The present study is an experimental investigation of the effects of the kinds and dimensions of dispersed fillers on the capillary flow behavior of a polypropylene. Two kinds of fillers were used: glass-fibers with two different fiberlengths, and glass-beads with two different diameters. The results may be summarized as follows: (1) The coefficient of viscosity of melts with dispersed fillers under a constant shear rate of 1 sec-1 increased with the increase of content of fillers, and the effects of filler content on the viscosity in the case of glass-fiber dispersed melts were generally larger than for melts containing glass beads. And the relation between the increasing of viscosity of fillers and volumetric content of fillers in the case of longer glass-fiber was larger than the calculated value using theoretical equations, such as those of Einstein and of Guth and Smallwood. (2) The viscosity increase with the dispersion of fillers decreased noticeably with the increase of shear rate. The relation between the relative viscosity and shear rate was represented by a master curve, which was obtained by moderate shifting on the horizontal axis of shear rate. (3) The pressure loss at the capillary inlet increased with the increase of filler content at low temperature such as 180°C, but the effects of fillers upon the pressure losses were generally complex at high temperatures such as 210°C. (4) The die swell ratio for filled melts was smaller than that of non-filled melts. The decrease of the die swell ratio of filled melts seems to be affected not only by the decrease of the volume ratio of resin in the system but also by the accelerated orientation of filler induced by flowing in the case of glass-fiber fillers.
It is well known that crazing occurs when a magnet wire is immersed in an impregnating bath of varnish after the wire was coiled up. A quantitative study was carried out in this paper for clarifying the relation between the crazing and the residual stress in the polymer film on the wire. As test specimen were used magnet wires which had poor adhesion strength between the polymer film and the conductor. The crazing in the polymer film on the magnet wire occurred most severely between 3% and 5% elongation. The residual stress in the film attained a maximum value in, the same range of elongation. That is, the crazing occurred most severely in the range of elongation where the stress in the polymer film was most hardly relaxed. A morphological study of crazing was made by using two types of magnet wires coated with cross-linked and linear polymers. The crazing observed in the cross-linked polymer films, polyesterimide, was identified as a sort of micro-cracks. In the case of linear polymer films, ployamide (Nylon 66), orientation of polymer chains in crazing was observed.
The dynamic viscoelastic properties of disperse systems containing some glass beads or aerosil powder in polystyrene solution were investigated using a coaxial cylinder viscometer. The results obtained are as follows: (1) The frequency dependence curves of the storage modulus G′ and the loss modulus G″ show the remarkable second plateau which was given by Onogi and his co-worker at fairlylower frequency range below so-called rubbery region. However, when these suspensions are sheared by violent disturbance, this plateau is completely disappeared. (2) Moreover, the height of this plateau has the tendency to increase with increasing particle concentration and with decreasing particle size. In the case of the suspension containing glass beads having larger than 30μ this plateau can not be observed as shown Fig. 11. (3) As a distinguishing behavior peculiar to the suspensions, two mechanisms are introduced; those are, (a) the thixotropic softening behavior caused by violent shearing disturbance and (b) the rheopectic hardening behavior caused by gentle oscillation. (4) The suspensions show nonlinear viscoelastic behavior at high concentration and low frequencies. Two kinds of nonlinearity are analyzed here; those are, (a) dependency of nonlinear behavior on the strain amplitude observed at higher measuring frequencies, and (b) distortion of Lissajous' figure from elliptical shape which is typical linear viscoelastic response.
For measuring the density of crosslinks in rubber vulcanizates, there are two kinds of methods. The mechanical method leads to a value νM(0), whereas the swelling method gives a value νS (0). In the ranges of lower crosslink density, the relation νM (0)>νS(0) is obtained for reasons which are well understood, whereas the inverse relation νM(0)<νS(0) is established in the range of higher crosslink density for reasons which have not yet been clarified. By introducing improved equations for such vulcanizates at higher crosslink densities, the relationνM(0)>νS(0) was obtained even for the higher crosslink density.
According to Tobolsky et al. random scission of natural rubber vulcanizates occurs preferentially on the main chain regardless of the type of crosslinks. On the other hand, Berry and Watson reported that scissions occur preferentially at crosslinks, and Horikx and Edwards observed from swelling measurements that random scissions on the main chains occur by oxidative degradation but, at the same time, the probability of scissions at crosslinks should be considered. The confusion arising from the above observations is settled in this paper. The oxidative and thermal degradation mechanisms of natural rubber vulcanizates which have carbon-carbon bond, carbon-monosulfur-carbon bond, and carbon-polysulfur-carbon bond crosslinks are classified and tabulated.
The dynamic and steady-flow properties of disperse systems of spherical particles of styrene-methyl methacrylate copolymer crosslinked by divinyl benzene in a polystyrene solution have been measured at long time-scale regions by means of a cone-and-plate type rheometer. The diameter of particles employed in the study was very uniform and found to be approximately 120 mμ. Four kinds of particles having different contents of methyl methacrylate (MMA) and ζ-potential were dispersed in a polystyrene solution at a content of about 10%. The rheological behavior observed for these different systems depend strongly not only upon the MMA content but also upon the ζ-potential. However, MMA content and ζ-potential are not deter-mining factors individually. Depending on the relative magnitude of attractive and repulsive forces between dispersed particles, the dispersion state can be classified into three different groups. When the methyl methacrylate content in the particles and the ζ-potential of electric double layer on the particle surface are assumed as the respective measure of the attractive and repulsive forces, the rheological behavior observed for the four different disperse systems can be explained without contradiction.