Process for cross-linked polyethylene production
A method of producing a silane cross-linked polyethylene is disclosed which includes maleating a polyethylene polymer to form a maleated polyethylene and reacting the maleated polyethylene with a primary or secondary amino silane to form a silane-grafted polyethylene. The method further includes treating the silane-grafted polyethylene in a moisture curing process to form the silane cross-linked polyethylene.
1. A method of producing a sliane cross-linked polyethylene comprising:
a. maleating a polyethylene polymer to form a maleated polyethylene, wherein maleating the polyethylene polymer comprises combining the polyethylene polymer, a free radical initiator, and maleic anhydride to form a reaction mixture, wherein the maleic anhydride concentration is from about 4 to about 7 wt % percent of the reaction mixture;
b. reacting the maleated polyethylene with a primary or secondary amino silane to form a silane-grafted polyethylene; and
c. treating the silane-grafted polyethylene in a moisture curing process to form the silane cross-linked polyethylene.
2. The method of claim 1 , wherein the primary or secondary amino silane is 3-aminopropyltriethoxysilane or N-(n-butyl)-3-amino-propyltrimethoxysilane.
3. The method of claim 1 , wherein the step of maleating the polyethylene polymer is performed in a screw extruder or a continuously stirred reactor.
4. The method of claim 1 , wherein the free radical initiator is selected from the group consisting of di-t-butylperoxide, di-(t-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di-(t-butylperoxy)-3-hexene, benzoyl peroxide, and 2,5-dimethyl-2,5-di(t-butylperoxy)hexane.
5. The method of claim 1 , wherein the free radical initiator is a peroxide, and wherein the peroxide concentration is at least 0.5 wt % of the reaction mixture.
6. The method of claim 5 , wherein the peroxide concentration is from about 0.6 to 0.8 wt % of the reaction mixture.
7. The method of claim 1 , wherein the polyethylene polymer is a homopolymer.
8. The method of claim 1 , wherein the polyethylene polymer further includes a C 3 -C 10 alpha olefin.
9. The method of claim 1 , wherein the step of maleating the polyethylene polymer is performed at a temperature of from about 130° C. to about 190° C.
10. The method of claim 1 further comprising after maleating the polyethylene polymer:
passing an inert gas over or through the maleated polyethylene.
11. The method of claim 1 , wherein the step of reacting the maleated polyethylene with a primary or secondary amino silane is performed at between 180° C. and 250° C.
12. The method of claim 1 , wherein the moisture curing process is performed by subjecting the silane-grafted polyethylene to a water bath or a steam sauna.
13. The method of claim 1 further comprising adding a silane crosslinking catalyst.
14. The method of claim 13 , wherein the silane crosslinking catalyst is a metal carboxylate, an organic base, an inorganic acid, or an organic acid.
15. The method of claim 14 , wherein the silane crosslinking catalyst is dibutyl tin dilaurate, dibutyl tin diacetate, dioctyl tin dilaurate, stannous acetate, stannous caprylate, lead naphthenate, zinc caprylate, cobalt naphthenate, ethyl amines, dibutyl amine, hexylamines, pyridine, sulphuric acid, hydrochloric acid, toluene sulphonic acid, acetic acid, or stearic acid.
16. The method of claim 1 , wherein the primary or secondary amino silane is N-(n-butyl)-3-amino-propyltrimethoxysilane.
17. The method of claim 1 , wherein treating the silane-grafted polyethylene in the moisture curing process initiates crosslinking between chains of the silane-grafted polyethylene to form the silane cross-linked polyethylene.