Radiation crosslinking of halogen-free flame retardant polymer

1. A flame retardant composition, comprising:

a polyamide;

a crosslinking agent, wherein the crosslinking agent comprises two or more groups capable of forming free radicals under beta or gamma radiation; and

a flame retardant system comprising a metal phosphinate salt, a metal diphosphinate salt, or combination thereof.

2. The composition of 1 , wherein the metal phosphinate salt is of the formula (I) and the metal diphosphinate salt is of the formula (IN)

wherein R 1 and R 2 are each independently hydrogen, a linear or branched C 1 -C 6 alkyl radical, or aryl radical; R 3 is a linear or branched C 1 -C 10 alkylene, arylene, arylarylene, or arylalkylene radical; M is calcium, aluminum, magnesium, strontium, barium, or zinc; m is 2 or 3; n is 1 when x is 1 and m is 2; and n is 3 when x is 2and m is 3.

3. The composition of claim 1 , wherein the metal salt is an aluminum salt of dimethylphosphinic acid, an aluminum salt of methylethylphosphinic acid, or an aluminum salt of methylpropylphosphinic acid.

4. The composition of claim 1 , wherein the flame retardant system further comprises at least one nitrogen compound selected from the group consisting of condensation products of melamine and/or reaction products of condensation products of melamine with phosphoric acid, and/or mixtures thereof, melam, melem, melon, melamine, melamine cyanurate, melamine phosphate compounds, dimelamine phosphate, melamine pyrophosphate, melamine polyphosphate compounds, benzoguanamine compounds, terepthalic ester compounds of tris(hydroxyethyl)isocyanurate, allantoin compounds, glycoluril compounds, ammeline, ammelide, and combinations thereof.

5. The composition of claim 4 , wherein the nitrogen compound comprises a compound of the formula (III) to (VIII) or combinations comprising at least one of the foregoing nitrogen compounds

wherein R 4 , R 5 , and R 6 are independently hydrogen, hydroxy, amino, or mono- or diC 1 -C 8 alkyl amino; or C 1 -C 8 alkyl, C 5 -C 16 cycloalkyl, -alkylcycloalkyl, wherein each may be substituted by a hydroxyl or a C 1 -C 4 hydroxyalkyl, C 2 -C 8 alkenyl, C 1 -C 8 alkoxy, -acyl, -acyloxy, C 6 -C 12 aryl, —OR 12 an —N(R 2 )R 13 wherein R 12 and R 13 are each independently hydrogen, C 1 -C 8 alkyl, C 5 -C 16 cycloalkyl, or -alkylcycloalkyl; or are N-alicyclic or N-aromatic, where N-alicyclic denotes cyclic nitrogen containing compounds; R 7 , R 8 , R 9 , R 10 and R 11 are independently hydrogen, C 1 -C 8 alkyl, C 5 -C 16 cycloalkyl or -alkylcycloalkyl, each may be substituted by a hydroxyl or a C 1 -C 4 hydroxyalkyl, C 2 -C 8 alkenyl, C 1 -C 8 alkoxy, -acyl, -acyloxy, C 6 -C 12 aryl, and —O—R 12 ; X is phosphoric acid, pyrophosphoric acid; q is 1, 2, 3, or 4; and b is 1, 2, 3, or 4.

6. The composition of claim 4 , wherein the nitrogen compound is allantoin, benzoguanaine, glycoluril, melamine, melamine cyanurate, melamine phosphate, melamine pyrophosphate, melamine polyphosphate, or urea cyanurate.

7. The composition of claim 1 , wherein the polyamide is selected from the group consisting of nylon-6, nylon-6,6, nylon-4, nylon-4,6, nylon-12, nylon-6,10, nylon-6,9, nylon-6,12, nylon-9T, copolymer of nylon-6,6 and nylon-6, polyamide copolymers, polyamide blends, and combinations thereof.

8. The composition of claim 1 , wherein the polyamide is present in an amount of about 30 to about 96 weight percent based on the total weight of the composition.

9. The composition of claim 1 , wherein the crosslinking agent comprises two or more unsaturated groups.

10. The composition of claim 1 , wherein the crosslinking agent is a polyallylic compound or a polyol poly(meth)acrylate prepared from an aliphatic diol, triol, or tetraol containing 2-100 carbon atoms.

11. The composition of claim 1 , further comprising up to about 60 weight percent of filler.

12. The composition of claim 11 , wherein the filler is glass fiber, zinc borate, or a combination thereof.

13. The composition of claim 1 , further comprising up to about 20 weight percent of a wear additive based on the total weight of the composition, wherein the wear additive is selected from the group consisting of polytetrafluoroethylene, molybdenum disulfide, graphite, aramide, carbon fiber, carbon powder, and combinations thereof.

14. The composition of claim 1 , wherein the composition is crosslinked with ionizing radiation to form a crosslinked composition.

15. The composition of claim 14 , wherein the composition after crosslinking exhibits at least one of the following:

i) a rating of V0 according to UL-94 within the range of 0.8 to 3.2 millimeters thickness;

ii) a Glow Wire Flammability Index as measured according to IEC-60695-2-1 of 960° C. or greater within the range of 0.8 to 3.2 millimeters thickness;

iii) a Glow Wire Ignition Temperature as measured according to IEC-60695-2-13 of 750° C. or greater within the range of 0.8 to 3.2 millimeters thickness; or

iv) a comparative tracking index measured according to International Electrotechnical Commission standard IEC-60112/3 rd of class 1 or class 0.

16. An article comprising the crosslinked composition of claim 14 .

17. A flame retardant composition, comprising:

a polyamide;

1 to about 20 weight percent of a polyallylic compound or a polyol poly(meth)acrylate crosslinking agent;

about 5 to about 60 weight percent of glass fiber; and

about 5 to about 25 weight percent of a flame retardant system comprising

i) a metal phosphinate salt, a metal diphosphinate salt, or a combination thereof; and

ii) optionally at least one nitrogen compound selected from the group consisting of condensation products of melamine and/or reaction products of condensation products of melamine with phosphoric acid, and/or mixtures thereof, melam, melem, melon, melamine cyanurate, melamine phosphate compounds, dimelamine phosphate, melamine pyrophosphate, benzoguanamine compounds, terepthalic ester compounds of tris(hydroxyethyl)isocyanurate, allantoin compounds, glycoluril compounds, ammeline, ammelide, and combinations thereof;

wherein all the amounts are based upon the total weight of the composition.

18. The composition of claim 17 , wherein the polyamide comprises about 15 to about 35 weight percent nylon-6 and about 15 to about 35 weight percent nylon-6,6;

1 to about 10 weight percent of a crosslinking agent selected from the group consisting of triallylisocyanurate, triallylcyanurate, ethyleneglycol di(meth)acrylate, and trimethylolpropane tri(meth)acrylate;

about 15 to about 30 weight percent of glass fiber; and

about 10 to about 20 weight percent of the flame retardant system wherein the nitrogen compound is melamine, melamine phosphate, melamine pyrophosphate, or melamine polyphosphate;

wherein all the amounts are based upon the total weight of the composition.

19. A method of forming a crosslinkable, flame retardant composition comprising:

blending a polyamide, a crosslinking agent, wherein the crosslinking agent comprises two or more groups capable of forming free radicals under beta or gamma radiation; and

a flame retardant system comprising

i) a metal phosphinate salt, a metal diphosphinate salt, or combination thereof; and

ii) optionally at least one nitrogen compound selected from the group consisting of condensation products of melamine and/or reaction products of condensation products of melamine with phosphoric acid, and/or mixtures thereof, melam, melem, melon, melamine, melamine cyanurate, melamine phosphate compounds, dimelamine phosphate, melamine pyrophosphate, melamine polyphosphate compounds, benzoguanamine compounds, terepthalic ester compounds of tris(hydroxyethyl)isocyanurate, allantoin compounds, glycoluril compounds, ammeline, ammelide, and combinations thereof, to form an intimate blend.

20. The method of claim 19 , further comprising molding the intimate blend into an article and crossliriking the composition with ionizing radiation.