Improving action of citric acid as compatibiliser in starch/polyester blown films

• The effect of citric acid and sodium hypophosphite (SHP – catalyst) on blown starch/polyester films was studied.
• Citric acid had the highest effect on film's water vapour permeability decrease.
• The catalyst intensified the effect of citric acid improving mechanical properties.
• Films with citric acid and SHP presented more homogeneous structures.

Starch/PBAT films plasticised with glycerol containing citric acid (CA) with and without sodium hypophosphite (SHP) were produced by blown extrusion. Some properties of the films were improved while others did not. The tensile strength of the films with CA and CA/SHP increased by 47.1% and 104.3%, respectively, compared with that of the control film (without CA and SHP). The elongation at break of the films with the compatibiliser and catalyst (CA/SHP) increased by 125.7% compared with that of the control. The films with CA and CA/SHP had much greater Young's Moduli than that of the control. There was a significant reduction in the water vapour permeability, from 6.72 × 10−11 g (m s Pa)−1 (control) to 4.02 × 10−11 and 4.37 × 10−11 g (m s Pa)−1 in the films with CA and CA/SHP, respectively. Micrographs of the fractures showed a more homogeneous structure in the films with CA/SHP. The combined effect of CA and SHP slowly increases the thermal stability of the films. Some properties have been improved when the catalyst was added while others do not, as a consequence of the balance between the many functions CA can perform and the impact of these on each property.