CA1278128C - Fire retardant polyolefin composition - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Polypropylene compositions having superior machanical properties, processability and flame retardancy are obtained by blending polypropylene resin, a halogen-containing flame retardant of decabromodiphenyl oxide or ethylene-bis-tetrabromophthalimide,antimony trioxide, a crosslinking agent and a radical generating agent or by blending polypropylene resin, a halogen-containing flame retardant of decabromodiphenyloxide or ethylene-bis-tetrabromophthalimide, antimony trioxide, boron compound, a crosslinking agent and a radical generating agent and subjecting the resultant mixture to melting and kneading treatment, or by blending a halogen-containing flame-retardant, antimony trioxide and a boron compound with a polypropylene resin having been subjected to the melting and kneading preteatment with said crosslinking agent and a radical generating agent.

Description

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SP~CIFICATION

Title of the Invention:
Flame retardant polyolefin composition Field of the Invention:
This invention relates to polyole~in compositions having high flame-retardancy. More particularly, it relates to polyolefin composition having superior mechan-ical properties,processability and flame retardancy which is obtained as its characteristic feature of production process, by blending polyolefin resin, a halogen-containing flame retardant, antimony trioxide, a crosslinking agent and a radical generating agent or by blending polyolefin resin, a halogen~containing flame retardant, antimony trioxide, a boron compound, a crosslinking agent and a radical generating agent and subjecting the resultant mixture to melting and kneading treatment, or by blending a halogen-containing flame-retardant, antimony trioxide or a halogen-containing flame-retardant, antimony trioxide and a boron compound with a polyolefin resin having been subjected to the melting and kneading pretreatment with said crosslinking agent and a radical generating agent.
Description of the Prior Art:
On account of superiority of processability, chemicals-resisting proper~y, weatherability, electrically charac-teristic properties, etc., polyolefin resin is widely used F ~

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7~ 8 in various fields including electric household appliances.On the other hand it has drawback in that it is extremely inflammable, liquefied once by pyrolysis at the -time of combustion, dropping of liquid drops formed with flaming or without flaming combustion, falling of burnt pieces cut by fusion (hereinafter -these dropped or fallen mate-rials will be referred to as drip and drip forming property as dripping property). Whether drip is existing or not is one of the important fac-tors for evaluating flame~retardancy. Even when a resin is superior in self-extinguishing property, its flame-retardancy is ranked in a lower grade if it has drip. Thus an improvement of dripping property is one of the important problem in the point of flame-retarding technique of said resin.
Further, since polyolefin resin has relatively higher crystallinity and non-polar property, it is inferior to in compatibility with a flame-retardant and shows a great reduction of physical properties by addition of a flame-retardant. On this account, for flame retardancy or retardance of polyolefin resin, there has been made heretofore various kind of proposal.
As general methods for making flame retardan-t polyolefin composition, a simultaneous use of an organic-~logen-containing flame-retardant with a certain kind of 25 metal oxide (Japanese patent publication of 25061 of 1976) ~7~

and addi-tion of a nitrogen containing compound, a boron-containing compound or a water-containing inorganic compound, as a flame-retardant have been prevailing.
However,an organic halogen-containing flame-retardant S is superior in self-extinguishing property but has drawback in that drip is formed at the time of burning.
On the other hand, an inorganic flame-retardant e.g.
magnesium hydroxide is superior in dripping property, and has a certain extent of self-extinguishing property but has drawback because for providing a high level of flame-retardancy, a large amount of addition is necessary.
A polyolefin composition containing a large amount of incorporated inorganic compound has drawback in the point of deterioration of processing characteris-tics due to the reduction of fluidity of molten material and reduction of mechanical properties of formed articles when said composition is used in forming. The range for addition is limitative in practical use because of reduction of mechanical strength of formed articles and attainment of high level of flame-retardancy is difficult.
In order to overcome these drawbacks, i-t has been proposed to use simultaneously a bromine-containing flame retardant and borofluoride salt to polypropylene resin (Japanese laid open application No. 163937 of 1979);
to mix ethylene-propylene rubber modified with silane compound and a flame-retardant with polyethylene resin, followed by crosslinking with an organic peroxide (Japanese laid open patent application No. 110139 of 1980); to use simultaneously a silane coupling agent, ethylene-propylene rubber, chlorinated polyethylene and a flame-retardant in forming, followed by crosslinking with water (Japanese laid open patent application No. 45716 of 1980).
However, according to the above-mentloned Japanese laid open application No, 163937 of 1979, the improvement of dripping property is still not in the state which can be said to be sufficient, the processes of Japanese laid open patent application No. 110139 of 1980 and No. 45716 of 1980 are those which have been applied to polyethylene, which create crosslinking very easily in the presence of an organic peroxide.
Summary of the Present Invention:
-The inventors of the present invention concentratedtheir effort in solving the above-mentioned problem relat-ing to flame-retardant polyolefin compositions. As the result, they succeeded in obtaining flame~retardant - polyolefin compositions which improve mechanical strength of formed articles, greatly improve dripping property at the time of burning, further improve drawdown of burnt resin pieces by melting and falling in drops of burnt r,esin pieces by incorporating a crosslinking agent and - 5 - ~ ~ ~8~

a radical generating agent to a polyolefin re3in in the presence of a halogen-containing flame-retardant and antimony trioxide or in the presence of a halogen-containing flame-retardant, antimony trioxide and a boron compound and ~ubjecting the resulting mixture to melting and kneading treatment or mixing a halogen-containing flame-retardant and antimony trioxide or a halogen-containing flame-retardant, antimony trioxide and a boron compound with a polyolefin resin having been, in advance, tr0ated with a crosslinking agent and a radical generating agent and subjecting the resulting mixture to melting and kneading treatment and completed the present invention.
As evident from the foregoing description, it i~
an object of the present invention to provide a flame-retardant polyolefin composition which provides formed articles having improved mechanical strength, and greatly improved dripping property at the time of burning.
~ he above-mentioned object can be attained by a flame-retardant polyprop~lene composition comprising following components (A), (B~, (C), (D) and (E); (A) 0.1 - 1~5% by weight of crosslinking agent relative to the total amount of the components (A), (B), (C), (D) and (E) as 100% by weight, (B) 0~005 - 5% by weight of a radical generating agent relative to the total amount of the all the components, (C) 5 - 60%
by weight of a halogen-containing flame-retardant selected from the group compositing of decabromodiphenyl oxide and ethylene-bis-tetrabromophthalimide, relative to the total rm/

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amount of the all the components, (D) lO0 - 10% by weight of antimony trioxide relative to the halogen-containing flame-retardant, (E) balance of polypropylene re~in; the poly-propylene resin being melted, and kneaded by the crosslinking agent and the radical generating agent.
The above-mentioned object can alqo be attained by a flame-retardant polypropylene composition comprising following component~ (A), (B), (C~ / (D), (E) and (F); (A) 0.1 - 15% by weight of crosslinking agent relative to the total amount of the component~ (A), (B), (C), (D), (E) and (F) as 100~ by weight, (B) 0.005 - 5% by weight of a radical generating agent relative to the total amount of the all the component~, (C) 5 - 60%
by weight of a halogen-containing flame-retardant ~elected from the group consisting of decabro~odiphenyl oxide and ethylene-bis-tetrabromophthalimide, relative to the total ~mount of the all the components, (D) 100 - 10% by weight, of antimony trioxide relative to the halogen-containing flame-retardant, (E) l - 10% by weight of a boron compound, (F) balance of polypropylene resin, the polypropylene resin being melted and kneaded by the crosslinking agent and the radical generating agent.
Di~cussion of_the Detail~ and Preferred Embodiment of the Invention . . _ As polyolefin resina u~ed in the pre~ent invention, a homopolymer of -olefin such as propylene, butylene or the like, a random copolymer, a block copolymer consisting of selected two or more members of ethylene, propylene and 1~

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butylene and ethylene vinylacetate copolymer, styrene-butadiene copolymer,ethylene-propylene rubber and a mixture of two or more of -these members can be mentione~.
Especially a polyolefin resin containing, as a main com-ponent, polypropylene resin, is preferable.
As a halogen-containing flame-retardant, an aromatic bromine compound having a melting point of 300CC or higher e.g. decabromodiphenyl oxide, ethylene bis-tetrabromo-ph-thalimide or the like is useful. Especially decabromo-diphenyl oxide is preferably used.
The amount of addition of said halogen-containing flame-retardant is in the range of 5 ~60~ by weight, preferably 5 ~50% by weight, most preferably 7 -30~ by weight.
The amount of addition of antimony trioxide is in the range of 100 ~lO~ by weight based upon the above-mentioned halogen-containing flame-retardant agent.
As crosslinking agent, polyfunctional monomers, monofunctional monomers, oxim nitroso compound, maleimide compound, silane coupling agent, etc. are used.
As concrete examples, there are, for example, triallyl cyanurate, triallylisocyanurate, diethylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, di~inylbenzene, ~ 8 - ~Z7~28 diallylphthalate, divinylpyridine, vinyltoluene, ethyl-vinylbenzene, styrene monomer ~uinonedioxime, benzo-quinonedioxime, p-nitrosophenol, etc~

The amount of addition of said crosslinking agent is in the range of 0.1 ~15~ by weight, preferably 0.5 -10%
by ~Jeight,most preferably 1 ~6~ by weight.
As radical genera-ting agents, materials which generate a radical by thermal decomposi-tion is useful. For example, they are dicumyl peroxide; 2,5-dimethyl-2,5 di(t-bu-tyl peroxy)hexane, 2,5-dimethyl-2,5-di(t-butyl peroxy)hexyne 3; 1,3-bis(t-butylperoxyisopropyl)benzene; 1,1,4,4,7,7-hexamethylcyclo 4,7-diperoxynonane; cumenehydroperoxide;
cumylperoxytrimethyl silane, etc.
The amount of addition of said radical generating agent varies according to the kind of it, and it is in the range of 0.005 -5~ by weight, particularly 0.01 ~1%
by weight.
As boron compounds, borax, borofluoride salt, for example, sodium borofluoride, potassium borofluoride, ammonium borofluorode are useful.

- The amoun-t of addition is in the range of 1 ~10% by weight, preferably 1 ~8~ by weight, most preEerably 2 ~6 by weight.

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8~L~8 g In the present invention, various kinds of addltives, for example, antioxidant, lubricant, pigment, inorganic filler (for example,calcium carbona-te, talc, clay, mica, magnesium hydroxide, glass flbers, etc.) can be used simultaneously.
In the production of the present composition, there is no particular limitation in -the order of addition of each component of the above~mentioned (A), (B), (C), (D) and (E). Any of the following methods i.e. a method of simultaneous mixing of (A), (B), (C), (D) and (E) followed by melting and kneading; a method in which (A) and (B) are added during the processing of melting and kneading of (C), (D) and (E) and a method in which after melting and kneading of (A), (B) and (E) in advance, (C) and (D~ are mixed and melting and kneading are carried out subsequently.
Further, there is also no particular limitation in the order of addition of each components of above-mentioned (A), (s), (C), (D), (E) and (F). Any one of the following methods i.e. a method in which (A), (s), (C), (D), (E) and (F) are simultaneously mixed and subjected to melting and kneading; a method in which after meltlng and kneading of (A), (B) and (F) in advance, (C), (D) and (E) are mixed and subjected to melting and kneading; or a method in which (A) and (B) are added during the processing of mixing, melting ~nd kneading of (C), (D), (E) and (F) and further subjected to melting and kneading, is applicable.

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~7~1Z8 As an apparatus for mixing the above-mentioned each components, a common mixing apparatus such as a mixer having an attached high speed stirrer e.g. Henschel mixer (name of article of trade) ribbon blender, tumbler may be useful. For melting and kneading, a common single or -twin screw extruder can be used. Melting and kneading temperature is in the range of 170C ~300C, preferably 200C ~260C. Retention time in the extruder of product mixed by melting will be sufficient if a retention time in a common extruder is used.
From the pellets of polyolefin composition, thus obtained, test specimen of predetermined dimension were molded and flame-retardancy and mechanical strength were measured. With regard to flame retardancy, extremely better flame-proofness and dripping property were indicated, compared with comparative test specimens. Further, in mechanical strength, flexural modulus, flexural strength, tensile strength, Izod impact strength, the test specimen show higher numerical values in all these tests compared with comparative test specimen and it has been revealed that increase of mechanical strength of formed articles as well as improvement of a large extent of flame-retardancy and dripping property can be attained.
The present invention will be more concretely illustrated by referring to specific examples and 7~

Comparatlve exmaples. Burni~g tests in the specific examples and Comparative examples were carried out according to the following method. Further the measure-ments of mechanical strength were carried out according to the method of JISK 6758-1981.
Burning test Test specimens having a length of 127 mm, a width of 12.7 mm and a thickness of 0.8 mm were vertically suspended by fixing at the top end in a room in which there is no movement of air. A flame of Bunsen burner having been controlled to produce a 19 mm blue flame was applied to a test specimen from its lower end fo-r 10 seconds. After 10 seconds, the burner was removed and a time at which the test specimen continues to burn with flaming after removal of the burner, was measured and this is recorded as the first flaming combustion time. Immediately after extinguishment of test specimen, a blue flame of burner was applied again to the test specimen at its lower end according to the same method for 10 seconds and a time elapsed until extinguishment was attained agaln was measured and this is recorded as the second flaming combustion time. Subsequently a time during which the - test specimen is burning with glowing combustion is also measured. This time are summed up with the above-mentioned - 25 second ~laming combustion time and recorded as a gLow time.

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Further, cotton is placed at the position 305 mm below the test specimens and observed whether it catches fire by flaming drip during the testing time and the result is recorded. Foregoing tests were carried out by using 5 test specimens and fire-retardancy was evaluated.
Specific examples 1 ~2 and Comparative examples 1 -3 After definite amounts of a halogen-containing flame-retardant, an-timony trioxide, a crosslinking agent, and a radical generating agent having the details described in Table 1 were mixed with, as polyolefin resin, ethylene-propylene block copolvmer having a melt flow rate (M.F.R.) of 2.5 g/10 min. (the extruded amount of melted resin for 10 minutes at the time when 2.16 Kg of load is applied at 230C) and ethylene content of 12% by weight or a pro-pylene homopolymer having a M.F.R. of 2.0 g/10 min. themixture was melted and kneaded (mean retention time of 25 sec.) at 230C by using a twin screw extruder having a diameter of 45 mm (Brand PCM-45 of Ikegai Tekkosho K.K.) to do pelletizing. As Comparative examples 1 ~3~ each of the components described in Table 1 was mixed, melted, and kneaded according to the method the same as that of E~amples 1 -2 to do pelletizing. Resulting pellets were charged to an injectlon molding machine to mold -test specimen of definite dimension, which were subjected to the measurement o~ flammability and mechanical strength. The result are shown in Table 1.

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- 15 - ~ 8 As evident from Example l, Comparative examples 1 ~2 those which did not use a crosslinking agent and a radical generating agent were not extinguished as in Comparative example and fall of drip with flaming combustion was observed. Further, those in which the amount of a flame-retardan-t and antimony trioxide were increased, were satisfactory in combustion time but melting and falling of test specimens were observed by the second combustion.
In contrast, Example 1 showed excellent extinguishment and dripping property in spite of i-ts same amounts of addition of the flame-retardant and antimony trioxide as in Compara-tive example l. Particularly, at the second combustion time, notable difference in dripping property was observed.
Further, as for mechanical strengths, higher numerical values were indicated in flexural modulus, flexural strength, tensile strength, Izod impact strength, etc.
compared with those of Comparative example 1.
In specific example 2, a propylene homopolymer having a melt-flow rate 2.0 g/10 min. was used as a polyolefin resin and subjected to similar tests but it was revealed that a great extent of flammability and dripping property were improved at the time of the second combustion as compared with those of Comparative example 3.
Examples 3 ~4 and Comparative examples 4 ~ 7 - To polypropylene homopolymer having a M.F.R. of 2.0 g/
lO min., as a polyolefin resin, a halogen-containing 16 ~ 28 flame-retardant, antimony trioxide, a crosslinking agent a radical generating agent, and a boron compound, the details of whi.ch are described in Table 2, each in deEinite amounts were admixed in a Henschel mixer (FM-75C
manufactured by Mitsui Miike Seisakusho), and thereafter by using a twin screw extruder having a diameter of 45 mm (PCM-45, of Ikegai Tekko K.K.), melting and kneading were carried out at 230C (mean retention time in the extruder 25 sec.) to effect pelletizing. As Comparative examples 4 -7, each of the components described in Table 2 were mixed, melted and kneaded according to the method the same with those of Examples 3 ~4, to effect pelletizing.
~esulting pellets were charged to an injection molding machine to mold into test specimen of definite dimension at a temperature of 250C, and the molded test specimens were subjected to the measurement of flammability and mechanical strength. The results of these tests are shown in Table 2.
Examples 5 _ 9 and Comparative examples 8 ~9 By using, as polyolefin resin, an ethylene-propylene block copolymer having a M.F.R. of 2.5 g/lO min. and further using, in Examples 6 ~7, as inorganic filler, talc and wollastonite, definite amounts of each of the components the detail of which are described in Table 3, were mixed, melted and kneaded according to a method similar to -that of specific examples 3 ~4 to effect pelletizing.

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By using the resulting pellets, test specimen of definite dimension were molded according to a method described in specific examples 3 ~4 and measurements of flammability and mechanical strength were conducted.
The results of these tests are indicated in Table 3.

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As understandable from -the description of Table 2, it can be seen that extinguishing property, glow time and dripping property are all greatly improved. Namely, as indicated in Comparative example 6, simple increase of the amount of a halogen-containing flame-retardant and antimony trioxide provides good extinguishing property but melt-falling of test specimen were observed and dripping property was not improved at all. It can be seen that those in which combination same wi-th that of specific example 3 was made except that a crosslinking agent and a radical generating agent as in Comparative example 4 were not added, did not show extinguishment and melt fallen materials were observed, and it is observed that neither extinguishing property nor dripping property was improved. Those in which addition of a halogen-containing flame retardant and antimony trioxide was merely increased, relative to Comparative example 4 as in Comparative example 7 improves extinguishing property but melt falling of test specimen was observed and dripping property was not improved. Further, in a system in which a boron compound was removed from specific example 3, as in Comparative example 5, extinguishment property and dripping property showed satisfactory result but a glow time was considerably longer. The first goal of this glow time is 30 seconds or less and the second goal is 60 seconds 7~

or less but considering from these results, it cannot be said that this system is satisfactory. Whereas it has been revealed that extinguishment property, glow time and dripping property were all improved. Further, specific example 4 is directed to a case where ethylene bis~tetra~bromophthalimide)was used as a halogen containing flame-retardant but extinguishment property and dripping property are improved.
Referring now Table 3, specific example 5 is directed to a case where an ethylene propylene block copolymer having an ethylene content of 12~ by weight (M.E'.R. 2.5 g/
10 min.) was used as a polyolefin resin and showed good extinguishment, glow time and dripping property, similarily as in specific example 3. Comparative example 8 is lS directed to a case where only a radical generating agent is removed from specific example 5 but it is seen that both extinguishment and dripping property were worse and the effectiveness of a crosslinking agent is not exhibited due to the non-existence of a radical generating agent.
It is observed that simple increase of the amounts of a halogen-containing flame-retardant, and antimony trioxide, makes extinguishment better similarily as in Comparative example 7, melt-falling of test specimens were observed.
Further, specific examples 6 _7 correspond to the cases where an inorganic filler are added to specific example 5.

Self-extinguishment and dripping property were good but a glow time is inferior to specific example 5 to some extent. Specific example 8 is directed to a case where pentaerythrltol triacrylate is used as a crosslinking agen-t and example 9 is directed to a case where borax is used as a boron compound and it has been revealed that superior extinguishment, dripping property and glow time were exhibited as in specific example 5.

Claims (9)

1. A flame-retardant polypropylene composition comprising following components (A), (B), (C), (D) and (E);
(A) 0.1-15% by weight of crosslinking agent relative to the total amount of said components (A), (B), (C), (D) and (E) as 100% by weight, (B) 0.005-5% by weight of a radical generating agent relative to the total amount of said all the components, (C) 5-60% by weight of a halogen-containing flame-retardant selected from the group compositing of decabromodiphenyl oxide and ethylene-bis-tetrabromophthalimide, relative to the total amount of said all the components, (D) 100-10% by weight of antimony trioxide relative to said halogen-containing flame-retardant, (E) balance of polypropylene resin; said polypropylene resin being melted, and kneaded with said crosslinking agent and said radical generating agent.

2. A flame-retardant polypropylene composition comprising following components (A), (B), (C), (D), (E) and (F);
(A) 0.1-15% by weight of crosslinking agent relative to the total amount of said components (A), (B), (C), (D), (E) and (F) as 100% by weight, (B) 0.005-5% by weight of a radical generating agent rela-tive to the total amount of said all the components, (C) 5-60% by weight of a halogen-containing flame-retardant selected from the group consisting of decabromodiphenyl oxide and ethylene-bis-tetrabromophthalimide, relative to the total amount of said all the components, sp: 25 (D) 100-10% by weight, of antimony trioxide relative to said halogen-containing flame-retardant, (E) 1-10% by weight of a boron compound, (F) balance of polypropylene resin, said polypropylene resin being melted and kneaded with said crosslinking agent and said radical generating agent.

3. A flame-retardant polypropylene composition according to claim 1 wherein said polypropylene resin is at least one member selected from the group consisting of propylene homo-polymer, ethylene-propylene block copolymer and ethylene-propylene random copolymer, the respective copolymers being composed mainly of propylene.

4. A flame-retardant polypropylene composition according to claim 2 wherein said polypropylene resin is at least one member selected from the group consisting of propylene homo-polymer, ethylene-propylene block copolymer and ethylene-propylene random copolymer, the respective copolymers being composed mainly of propylene.

5. A flame-retardant polypropylene composition according to claim 1 wherein said crosslinking agent is at least one member selected from the group consisting of triallyl cyanurate, triallyl isocyanurate, diethyleneglycol dimeth-acrylate, trimethylol propanetriacrylate, trimethylol propane trimethacrylate, pantaerythritol triacrylate, pantaerythritol tetraacrylate, divinyl benzene, diallyl phthalate, divinyl pyridine, vinyl toluene, ethyl vinyl benzene, styrene monomer, quinone dioxime, benzoquinone dioxime and p-nitrosophenol.

6. A flame-retardant polypropylene composition according to claim 2 wherein said crosslinking agent is at least one member selected from the group consisting of triallyl cyanurate, triallyl isocyanurate, diethyleneglycol dimethacrylate, trimethylol propanetriacrylate, trimethylol propanetrimethacrylate, panterythritol triacrylate, pantaerythritol tetraacrylate, divinyl benzene, diallyl phthalate, divinyl pyridine, vinyl toluene, ethyl vinyl benzene, styrene monomer, quinone dioxime, benzoquinone dioxime, and p-nitrosophenol

7. A flame-retardant polypropylene composition according to claim 1 wherein said radical generating agent is at least one member selected from the group consisting of dicumyl peroxide, 2,5-dimethyl1-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3; 1,3-bis (t-butylperoxyisopropyl) benzene, 1,1,4,4,7,7-hexamethylcyclo-4,7-diperoxynonane, cumenehydroperoxide and cumylperoxy-trimethylsilane.

8. A flame-retardant polypropylene composition according to claim 2 wherein said radical generating agent is at least one member selected from the group consisting of dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3; 1,3-bis (t-butylperoxyisopropyl) benzene, 1,1,4,4,7,7-hexamethylcyclo-4,7-diperoxynonane, cumenehydroperoxide and cumylperoxy-trimethylsilane.

9. A flame-retardant polypropylene composition according to calim 2.wherein said boron compound is at least one member selected from the group consisting of borax, potassium borofluoride, sodium borofluoride and ammonium borofluoride.