The orientation of molecular chains in injection-molded resins significantly affects their properties such as mechanical and optical properties, and is important from engineering point of view. The process of injection-molding is an exceedingly complex phenomenon involving an unsteady flow and heat conduction, and in the case of semicrystalline polymers, nonisothermal crystallization as well. Essentially, the orientation of molecular chains in injection-molded resins can be regarded as the flow-induced orientation which has subsequently been frozen-in by cooling and solidification, and rheological and thermal properties of polymers play important roles in orientation process. Interest in the analysis of the orientation process of molecular chains in injection-molding has continued for many years, and recently the analysis has reached to the stage of quantitative treatments. This paper reviews these studies. Most of these analyses are made by taking account of the growth of stresses (shear stress cr shear and normal stresses) in resins and their relaxation within the mold cavity.

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It is still impossible to estimate the distribution of the molecular-weight (chain-length) between two crosslinks of a crosslinked polymer, because of its insolubility and infusibility. The distribution p (x) of chain-length between crosslinks x will be estimated by chemorheological means.
If the scission rate of chain is proportional to x, the rate of stress relaxation due to the main chain scission is related to p (x) through Laplace transformation. p (x) thus obtained is likely to indicate the real distribution, because the same result can be obtained for a given crosslinked polymer from different chemical stress relaxation curves at different high temperatures.

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Draw resonance in isothermal melt spinning was studied for the Newtonian, the power law and the viscoelastic liquids, respectively. The viscoelastic fluid model used was a convected Maxwell model with deformation rate-independent viscosity. The onset and growth of the draw resonance instability were found to be dependent upon the draw-down ratio and the melt flow properties of molten polymers.
Further, disturbance amplification in isothermal melt spinning was studied for the Newtonian thread on which a continuous disturbance with a sinusoidal wave was imposed. Exact wave form of spinline diameter was sought by solving numerically the simultaneous partial differential equations of melt spinning in their original form without recourse to perturbation. The solutions were obtained in terms of the growth of disturbances imposed at the spinneret exit end of the threadline. Theoretical analysis showed the existence of characteristic frequencies giving maximum sensitivity to the sinusoidal wave disturbances. Further, it was suggested that onset and growth of draw resonance became depressed by imposing disturbances having certain frequencies on the threadline.
The draw resonance and disturbance growth experiments were carried out using a water quenched air gap melt spinning apparatus. Continuous disturbances of a frequency range more than 20 Hz were imposed on the running spinline using an oscillator which was set near a winding device. The changes in diameter of the taken-up filament were investigated in terms of the draw-down ratio and the frequency of disturbances. In the case of draw-down ratio more than 20, which is the critical value of occurrence of draw resonance for a Newtonian fluid, the original draw resonance wave amplitude decreased under certain disturbances having a characteristic frequency. This dynamical phenomenon was in good agreement with that obtained theoretically. On the other hand, when the draw-down ratio is below 20, which corresponds to the stable melt spinning region, a characteristic frequency which makes the filament diameter variation maximum was found to exist. This also showed good agreement with our theoretical computation results.

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Present situation of the application of polymer rheology to industrial problems was discussed from a macroscopic point of view, and it was concluded that it still remains below the level we can reasonably expect. It was also pointed out that two sets of systems of different principles are generally standing in parallel for testing materials; namely the traditional one modified originally from that for steel and iron and the new one based on the application of polymer rheology.
Two pieces of proposal were then recommended to raise the level up to that expected. The first one is the use of the material parameters of the phenomenological rheology model to characterize the rheological properties of polymer samples when the chemists employ the black-box technique to optimize the polymerization recipe. The second one is to reconstruct the entire series of traditional performance tests by the application of polymer rheology and others so as to reproduce substantially the mechanical excitation in service condition. Practical ways of approach of the proposal were also discussed somewhat in detail.

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High-resolution solid-state ¹³C NMR analyses have been carried out for dry gel films and their ultradrawn films of high molecular weight polyethylene in terms of ¹³C chemical shifts, spin-lattice and spin-spin relaxation parameters. In the dry gel films, the noncrystalline region consists of the crystalline-amorphous interphase with the thickness of about 20 Å and the rubbery amorphous component is completely devoid. This characteristic structure is subjected to a drastic change by annealing at 145°C; a large amount of rubbery component appears with thickening of the crystalline lamella. Although such a structural change will also occur prior to and during drawing at 145°C, ultradrawing is possible up to 150 times under the condition used in this work. The effects of drawing appear mainly in the noncrystalline region at lower draw ratios; the rubbery component considerably decreases in mass fraction and the halves of the decreased fraction are transformed to the interfacial component and the monoclinic crystalline component. At draw ratios higher than 100 the noncrystalline chains seem to undergo further extension and the orthorhombic crystals increase possibly as a result of the transformation of the rubbery component→the interfacial component→the orthorhombic crystals.

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Light scattering and rheological properties of the chitosan (degree of deacethylation=74.8%) solutions in 8.5% formic acid/0.5M sodiumformate (F/FNa) or 2% acetic acid (Ac) aqueous solutions were measured by means of a low angle laser light scattering photometer (Chromatix, KMX6) and a cone-and-plate type Weissenberg Rheogoniometer (Sangamo Controls, R18). Rayleigh ratio of the extremely dilute F/FNa system (~10^-5g/ml) increases with increasing time and becomes constant within 20~30min. Weight average molecular weight M_w increases from 87.3×10⁴ to 625×10⁴. That is, even in the low concentration, chitosan molecules are likely to associate in the F/FNa system. On the other hand, molecular association can not be observed in the Ac system. The persistence length of the chitosan molecule which is obtained with SAXS is about 120Å and 147Å in the F/FNa and the Ac system, respectively. The zero shear viscosity of solution subtracted the solvent viscosity is proportional to c¹ in c<0.1% and to c^4·4 in c<0.5% in the F/FNa system and it is proportional to c^1·8 and c^5·4 in the Ac system below and above 1.29%, respectively. Here, c is the concentration of the chitosan. Although the apparent molecular weight of the chitosan in the F/FNa system is much higher than that in the Ac system, the viscosity of the former system is lower than that of the latter system in dilute region (c<0.7%). This suggests that the chitosan molecules associate relatively compact in the F/FNa system.

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The dynamic viscoelastic properties of six commercial isotactic polypropylenes with well-characterized molecular weight and molecular weight distribution were investigated in molten state. For the series of polypropylenes, the molecular weight distribution at high molecular weight range, as expressed by M_z/M_w, was broader as the melt flow index was higher or the molecular weight was lower. Following relations were obtained for the zero-shear viscosity η₀, the characteristic relaxation time λ₀, and the ratio λ₀/η₀: η₀∝M_w^3.1, λ₀∝M_z^3.3, λ₀/η₀∝(M_z/M_w)^2.7, λ₀/η₀∝M_z·M_z+1/M_wM_n. The temperature dependence of η₀, λ₀, and λ₀/η₀ was of the Arrhenius type and the activation energies were 10.0 kcal/mol, 5.7 kcal/mol, and -4.3 kcal/mol, respectively: Contrary to the common knowledge, the ratio λ₀/η₀ increased as temperature increased. The storage modulus G′(ω) and loss modulus G″(ω) increased more slowly as the molecular weight distribution was broader, and the modulus at which G′(ω) is equal to G″(ω) was lower as the molecular weight distribution was broader. Irrespective of the kind of sample and temperature, the plots of log G′ against logG″fell on a curve approximated by a straight line, and hence it was conjectured that the elasticity at fixed value of viscosity does not change over the range of samples and temperatures studied in this experiment.

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By using a tensile testing instrument (UTM-4L Toyo Baldwin) and a Log-timer ( Japan Synthetic Rubber Co.) stress-strain diagrams and stress relaxation curves were examined with three kinds of synthetic artificial grafts, Tricot knitted Dacron (TD), Woven Dacron (WD) and Gore Tex (GT), in wet and dry states. Each graft was cut up into equal pieces with the initial length of ca. 10mm and the width of 5.0mm. The specimen of WD was composed of 22 warps in longitudinal (Lon) and 20 wefts in circumferential (Cir) directions and the specimen of TD was composed of 15 wales in Lon and 8 courses in Cir. In the wet state, the strips were immersed in Ringer's solution at 20°C or 37°C while in the dry state the strips were kept at 20°C with 60-65% in humidity or at 37°C with 64-67% in humidity. Stress-strain curves were fitted by an exponential function: σ=σ₀{exp (γ/γ₀)-1}, where σ is the stress, γ is the Green-St. Venant strain and σ₀ and γ₀ are constants evaluated by a non-linear least squares method for the stress up to 5×10⁷dyn/cm² The relaxation force f (t) was fitted to an equation f (t)=f₀/(t-t₀)^m with f₀, t₀ and m being constants determined by a least squares method. It is discussed in relation to the structure and the material of the artificial grafts.

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The dynamic viscoelastic properties of polypropylene melts filled with calcium carbonate and talc of 0-60wt% have been measured in the temperature range of 200-280°C. Irrespective of the kind of filler, filler content, and temperature, double logarithmic plots of storage modulus G′against loss modulus G″fall on a curve approximated by a straight line, including the cases where G′(ω) shows a second plateau. It is conjectured that the relative strength of elasticity at fixed value of viscosity does not change in particulate-filled polypropylene melts at small deformations.

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