The size of the minor phase in an immiscible polymer blend can have a significant effect on properties such as the impact strength. Few studies, however, have quantitatively considered the parameters controlling the size of the dispersed phase. In this paper, light and scanning electron microscopy have been used to examine the size of the minor phase in polypropylene/polycarbonate blends after melt processing. The size was examined as a function of both the viscosity ratio (p) and the torque ratio (TR). The viscosity ratio is studied in the regions of p > 1 and p < 1. p has a marked effect on the morphology of the dispersed phase with the phase size increasing by a factor of 3 to 4 times from p = 4.5 to p = 17.3. Reduction in the size of the minor phase was achieved below p = 1 with the minimum particle size occurring at p ≃ 0.15. The results for these systems indicate the presence of upper and lower limits of p beyond which deformation becomes difficult. This is shown to be similar in some respects to the behavior of Newtonian fluids in shear flow, although the upper limit extends beyond that observed in the Newtonian fluid studies.

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Edge notched samples of polypropylene (PP) and high-density polyethylene (HDPE) containing different mica concentrations were tested in mode I tensile loading. Crack growth was approximated by a non-linear regression of exponential form using statistical software (SAS). Characterization of fatigue crack propagation (FCP) was made using the Paris-Erdogan law. The crack front in PP was preceded by a wide plastic zone in which craze developed, leading to a discontinuous crack growth. Using spline functions, a margin between maximum and minimum FCP rates, recorded during the crack progression, is presented along with the average FCP rates. It is shown that mica-reinforced PP samples exhibit higher FCP rates than unfilled PP. In HDPE, mica reduces FCP rates resulting in a higher resistance to fatigue crack propagation. Effect of test frequency is presented for unfilled polymers and 10 percent mica concentration by weight in both matrices. An increase in the test frequency has no significant effect on FCP rates for both raw and mica-reinforced PP. Unfilled and mica-filled HDPE show noticeable decrease in FCP rates with increasing frequency.

3A7As an engineering thermoplastic acetal homopolymer is often used in the manufacture of parts subjected to fatigue. This article presents the results of flexural fatigue tests on acetal Delrin 550 under different environmental conditions, namely ambient air, forced-air ventilation at ambient temperature, or oil kept at a constant temperature at 40°C. The fatigue tests were performed on specimens cut from extruded sheets at a constant frequency of 30 Hz. Surface temperatures of the test specimens were measured either optically or electrically, depending on the environment. The test results show that both acetal stress and surface temperature of specimen, which are somehow related, vary considerably from one type of environment to another. However, results show that the fatigue life of the specimen is mainly governed by the amplitude of the initial stress and is almost independent of the environment. Another subject examined was the effect of oil on acetal's mechanical properties. It was found that prolonged contact with oil produced slight variations in tensile properties, but no significant effect on fatigue life. This device makes it possible to test u p to 16 specimens simultaneously, in groups of four, using t h e same or different test conditions for each group.The specimen geometry and testing mode are given in Fig. 1 . They were cut lengthwise from an extruded sheet of acetal Delrin 550. The minimum 548