Barrier and surface properties of chitosan-coated greaseproof paper

Greaseproof papers with different air permeances were coated with chitosan, both on a bench scale and on a pilot scale to study the conditions necessary to obtain a packaging material with good barrier properties towards oxygen, nitrogen, carbon dioxide and air. In addition, barrier properties against grease and water were measured. The results showed that an oxygen permeability in the same range as that of poly(ethylene terephthalate) was obtained at coat weights exceeding 5 g/m2. The oxygen permeability was not substantially affected by temperature changes, provided that the air permeance of the base paper was low. Carbon dioxide and nitrogen permeabilities were low enough to be measurable only at a coat weight exceeding 5 g/m2 and only on the two base papers with the lowest air permeance. The mechanical properties were characterized by tensile strength and fracture strain. The tensile strength was not affected by the coat weight, whereas the fracture strain was highest for coat weights exceeding 5 g/m2. High grease resistance values were also obtained at this coat weight, whereas the water resistance deteriorated slightly due to the hygroscopic character of the chitosan. However, a coat weight as high as 5 g/m2 could only be achieved on a bench scale. On a pilot scale, the maximum coat weight was 0.2 g/m2 because the solids content of the coating solution used was limited to 1.0 wt% due to the high molecular weight of the chitosan used and the resultant high viscosity of the polymer solution. The coating on a pilot scale was performed using the metered size press technique.