Patent GB-1174959-A (GB)
Title: Whisker Orientation and Shaped Bodies containing Uniaxially Oriented Whiskers
IPC: D01F9/12
Filed: 1967-09-14
Abstract: 1,174,959. Filaments &c. containing oriented "whiskers". CARBORUNDUM CO. 14 Sept., 1967 [16 Sept., 1966], No.41987/67. Heading B5B. [Also in Divisions C1 C3 and D1] Shaped structures including a non-flowable matrix having uniaxially oriented "whiskers" embedded therein are produced by dispersing the whiskers in a flowable dispersion medium which comprise a matrix-forming material, causing the dispersion to flow as a liquid stream and constricting the stream in - such a manner that the whiskers are uniaxially oriented in the stream, and causing the stream to solidify. The shaped body or structure may be a filament or film. The constriction may be effected by spinning the dispersion through an orifice or extruding it through an extrusion die, e.g. a die having a slot-shaped extrusion orifice. The liquid stream, after spinning or extrusion, may be drawn to cause further constriction or attenuation of the liquid stream. The term "whisker" is defined as a short acicular single crystal fibre generally having a diameter of the order of magnitude of one micron and a length of about 1 to 3 mm. or less. The fibres may consist of a metallic or non-metallic solid element, an alloy or an inorganic compound such as silicon carbide. In producing the shaped structure the extruded liquid stream may be solidified by contact with a coagulating liquid, by cooling, or by evaporation of a volatile solvent in which the matrix has been dissolved. The dispersion may contain, in addition to whiskers, at least one additional finely divided solid substance such as a metal powder. The orientation of the whiskers in the shaped structure may be increased by stretching the structure in the direction of whisker orientation at a temperature at least as high as the glass transition temperature of the polymer. The matrix forming material may be removed from the shaped structure without materially disturbing the orientation of the whiskers whereby a matrixfree fibrous body consisting of oriented whiskers is left. The matrix may be removed by dissolving it in a suitable solvent. The matrix may be an organic polymeric material and the body or shaped structure may be heated under non-oxidizing conditions to pyrolize the material without removing it entirely so as to form a matrix of carbon. Bodies or shaped structures comprising uni-axially oriented whiskers in a form specially adapted for the fabrication of whisker reinforced bodies or shaped structures may be made by impregnating a fibrous body consisting of matrix-free uniaxially oriented whiskers (as referred to above) with an organic matrix-forming material. The fibrous body may be in the form of a yarn or a sheet. The term "whisker" is defined as an acicular single crystal characterized by a large length to diameter ratio (e.g. about 100 to 1000) and a high degree of crystal perfection. In an example, a solution of 20 grams of polyacrylonitrile in 80 grams of N,N-diamethylformamide has dispersed in it 5 grams of silicon carbide whiskers having an average length of about 100 and an average diameter of about 1-2 Á. The dispersion is allowed to flow by gravity through a circular orifice having a diameter of 4-0 mm. into a coagulating bath consisting of a wateracetone mixture in a 3 : 4 volume ratio to form a deformable filament which is drawn through and out of the bath and thereafter through a dryer before being wound under tension on a spool in the form of a dry filament having a diameter of about 150 Á. Filaments containing dispersed oriented silicon carbide whiskers may be formed by melt spinning a dispersion of the whiskers in molten nylon at 260-290‹ C. into a water bath. The filaments thereby formed have a diameter of e.g. about 0À5-1À0 mm. and may be stretched at a temperature of 65-95‹ C. at a stretch ratio of 3 to 4 to form a filament having a diameter of about 150-200 and an improved degree of whisker orientation.