Rheological and related physicochemical studies on biopolymers are reviewed. Methods of determining viscoelastic constants of cylindrical gels were proposed and applied to various polymer gels. This was convenient to study the rheological changes induced by diffusion of ions into gels, and those induced by retrogradation of starch gels. A reel-chain model was proposed to understand the temperature dependence of elastic modulus of thermoreversible gels such as agarose, gelatin, poly(vinyl alcohol), gellan etc. This model was extended recently to understand the large deformation and yield behaviour of physical gels. Gelation process of various food biopolymers, soybean protein, casein, konjac glucomannan, gellan as well as the interaction between different biopolymers have been studied by dynamic viscoelastic measurement in combination with other physicochemical methods. Rheological behaviors of hyaluronan, a major component of synovial fluid, and of schizophyllan, anti-tumor active and very rigid rod polysaccharide, were studied. Viscoelastic properties of films of polysaccharides, amylose, pullulan, cellulose derivatives, konjac glucomannan were studied as a function of temperature and were analysed from the view point of molecular motion with NMR and dielectric studies as a basis of molecular understanding of biodegradability.
Polymer and rubber materials show remarkable nonlinear viscoelasticity. The nonlinearity may be due to change in material structures, i.e. entanglement and filler structures. The way of thinking leads us to make simultaneous measurements of the responses to large stimuli and additional responses to perturbative stimuli, i.e. differential dynamic modulus and volume resistivity. It has been found that nonlinear viscoelastic properties of entanglement and filler dispersed polymeric systems originate with ruptures in entanglement and filler networks. In addition, microphase separation structures of model graft copolymers have been studied.
Low molecular weight polyethylene based on metallocene technology was first commercialized in the world in 2004 as a functional additive by Mitsui Chemicals, INC. We found many advantages for polymer processing, these are increase output, save energy consumption, reduce die build-up and scorching using the new additive without any side effect on products quality. In this work, the improvement mechanisms of polymer processing properties were investigated quantitatively by means of single screw extruder experiments and rheological analyses. Effect of wall slip is dominant for improve the extrusion property.
This paper includes two topics on the nonlinear elongational flow behavior from the viewpoints of a small amount of long relaxation time mode and physical gelation network structure. First one is polypropylene (PP). PP is a well-balanced material in terms of the physical properties such as the stiffness and heat resistance, and the cost. PP is, however, one of the linear polymers exhibit low melt strength and weak strain hardening. We focused on an introduction of a small amount of high molecular chain in order to enhance the strain hardening under elongational flow. This system showed unusual rheological behavior: strong elasticity, two-step nonlinear damping, strong strain hardening. This polymer system is very complex comparing with conventional PP in terms of the miscibility of the matrix and ultra-high molecular weight component. Another is poly(vinyl chloride)(PVC)/plasticizer systems. PVC forms physical gels in various solvents. We focused on the rheological behavior of high PVC concentration systems, since the physical properties and structure have been extensively studied mainly for low polymer concentration system. PVC/DINP system showed same relaxation exponent n with the value of the low concentration system reported previously. We observed change of the elongational flow behavior of sol-gel system such as PVC/plasticizer system with temperature. These behaviors from the view point of critical gelation phenomena has not been reported so far as much as we know.
A novel diisocyanate, 1,2-bisisocyanate ethoxyethane (TEGDI) whose backbone is ether bonds, was used for the preparation of polyurethane elastomers (PUEs). Highly softened TEGDI-based PUEs were successfully prepared on account of flexibility of TEGDI itself and weaker phase separation. A relationship between conformation and molecular mobility of the soft segment were investigated using dynamic viscoelastic measurement. The peaks of α relaxation of the soft segment chains were clearly observed in the loss tangent (tan δ) curves at various strains. The onset temperature of α relaxation decreased with increasing strain. This result indicates that the size of cooperative motion of the glass transition decreased due to the orientation of the soft segment chains with increasing strain. The effect of the micro-aggregation structure on the rheological properties of thermoplastic polyurethane (TPU) were investigated. The TPUs showed the strain hardening of uniaxial elongation viscosity with increasing annealing temperature owing to residual hard segment domains at an operating temperature. It was revealed that the formation of well-organized hard segment domains had a profound effect on the rheological properties of TPUs, in particular on their elongational viscosity.
Viscoelastic properties of wet pulp fiber networks as a function of fiber concentration were investigated with a parallel-plates type rheometer. The dynamic storage moduli, G', of the networks were independent of angular frequency: i.e., they are the pseudo-equilibrium moduli. A power law correlation was found between the moduli and volume concentrations, cv, of the networks: G' = kcvα. The factor, k, changed with the beating degree, which is an index of fiber flexibility. This indicates that the factor, k, reflects the individual fiber characteristics. On the other hand, the exponent, α, was constant and the value was written as three for all the measured fiber networks, regardless of the beating degree. This indicates that the exponent does not reflect the individual fiber properties but the properties of the whole network structure.
This article investigates the applicability of inverse methods in estimating the best values to be assigned to certain parameters which appear in turbulent flow studies of dilute polymer solutions in circular pipes. These parameters naturally arise when the Nagano-Hishida low-Re, k-ε model is combined with a special form of the Generalized Newtonian Fluid model modified in such a way that it could account for the elasticity of dilute polymer solutions. This multi-objective problem is treated by a positively weighted convex sum of the objectives. Then the procedure is followed by a well-known Gauss-Newton nonlinear optimization method for optimizing model parameters in order to better predict the drag reduction phenomenon using polymeric additives. Parameter optimization relies on the availability of experimental data for the velocity profiles, friction factor, and turbulence kinetic energy for at least one concentration of a given polymer. It is shown that using these optimized parameters, it is possible to predict with more accuracy the amount of drag reduction achievable using a given polymeric additive. It is also shown that these parameters may neither work for other concentrations of the same polymer nor necessarily for any concentration of any other polymer, inferring that for non-Newtonian fluids these parameters are not at all universal.