a partial wetting morphology, dispersed in the polymer matrix. This morphology was observed whatever the composition, the viscosity level of the PBAT phase and the processing conditions. A further calculation of the free energy confirmed this 2 morphology. The formation process of this semi-encapsulated morphology was observed during blending.

Four processing tools (two twin-screw extruders, one being a mini-extruder, and two mixers) were used to prepare plasticized cellulose acetate with 20 wt% of glycerol triacetate. The goal was to deduce if the scale of the processing tool influences the dispersion of the plasticizer as estimated by the thermal, rheological, and mechanical properties of the obtained materials. The amount of polymer used ranged from 5 g for mini-extruder to a 10 kg/h for pilot-scale extruder. The specific mechanical energy was used to compare the thermal, rheological, and mechanical properties of cellulose acetate obtained with the four processing tools using different processing conditions. The measurement of the glass transition temperature was not able to discriminate the four tools used. Rheology shows differences, not as a function of small or large tools, but in terms of specific mechanical energy. The larger was the tool, the higher were the Young's moduli. This was ascribed to an overall better distribution and dispersion of the plasticizer. However, all variations were small, showing that small laboratory processing machines can prepare thermoplastic compounds with similar properties as pilot scale extruders, at least in what concerns cellulose acetate. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers

Epoxy resins with mesogenic groups were prepared from diglycidyl ether of 4,4'-biphenol (DGEBP) as rigid block and 4,4'-diaminodiphenylsulphone (DDS). Curing kinetics were investigated using size exclusion chromatography in the 155-175°C range above the melting temperature. It was found that the ratio R=k 2 /k 1 or secondary to primary amino hydrogen rate constants displays unusual values higher than unity and decreased on increasing the temperature. This effect was assumed to be due to the neumatic structure in which polymerization takes place before reaching the gel point.

International audience; At a shear rate of 10 s−1, a flow-induced phase inversion has been observed in-situ by optical microscopy on a blend of polydimethylsiloxane with solution of 50% of hydroxypropylcellulose in water for a range of concentrations. By increasing the shear rate up to 30 s−1, the elasticity ratio of the components can be changed without changing the viscosity ratio. The resultant steady-state morphology is not influenced by the variation of the elasticity ratio, contrary to a theoretical model.

International audience; The shear rheology of diluted to concentrated suspensions of weakly cross-linked sodium polyacrylate hydrogels were investigated by concentric cylinder rheometry. The size of the swollen gel particles is dependent on the initial size of the dry particle and on the nature of the added salt. Polyvalent salts are more efficient for contracting the swollen particles than monovalent ones. When suspended in water or in monovalent salt solutions, the viscosity at low concentrations shows a behaviour very similar to the one of flexible polymer solutions. Below the critical overlap concentration, the viscosity is independent of shear rate. The intrinsic viscosity is very large, on the order of 10-15 dL/g. This is in agreement with the large size of these swollen particles. Suspensions of such swollen gel particles are thus a good model for extremely high molecular weight polymer solutions. In polyvalent salt solutions different behaviour of the viscosity curves versus concentration was observed. This effect is caused by chemical cross-linking of the hydrogel by polyvalent ions

With the help of a counter-rotating transparent rheometer equipped with an optical microscope, the erosion of single, commercial carbon black agglomerates suspended in a polyisobutylene fluid was accurately recorded in situ. We observed that clouds of very small aggregates were leaving the agglomerate at 45 and 225° in the shear gradient–flow direction plane, where the stress is maximum. The distribution of the arrached aggregates is more efficient when the carbon black agglomerate is more asymmetric. A spherical agglomerate of critical radius R0 will reach a radius Rt at time t following R − R = at, a being a constant. This implies that the rate at which the number of aggregates is leaving the agglomerate is a constant, independent of the size of the agglomerate. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1627–1629, 2001

International audience; The Rayleigh-Gans-Debye approximation is used to investigate the small-angle, cross-polarized light scattering by a sphere of radius a, birefringence Δμ and relative index μ. If θmax is the polar scattering angle of the intensity maxima, the quantity Ûmax = 4πa/λ × sin (θmax/2) behaves in two different ways according to the signs of Δμ and μ − 1. When Δμ > 0, μ > 1 or Δμ < 0, μ < 1, then Ûmax varies from 2.8 to 4.1 as Δμ increases from zero. If Δμ < 0, μ > 1 or Δμ > 0, μ < 1, then Ûmax goes from 2.8 to about 6, thereafter decreasing to 4.1. Another interesting result is that the value of Ûmax for a highly briefringent sphere is 4.1 only for large diameters. It decreases to 4.0 when the diameter decreases.

Solutions of cellulose were prepared with liquid crystal phases by mixing cellulose, water and N-methylmorpholine N-oxide under appropriate conditions of concentration and temperature. Their rheological behaviour was studied using capillary rheometry. For each solution, flow curves were plotted over a temperature range of 70--120°C, and a shear rate range of 1--500 sec−1. Considerable agreement was found between the rheological and optical characterisations of the anisotropic-isotropic transition temperature T*. The variations of the strain rate sensitivity parameter m were studied over a large temperature range and particularly around T*. These results, new for cellulose solutions, provide some valuable information about the rheology of anisotropic polymer fluids.

Des solutions aqueuses anisotropes d'HPC presentent une texture en bande apres cessation du cisaillement et une contraction de l'extrudat en sortant du capillaire

Loss and storage moduli were measured by eccentric disk rheometry for isotropic and anisotropic hydroxypropylcellulose solutions. Two rheological regimes exist for the anisotropic solution, one at low deformation ratios (less than 80%) and one at high deformation ratios (more than 100%). For the high-deformation regime, the comparison between dynamic and steady-state parameters is consistent with what is known from the literature. The data on the low-deformation regime are new and are characterized by loss and storage moduli two orders of magnitude larger than those in the high-deformation regime. This difference is not due to a cholesteric to nematic transition nor to an elastic to viscoelastic transition (yield stress). It is postulated that a network of defects stabilized by chain molecules could give such a low deformation behavior.

The rheology of hydroxypropylcellulose (HPC)—acetic acid solutions was investigated by using a cone-and-plate rheometer and a capillary rheometer, for polymer concentrations ranging from 10 to 80%. Isotropic solutions exhibit a Newtonian plateau followed at higher shear rates by a pseudoplastic zone. The apparent viscosity varies as C5.2 if concentration C is less than 27% and as C13 for 27% < C < 30%. A biphasic interval (isotropic and cholesteric phases) exists between 30 and 35%. A maximum in viscosity is observed at C = 30%, the height of the viscosity peak being a decreasing function of shear rate. Anisotropic solutions are strongly viscoelastic. Both isotropic and anisotropic solutions give results (apparent viscosity, first normal-stress difference, relaxation time, etc.) which are not in good agreement with Doi's theory. This is understandable since the HPC chain cannot be modeled by a rigid rod. Upon heating, anisotropic HPC—acetic acid solutions undergo an anisotropic to isotropic phase transition which is easily detected by a maximum in the temperature dependence of the first normal-stress difference and of the apparent viscosity.

Small-angle light-scattering measurements have been made using micron-diameter isotropic and spherical polymer latex particles placed between crossed polarizers. Four-leaf clover patterns are obtained, reminiscent of those commonly found for spherical birefringent scatterers. The experimental results compare closely with predictions of Mie scattering theory for isotropic spheres.

Upon shearing, some polymeric liquid crystals develop a particular texture, called “band texture,” consisting of fine equidistant black lines as viewed between crossed polarizers. In mesomorphic hydroxypropylcellulose–water solutions, these bands are due to relaxation of the shear. The band texture appears after shearing at low shear rates and seems to exist during shearing at high shear rates (> 200 S−1). In the latter case, the steady-state first normal-stress difference is negative. The bands relax in a few minutes and parts of the bands form elongated domains. This texture gives a Hv light-scattering pattern which can be interpreted by the theory of scattering by anisotropic rods. These domains lose their elongated shape with time.

The band texture of a thermotropic cellulose derivative, trifluoroacetoxypropylcellulose, was studied by optical microscopy. The texture consists of parallel, long, thin, black lines when viewed between crossed polarizers with one polarizer parallel to the shear direction. These lines are perpendicular to the shear direction. Their optical properties indicate that the molecules are cooperatively oriented and this orientation director alternates from 0° to ±45° from the shear direction, with most of them at ±45°. This band phenomenon is identical to that observed with thermotropic nematic copolyesters.

Mean-square optical anisotropies, γ2, of cyanocyclohexane, bicyclohexyl, and the trans-4-cyano-trans-4′-n-alkylbicyclohexyls, NC—C6H10—C6H10—CmH2m+1, with m= 2, 5 and 7, have been determined from depolarized Rayleigh light-scattering measurements conducted on dilute solutions in carbon tetrachloride. The results are treated on the basis of additive contributions of group anisotropies: ΓCC=ΔαCC– 2ΔαCH and ΓCCN=ΔαCCN–ΔαCH, where the Δα denote the anisotropies of the polarizabilities of the indicated bonds. Diverse conformations of the bicyclohexyl system are taken into account. The value Γ′CC= 0.68 A3 required for bonds comprising this group appreciably exceeds the value of ΓCC= 0.53 A for the n-alkanes and presumably for the alkyl chains. Similarly, ΓCCN= 3.3 A3 is required for the cyano group attached to bicyclohexyl, compared with 2.15 A3 for the same group in acyclic nitriles and in cyanocyclohexane. These differences appear to be due to inductive effects that are known to impair a simple additive scheme. Contributions of members of the alkyl chain beyond the first to the tensor â representing the anisotropy of the polarizability virtually vanish when averaged over the configuration of the chain. Hence, properties such as the electric birefringence should be independent of the length of the alkyl chain under conditions that allow the latter to be in a random configuration. The quadratic tensor invariant, γ2=Tr(ââ), should increase gradually with chain length. The relatively large alternating effects in the values of γ2 for odd and even values of m are explained by the persistence of correlations in the directions of successive bonds of the alkyl chain. The effect of a departure of the principal axis of the polarizability tensor from the major geometric axis of the molecule is illustrated and its relevance to the anisotropic dispersion forces operative in liquid crystals is pointed out. The orientation-dependent energy attributable to the anisotropy of the polarizability is much smaller than would be required by the observed nematic–isotropic transition temperatures. This suggests that the large dipole moment of the molecules may be responsible for the nematic stability of the cyanobicyclohexyls.

International audience; Etude de la diffusion centrale de lumière polarisée par des bulles d'air dans une solution de cellulose dans le N-méthyl N-oxyde morpholine. La relation entre l'angle polaire θm et le diamètre de la bulle dépend de ce même diamètre