Patent GB-837504-A (GB)
Title: Method of making cellular polyethylene
IPC: C08J9/14
Filed: 1957-10-08
Abstract: Polyethylene in the form of shaped or moulded articles is subjected to 2 to 20 megareps per square centimetre of high energy ionizing radiation, sufficient to render it insoluble in boiling decahydronaphthalene, prior to being expanded to produce a cellular product.  The polyethylene is preferably linear with a molecular weight of at least 4000.  In an example, polyethylene having a melt index of 6.6 is subjected to 8 megareps of radiation with accelerated electrons.ALSO:A process of making cellular articles from ethylene polymer comprises subjecting normally solid polyethylene in particulate form or in the form of shaped or moulded articles to an amount of ionizing radiation corresponding to a dosage of from 2 to 20 megareps per square centimetre, placing the irradiated polyethylene under pressure of a volatile organic fluid consisting of tetramethylmethane, monochlorodifluoromethane, dichlorodifluoromethane, dichlorotetrafluoroethane and mixtures thereof, at temperatures between 100 DEG  and 200 DEG  C. and above the crystalline melting-point of the polyethylene until the fluid is uniformly or substantially uniformly distributed throughout the irradiated material and suddenly releasing the pressure.  The ionizing radiation may be beta rays, gamma rays, X-rays, neutrons or accelerated electrons.  The amount of radiation is sufficient to cause the polymer to be insoluble in boiling decahydronaphthalene. Preferably the polyethylene has a substantially linear structure and a molecular weight of at least 4000.  In a typical example, (1), polyethylene of melt index 6.6 is subjected to irradiation with accelerated electrons for a total dosage of 8 megareps.  Portions are then sealed, together with various organic fluids specified, in a stainless steel bomb, and heated to 115 DEG  C.  The pressure is suddenly released, to give foamed polyethylene containing uniform small cells.  Specification 524,063 and U.S.A.  Specification 2,387,730 are referred to.ALSO:A process of making cellular articles from ethylene polymer comprises subjecting normally solid polyethylene in particulate form or in the form of shaped or moulded articles to an amount of ionizing radiation corresponding to a dosage of from 2 to 20 megareps per square centimetre, placing the irradiated polyethylene under pressure of a volatile organic fluid consisting of tetramethylmethane, monochlorodifluoromethane, dichlorodifluoromethane, dichlorotetrafluoroethane and mixtures thereof, at temperatures between 100 DEG  and 200 DEG C. and above the crystalline melting point of the polyethylene until the fluid is uniformly or substantially uniformly distributed throughout the irradiated material and suddenly releasing the pressure.  The ionizing radiation may be beta rays, gamma rays, X-rays, neutrons or accelerated electrons.  The amount of radiation is sufficient to cause the polymer to be insoluble in boiling decahydronaphthalene. Preferably the polyethylene has a substantially linear structure and a molecular weight of at least 4000.  In a typical example (1), polyethylene of melt index 6,6 is subjected to irradiation with accelerated electrons for a total dosage of 8 megareps.  Portions are then sealed, together with various organic fluids specified, in a stainless steel bomb and heated to 115 DEG C.  The pressure is suddenly released, to give foamed polyethylene containing uniform small cells.  Specification 524,063 and U.S.A.  Specification 2,387,730 are referred to.