Biofuels Barrier Properties of Polyamide 6 and High Density Polyethylene

• Main Authors: Fillot L.-A., Ghiringhelli S., Prebet C., Rossi S.
• Format: Article
• Language: English
• Published: EDP Sciences 2015-02-01
• Series: Oil & Gas Science and Technology
• Online Access: http://dx.doi.org/10.2516/ogst/2013213

In this paper, a comparison of the biofuels barrier properties of PolyAmide 6 (PA6) and High Density PolyEthylene (HDPE) is presented. Model fuels were prepared as mixtures of toluene, isooctane and ethanol, the ethanol volume fraction varying between 0% and 100%. Barrier properties were determined at 40°C by gravimetric techniques or gas chromatography measurements, and it was shown that polyamide 6 permeability is lower than that of polyethylene on a wide range of ethanol contents up to 85% of ethanol (E85) in the biofuel, permeability of PA6 being 100 times lower than that of HDPE for low ethanol content fuels (E5, E0). The time-lags were also compared, and on the whole range of ethanol contents, HDPE permeation kinetics appears to be much faster than that of PA6, the time lag for a 1 mm thick specimens in presence of E10 being 50 days for PA6 and 0.5 days for HDPE. The compositions of the solvent fluxes were analyzed by FID gas chromatography, and it turned out that the solvent flux was mainly made up of ethanol (minimum 95%) in the case of PA6, whereas in the case of HDPE, solvent flux was mainly made up of hydrocarbons. The implication of this difference in the solvent flux composition is discussed in the present article, and a side effect called the “fuel exhaustion process” is presented. The influence of the sample thickness was then studied, and for the different biofuels compositions, the pervaporation kinetics of polyamide 6 appeared to evolve with the square of the thickness, a long transitory regime being highlighted in the case of PA6. This result implies that the time needed to characterize the steady state permeability of thick PA6 parts such as fuel tanks can be very long (one year or more), this duration being far superior to the Euros 5 or Euro 6 standard emission measurements time scale. The influence of temperature on the permeability was finally assessed, and the activation energy that is the signature of the temperature dependence of the barrier property turned out to be similar for the different biofuels compositions.