An experimental study of elongational flow behavior in melt spinning process is reported. In general, elongation al viscosity of running filament is a function of shear history, elongational strain rate, and time, as well as temperature. Viscosity in the vicinity of the spinneret along the spinline is influenced by the shear flow in the spinneret, and is different from that of the elongational flow. The elongational viscosity increases with decreasing temperature and still increases as time passes in the region far from the spinneret, where elongational flow is fully developed. The increase of the elongational viscosity with time in melt spinning corresponds well to the results of constant-strain-rate experiments. The elongational viscosity in constant-strain-rate experiments rapidly increases with time at a certain critical strain. The rapid increase behavior does not depend on strain rate, temperature, and average molecular weight, but depends on molecular weight distribution and chain branching. These elongational flow properties have been discussed in terms of rheological models

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The shear stress and a normal stress difference, equivalent to the sum of the first and the second normal stress differences, were measured for a concentrated polystyrene solution in double-step shear deformations; i. e., two shear deformations were applied to the material in sequence and then the stresses were measured. When the time interval between two deformations was relatively small, the observed stresses long after the deformations were described well with the BKZ constitutive model. The stresses at short times were smaller than the values predicted with this model except for the case where two deformations have the same sign, or the same sense. A simple calculation based on the tube model of entanglement led to an expression, which gave a better prediction of the stresses. The BKZ model fails at short times probably because it does not take proper account of two different relaxation mechanisms, one due to the equilibrium process of chain contour length and the other due to the disengagement process of the chain from the deformed tube-like region.

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The “dielectric normal mode process”, dielectric relaxation due to fluctuation of the end-to-end vector of flexible polymer chains, was investigated for solutions of cis-polyisoprene in two good solvents, benzene and toluene, and in a θ solvent, dioxane. The width of the distribution of the relaxation time increased with increasing concentration C. This behavior was explained based on the tube model by considering three kinds of motions of the chain: (i) orientation of the parts of the chain ends having a size of molecular weight between entanglements M_e, (ii) stretching of the chain in a tube, and (iii) chain disengagement from tube or reptation motion. The relaxation time τ_n for the normal mode process also increased with increasing C. In the semidilute range of 0.02<C<0.2g/cm3, the C dependence of τ_n conformed to the dynamic scaling law by de Gennes. In the C range above 0.2, τ_n increased steeply with C on account partly of the increase in the friction constant ζ for the molecular motion and partly of the entanglement effect. We reduced the values of τ_n to those for the iso-friction-constant state (τ_nζ), assuming a linear relation between the relaxation time τ_s for the segmental motion and ζ. The τ_nζ thus obtained was proportional to C^1.3 in the semidilute range and satisfactorily compared with the dynamic scaling theory based on the free draining model.

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The rheological properties in the melt state were investigated for several blends composed of butyrylated, caproylated or lauroylated wood and synthetic polymers, methyl methacrylate (MMA)-ethyl methacrylate (EA) copolymer and poly (methyl methacrylate) (PMMA). The results of viscoelastic measurements gave excellent time-temperature superposition for most of the blends. However, the superposition was not possible for blends with more than 90 % of the wood esters of higher aliphatic acids. Similar behavior is known for corresponding cellulose derivatives which are partially crystalline. The successful time-temperature superposition for the blends suggests the mutual plasticization among the derivatized wood components and also with the synthetic polymers in the blends. Also, it has been found that the better the compatibility of the chemically modified wood with synthetic polymer, the easier the occurrence of thermal flow, and the smaller the broadening of the second plateau, which is caused from the formation of higher ordered structures with longer relaxation times. In fact, the blend of butyrylated wood with MMA-EA copolymer, which shows the highest compatibility among samples used in this study, reveals the flow phenomenon within the range of the measurements, showing typical viscoelastic behavior starting from rubbery plateau to the flow. In the case of the blend of lauroylated wood with PMMA, which was confirmed to be a blend composed of two distinct phases, the viscoelastic properties of the blend sample became less temperature sensitive as the amount of lauroylated wood in the blend was increased. This trend can be understood by the reflection of the low temperature-dependent viscoelastic properties inherent in lauroylated wood. The compatibility of the chemically modified woods with synthetic polymer was measured on the corresponding films by the torsional-pendulum method, and evaluated in regard with the appearance of T_g, peaks in the logarithmic decrement-temperature curve. Furthermore, it was confirmed by the observation with a scanning electron microscope that the second plateau, which appears from the end parts of the rubbery plateau, broadens, when some fibrous residues of the chemically modified wood remain in the blend sample.

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Flow behavior of suspensions of needle-like pigmental goethite dispersed in ethylene glycol has been studied with the steady-s ate and the step-shear-rate methods. All suspensions exhibited pseudoplastic flow in both methods. In the step-shear-rate method, the dispersing state of powder was assumed to be constant during the measurement. The flow curves in the low shear rate region were expressed by
τ=α_1/2φ_F²D^1/22+η₀(1-φ_F/0.74)^-1.85D (1)
where τ is shear stress, D shear rate and φ_F effective volume fraction of the dispersed phase, a measure of dispersed state. The value of φ_F at each shear rate was estimated from the results of the step-shear-rate measurements. Applying the value of φ_F thus obtained to the corresponding shear rate in the steady state flow, steady state flow curves in the high shear rate region were expressed by
τ=α₁φ_F²D+η₀(1-φ_F/0.74)^-1.85D (2).

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Stress relaxation and hysteresis curves were measured for six types of surgical sutures, i.e. Plain and Chromic Catguts, Dexon, Silk, Nylon and Nespolen, by means of the Tensilon (UTM-4L, Toyo Baldwin). The relative relaxation strength or the per cent decrease of stress at 10m was high in Silk and Nylon, while low in Plain and Chromic Catguts. The relative relaxation strength did not depend significantly on the size in each kind of sutures except Silk, Nylon and Nespolen with size No.1-0. Stress relaxation was measured over the time range of 0.01s-600s. The results were well reproduced through f(t)=f₀/(t-t₀)^m. The constants f₀, t₀ and m were evaluated by the least square method. The relaxation spectra H(τ) for simple elongation were analytically derived as H(τ)=(t_m/τ)^m{E_g/Γ(m)}exp(-t_m/τ) by using the inverse Laplace transformation of the relaxation modulus E(t), where E_g is the glasslike elastic modulus, t_m=t₁-t₀, t₁ time with the practically maximum stress, Γ(m) the gamma function.

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Aromatic Polyamideimide (PAI) films were reinforced by aromatic polyamide fiber as unidirectionally oriented composite (Type 1), bidirectionally oriented laminate composite (Type 2), and bidirectionally oriented cloth composite (Type 3). The stress relaxation and thermal expansion of the composite films were investigated with respect to direction of fiber orientation. The behavior of the unidirectionally oriented composite film was more anisotropic than that of other composite films. In the cloth composite film, the elastic behavior was isotropic. The thermal expansion behavior was isotropic in the laminate composite film. Thus the anisotropy of elasticity of the composite films does not always correspond to that of thermal expansion.

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Natural rubber vulcanized in swollen state (SC-sample) is expected to have different topology of chain network compared with the sample vulcanized in dry state (NR-sample,. These two types of samples were employed to investigate the effect of the physical flow on chemical stress relaxation. SC-samples showed much lower values of Mooney-Rivlin's C₂ term than those for NR-samples, and broke at relatively small strains before the hardening due to crystallization occurred. The unique stress-strain behavior of the SC-samples, especially at the low network chain density, may be attributable to the sparseness of inextricable chain entanglement. The stress for SC-samples decreased exponentially with time and the rate of stress decay at short times was lower than that for NR-samples on chemical stress relaxation tests. Furthermore, the stress decreased very rapidly at the last stage of degradation. It is suggested that the most important difference between SC and NR-samples lies in the degree of trapped entanglement of the network chain. Such entanglements present amply in NR-samples give rise to a physical flow in addition to the chemical stress relaxation.

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