Differences in molecular properties of celluloses from different biological origins were investigated chiefly in terms of the rheological properties of their solutions in 8 wt % LiCl/N, N-dimethylacetamide (DMAc). Cotton linter (CC) and dissolving pulp (DP) were used as cellulose samples derived from plant, and a cellulose from Acetobacter xylinum was also used as a bacterial cellulose (BC). For the three kinds of cellulose solutions, the values of η0 − ηs (η0: zero shear rate viscosity of solution, ηs: solvent viscosity) were in proportion to the weight fraction of polymer, φw, in the dilute region. On the other hand, they were in proportion to φw4 for the CC and the DP solutions and φw3 for the BC solution in the semidilute or concentrated region. This φw-dependence of η0 − ηs shows that CC and DP, celluloses from plants, behave as a flexible polymer and that BC behaves as a rodlike polymer, according to several molecular theories. Plateau modulus, GN, was in proportion to φw2 for the CC solution, signifying that network structure by entanglement was formed in the CC solution, as is often observed for solutions of flexible synthetic polymers. On the other hand, the concentrated solution of BC showed the typical small-angle X-ray scattering (SAXS) profile of two-phase systems, which can be well approximated by Debye-Bueche equation. This fact indicates that the structure of the BC solution apparently differs from the network structure.
Molecular orientations of the crystalline and the amorphous phases are studied in relation to morphology using an instrument constructed for simultaneous kinetic measurement of microscopic infrared (MicIR) dichroism from a pre-determined sampling area and macroscopic stress of isotactic polypropylene (iPP) thin film uniaxially stretched at a constant strain rate at room temperature. The morphology imposes important influences on profiles of MicIR dichroism as a function of stretching time and also on a relationship between the orientation functions, fc and fam, of the crystalline and the amorphous phases. Linear relationships between fc and fam are found for the local areas without giant spherulite inclusions when fam<0.3~0.4, suggesting the harmonious developments of amorphous chain deformation and lamellar orientation during the necking propagation. The proportionality constant between fc and fam is not universal but is strongly dependent on the morphology of the surrounding area where the local area under examination is located. The linear relationship between fc and fam is completely invalidated for describing the relationship between the amorphous chain deformation and the lamellar orientation inside the spherulites, which reveals that the deformation mechanism in the spherulite is different from that in the microcrystalline region.
The dynamic viscoelasticity of solutions of multi-arm star polystyrenes is investigated. The relaxation spectrum is calculated from the master curves of the dynamic storage and loss moduli. The relaxation spectra for the solutions as well as the melts exhibit a shoulder at long times. The relaxation intensity and the relaxation time for the long time relaxation are estimated from the relaxation spectra. The relaxation intensity strongly depends on the number density of the star molecules, suggesting that the number density dependence of the relaxation intensity is closely related with the degree of interpenetration between the star polymers, while the relaxation time of the long time relaxation is almost independent of the number density of the star molecules.
The 2D flow of a molten film in the film casting process is studied by particle tracking method. From the image analysis, the velocity field and the film thickness are obtained in the area between the exit of an extrusion die and the contact line on a chill roll. The results indicate that the central part of a film undergoes planar deformation while the edge part undergoes uniaxial deformation. This is the first direct confirmation of the Dobroth-Erwin's model for the flow of the film casting process.
We propose a theory to predict the neck-in behaviour of polymer materials in the film casting process. To calculate the neck-in length, we employ the Dobroth-Erwin model 2) which assumes that the film deformation is planar in the central part, and uniaxial at the edge. We derive an equation for the edge line of the film and an expression for the neck-in length. For Newtonian fluid, the neck-in length is shown to be given by L/√2 , where L is the length of the air gap. For viscoelastic fluid, the neck-in length depends on the draw ratio. As an example, the neck-in length is calculated for Maxwell model, and the result is compared with experimental data.
Experimental evidence for radial particle migration in a pressure driven tube flow of a non-Newtonian viscous concentrated suspension will be presented. The suspension is a well-characterized, mono-modal nickel spherical particles having 30% volume fraction. The particles experienced a drift particle concentration profile as a function of the radial position. SEM technique was used to capture micrographs of the sample at various sections in the axial flow direction with a specially designed capillary split die. With the help of image analytical software, the distribution of particle concentration as a function of radial position was obtained. Finally, comparisons were made between experimental results and numerical predictions based on a continuum diffusive-flux model for shear-induced particle migration. Good agreement between experimental observations and numerical predictions indicated that the procedures were useful in capturing particle migration in steady-state isothermic extrusion flow which exhibits a near plug-like concentration profile.