Process for recovering wastes of a polymeric composition including a peroxidic crosslinking agent

Abstract

A process for recovering wastes of a polymeric composition including at least one peroxide-curable polymer and at least one peroxidic crosslinking agent, which includes compounding the wastes with at least one antioxidant agent suitable for sulfur-vulcanized elastomeric compositions, at a temperature lower than the decomposition temperature of the at least one peroxide crosslinking agent. The compounding of the polymeric wastes with the antioxidant agent is carried out at a temperature lower than the decomposition temperature of the peroxide crosslinking agent, so as to avoid any premature activation of the crosslinking agent. The process is particularly suitable for compositions based on elastomeric polyolefins, more preferably for elastomeric ethylene copolymers such as ethylene-propylene copolymers (EPR) and ethylene-propylene-diene terpolymers (EPDM), which can be processed at relatively low temperatures, much lower than the decomposition temperatures of the most common peroxide crosslinking agents.

Claims

1. A process for recovering wastes of a polymeric composition comprising at least one peroxide-curable polymer and at least one peroxidic crosslinking agent, which comprises quenching the at least one peroxide crosslinking agent contained in the wastes by compounding the wastes with at least one antioxidant agent suitable for sulfur-vulcanized elastomeric compositions, at a temperature lower than the decomposition temperature of the at least one peroxide crosslinking agent.

2. The process according to claim 1, wherein the at least one antioxidant agent is selected from primary antioxidants having reactive OH and/or NH groups.

3. The process according to claim 2, wherein the at least one antioxidant agent is selected from secondary phenylamines and low molecular weight hindered phenols.

4. The process according to claim 3, wherein the at least one antioxidant agent is selected from: 2,6-di-t-butyl-hydroxytoluene (BHT), 2,6-di-t-butyl-4-nonylphenol, 2,6-di-t-butyl-4-ethylphenol, 4-nonylphenol, 3-(2,3-di-t-butyl-4-hydroxyphenyl) propionic methyl ester, 3,5-di-t-butyl-4-hydroxyhydrocinnamic acid octadecyl ester, poly(dicyclopentadiene-co-p-cresol), and mixtures thereof.

5. The process according to claim 3, wherein the secondary phenylamines are selected from: secondary phenylenediamines, diphenylamines, derivatives thereof, and mixtures thereof.

6. The process according to claim 5, wherein the secondary phenylenediamines are selected from: N-phenyl-N-iso-propyl-p-phenylenediamine (IPPD), N-(1,3-dimethylbutyl)-N-phenyl-p-phenylenediamine (6PPD), N,N-bis-(1,4-dimethylpentyl)-p-phenylenediamine (77PD), N,N-bis-(1-ethyl-3-methylpentyl)-p-phenylenediamine (DOPD), N,N-diphenyl-p-phenylenediamine (DPPD), N,N-ditolyl-p-phenylenediamine (DTPD), N,N-di--naphthyl-p-phenylenediamine (DNPD), N,N-bis-(1-methylheptyl)-p-phenylenediamine, N,N-di-sec-butyl-p-phenylenediamine (44PD), N-phenyl-N-cyclohexyl-p-phenylenediamine, N-phenyl-N-1-methylheptyl-p-phenylenediamine, and mixtures thereof.

7. The process according to claim 1, wherein the antioxidant agent is compounded with the wastes to be recovered in an amount of from 0.2 to 10 phr.

8. The process according to claim 7, wherein the antioxidant agent is compounded with the wastes to be recovered in an amount of from 0.5 to 5 phr.

9. The process according to claim 1, wherein the peroxide-curable polymer is an elastomeric polyolefin.

10. The process according to claim 1, wherein the at least one peroxide-curable polymer is a thermoplastic polyolefin.

11. The process according to claim 1, wherein the at least one peroxidic crosslinking agent has a decomposition temperature equal to or greater than 90 C.

12. The process according to claim 11, wherein the at least one peroxidic crosslinking agent has a decomposition temperature from 105 C. to 145 C.

13. The process according to claim 11, wherein the at least one peroxidic crosslinking agent is selected from: dicumyl peroxide, t-butyl cumyl peroxide, bis(t-butylperoxyisopropyl) benzene, bis(t-butylperoxy)2,5 dimethyl hexane, bis(t-butylperoxy)2,5 dimethyl hexyne, 2,4-dimethyl-2,5-di(t-butylperoxy) hexane, di-t-butyl peroxide, and mixtures thereof.

14. The process according to claim 1, wherein the compounding of the wastes with the at least one antioxidant agent is carried out at a temperature lower than 150 C.

15. The process according to claim 14, wherein the compounding of the wastes with the at least one antioxidant agent is carried out at a temperature from 100 C. to 120 C.

16. The process according to claim 1, wherein at least one processing aid is added to the polymeric wastes.

17. A cable comprising at least one cable core and a component made of a recovered polymeric composition comprising a product of the quenching reaction between a peroxidic crosslinking agent and an antioxidant agent suitable for sulfur-vulcanized elastomeric compositions.

18. A filling material for electrical cable cores comprising a polymeric composition obtained from the process for recovering wastes according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) Particularly, the polymeric composition obtained from the process according to the present invention can be used as filling material for a tripolar electrical cable as illustrated in FIG. 1 attached herewith (transversal cross section).

DETAILED DESCRIPTION OF THE INVENTION

(2) With reference to FIG. 1, the tripolar electrical cable (100), particularly for medium voltage (MV) or high voltage (HV) applications, includes three cable cores (1), wound together and surrounded by two protective layers (2) and (4). In particular, the first protective layer (2) can be made from a metal tape (such as a steel tape) or by an expanded polymeric material, as disclosed for instance in patent application WO 98/52197. A second protective layer (4) is applied around and in contact with the first protective layer (2). The second protective layer (4) is the outermost external layer and is typically a polymeric sheath.

(3) Each cable core (1) includes a metal conductor (10), an electrically shielding layer (11) and a metal shield (12). The electrically shielding layer (11) is constituted by an inner semiconductive layer, an electrically insulating layer and an outer semiconductive layer (for sake of simplicity not specifically shown in FIG. 1). The space surrounding the three cable cores (1) and delimited by the first protective layer (2) is filled by a polymeric filling material (3), which is applied by extrusion around the three wound cable cores (1).

(4) The polymeric composition obtained from the process according to the present invention may be advantageously used as polymeric filling material (3), since it has a suitable viscosity to be extruded and to completely fill the voids between the wound cable cores, and it does not show any crosslinking during extrusion.

(5) The following examples are provided to further illustrate the invention.

Examples 1-8

(6) The process according to the present invention was applied to recover a waste of a polymeric composition typically used for electrical medium voltage cable insulations having the following composition:

(7) TABLE-US-00001 EPR rubber 100 phr Kaolin 60 phr Pb.sub.3O.sub.4 5 phr ZnO 5 phr Dicumyl peroxide 2.5 phr

(8) Different commercial antioxidant agents were used:

(9) Irganox 1010 (Ciba): pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (CAS Registry No. 98584-37-3), typically used as antioxidant for electrically insulating compositions, not for sulfur-vulcanized elastomeric compositions (MW=1178):

(10) ##STR00001##

(11) Lowinox CPL (Chemtura): poly(dicyclopentadiene-co-p-cresol) (synonym: phenol, 4-methyl-, reaction products with dicyclopentadiene and isobutene) (CAS Registry No. 68610-51-5), typically used as antioxidant for sulfur-vulcanized elastomeric compositions (MW=600-700):

(12) ##STR00002##

(13) Octamine (Chemtura): octylated diphenylamine (CAS Registry No. 26603-23-6), typically used as antioxidant for sulfur-vulcanized elastomeric compositions:

(14) ##STR00003##

(15) Vulkanox 4020 LG (Lanxess): N-(1,3-dimethylbutyl)-N-phenyl-p-phenylenediamine (CAS Registry No. 793-24-8), typically used as antioxidant for sulfur-vulcanized elastomeric compositions:

(16) ##STR00004##

(17) In each test, the polymeric waste was fed to a Banbury mixer in a granulated form together with the antioxidant in the predetermined amounts. The compounding was carried out with a mixer filling factor of 85%, a rotor speed of 50 rpm, a discharge temperature of the final composition of about 120 C.

(18) The added amounts of antioxidants in the different tests are reported in Table 1 (as parts by weight).

(19) TABLE-US-00002 TABLE 1 Example 1* 2* 3 4 5 6 7 8 Waste mix 100 100 100 100 100 100 100 100 Irganox 5.0 10.0 1010 Lowinox 5.0 10.0 CPL Octamine 5.0 10.0 Vulkanox 5.0 10.0 4020 LG *comparative

(20) The resulting polymeric compositions were subjected to rheometric analysis using a Moving Die Rheometer (MDR) from Monsanto, the tests being carried out at 180 C. for 15 minutes, with an oscillation frequency of 50 Hz and oscillation amplitude of 3.

(21) The scorch time at 155 C. was determined by means of a scorch viscosimeter at 2+22, according to a standard technique.

(22) As reference, the MDR and scorch characteristics were determined also on the waste material as such, i.e. without adding any antioxidant (Ref. in Table 2). The results are reported in Table 2.

(23) TABLE-US-00003 TABLE 2 Example Ref. 1* 2* 3 4 5 6 7 8 M.sub.L @ 180 C. (dN .Math. m) 0.43 0.31 0.16 0.28 0.23 0.27 0.18 0.22 0.16 M.sub.H @ 180 C. (dN .Math. m) 10.22 2.11 0.67 0.86 0.35 0.88 0.32 0.30 0.19 t.sub.s2 @ 180 C. (min) 0:54 >24 >24 >24 >24 >24 >24 >24 >24 scorch t.sub.3 @ 155 C. (min) 4:58 12:36 13:02 >24 >24 13:25 >24 >24 >24 scorch t.sub.10 @ 155 C. (min) 6:57 >24 >24 >24 >24 >24 >24 >24 >24 *comparative M.sub.L = minimum torque; M.sub.H = maximum torque; t.sub.s2 = time period to increase the torque value of 2 dN .Math. m from the minimum value M.sub.L; scorch t.sub.3 = time necessary to increase the torque value of 3 dN .Math. m from the minimum value M.sub.L; scorch t.sub.10 = time necessary to increase the torque value of 10 dN .Math. m from the minimum value M.sub.L.

(24) From the data reported in Table 2, it is apparent that, by adding the antioxidant according to the present invention to the polymeric waste, the organic peroxide present in the latter is almost completely quenched, as shown by the very low values of M.sub.H and the increased values of scorch time, with respect to the waste material as such.

(25) The compositions 1* and 2* containing an antioxidant for electrically insulating compositions, not for sulfur-vulcanized elastomeric compositions, showed scorch values (t.sub.3) unsuitable for a further use, and this is because such antioxidant is not capable of quenching the unreacted peroxide included in these compositions.

Examples 9-12

(26) The process according to the present invention was applied on the same waste material of Examples 1-8 above, by compounding therein Vulkanox 4020 LG (Lanxess) in the amounts reported in Table 3 (parts by weight), by using the same mixing process described for Examples 1-8. The compositions were also added with relevant amounts of calcium carbonate as filler. Therefore, to improve processability, it was necessary to supplement plasticizers and/or processing aids, particularly a paraffinic oil, a paraffinic wax and stearic acid.

(27) The compositions are reported in Table 3. The resulting polymeric compositions were subjected to rheometric analysis (MDR) according to the same method of Example 1-8. Moreover, Mooney ML(1+4) viscosity was measured at 100 C. according to ISO Standard 289/1.

(28) The results are reported in Table 4.

(29) TABLE-US-00004 TABLE 3 Example 9 10 11 12 Waste mix 100 100 100 100 Vulkanox 4020 LG 3.0 6.0 3.0 6.0 Omyacarb 10 AV 225 225 225 225 Celtis 933 15 15 7.5 7.5 Riowax 721 10 10 10 10 Stearic acid 1.5 1.5 Omyacarb 10 AV (Omya) = calcium carbonate; Celtis 933 (ENI) = paraffinic oil; Riowax 721 (Lehmann & Voss & Co.): wax.

(30) TABLE-US-00005 TABLE 4 Example 9 10 11 12 M.sub.L @ 180 C. (dN .Math. m) 0.16 0.11 0.46 0.32 M.sub.H @ 180 C. (dN .Math. m) 0.23 0.15 0.49 0.34 t.sub.s2 @ 180 C. (min) >24 >24 >24 >24 Mooney ML(1 + 4) viscosity 25 22.2 57.3 48.9 Scorch t.sub.3 @ 155 C. (min) >24 >24 >24 >24 Scorch t.sub.10 @ 155 C. (min) >24 >24 >24 >24

(31) From Examples 9-12 it is apparent that the addition of the antioxidant agent according to the present invention allowed to remarkably reduce the amount of paraffinic oil and to eliminate stearic acid in the composition, which were added along with the paraffinic wax to improve processability which was inevitably reduced by the large amount of calcium carbonate filler incorporated into the composition. An increase of the Mooney viscosity was observed because of the reduction of the processing aids: it however remained within acceptable values for the subsequent processing of the polymeric composition.