Analysis of the Deterioration of Nylon-66 Immersed in GTL Diesel Fuel Part 1. Analysis and Test of Nylon and GTL Diesel Fuel Before and After Immersion

The effect of GTL diesel fuel on organic materials used in fuel delivery systems of vehicles was investigated. Specimens made from 16 kinds of organic materials were immersed in GTL diesel fuels synthesized at Refinery-A and Refinery-B (referred to as GTL-A and GTL-B, respectively) and then subjected to tensile testing. The tensile test results revealed that elongation of the nylon sample immersed in GTL-A was extremely small, about 4% of that of untreated nylon. In the light of this finding, the GTL diesel fuels and nylons before and after immersion test were analyzed in detail using about 20 analysis methods to determine the cause for poor elongation. The following points were found. (1) GTL-A consisted of low molecular-weight paraffins. (2) GTL-A had low molecular-weight i-paraffins. (3) The nylon immersed in GTL-A contained low molecular-weight paraffins. (4) The paraffins in the nylon immersed in GTL-A were richer in i-paraffins than the original GTL-A. From previous experiments using model fuel, it was found that i-paraffins penetrate nylon and oxidize more rapidly in the nylon than n-paraffins. (5) The nylon immersed in GTL-A was oxidized from the surface to a depth of 400 μm. (6) i-Paraffins produced about 100 times as many oxidation products as n-paraffins. From these results, it was concluded that the low molecular-weight paraffins in GTL-A penetrated the nylon and caused it to swell. These paraffins oxidized in the nylon and became free radicals, which then oxidized and depolymerized the nylon molecules. This depolymerization of the nylon caused the poor elongation as a result of the dissociation of hydrogen bonds between the nylon molecules.