Effect of the method of production of the blends on mechanical and structural properties of biodegradable starch films produced by blown extrusion

Biodegradable starch films can be produced by blown extrusion, but it is necessary to add a plasticizer, e.g., glycerol, to decrease the rigidity and blend with other biodegradable polymers, such as poly (butylene adipate co-terephthalate) (PBAT) because films with only starch and glycerol are fragile. A method for producing these films is to produce pellets of thermoplastic starch (starch + glycerol) and extrude them again along with PBAT pellets (M1) or extrude the starch granules with PBAT and glycerol pellets (M2), reducing the processing cost. The objective of this work was to evaluate the effect of the method of producing PBAT + starch blends (M1 and M2) on the mechanical, structural, and micro-structural barrier to water vapor of biodegradable films produced by blown extrusion. Films with a higher amount of starch had characteristics similar to those of films with lower concentrations when the blends were prepared by the method M2, probably due to the increased contact area of the starch granules compared to pellets of TPS, allowing greater interaction between starch and PBAT. The method M1 resulted in films with better mechanical properties when the concentration of PBAT was equal to 50%. With increasing concentration of starch (>50%), blends can be prepared with the method M2 (starch granules) in a single extrusion phase without loss of mechanical properties, which can result in lower production cost.