This report extensively summarized a series of researches on the properties, especially flow behavior, of high polymeric materials concerning the polymer processing made by the author of this paper and his co-workers. Since the high polymeric materials are in most cases viscoelastic, they show a lot of peculiar and diverse flow behaviors. In this paper, various types of the peculiarities and problems in the flow behavior of the polymer melts, such as melt viscosity characteristics, melt fracture, and p-v-T characteristics are discussed. Flow characteristics has long been known to be one of the most fundamental properties govering the polymer processing operation. In recent years, many researchers found the great importance of the pressure effect on the melt flow properties and cooling effect on the mechanical properties of the products. As a result, it will be one of the research trend to study the p-v-T state characteristics of the high polymer, which would give a clear explanation to the above mentioned effects. The matter the author wish to emphazise throughout this paper is that the rheology has a close relationship with polymer processing and many problems in the polymer processing can be solved through detailed rheological investigations. Thus the author and his co-workers will find it a great pleasure if their researches on polymer processing will be help of progress in the polymer technology. Finally, the author is deeply indebted to many distinguished researchers and outstanding scientists for promotion of the researches mentioned above.
Studies on integral and differential consitutive equations by the present authors are summarized and some new results are presented. Applicability of various constitutive equations to some typical deformation modes is investigated. In integral equations, superiority of the BKZ model is established. But it is also known that the model fails in a prediction of stress relaxation for double-step shear strains in which the second step strain is applied in the opposite direction to the first. A stress dependent constitutive model of integral type proposed by the present authors can describe this double-step stress relaxation very well as well as ordinary single-step stress relaxation and shear rate dependence of viscosity. Compared to integral equations, applicability of differential equations is limited. The Leonov model is very useful to predict viscoelastic functions in steady shear flow, but it fails in describing both stress relaxations for a step strain and after cessation of steady shear flow. The Giesekus model gives slightly better predictions for steady shear flow and for these stress relaxations, but fundamentally the Giesekus and Leonov models cannot be accepted as exact models for stress relaxation. On the other hand, the Larson model can describe both stress relaxations well, but it gives too strong shear rate dependences for viscosity and coefficient of first normal stress difference. It is concluded that further studies on stress dependent model of either integral or differential type will yield fruitful development of constitutive equations.
When a high-molecular-weight polymer chain adsorbs onto more than two particles and causes flocculation in colloidal suspensions, the effect is referred to as bridging flocculation. The suspensions flocculated by polymer bridging show unique rheological behavior due to long-range interaction and flexibility of bridges. The mechanisms of unique rheological behavior are discussed in relation to the bridging conformation. The suspensions respond elastically to small deformation when both the particle and polymer concentrations are increased above some critical levels. Although the elasticity arises only from the attractive forces between particles, the three-dimensional network structure must be developed over the system for elastic responses of suspensions. The network formation process is analyzed on the basis of site-bond percolation. Scaling arguments enable us to show a power law dependence of elasticity on the difference of probability from the critical value. For site percolation process, the critical site probability and scaling exponent are independent of bridging conformation. However, the scaling analysis is not applicable to the bond process, because a collection of particles connected by one polymer chain may behave as a unit floc and a series of bridges in the floc cannot be broken to non-interacting bonds.