Tuning Barrier Properties of Low-Density Polyethylene:  Impact of Amorphous Region Nanostructure on Gas Transmission Rate

This work focused on determining the factors that are of key importance in the oxygen barrier properties of low-density polyethylene (LDPE). It has been shown that, depending on the type and amount of the low-molecular-weight compound (tetracosane, paraffin wax, paraffin oil) introduced into the LDPE matrix, it can contribute to the improvement or deterioration of barrier properties. Tetracosane and paraffin wax incorporated into the LDPE matrix caused a reduction in oxygen permeability parameters compared to neat polyethylene. As their content increased, the barrier properties of the samples towards oxygen also increased. A completely opposite effect was achieved with paraffin oil. The results of comprehensive studies provide evidence that in the case of LDPE blends, two mechanisms are responsible for changing/controlling their transport properties. The first mechanism is associated with changes in the molecular packing in the interlamellar amorphous regions, while the second is related to the crystallinity of the samples. In cases where there are no changes in crystallinity, the density of the amorphous phase becomes the decisive factor in barrier properties, as clearly shown by results assessing chain dynamics.