CROSSLINKABLE COMPOSITION COMPRISING POLYETHYLENE AND USE THEREOF FOR ROTATIONAL MOLDING

Abstract

Crosslinkable composition comprising: (a) from 80% by weight to 98% by weight, preferably from 85% by weight to 95% by weight, of at least one high density polyethylene (HDPE); (b) from 2% by weight to 20% by weight, preferably from 5% by weight to 15% by weight, of at least one linear low density polyethylene (LLDPE); (c) from 0.2 parts by weight to 1.5 parts by weight, preferably from 0.5 parts by weight to 0.8 parts by weight, with respect to 100 parts by weight of (a)+(b), of at least one crosslinking agent selected from organic peroxides; (d) from 0.2 parts by weight to 2.5 parts by weight, preferably from 0.5 parts by weight to 1.0 parts by weight, with respect to 100 parts by weight of (a)+(b), of at least one co-crosslinking agent selected from allyl compounds. Said crosslinkable composition can advantageously be used in rotational molding (“rotomolding”).

Claims

1. Crosslinkable composition comprising: (a) from 80% by weight to 98% by weight, of at least one high density polyethylene (HDPE); (b) from 2% by weight to 20% by weight, of at least one linear low density polyethylene (LLDPE); (c) from 0.2 parts by weight to 1.5 parts by weight, with respect to 100 parts by weight of (a)+(b), of at least one crosslinking agent selected from organic peroxides; (d) from 0.2 parts by weight to 2.5 parts by weight, with respect to 100 parts by weight of (a)+(b), of at least one co-crosslinking agent selected from allyl compounds.

2. Crosslinkable composition according to claim 1, wherein said high density polyethylene (HDPE) (a) is selected from polyethylenes having a density higher than 0.940 g/cm.sup.3, and a Melt Flow Index (MFI), measured at 190° C. with a load of 2.16 kg in accordance with ISO 1133-1:2011 standard, ranging from 10 g/10 minutes to 100 g/10 minutes.

3. Crosslinkable composition according to claim 1, wherein said linear low density polyethylene (LLDPE) (b) is selected from polyethylenes having a density lower than 0.940 g/cm.sup.3, and a Melt Flow Index (MFI), measured at 190° C. with a load of 2.16 kg in accordance with ISO 1133-1:2011 standard, ranging from 1 g/10 minutes to 100 g/10 minutes.

4. Crosslinkable composition according to claim 1, wherein said high density polyethylene (HDPE) (a) and said linear low density polyethylene (LLDPE) (b) have the same Melt Flow Index (MFI).

5. Crosslinkable composition according to claim 1, wherein said linear low density polyethylene (LLDPE) (b) has a Melt Flow Index (MFI) higher than said high density polyethylene (HDPE).

6. Crosslinkable composition according to claim 1, wherein said organic peroxides (c) are selected from organic peroxides having general formula (I): ##STR00003## in which: R is a divalent hydrocarbon group, preferably selected from: ##STR00004## in which m represents a number between 1 and 8; R.sub.1 and R.sub.2, equal or different, represent a linear or branched C.sub.1-C.sub.12 alkyl group; R.sub.3 and R.sub.4, equal or different, represent a linear or branched C.sub.1-C.sub.12 alkyl group; n is 0 or 1.

7. Crosslinkable composition according to claim 5, wherein said organic peroxides having general formula (I) are selected from: a group of bis(alkylperoxy) alkanes selected from 2,5-bis(t-amylperoxy)-2,5-dimethylhexane, 2,5 bis(t-butylperoxy)-2,5-dimethylhexane, 3,6-bis(t-butylperoxy)-3,6-dimethyloctane, 2,7-bis(t-butylperoxy)-2,7-dimethyloctane, 8,11-bis(t-butylperoxy)-8,11-dimethyloctadecane, or mixtures thereof; a group of bis(alkylperoxy)benzenes selected from αα′-bis(t-amylperoxy-iso-propyl) benzene, αα′-bis(t-butylperoxy-isopropyl)benzene, or mixtures thereof; a group of bis(alkylperoxy)acetylenes selected from 2,7-dimethyl-2,7-di(t-butylperoxy)-octadiyne-3,5, 2,7-dimethyl-2,7-di(peroxyethylcarbonate)-octadiyne-3,5, 3,6-dimethyl-3,6-di(peroxyethylcarbonate)octyne-4, 3,6-dimethyl-3,6-di(t-butyl-peroxy)octyne-4, 2,5-dimethyl-2,5-di(peroxy-n-propyl-carbonate)hexyne-3, 2,5-dimethyl-2,5-di(peroxy-iso-butylcarbonate)hexyne-3, 2,5-dimethyl-2,5-di(peroxyethyl-carbonate)hexyne-3, 2,5-dimethyl-2,5-di(a-cumylperoxy)hexyne-3, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, or mixtures thereof; or mixtures thereof.

8. Crosslinkable composition according to claim 1, wherein said allyl compounds (d) are selected from: allyl methacrylate, diallyl itaconate, diallyl phthalate, triallyl trimellitate, triallyl trimethallyl trimellitate, triallyl cyanurate (TAC), triallyl iso-cyanurate (TAIL), triallyl phosphate, or mixtures thereof.

9. Crosslinkable composition according to claim 1, wherein said crosslinkable composition comprises (e) at least one peroxide scavenger selected from: a group of sulfur-containing compounds selected from such as esters of thiodipropionic acid, or mixtures thereof; organic phosphites, organic phosphonates, organic phosphonites, organic phosphates, or mixtures thereof.

10. Crosslinkable composition according to claim 9, wherein said peroxide scavenger (e) is present in said crosslinkable composition in an amount ranging from 0.01 parts by weight to 0.1 parts by weight, with respect to 100 parts by weight of (a)+(b).

11. Crosslinkable composition according to claim 1, wherein said crosslinkable composition comprises (f) at least one antioxidant selected from sterically hindered phenols.

12. Crosslinkable composition according to claim 11, wherein said antioxidant (f) is present in said crosslinkable composition in an amount ranging from 0.01 parts by weight to 0.1 parts by weight, with respect to 100 parts by weight of (a)+(b).

13. Use of the crosslinkable composition according to claim 1 in rotational molding (“rotomolding”).

14. End-products obtained by rotational molding (“rotomolding”) of the crosslinkable composition according to claim 1.

Description

EXAMPLE 1

Comparative

[0077] 100 g of high density polyethylene (HDPE) (Eraclene® MR 80 U from versalis spa) having the following features: [0078] density of 0.955 g/cm.sup.3; [0079] Melt Flow Index (MFI), measured at 190° C. with a load of 2.16 kg in accordance with ISO 1133-1:2011 standard, of 25 g/10;
0.9 g of triallyl cyanurate (TAC) (Luvomaxx® TAC DL 50 from Lehvoss) and 0.65 g of 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3 (Trigonox® 145-45B-pd from Akzo Nobel), were placed in a laboratory screw mixer at a temperature of 25° C., for 20 minutes, at a mixing speed of 60 rpm. Subsequently, the crosslinkable composition obtained was removed from the internal mixer and supplied to a co-rotating twin-screw extruder (D=30 mm; L/D=28) and extruded while working with a constant temperature profile of 135° C., at a flow rate of 7.5 kg/h, and at a screw rotation speed of 100 rpm. The extruded material in the form of “spaghetti” was cooled in a water path, dried in air, granulated using a chopper, and subsequently subjected to grinding in a rotating-blade mill, to obtain a powder having an average particle diameter of 350 μm.

[0080] The mechanical properties of the crosslinkable composition obtained were measured. For this purpose, samples of said crosslinked composition, obtained by compression molding at 200° C. at a pressure of 500 kg/cm.sup.2, for 20 minutes, having a thickness of 3.2 mm, a height of 150 mm and a width of 150 mm, underwent measurements for: [0081] Elongation at Break, in accordance with ASTM D 638-10 standard; [0082] Izod Impact Strength, in accordance with ASTM D 256-10 standard; [0083] Environmental Stress Crack Resistance (ESCR), in accordance with ASTM D 1693 standard, in the presence of a 10% solution of surfactant (Igepal® CO-630) in water, at a temperature of 50° C.

[0084] The results obtained are shown in Table 1.

EXAMPLE 2

Comparative

[0085] Example 2 was carried out in the same way as Example 1, except that 0.65 g of triallyl cyanurate (TAC) (Luvomaxx® TAC DL 50 from Lehvoss) and 0.9 g of 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3 (Trigonox® 145-45B-pd from Akzo Nobel) were used.

[0086] The mechanical properties were measured as in Example 1: the results obtained are shown in Table 1.

EXAMPLE 3

Invention

[0087] Example 3 was carried out in the same way as Example 1, except that the following components were used: [0088] 90 g of high density polyethylene (HDPE) (Eraclene® MR 80 U from versalis spa) having the following features: [0089] density of 0.955 g/cm.sup.3; [0090] Melt Flow Index (MFI), measured at 190° C. with a load of 2.16 kg in accordance with ISO 1133-1:2011 standard, of 25 g/10; [0091] 10 g of linear low density polyethylene (LLDPE) (Flexirene® MS 20 U from versalis spa) having the following features: [0092] density of 0.920 g/cm.sup.3; [0093] Melt Flow Index (MFI), measured at 190° C. with a load of 2.16 kg in accordance with ISO 1133-1:2011 standard, of 25 g/10; [0094] 0.65 g of triallyl cyanurate (TAC) (Luvomaxx® TAC DL 50 from Lehvoss) and [0095] 0.9 g of 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3 (Trigonox® 145-45B-pd from Akzo Nobel).

[0096] The mechanical properties were measured as in Example 1: the results obtained are shown in Table 1.

EXAMPLE 4

Comparative

[0097] Example 4 was carried out in the same was as Example 1, except that 100 g of high density polyethylene (HDPE) (Eraclene® MR 80 U from versalis spa) were used. The mechanical properties were measured as in Example 1: the results obtained are shown in Table 1.

TABLE-US-00001 TABLE 1 EXAM- EXAM- PLE 3 PLE 4 MECHANICAL EXAMPLE 1 EXAMPLE 2 (inven- (compara- PROPERTIES (comparative) (comparative) tion) tive) Elongation at 280 370 453 120 break (%) Izod Impact 202.5 277.6 s.n.b. 40 Strength (23° C.) (J/m) Izod Impact 75 85 95 35 Strength (−20° C.) (J/m) ESCR >1000 >1000 >1000 <20 (hours) s.n.b.: sample not broken.

[0098] From the data shown in Table 1, it can be seen that the crosslinkable composition object of the present invention [Example 3 (invention)] has improved mechanical properties, in particular Elongation at Break and Izod Impact Strength, both by comparison with the use of crosslinkable compositions containing only linear high density polyethylene (HDPE) [Examples 1 and 2 (comparative)] and by comparison with the non-crosslinkable composition containing only linear high density polyethylene (HDPE) [Example 4 (comparative)].