Multilayer structure based on polyamides and tube or conduit with multilayer structure

Abstract

The invention concerns a multilayer structure based on polyamides, particularly suitable for making tubes or conduits for transporting liquid fluids such as alcohol's, liquid fuels, fuel containing oxygen-containing compounds such as, for example alcohol's or refrigerating fluids. The multilayer structure comprises two superposed layers: at least one internal layer and at least one external layer. The invention is characterized in that at least the internal layer is based a composition comprising at least one thermoplastic polyamide and at least one agent modifying resistance to shocks in a weight proportion between 10 and 50% of said composition, and at least the external layer is based on a composition containing as polymeric matrix a polyamide composition selected among the group comprising: (i) a thermoplastic copolymer obtained by copolymerization of ε-caprolactam with at least one of the monomers selected among the group comprising: an aminoacid containing at least 9 carbon atoms, or the corresponding lactam, a mixture of hexamethylenediamine with a diacid comprising at least 9 carbon atoms, the weight ratio between the ε-caprolactam and the total hexamethylenediamine and diacid and/or aminoacid ranging between 4 and 9, or (ii) a mixture of at least said thermoplastic copolymer and at least a second thermoplastic polyamide or copolyamide obtained by polymerization of monomers containing less than 9 carbon atoms. The weight content of the second polymer or copolymer in the polymeric matrix is between 0 and 80 wt. %, preferably between 0 and 40 wt. %. The multilayer structure has high barrier properties against fuel vapor and good mechanical properties such as good resistance to cracking.