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New nanocomposite films were prepared with atactic polypropylene as the matrix and either of three types of cellulose whiskers, with various surface and dispersion characteristics, as the reinforcing phase:  aggregated without surface modification, aggregated and grafted with maleated polypropylene or individualized and finely dispersed with a surfactant. Films obtained by solvent casting from toluene were investigated by means of scanning electron microscopy, dynamic mechanical analysis, and tensile testing. In the linear region, the mechanical properties above the glass−rubber transition were found to be drastically enhanced for the nanocomposites as compared to the neat polypropylene matrix. These effects were ascribed to the formation of a rigid network with filler/filler interactions. In addition, interactions between the filler and the matrix as well as the dispersion quality were found to play a major role on the mechanical properties of the composites when investigation of the films was performed in the nonlinear region.

Apolar organic suspensions of rodlike cellulose whiskers modified by a surfactant are investigated by small angle neutron scattering. Guinier and Porod analyses are performed to characterize the increase of cross-sectional radius of gyration observed between organic and aqueous suspensions of whiskers. In addition, a comparison with theoretical curves for fibers with homogeneous rectangular cross sections finally leads to typical cross-sectional dimensions of ca. 120 × 210 Ų for the modified whiskers in organic solutions while those in water have 88 × 180 Ų sizes. It is concluded that the modified whiskers are coated with a surfactant layer of 15 Å thickness in a rather folded conformation.

The mechanical properties and structure of composite films made of high-Tg polystyrene (PS) nodules dispersed in a low-Tg poly(butyl acrylate) (PBuA) matrix were studied by means of dynamic mechanical spectrometry and small-angle neutron scattering. At temperatures between the Tg of PS and PBuA, the mechanical properties depend drastically on the spatial distribution of the glassy PS domains. For films cast from mixtures of PS and PBuA latexes, an aggregation of PS particles into dense clusters dispersed in the PBuA matrix was observed. As a consequence, a large density of contacts between PS particles in the dry films ensured a strong mechanical reinforcement above a percolation threshold of 30% PS volume fraction. Extensive coalescence of PS particles occurred at their contacts upon annealing the films above the Tg of PS, leading to further mechanical reinforcement. For films cast from core−shell particles, the aggregation phenomenon was prevented, depending on the coverage of the PS core by the PBuA shell. An efficient core encapsulation in the core−shell morphology led to poor contact between PS cores, the elastic moduli were then close to that of the PBuA matrix, and the PS coalescence upon annealing was prevented.

The alignment of cellulose microcrystals in a 6.9% (w/w) colloidal aqueous suspension under shear was characterized using small angle synchrotron radiation scattering. Prior to shearing, the microcrystals appeared randomly oriented and went through a two-step alignment process with increasing shear rate. At shear rates lower than 5 s^-1, the X-ray scattering patterns indicated little or no preferential alignment in the shear direction; however, in the plane perpendicular to the shear direction, the microcrystals were preferentially oriented in the vertical direction. At shear rates of 5 s^-1 and higher, the microcrystals were aligned horizontally along the shear direction. These orientation phenomena were found to be dependent on shear rate and completely reversible. They are likely due to the presence of planar domains of randomly oriented microcrystals which align at low shear rates and are broken up at higher shear rates enabling alignment of the individual microcyrstals.

The mechanical modulus and internal friction of As2 Se18, glass were measured in the temperature range 175-290K and frequency range 103-1 Hz. The results show that physical ageing at 293 K decreases the height of secondary relaxation peak by more than half its original value, and little change in the temperature dependence of the modulus occurs. The rates of secondary relaxation obtained from the isochronal and isothermal methods differ, due mainly to the rapid increase in the amplitude of relaxation with temperature.

Amorphous cellulose exhibits two mechanical relaxation processes, so-called γ and β, below its glass transition temperature Tg. Though much work has already been published on the subject, the origin of these relaxations is still uncertain, especially because most of the dynamic mechanical data were obtained at constant frequency and mixed together with dielectric data. In order to reach more definitive answers, two main approaches were taken in this work, namely (i) the use of a low-frequency mechanical spectroscopic technique and (ii) the comparison with data of different polysaccharides, having different lateral groups and different intramolecular links along the main chain. In addition, preliminary molecular modeling based on molecular mechanics was performed on isolated chains in vacuum. The work is focused on dried cellulose, to minimize the effect of relaxation overlap, which becomes negligible for moisture content lower than 2%. The results show that the γ process occurs without cooperativity and confirm its origin in the rotation of primary hydroxyl groups. In fact, in contrast with the β relaxation, its activation energy does not involve significant entropic contribution, and molecular modeling suggests that the rotation of those lateral groups does not lead to conformational change in the rest of the chain (no cooperativity). The activation energy of the β relaxation involves an entropy contribution that varies with the water content.