A wide angle x‐ray diffraction technique has been used to determine the orientation of mica flakes in composites. The mica used was a fine grade Phlogopite, and the polymers were polystyrene, polycarbonate and poly(vinyl chloride). Composite samples of varying mica contents and orientations were prepared. The x‐ray method can give the orientation distribution function of mica flakes across and parallel to the surface of the sample. From this function, an average orientation parameter was calculated. The results show that there is no orientation of mica across the surface of the sample (the x‐ray beam is normal to the surface), but that there is a strong orientation in a direction parallel to this surface, the average orientation parameter being strongly dependent upon the particle size of mica and mode of preparation.

No abstract

Reaction injection molded polyurethanes are reinforced with inorganic materials to improve stiffness and structural integrity at elevated temperatures and to reduce the coefficient of thermal expansion. This work describes the reinforcement obtained with an experimental grade of mica designed to achieve low viscosity of mica suspensions in polyol. The effect of mica on properties is essentially identical to that of glass flake (i.e., improved stiffness at the cost of reduced impact strength). Compared to hammer milled glass fiber, mica and glass flakes yield more isotropic, albeit weaker, materials. The study of unreinforced polyurethane shows that mechanical properties (tensile and impact strength, flexural modulus) are approximately proportional to the square of foam density.

Surface roughness of polypropylene/mica extrudates was related to the presence of entrapped air in the melt. Orientation of mica flakes inside the extruder hinders the escape of air from within the molten polymer. Upon exiting from the die escaping air bursts out through the sheet skin creating surface discontinuities which are responsible for surface roughness. Direct extrusion of polypropylene powder/mica dry blends also produces rough surfaced extrudate, but the pores are significantly smaller. In single screw extrusion, feeding at degrees of starve feeding of 15% and more permit the production of air-free smooth extrudates. In addition, operation in the starve feeding mode, results in a reduced specific power consumption by as much as 50%. Flake orientation in the extrudate is controlled by extrusion conditions: smaller gap, higher convergence ratio and shear rate favor the flake alignment which translates into smoother surfaces. In thin extrudates, the flake orientation is so developed that the surface had sufficient cohesion to prevent the air from escaping at the die exit giving extrudates which, though very porous inside, were smooth surfaced.Brought to you by | Purdue University Libraries Authenticated Download Date | 5/30/15 7:39 AM