Crosslinked olefin polymer having improved flame retardance

Abstract

Markedly improved flame retardance is imparted to crosslinked olefin polymers containing halogenated organic moiety by incorporating therein elemental red phosphorus. The resulting flame retardant compositions are particularly useful in fabrication of crosslinked olefin polymer foams.

What is claimed is: 
     
       1. In an olefin polymer composition containing a halogenated organic moiety which is active chlorinated organic compound, active brominated organic compound, passive brominated organic compound or hexachlorocyclopentadiene, dimerized hexachlorocyclopentadiene, hexachloroendomethylene tetrahydrophthalic acid or a derivative thereof and having the halogen concentration from about 5 to about 95 weight percent based on said moiety, the olefin polymer being selected from the group consisting of homopolymers and copolymers of aliphatic hydrocarbon monoolefins having no more than 12 carbon atoms, substituted α-monoolefins wherein the substituent is carboxylic acid, alkyl or haloalkyl ester of carboxylic acid wherein alkyl or haloalkyl has from 1 to 12 carbon atoms, acyl having from 1 to 12 carbon atoms, carboxylate having from 1 to 12 carbon atoms, alkoxyl having from 1 to 12 carbon atoms, and aryloxy having 6 to 12 carbon atoms, the improvement wherein the olefin polymer is crosslinked to at least its gel point and contains a flame retarding amount of elemental phosphorus having a specific gravity greater than 2.0. 
     
     
       2. The improvement according to claim 1 which contains a self-extinguishing amount of elemental phosphorus having a specific gravity greater than 2.0. 
     
     
       3. The improvement according to claim 1 wherein the concentration of phosphorus is from about 0.5 to about 20 parts by weight per 100 parts of polymer and the atomic ratio of phorphorus to halogen is from about 4:1 to about 1:6. 
     
     
       4. The improvement according to claim 1 wherein the halogenated organic moiety is chlorinated paraffin wax, the chlorine concentration being from about 25 to about 97 weight percent based on the halogenated organic moiety. 
     
     
       5. The improvement according to claim 1 wherein the concentration of phosphorus is from about 1 to about 10 parts, the atomic ratio of phosphorus to halogen is from about 2:1 to about 1:3 and the sum of amount of phosphorus and amount of halogenated moiety is at least 5 parts based on 100 weight parts of polymer. 
     
     
       6. The improvement of claim 1 wherein the olefin polymer composition is foamed. 
     
     
       7. The improvement according to claim 1 wherein the olefin polymer is an aliphatic hydrocarbon α-monoolefin polymer and the halogenated organic moiety is hexachlorocyclopentadiene, dimerized hexachlorocyclopentadiene, hexachloroendomethylene tetrahydrophthalic acid or a derivative thereof. 
     
     
       8. The improvement according to claim 1 wherein the olefin polymer is an ethylene/vinyl acetate copolymer or polyethylene. 
     
     
       9. The improvement according to claim 7 wherein the α-monoolefin polymer is polyethylene and the halogenated organic moiety is hexabromocyclododecane. 
     
     
       10. The improvement according to claim 3 wherein the olefin polymer is polyethylene and the halogenated organic moiety is a passive brominated organic compound selected from the group consisting of decabromo diphenyl oxide 2,3,3-triboromoallyl 2,4,6-tribromophenyl ether, 1-(2,4,5-triboromophenyl)-1-(2,4,6-tribromophenoxy)ethane, pentaerythrityltetrabromide and bis(2,3,3-tribromoalkyl)maleate. 
     
     
       11. The improvement of claim 1 wherein the olefin polymer is crosslinked by exposing said polymer to ionizing irradiation at a dosage from about 0.1 to 10 megarad. 
     
     
       12. The process for preparing a fire retardant, crosslinked olefin polymer foam which comprises subjecting a sheet of an olefin polymer containing a halogenated organic moiety, a flame retarding amount of elemental phosphorus having a specific gravity greater than 2 and a foaming amount of a foaming agent to a dosage of ionizing radiation in the range from about 0.2 to about 6 megarad and thereafter floating the sheet on a heated salt bath while irradiating the sheet with heat rays. 
     
     
       13. The improvement of claim 1 wherein the olefin polymer is crosslinked using a chemical crosslinking agent. 
     
     
       14. The improved olefin polymer composition prepared by the process of claim 12.