GB852663A - Improved cellular materials - Google Patents

Abstract

A highly crystalline polymer of an alphaolefin, preferably polypropylene, prepared as described in the parent Specification is made cellular and, for example, rigid and porous in the following ways:-(1) The highly crystalline polymer is mixed with a blowing agent, such as dinitrosopentamethylenetetramine, azodicarbonamide or lactose, which decomposes with the evolution of a gas when heated. The mixture is made completely homogeneous by being softened e.g. at a temperature between 140 and 180 DEG C., and is then filled into moulds and heated, for example at a temperature between 140 and 180 DEG C. and is then filled into moulds and heated, for example to between 180 and 190 DEG C., to decompose the blowing agent. The mixture may be heated to 170 DEG C. under the pressure of the gas evolved, cooled until the gas achieves atmospheric pressure and then reheated to between 140 and 160 DEG C. (2) The highly crystalline polymer is mixed with a stabilizer such as 4, 4, 1-thio-bis-3-methyl-6-tertiary butyl phenol. The mixture is heated to between 190 and 200 DEG C. in a vessel containing nitrogen at a pressure of 120 to 130 atmospheres and then discharged into another vessel packed with a plurality of spirally arranged grids. In this vessel, the mixture is heated to 200 DEG C. in nitrogen at a pressure of 15 to 20 atmospheres and then discharged into moulds wherein it is heated to between 130 and 140 DEG C. for at least 20 minutes. (3) A mixture of the highly crystalline polymer and a stabilizer is pulverized and mixed with pulverized sodium chloride. The resulting mixture is filled into moulds and heated therein, for 20 minutes at 190 to 200 DEG C., in nitrogen at a pressure of 100 atmospheres. The moulds are then cooled and the castings produced are washed with water to dissolve out the sodium chloride.ALSO:A highly crystalline polymer of an alpha-olefin, preferably polypropylene, prepared as described in the parent Specification is made cellular and, for example, rigid and porous in the following ways: (1) The highly crystalline polymer is mized with a blowing agent, such as dinitrosopentamethylenetetramine, azodicarbonamide or lactose, which decomposes with the evolution of a gas when heated. The mixture is made completely homogeneous by being softened, e.g. at a temperature between 140 and 180 DEG C. and is then filled into moulds and heated, e.g. to between 180 and 190 DEG C. to decompose the blowing agent. The mixture may be heated to 170 DEG C. under the pressure of the gas evolved, cooled until the gas achieves atmospheric pressure and then reheated to between 140 and 160 DEG C. (2) The highly crystalline polymer is mixed with a stabilizer such as 4, 4, 1-thio-bis-3-methyl-6-tertiary butyl phenol. The mixture is heated to between 190 and 200 DEG C. in a vessel containing nitrogen at a pressure of 120 to 130 atmospheres and then discharged into another vessel packed with a plurality of spirally arranged grids. In this vessel, the mixture is heated to 200 DEG C. in nitrogen at a pressure of 15 to 20 atmospheres and then discharged into moulds wherein it is heated to between 130 and 140 DEG C. for at least 20 minutes. (3) A mixture of the highly crystalline polymer and a stabilizer is pulverised and mixed with pulverised sodium chloride. The resulting mixture is filled into moulds and heated therein, for 20 minutes at 190 to 200 DEG C. in nitrogen at a pressure of 100 atmospheres. The moulds are then cooled and the castings produced are washed with water to dissolve out the sodium chloride.