It is necessary to consider both the processing property and the product property as the quality of plastics. The product properties are determined by the primary structures of resin and the higher-order structures of product which are produced as a result of processing, and it is important to clarify the relationships among the primary structures of resin, the processing conditions, the higher-order structures of the product and the product properties. The processing properties contain two aspects, the behavior of resin in processing and its influence on the higher-order structures of product. The processing properties are determined by the primary structures of resin and the processing conditions, and are related with the rheological and thermal properties of resin. This paper takes the injection-molding of polypropylenes as an example of polymer processings, and treats structure-property relationships and an analysis of molecular orientation process based on the rheological and thermal properties, namely the influence of the processing behavior on a higher-order structure of product.
Viscoelastic properties of disperse systems of pigments, especially of carbon black in linseed oil, were investigated. The dynamic modulus and dynamic viscosity decrease with increasing amplitude of strain. The decrease of the former is more marked. The difference may be consistent with the concept that the stress is supported by the network structure formed by the particles and that the structure is destroyed with increasing amplitude. The second plateau modulus, the equilibrium value of the dynamic modulus in the low frequency region, continues to be observed up to quite a high amplitude. The effects of varying magnitude of shear strain and rate of shear on dynamic viscoelastic properties and the stress relaxation can be described using the box type relaxation spectrum, which varies with deformation state. The long time portion of the relaxation spectrum becomes lower in deformation; the critical relaxation time is determined by the rate of shear and the degree of lowering depends also on the period of flow. The behavior is interpreted by taking into account the process of network formation and breaking down. Shear stress development after sudden initiation of steady shear flow showed a remarkable overshoot phenomenon. The elastic properties of the network structure of dispersed particles can also be evaluated from the creep and creep recovery experiments. The critical strain for breaking down of the structure, determined from the relationship between shear stress under steady flow and recoverable strain, is approximately equal to the strain at which the stress attains maximum at the start of shear flow.
Rubber vulcanizates in the state of swelling equilibrium with benzene were cooled, and the freezing point depressions (FPD) were measured. It was found that the FPD of the crosslinked rubber sample was larger than that of the uncrossliked one at the same concentration. For polydimethylsiloxane the FPD of bimodal network was larger than that of unimodal network. Here the bimodal network means the network prepared by the end-linking of two prepolymers having different average molecular weights; it has a wider distribution in mesh size of network (chain weights between crosslinking points) than the unimodal network, and may be regarded as a model of the inhomogeneous network. Thus, the result suggests that the inhomogeneity of the network structure can be detected by the cryoscopic method. For uncrosslinked rubber systems the larger FPD was observed with increasing concentration, decreasing molecular weight, and decreasing χ-parameter. Though we may qualitalively explain these features by the Flory-Huggins lattice model, we observemore complex behavior: the compressive moduli of swollen rubber vulcanizates decreased with lowering temperature, and fell rapidly from a certain value to zero when the sample freezes. This may be considered to be associated with a phase transition phenomenon. With lowering temperature, the intrinsic viscosity of rubber solutions decreased and the content of benzene in swollen samples decreased. Swollen samples became turbid in the vicinity of 283K. The result may suggest that with lowering temperature the concentration fluctuation becomes large as the solvent becomes poor. By further cooling, it is considered that crystallization of benzene occurs first and then the swollen samples freezes and contracts.
The rolling ball method was used to study rheological properties of gelatin solution. The motion of a stainless steel ball in a slanting glass tube filled with the solution was observed. In order to attain turbulent flow, we chose the ball of 1.113 cm diameter and the tube of 1.650 cm diameter. The achievement of the turbulent flow condition was checked from the theoretical and experimental points of view. The terminal velocity of the ball in the 0.5% aqueous solution of gelatin exceeded that in water when the slope of tube exceeded 64°. Whether the ball was rolling or sliding in this region was examined by taking multiple exposure photographs, using the ball marked with a small piece of fluorescent adhesive tape. At the beginning the ball was rolling normally. Soon the sliding was combined with rolling, the rate of rotation gradually decreased, and then the rotation completely stopped. Finally, the ball rotated in reverse direction. Such behavior was never observed in pure water. The possible causes of this unique phenomenon were discussed. This may be one mode of appearance of the Toms effect of gelatin.