Effects of addition of plasticizers on mechanical and physicochemical properties of edible methylcellulose films

Edible coatings are thin layers of edible biopolymers applied on the surface of foods as protective coatings. There has been a great interest in production of edible films and coatings from biopolymers in recent years. The most widely used edible and biodegradable films are cellulose derivatives. The objective of this research was to investigate the effects of adding 4 plastisizers, namely, glycerol (Gly), polyethylene glycol400 (PEG400), palmitic acid (PA) and GLY+PA, on some mechanical and physicochemical properties of edible methylcellulose (MC) films.

Edible films were prepared from methylcellulose (MC) and plasticized with Gly, PEG400, PA or GLY+PA. Then the water vapor transmission rates (WVTR), tensile strength (TS), percent elongation (E), and percent soluble matter (SM) of the plastisized films were measured.

Tensile strength of the plasticized MC films was significantly lower than that of the pure MC films (p<0.05), while percent elongation of MC films containing Gly or PEG400 was significantly higher than that of the pure MC films and films containing PA (p<0.05). WVTR and percent SM of the films plasticized with PA roPA + GLY were significantly lower than those of the pure MC films and the films containing Gly or PEG (p <0.05).

The results of the present study indicate that pure MC films were very brittle. Plasticizers with low molecular weights (Gly) were most effective with regard to decreasing TS and increasing percent elongation of the MC films. On the other hand, plasticizers with higher molecular weights (PA) produced the greatest effect as regards decreasing WVTR of the MC films. PA + GLY is more suitable for applications that require a lower permeability to water vapor, such as coatings on the surface of fruits.