Oxygen barrier mechanisms of polyethylene extrusion coated high-density papers

This work gives new knowledge about the oxygen barrier mechanisms of polyethylene extrusion coated high-density paper used as barrier material in the packaging of foods. The prevailing hypothesis about the mechanisms of the extraordinary and unexpected good oxygen barrier properties of the laminate is blocking of the paper pores. This work shows that the oxygen transmission rate through such laminates is strongly influenced by an uneven transcrystalline layer in the polyethylene coating in contact with the paper surface. The polyethylene coating is a dynamic entity in where chain mobility of the polyethylene and the optimal properties of the paper surface improve the oxygen barrier during storage where conditions for transcrystallisation are present. Paper made of intensively refined fibres not dried prior to papermaking gives more optimal surfaces than papers made of previously dried fibres. The "wet" pulp seems to give a more favourable surface for transcrystalline structural formation and an improved contact between the materials, giving a better oxygen barrier as a consequence. 1H NMR T2-relaxation measurements show higher mobility of the water bound in these papers/fibres. Coating of the respective sides of paper samples shows that the side coated is not indifferent with respect to oxygen transmission rates achieved. These values correspond well with the surface free energy for the respective sides coated.