Primer mixture of crosslinking initiator and promoter

Abstract

A primer mixture intended for crosslinking polyethylene, including at least an initiator of free radicals chosen from organic peroxides, azo compounds or mixtures thereof, wherein the mixture has said free-radical initiator and at least one crosslinking promoter chosen from the cycloalkanes having 5 to 7 carbon atoms, substituted by 1 to 3 vinyl, allyl or isopropenyl groups, the aromatic compounds substituted by 1 to 3 vinyl, allyl or isopropenyl groups, the methacrylate, acrylate and maleimide monomers being multi-substituted, and in that the weight ratio of free-radical initiator to the crosslinking promoter is greater than or equal to 1, and preferably between 1.5 and 4. Also, a method and to a use related to this primer mixture.

Claims

1. A primer mixture configured for crosslinking polyethylene, comprising at least one free-radical initiator chosen from organic peroxides, azo compounds or mixtures thereof, and at least one crosslinking promoter chosen from cycloalkanes containing 5 to 7 carbon atoms, substituted with 1 to 3 vinyl or allyl groups, wherein the weight ratio of free-radical initiator to crosslinking promoter is greater than or equal to 1, and wherein the primer mixture is subjected to a dissolution and homogenization operation, which results in dissolution of the free-radical initiator in the crosslinking promoter.

2. The mixture of claim 1, wherein the crosslinking promoter is trivinylcycloalkane.

3. The mixture of claim 1, wherein the free-radical initiator is dicumyl peroxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane or bis[(t-butylperoxy)isopropyl]benzene or a mixture of these initiators.

4. The mixture of claim 1, wherein the primer mixture is in liquid form at room temperature.

5. A process for manufacturing crosslinked polyethylene, comprising a final step of crosslinking polyethylene, wherein: a free-radical initiator is chosen from organic peroxides, azo compounds or mixtures thereof, wherein at least one crosslinking promoter is chosen from cycloalkanes containing 5 to 7 carbon atoms, substituted with 1 to 3 vinyl or allyl groups, and wherein a step of dilution of said free-radical initiator with said crosslinking promoter is initially performed, and impregnation of polyethylene with the primer mixture thus formed of claim 1, in liquid form.

6. The process of claim 5, wherein the crosslinking promoter is present in liquid form at room temperature and ambient pressure.

7. The process of claim 5, wherein the step of crosslinking polyethylene is performed by extrusion or by injection-molding.

8. A method of producing cables comprising forming a cable from the primer mixture of claim 1, wherein the cable is configured for transporting fluid or electrical current.

9. The mixture of claim 1, wherein the weight ratio of free-radical initiator to crosslinking promoter is between 1.5 and 4.

10. The mixture of claim 1, wherein the primer mixture is in liquid form at least for a temperature of between 10 C. and 50 C. at ambient pressure (1 bar).

11. The process of claim 5, wherein said initiator is chosen from dicumyl peroxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane and bis[(t-butylperoxy)isopropyl]benzene or a mixture of these initiators.

12. The process of claim 5, wherein-the crosslinking promoter is present in liquid form at a temperature of between 10 C. and 50 C. at a pressure of 1 bar.

13. A process for manufacturing crosslinked polyethylene, comprising: dissolution and homogenization of a free-radical initiator in at least one crosslinking promoter to form a primer mixture in liquid form, wherein said free-radical initiator is chosen from organic peroxides, azo compounds or mixtures thereof, and wherein said at least one crosslinking promoter is chosen from cycloalkanes containing 5 to 7 carbon atoms, substituted with 1 to 3 vinyl or allyl groups, aromatic compounds substituted with 1 to 3 vinyl or allyl groups, multi-substituted monomers based on methacrylate, acrylate, maleimide, and in that the weight ratio of free-radical initiator to crosslinking promoter is greater than or equal to 1; wherein the primer mixture is impregnated into granules of polyethylene; and crosslinking the polyethylene.

14. The process of claim 13, wherein the crosslinking promoter is present in liquid form at room temperature and ambient pressure.

15. The process of claim 13, wherein the crosslinking polyethylene is performed by extrusion or by injection-molding.

16. The process of claim 13, wherein said free-radical initiator is chosen from dicumyl peroxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane and bis[(t-butylperoxy)isopropyl]benzene or a mixture thereof, and wherein said crosslinking promoter is chosen from trivinylcycloalkane and/or divinylbenzene.

17. The process of claim 13, wherein-the crosslinking promoter is present in liquid form at a temperature of between 10 C. and 50 C. at a pressure of 1 bar.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings, which are incorporated in and constitute a part of the Specification, illustrate graphical results of examples.

(2) FIG. 1 illustrates a change in crosslinking densities as a function of the impregnation time for the four systems studied.

(3) FIG. 2 illustrates a change in crosslinking densities as a function of the storage time at 5 C. for the three systems studied.

DETAILED DESCRIPTION OF THE INVENTION

(4) The present invention is directed toward the crosslinking of polymer. The polymer according to the invention may be any type of polymer that may be crosslinked with organic peroxides, the present invention being more particularly directed toward the crosslinking of polyethylene.

(5) As regards polyethylene, it is understood that high-density polyethylenes (HDPE), low-density polyethylenes (LDPE), linear low-density polyethylene (LLDPE), very low density polyethylenes (VLDPE), polyethylenes obtained by metallocene catalysis, copolymers of ethylene with one or more comonomers, such as ethylene-propylene-diene terpolymers (EPDM), ethylene-propylene copolymers (EPM), ethylene-vinyl acetate (EVA) copolymers, copolymers of ethylene-alkyl acrylate (EMA, EEA, EBA) and copolymers of ethylene-(,)-alkadienes are included.

(6) The other polymers concerned by the present invention are hydrogenated butadiene-acrylonitrile copolymers (HNBR), butadiene-acrylonitrile copolymers (NBR), fluoroelastomers (FKM) and polybutadienes (PBU). Polymers such as high-density polyethylenes, low-density polyethylenes and ethylene-propylene copolymers are particularly preferred. However, in the specific context of polyethylene crosslinking and for this invention, low-density polyethylenes will preferentially be chosen.

(7) As regards the free-radical initiator, it is understood to be organic peroxides, and more particularly organic peroxides used as crosslinking agents such as dialkyl peroxides, diperoxyketals and certain monoperoxycarbonates, to which may be added azo compounds. The free-radical initiator of the primer mixture according to the invention may consist of one or more organic peroxides and/or azo compounds.

(8) Among the dialkyl peroxides, the preferred initiators are: dicumyl peroxide (sold as Luperox DC or Luperox DCP), di-t-butyl peroxide (Luperox DI), t-butylcumyl peroxide (Luperox 801), 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane (Luperox 101), 2,5-dimethyl-2,5-bis(t-amylperoxy)hexane, 2,5-dimethyl-2,5-bis(t-butylperoxy)-3-hexyne (Luperox 130), 2,5-dimethyl-2,5-bis(t-amylperoxy)-3-hexyne, ,-bis-[(t-butylperoxy)isopropyl]benzene (Luperox F), ,-bis[(t-amylperoxy)isopropyl]benzene (Luperox 180), di-t-amyl peroxide (Luperox DTA), 1,3,5-tris[(t-butylperoxy)isopropyl]benzene, 1,3-dimethyl-3-(t-butylperoxy)butanol, 1,3-dimethyl-3-(t-amylperoxy)butanol. The mixture of dicumyl peroxide and 1,3- and 1,4-isopropylcumyl cumyl peroxide (Luperox DC60) is also advantageous.

(9) Certain monoperoxycarbonates such as O,O-tert-butyl-O-(2-ethylhexyl) monoperoxycarbonate (Luperox TBEC), O,O-tert-butyl-O-isopropyl monoperoxycarbonate (Luperox TBIC) and O,O-tert-amyl-O-2-ethylhexyl monoperoxycarbonate (Luperox TAEC) are also used.

(10) Among the diacyl peroxides, the preferred initiator is benzoyl peroxide (Luperox A75).

(11) Among the diperoxyketals, the preferred initiators are: 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane (Luperox 231), n-butyl 4,4-bis(t-amylperoxy)valerate (Luperox 230), ethyl 3,3-bis(t-butylperoxy)butyrate (Luperox 233), 2,2-bis(t-amylperoxy)propane, 3,6,6,9,9-pentamethyl-3-ethoxycarbonyl-methyl-1,2,4,5-tetraoxacyclononane, 3,3,5,7,7-pentamethyl-1,2,4-trioxepane, n-butyl 4,4-bis(t-butylperoxy)valerate, ethyl 3,3-bis(t-amylperoxy)butyrate, 1,1-bis(t-butylperoxy)cyclohexane (Luperox 331), 1,1-bis(t-amylperoxy)cyclohexane (Luperox 531), and mixtures thereof.

(12) As azo compounds, examples that may be mentioned include 2,2-azobis-(2-acetoxypropane), azobisisobutyronitrile, azodicarbamide, 4,4-azobis(cyanopentanoic acid) and 2,2-azobismethylbutyronitrile.

(13) As regards the crosslinking promoter, this is understood as being cycloalkanes containing 5 to 7 carbon atoms, substituted with 1 to 3 vinyl, allyl or isopropenyl groups, aromatic compounds substituted with 1 to 3 vinyl, allyl or isopropenyl groups, or multi-substituted monomers based on methacrylate, acrylate or maleimide.

(14) Mention may be made, for example, of vinylcyclohexane, divinylcyclohexane, trivinylcyclohexane, vinylcyclopentane, diisopropenylcyclohexane and triisopropenyl cyclohexane.

(15) Cyclohexane substituted with 1 to 3 vinyl or allyl groups is advantageously used, in particular trivinylcyclohexane.

(16) Commercial trivinylcyclohexane predominantly contains 1,2,4-trivinylcyclohexane.

(17) As crosslinking promoter of multi-substituted aromatic type, mention may be made of divinylbenzene, diisopropenylbenzene, -methylstyrene, -methylstyrene dimer and triallyl trimellitate.

(18) As crosslinking promoter based on multi-substituted methacrylate, mention may be made of ethylene glycol dimethacrylate, phenylene dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol 200 dimethacrylate, polyethylene glycol 400 dimethacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, 1,12-dodecanediol dimethacrylate, 1,3-glycerol dimethacrylate, diurethane dimethacrylate and trimethylolpropane trimethacrylate.

(19) The crosslinking promoter based on multi-substituted methacrylate is advantageously used, in particular ethylene glycol dimethacrylate and trimethylolpropane trimethacrylate.

(20) As crosslinking promoter based on multi-substituted acrylate, mention may be made of bisphenol A epoxy diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, polyethylene glycol 600 diacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, neopentyl glycol ethoxylate diacrylate, butanediol diacrylate, hexanediol diacrylate, aliphatic urethane diacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, trimethylolpropane propoxylate triacrylate, glycerol propoxylate triacrylate, aliphatic urethane triacrylate, trimethylolpropane triacrylate and dipentaerythritol pentaacrylate.

(21) As nitrogenous crosslinking promoter, mention may be made of triallyl cyanurate, triallyl isocyanurate and N,N-m-phenylenedimaleimide.

(22) Mention may also be made, as monomer multi-substituted with vinyl groups, of butadiene, chloroprene and isoprene.

(23) In the context of the present invention, trivinylcyclohexane and divinylbenzene will preferentially be chosen as crosslinking promoter.

(24) Among the antioxidants, mention may be made of those of the hydroquinone family, such as hydroquinone, hydroquinone bis(-hydroxyethyl)ether, hydroquinone monomethyl ether, mono-tert-butylhydroquinone, di-tert-butylhydroquinone and di-tert-amylhydroquinone; mention may be made particularly of antioxidants of the phenol family, such as 2,2-thiodiethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 4,6-bis(octylthiomethyl)-o-cresol and 4,4-thiobis(2-t-butyl-5-methylphenol).

(25) The present invention relates to a primer mixture comprising only two components, namely the free-radical initiator and the crosslinking promoter. Once this primer mixture has been made, it is intended to impregnate polyethylene.

(26) Various components may then be added to this composition (primer mixture according to the invention with polyethylene), which may comprise UV stabilizers; processing agents, having the function of improving the final appearance during its use, such as fatty amides, stearic acid and salts thereof, ethylenebisstearamide or fluoro polymers; antifogging agents, antiblocking agents such as silica or talc; fillers such as calcium carbonate and nanofillers, for instance clays; couplers such as silanes; antistatic agents; nucleating agents, pigments; dyes; plasticizers; fluidizers and flame-retarding additives such as aluminum or magnesium hydroxides.

(27) According to the invention, one or more crosslinking retardants may also be introduced, after preparing/manufacturing the primer mixture according to the invention, such as antioxidant compounds of the hydroquinone family and phenolic antioxidants.

(28) These additives are generally used in contents of between 10 ppm and 10 000 ppm by weight relative to the weight of final polymer. The plasticizers, fluidizers and flame-retardant additives may be in amounts much greater than 10 000 ppm.

(29) Example of preparation of a primer mixture according to the invention:

(30) First, ten (10) grams (g) of dicumyl peroxide are added to 10 g of trivinyl-cyclohexane, and the mixture is then stirred at a temperature of 50 C. (Celsius) for a period of five (5) minutes; the mixture obtained is homogeneous. At this stage, the primer mixture according to the invention is obtained.

(31) Next, 300 g of low-density polyethylene (LDPE) are placed in a glass container, such as one (1) liter (L) Schott bottle. Next, 6 g of the primer mixture preheated to 60 C. are added to the LDPE, and the closed container is placed on a roll mixer at a speed of 15 rpm (revolutions per minute). Once the impregnation time has elapsed, the LDPE-based component is recovered and may be crosslinked at the appropriate temperature (typically between 170 C. and 200 C.).

(32) Tests Performed:

(33) Measurement of the Impregnation Time

Example 1: Free-Radical Initiator Used Alone

(34) 300 g of low-density polyethylene (LDPE) preheated to 60 C. are placed in a glass container, a 1 L (one liter) Schott bottle. Next, 6 g of dicumyl peroxide preheated to 60 C. are added to the LDPE, and the container is closed and placed on a roll mixer at a speed of 15 rpm at 60 C. At regular time intervals, 13 g of the LDPE-based component are taken from the bottle and placed in 20 ml of methanol to be mixed for 30 seconds (s) using a wooden spatula, and the mixture is then filtered on a screen. The peroxide not adsorbed is thus removed from the surface of the LDPE by the methanol, the adsorbed peroxide remaining in the LDPE granules, which are then heated on an screen under a fume cupboard and then analyzed using an RPA2000 rheometer.

(35) The change in crosslinking density is detailed in table 1 below.

(36) TABLE-US-00001 TABLE 1 Change in crosslinking densities and kinetics as a function of the impregnation time for dicumyl peroxide used alone. DCP 2 phr RPA @ 190 C. Mean values M.sub.H-M.sub.L t.sub.90 ts2 M.sub.H-M.sub.L t.sub.90 ts2 Withdrawal Test No. (dNm) (m:s) (m:s) (dNm) (m:s) (m:s) 00:15:00 Test 1 1.72 02:18 1.69 02:21 Test 2 1.65 02:24 00:30:00 Test 1 2.63 02:27 01:41 2.65 02:22 01:38 Test 2 2.66 02:16 01:35 00:45:00 Test 1 3.43 02:17 01:09 3.57 02:17 01:07 Test 2 3.70 02:18 01:05 02:10:00 Test 1 10.63 02:04 00:34 11.16 02:04 00:34 Test 2 11.68 02:04 00:33 03:10:00 Test 1 14.20 01:59 00:31 14.59 02:00 00:31 Test 2 14.97 02:01 00:30 04:00:00 Test 1 18.45 02:00 00:29 18.38 02:00 00:30 Test 2 18.31 01:59 00:31 05:00:00 Test 1 20.39 02:00 00:28 20.05 01:59 00:28 Test 2 19.71 01:58 00:28

Example 2: Free-Radical Initiator Predissolved in the Crosslinking Promoter 1,2,4-Trivinylcyclohexane (50/50 Composition)

(37) 300 g of low-density polyethylene (LDPE) preheated to 60 C. are placed in a glass container, namely, for example, a 1 L Schott bottle. Next, 7.2 g of a mixture containing 50% dicumyl peroxide and 50% trivinylcyclohexane preheated to 60 C. are added to the LDPE, and the container is closed and placed on a roll mixer at a speed of 15 rpm at 60 C. At regular time intervals, 13 g of LDPE-based component are withdrawn from the bottle and placed in 20 milliliters (ml) of methanol and mixed for 30 seconds with a wooden spatula, and the mixture is then filtered on a screen. The peroxide not adsorbed is thus removed from the surface of the LDPE by the methanol, the adsorbed peroxide remaining in the LDPE granules, which are then dried on a screen under a fume cupboard and then analyzed using an RPA2000 rheometer.

(38) The change in crosslinking density is detailed in table 2 below.

(39) TABLE-US-00002 TABLE 2 Change in crosslinking densities and kinetics as a function of the impregnation time for dicumyl peroxide premixed with trivinylcyclo- hexane in mass proportions of 50% peroxide/50% trivinylcyclohexane. DCP/TVCH 50/50 2.43 phr RPA @ 190 C. Mean values M.sub.H-M.sub.L t.sub.90 ts2 M.sub.H-M.sub.L t.sub.90 ts2 Withdrawal Test No. (dNm) (m:s) (m:s) (dNm) (m:s) (m:s) 00:15:00 Test 1 1.10 02:25 1.09 02:31 Test 2 1.08 02:38 00:30:00 Test 1 4.01 02:27 01:09 4.21 02:29 01:07 Test 2 4.41 02:31 01:05 02:10:00 Test 1 16.60 02:19 00:36 16.84 02:20 00:36 Test 2 17.08 02:21 00:36 04:00:00 Test 1 17.89 02:26 00:37 18.15 02:24 00:37 Test 2 18.41 02:22 00:37 05:00:00 Test 1 21.62 02:26 00:37 21.44 02:28 00:39 Test 2 21.25 02:29 00:41

Example 3: Free-Radical Initiator Predissolved in the Crosslinking Promoter 1,2,4-Trivinylcyclohexane (75/25 Composition)

(40) 300 g of low-density polyethylene (LDPE) preheated to 60 C. are placed in a glass container, a 1 L Schott bottle. Next, 5 g of a mixture containing 75% dicumyl peroxide and 25% trivinylcyclohexane preheated to 60 C. are added to the LDPE, and the container is closed and placed on a roll mixer at a speed of 15 rpm at 60 C. At regular time intervals, 13 g of LDPE-based component are withdrawn from the bottle and placed in 20 ml of methanol and mixed for 30 seconds with a wooden spatula, and the mixture is then filtered on a screen. The peroxide not adsorbed is thus removed from the surface of the LDPE by the methanol, the adsorbed peroxide remaining in the LDPE granules, which are then dried on a screen under a fume cupboard and then analyzed using an RPA2000 rheometer.

(41) The change in crosslinking density is detailed in table 3 below.

(42) TABLE-US-00003 TABLE 3 Change in crosslinking densities and kinetics as a function of the impregnation time for dicumyl peroxide premixed with trivinylcyclo- hexane in mass proportions of 75% peroxide/25% trivinylcyclohexane. DCP/TVCH 75/25 1.66 phr RPA @ 190 C. Mean values M.sub.H-M.sub.L t.sub.90 ts2 M.sub.H-M.sub.L t.sub.90 ts2 Withdrawal Test No. (dNm) (m:s) (m:s) (dNm) (m:s) (m:s) 00:15:00 Test 1 1.83 02:26 1.80 02:25 Test 2 1.77 02:25 00:30:00 Test 1 3.92 02:29 01:09 3.95 02:28 01:08 Test 2 3.97 02:26 01:08 01:00:00 Test 1 10.44 02:15 00:38 10.36 02:15 00:39 Test 2 10.28 02:14 00:39 01:30:00 Test 1 14.48 02:07 00:33 14.40 02:08 00:34 Test 2 14.31 02:09 00:34 02:00:00 Test 1 17.11 02:04 00:32 17.04 02:05 00:33 Test 2 16.97 02:06 00:33 02:30:00 Test 1 16.30 02:03 00:33 16.91 02:00 00:32 Test 2 17.52 01:57 00:30 05:00:00 Test 1 21.22 02:04 00:33 21.10 02:06 00:35 Test 2 20.98 02:08 00:36

Example 4: Free-Radical Initiator Predissolved in the Crosslinking Promoter Divinylbenzene (50/50 Composition)

(43) 300 g of low-density polyethylene (LDPE) preheated to 60 C. are placed in a glass container, a 1 L Schott bottle. Next, 7.2 g of a mixture containing 50% dicumyl peroxide and 50% trivinylcyclohexane preheated to 60 C. are added to the LDPE, and the container is closed and placed on a roll mixer at a speed of 15 rpm at 60 C. At regular time intervals, 13 g of LDPE-based component are withdrawn from the bottle and placed in 20 ml of methanol and mixed for 30 seconds with a wooden spatula, and the mixture is then filtered on a screen. The peroxide not adsorbed is thus removed from the surface of the LDPE by the methanol, the adsorbed peroxide remaining in the LDPE granules, which are then dried on a screen under a fume cupboard and then analyzed using an RPA2000 rheometer.

(44) The change in crosslinking density is detailed in table 4 below.

(45) TABLE-US-00004 TABLE 4 Change in crosslinking densities and kinetics as a function of the impregnation time for dicumyl peroxide premixed with divinyl- benzene in mass proportions of 50% peroxide/50% divinylbenzene. DCP/DVB 50/50 2.43 phr RPA @ 190 C. Mean values M.sub.H-M.sub.L t.sub.90 ts2 M.sub.H-M.sub.L t.sub.90 ts2 Withdrawal Test No. (dNm) (m:s) (m:s) (dNm) (m:s) (m:s) 00:15:00 Test 1 0.801 02:26 0.80 02:26 Test 2 00:30:00 Test 1 2.868 02:27 01:28 2.82 02:24 01:29 Test 2 2.779 02:22 01:31 00:45:00 Test 1 4.369 02:18 00:55 4.40 02:18 00:54 Test 2 4.428 02:18 00:54 02:10:00 Test 1 14.56 02:04 00:29 14.61 02:05 00:29 Test 2 14.65 02:07 00:29 03:10:00 Test 1 17.85 02:01 00:27 17.92 02:01 00:27 Test 2 17.79 02:01 00:27 04:00:00 Test 1 18.12 02:02 00:28 18.52 02:01 00:27 Test 2 18.58 02:00 00:27 05:00:00 Test 1 18.46 01:59 00:27 18.48 01:59 00:27 Test 2 18.48 02:00 00:27

(46) FIG. 1 shows the comparison of the crosslinking density values obtained using an RPA2000 rheometer between the 4 systems, i.e. examples 1, 2, 3 and 4 described above.

(47) It is clearly seen that premixing the peroxide with trivinylcyclohexane brings about a very significant reduction in the adsorption time. After two hours of mixing, for example, the two samples of polyethylene supplemented with the mixtures of trivinylcyclohexane plus dicumyl peroxide show a crosslinking density of greater than 16 dN.Math.m, whereas it takes about four hours to reach this same crosslinking density with dicumyl peroxide added alone to the polyethylene (example 1).

(48) The use of divinylbenzene also improves the adsorption of the dicumyl peroxide: the mixture containing this additive requires 3 hours to reach a crosslinking density of 16 dN.Math.m.

Measurement of the Desorption Time

Example 5: Free-Radical Initiator Used Alone

(49) 300 g of low-density polyethylene (LDPE) are placed in a glass container, more precisely, for example, a 1 L Schott bottle. Next, 6 g of dicumyl peroxide preheated to 60 C. are added to the LDPE, and the container is closed and placed on a roll mixer at a speed of 15 rpm at 60 C. Once the impregnation time has elapsed, the bottle is placed in a hermetic container at a temperature of 5 C. At regular time intervals, 13 g of LDPE-based component are withdrawn from the bottle and placed in 20 ml of methanol to be mixed for 30 seconds with a wooden spatula, and the mixture is then filtered on a screen. The LDPE granules are thus freed of the peroxide that may have been desorbed. The granules are then dried on a screen under a fume cupboard and then analyzed using an RPA2000 rheometer.

(50) The change in crosslinking density is detailed in table 5 below, which shows that desorption takes place from the first day in the case of dicumyl peroxide used alone.

(51) TABLE-US-00005 DCP 2 phr RPA @ 190 C. Mean values M.sub.H-M.sub.L t.sub.90 ts2 M.sub.H-M.sub.L t.sub.90 ts2 Withdrawal Test No. (dNm) (m:s) (m:s) (dNm) (m:s) (m:s) 0 day.sup. Test 1 20.39 02:00 00:28 20.05 01:59 00:28 Test 2 19.71 01:58 00:28 1 day.sup. Test 1 14.85 01:58 00:31 14.60 01:59 00:31 Test 2 14.35 02:00 00:31 2 days Test 1 14.32 01:59 00:32 14.49 01:59 00:32 Test 2 14.66 01:59 00:31 3 days Test 1 14.73 02:00 00:31 14.62 02:00 00:31 Test 2 14.51 02:00 00:31 4 days Test 1 14.19 02:03 00:32 14.29 02:01 00:32 Test 2 14.39 02:00 00:32 5 days Test 1 14.27 02:03 00:31 14.44 02:01 00:31 Test 2 14.60 01:59 00:30

Example 6: Free-Radical Initiator Predissolved in a Crosslinking Promoter (50/50 Composition)

(52) 300 g of low-density polyethylene (LDPE) are placed in a glass container, a 1 L Schott bottle. Next, 7.2 g of a mixture containing 50% dicumyl peroxide and 50% trivinylcyclohexane preheated to 60 C. is added to the LDPE, and the container is closed and placed on a roll mixer at a speed of 15 rpm at 60 C. Once the impregnation time has elapsed, the bottle is placed in a hermetic container at 5 C. At regular time intervals, 13 g of LDPE-based component are withdrawn from the bottle and placed in 20 ml of methanol to be mixed for 30 seconds with a wooden spatula, and the mixture is then filtered on a screen. The LDPE granules are thus freed of the peroxide that may have been desorbed, and are then dried on a screen under a fume cupboard and then analyzed using an RPA2000 rheometer. The change in crosslinking density is detailed in table 6 below, which shows that no desorption is detected in the first five (5) days in the case of dicumyl peroxide used premixed with trivinylcyclohexane in mass proportions of 50% peroxide/50% trivinylcyclohexane.

(53) TABLE-US-00006 TABLE 6 Change in crosslinking densities and kinetics as a function of the storage time at 5 C. for dicumyl peroxide premixed with trivinylcyclo- hexane in mass proportions of 50% peroxide/50% trivinylcyclohexane. 50/50 2.43 phr RPA @ 190 C. Mean values M.sub.H-M.sub.L t.sub.90 ts2 M.sub.H-M.sub.L t.sub.90 ts2 Withdrawal Test No. (dNm) (m:s) (m:s) (dNm) (m:s) (m:s) 0 day.sup. Test 1 20.41 02:20 00:35 20.80 02:20 00:35 Test 2 20.80 02:19 00:35 1 day.sup. Test 1 21.08 02:36 00:35 20.69 02:30 00:36 Test 2 20.30 02:24 00:36 2 days Test 1 20.78 02:26 00:36 20.55 02:24 00:36 Test 2 20.31 02:22 00:36 3 days Test 1 20.28 02:27 00:35 20.32 02:25 00:36 Test 2 20.35 02:23 00:36 4 days Test 1 20.24 02:19 00:35 20.57 02:20 00:35 Test 2 20.89 02:21 00:35 5 days Test 1 20.38 02:23 00:36 20.76 02:22 00:36 Test 2 21.13 02:22 00:35

Example 7: Free-Radical Initiator Predissolved in a Crosslinking Promoter (75/25 Composition)

(54) 300 g of low-density polyethylene (LDPE) are placed in a glass container, a 1 L Schott bottle. Next, 7.2 g of a mixture containing 50% dicumyl peroxide and 50% trivinylcyclohexane preheated to 60 C. is added to the LDPE, and the container is closed and placed on a roll mixer at a speed of 15 rpm at 60 C. Once the impregnation time has elapsed, the bottle is placed in a container (adiabatic) at 5 C. At regular time intervals, 13 g of LDPE-based component are withdrawn from the bottle and placed in 20 ml of methanol to be mixed for 30 seconds with a wooden spatula, and the mixture is then filtered on a screen. The LDPE granules are thus freed of the peroxide that may have been desorbed, and are then dried on a screen under a fume cupboard and then analyzed using an RPA2000 rheometer. The change in crosslinking density is detailed in table 7 below, which shows that no desorption is detected in the first five (5) days in the case of dicumyl peroxide used premixed with trivinylcyclohexane in mass proportions of 75% peroxide/25% trivinylcyclohexane.

(55) TABLE-US-00007 TABLE 7 Change in crosslinking densities and kinetics as a function of the storage time at 5 C. for dicumyl peroxide premixed with trivinylcyclo- hexane in mass proportions of 75% peroxide/25% trivinylcyclohexane. 75/25 1.66 phr RPA @ 190 C. Mean values M.sub.H-M.sub.L t.sub.90 ts2 M.sub.H-M.sub.L t.sub.90 ts2 Withdrawal Test No. (dNm) (m:s) (m:s) (dNm) (m:s) (m:s) 0 day.sup. Test 1 19.27 02:03 00:31 18.88 02:04 00:32 Test 2 18.49 02:05 00:32 1 days Test 1 19.57 02:05 00:32 19.71 02:05 00:32 Test 2 19.84 02:05 00:32 2 days Test 1 20.02 02:04 00:32 20.06 02:03 00:32 Test 2 20.09 02:03 00:32 3 days Test 1 19.75 02:06 00:31 19.91 02:06 00:32 Test 2 20.06 02:05 00:32 4 days Test 1 19.82 02:01 00:31 19.71 02:03 00:32 Test 2 19.59 02:05 00:32 5 days Test 1 19.75 02:06 00:33 19.75 02:05 00:32 Test 2 19.75 02:03 00:31

(56) FIG. 2 shows the comparison of the crosslinking density values obtained using an RPA2000 rheometer between the 3 systems (examples 5, 6 and 7 presented above).

(57) It is clearly seen that premixing the peroxide very significantly slows down the desorption phenomenon, since no desorption was detected after five (5) days at 5 C., whereas the reference (example 5), peroxide used alone, desorbs from the first day under the chosen experimental conditions.

(58) The present invention makes it possible to significantly reduce the volatile products, and more particularly methane, which are predominantly derived from the decomposition of the organic peroxide. Specifically, it has been shown that the present invention makes it possible to obtain acceptable levels of crosslinking by using up to 40% less organic peroxide, and in consequence the amount of volatile products is also reduced, this reduction being up to 40%.