The properties of mica‐filled polypropylenes

Abstract

Water-ground Phlogopite micas were classified into narrow particle-size distributions containing flakes with well-defined diameters and thicknesses in order to evaluate the influence of particle size and flake aspect ratio on the mechanical properties of mica-filled polypropylenes. For the purposes of comparison, most of the injection-molded specimens contained 40 percent (by weight) mica. As expected, the flexural and tensile modulus values increased in proportion to the aspect ratio over the range from 30 to 60 to a maximum of 8 GPa. The measured tensile strengths of the mica-filled polypropylenes increased substantially as the flake diameter became smaller, but did not correlate with the flake aspect ratio. The attainable properties were frequently dependent upon the method of mixing, and considerable care was necessary to ensure proper dispersion and adequate coupling. Intensive mixing, as in a Gelimat Mixer, may cause in situ delamination and particle-size reduction of the mica filler particles, leading to a marked increase in tensile strength of the resulting composite. The mica-filled compounds could be reprocessed many times without significant loss of properties, particularly compounds having mica particles less than 40 pm in diameter. The fracture energies (notched Izod) and the heat-distortion temperatures were not appreciably influenced by the size or aspect ratios of the mica within this range. Increased fracture toughness could be achieved by reducing the mica concentration or employing a polypropylene copolymer. Guidelines are presented to indicate the preferred characteristics of mica fillers and the influence of mixing conditions on performance.

Polymer micro and nanocomposites: Structure, interactions, properties

“…However, it is difficult to obtain a clear picture about the effect of particle characteristics on composite properties for anisotropic fillers. Modulus seems to increase with aspect ratio [62,95], although Parrinello [96] found the stiffness of short glass fiber filled PP to be independent both from the length and the diameter of the fibers. According to Riley et al [62] impact resistance increases with decreasing particle size, large particles act as flaws, while large aspect ratio results in increased stress concentration.…”

Crystallization Behavior in Poly(propylene) Containing Wollastonite Microfibrils

“…In this regard, various mineral fillers such as calcium carbonate, [1,2] silica, [3] talc, [4] mica, [5,6] wollastonite, etc., have been incorporated in poly(propylene) (PP). Amongst these, the fillers having a high aspect ratio in the particle shape were found to be very effective and gave dramatic improvement in mechanical properties.…”

Particulate Fillers in Thermoplastics

“…The cleavage of these fillers is relatively easy and considerable delamination may take place during processing, especially in injection molding at the very high shear stresses developing [136,147]. Delamination of mica particles was shown to improve most properties, but decreasing particle size may lead to aggregation [138].…”

“…However, based on published papers, it is difficult to obtain a clear picture about the effect of particle characteristics on composite properties for anisotropic fillers. Modulus seems to increase with aspect ratio [63,138], although Parrinello [139] found the stiffness of short glass fiber filled PP to be independent both of the length and the diameter of the fibers.…”

“…However, based on published papers, it is difficult to obtain a clear picture about the effect of particle characteristics on composite properties for anisotropic fillers. Modulus seems to increase with aspect ratio [63,138], although Parrinello [139] found the stiffness of short glass fiber filled PP to be independent both of the length and the diameter of the fibers.According to Riley [63] impact resistance increases with decreasing particle size, since large particles act as flaws, while large aspect ratio is claimed to result in increased stress concentration. Tensile strength is said to decrease with increasing particle size, although 7 Trotignon [140] did not observe any change in strength as a function of this characteristic.…”