Patent ID: 8658756

Claim:
A composite tank for storing a fluid, said tank comprising an impermeable envelope obtained by process of manufacturing comprising: (a) providing a composition and introducing said composition to a rotomould wherein the composition comprises in % by weight relative to the total weight of the composition: from 70 to 90% of an ε-caprolactam monomer of formula (I); from 0.1 to 1% of an ε-caprolactam activator of formula (II), in which R is selected from the group consisting of C n H 2n+1 , n being an integer chosen from 1 to 10; —OH; —OC n H 2n+1 , n being an integer chosen from 1 to 10; and —NHR′ where R′ is either C n H 2n+1 , n being an integer chosen from 1 to 10, or an amine functional group; from 2 to 6% of an ε-caprolactam catalyst of formula (III), in which X is chosen from the group consisting of MgBr, MgI, Li and Na; and from 10 to 20% of an ε-caprolactone additive of formula (IV); wherein the formulae (I), (II), (III) and (IV) are the following: (b) rotating the rotomould and polymerizing through anionic polymerization an ε-caprolactam monomer of said composition to polycaprolactam, said composition being heated to a polymerization temperature greater than or equal to the melting point of the ε-caprolactam and less than the melting point of said polycaprolactam, thereby forming said element by rotomoulding coupled with polymerization without melting of the polycaprolactam obtained; (c) cooling of the rotomould thereby crystallizing the polycaprolactam obtained; and (d) demoulding the polycaprolactam liner formed in the rotomould.