Permeability is driven by both the solubility and the diffusivity of solvents in polymers, and in polyamide, diffusion of polar solvents like ethanol contained in biofuels is strongly linked to the molecular mobility of PA amorphous phase. By increasing intermolecular interactions in polyamide 66 (introduction of phenolic comonomers or sulfonated comonomers), the Tg was significantly increased, and fuel barrier properties were enhanced despite sometime an increase of ethanol solubility in the material (permeability of PA66/6AISli (95/5)mol to ethanol 4 times lower than that of PA66). One patent was filed in 2010. An attempt was also made to optimize the permeability / impact properties of polyamide by designing additives inducing an hindering effect on solvent solubility, without increasing too much the Tg of Polyamide, a Tg increase inducing a decrease of impact properties. Unfortunately, the developed additive did not provide any sufficient solvent inhibition effect, and the compromise was not reached.
We study the interactions of PA66 with a broad range of polar and apolar solvents and characterize amorphous phase molecular mobility by mean of dielectric spectroscopy, DMA and DSC.