The mixing mechanism in a Brabender Plasti-Corder was studied on EPM- and EPDM- carbon black recipes by measuring the changes in maximum tensile strength, Mooney viscosity, extrusion shrinkage, resistivity, and morphology of the compounds during mixing. The molecule-level mechanism was also examined by correlating the above observations to the changes in free induction decay of pulsed NMR of the compounds and also to the molecular structure of EPR. The following conclusions were obtained. 1) Mixing process consists of four steps-subdivision, incorporation, dispersion, and simple mixing-as suggested by Palmgren. 2) The third dispersion step may be regarded as scraping of aggregates, either individually or collectively, on the surface of agglomerates. This is named the“onion”model. 3) Immobile polymer layer adsorbed by carbon black founds a huge net work which restricts dispersion. 4) The chance of adsorption of a polymer fraction might be proportional to the existing amount in matrix and the square of the molecular weight. Therefore, a large amount of large molecules results in ill performance of mixing. 5) The effect of branched molecules on PI value, one of mixing-processability indices, is equal to that of the linear polymer of smaller molecular weight by the conversion factor which is estimated at about 0.6 powers of the Zimm-Stockmayer g-factor of the molecule. 6) With the lapse of mixing time, adsorbed molecules are orderly rearranged, making dispersion more difficult. EPRs were characterized by GPC-LALLS. For the accuracy, GPC-inherent phenomena such as molecular scission in columns, polymer plugging on a filter, sample-preparation method, and concentration effect of polydisperse samples have been successfully investigated. Particularly, we demonstrated that exponent b of EPR in the equation g′=gb (where g′=[η]br[η]l) is determined 1.1 by computer simulation of GPC and characterization of gamma-ray-irradiated EPM as the model of the branched polymer.
The shear viscosities of poly (methyl acrylate) (PMA)-isoamyl acetate, poly (vinyl acetate) (PVAc)-3-heptanone, and poly (methyl methacrylate) (PMMA)-3-heptanone mixtures were measured with capillary-type viscometers near the critical point in the several ranges of shear rate. The results were analyzed in terms of a theoretical equation for the anomalous viscosities near the critical point, and the nonlinear effect for the shear viscosities was discussed. A leveling off of the shear viscosities was observed very near the critical point in PMA-isoamyl acetate and PVAc-3-heptanone mixtures, which might be the result of shear rate effect predicted by Oxtoby and Kawasaki. Taking this effect into account, we found that the results are in good agreement with the theoretical equation with an assumption that the background viscosity can be represented by Arrhenius equation. On the other hand, a very strong divergence of shear viscosities was observed in PMMA-3-heptanone mixture near the critical point. This behavior was beyond theoretical prediction. The additional viscosity effect was introduced to compare this anomaly with theory for critical mixture, and it was discussed from the viewpoint of the nonlinear effect and apparent activation energy.
The gelation process of aqueous solutions of a syndiotacticity-rich poly (vinyl alcohol), which was derived from vinyl trifluoroacetate, has been studied by measuring the zero- shear solution viscosity ηt0 as functions of the standing time t at a constant temperature, 30 or 50°C. After the solutions with polymer concentrations higher than about 1.0g/di were transferred from high temperature to the test temperature, the viscosity ηt0 increased with time t until the gelation took place. The plot of log ηt0 versus t is generally divided into three linear regions with different slopes, i. e., the slow initial, the steep second, and the still steeper third regions. The second and third regions obey Avrami's equations with exponents, 1.7 and 3.6, respectively, suggesting that these regions correspond to the linear growth and three dimensional growth of crystallite in a heterogeneous nucleation system. The linear dependence of log ηt0 on t has been derived theoretically by using a linear association model of polymer chains. It has been conjectured that 7~8 mol% of polymer molecules participates in bimolecular association in the initial region and about 20 mol% in the second region.
Rheopexy of a disperse system consisting of silica-gel (Si) particles suspended in a polyoxyethylene was examined in relation with the state of dispersion of the Si particles. The suspension was subjected to a double-step shearing test. The rheopectic stress recovery was determined as a function of the preshearing rate γ1, the second shear-rate γ2, and the time t ellapsed after the shear-rate change. Aggregates of the Si particles destroyed at the high shear-rate γ1, reached to a new steady state of aggregation coressponding to the low rate γ2, accompanying a recovery of stress. The stress recovery was interpreted as a change in the effective volume fraction φeff(t) with t by using an empirical equation of viscosity-volume fraction relation proposed by Mori for nonaggregating suspension. The initial rate of particle aggregation was found propotional to the effective collision volume Vc, and dependent on γ2 Employing Zeichner's method for calculating collision rate of two particles in steady shear flow, we calculated γ2, dependence of the initial rate of particle aggregation. The agreement between the theory and experiments was semiquantitative and fairly satisfactory.
In order to know the mechanical properties of human cancellous bone, regional differences of viscoelasticity and compressive strength have been investgated in normal and pathological human patella by a viscoelastic spectrometer and a testing machine of Instron type. In the normal human patella, the averaged dynamic compressive elastic modulus at lateral side was 627.1MPa and that at medial side 245.8MPa. In the pathological patella, this modulus was 246.1MPa at the lateral side and 917.5MPa at the medial side. The stereological pattern analysis indicated that the internal structure of cancellous bone in the normal patella was highly load-adapted structure. This fact implies that the lateral side of the patella is stiffened as the result of functional adaption.
Measurements of penetration depth of a rod perpendicular to a surface of a powder mass versus weight of the rod have been done by Yuasa et al. for glass beads and styrol resin. Regarding to the measurements, we derived a theoretical equation relating the potential energy of the rod and the friction of the powders. The equation shows that the penetrated depth is an irrational function of the weight and that the depth is deep for a rod of small radius, or a powder of small specific gravity. The theoretical result seems to agree with the measurements.