Mechanical and barrier properties of simultaneous biaxially stretched polylactic acid/thermoplastic starch/poly(butylene adipate-co-terephthalate) films

Polylactic acid/thermoplastic starch/poly(butylene adipate-co-terephthalate) (PLA/TPS/PBAT) blend is a promising biodegradable material for flexible packaging applications. However, this material still has insufficient mechanical and gas barrier properties for flexible packaging applications due to the immiscibility and random molecular orientation of the polymers. The objective of this work was to improve the performance of the blend using the biaxial stretching process. The effect of the biaxial stretching parameters (stretching rate and annealing time) on the morphological, mechanical, thermal, and gas barrier properties of PLA/TPS/PBAT (40/40/20) films was investigated. The stretching rate and annealing time were varied in the ranges of 22.5-300 mm/s and 0-180 s, respectively. The biaxial stretching parameters affected the morphology of the stretched films of PLA/TPS/PBAT blend. Results obtained from X-ray diffraction and differential scanning calorimetry revealed that biaxial stretching increased ordered structure and crystallinity of PLA and PBAT. For unannealed stretched films, increasing the stretching rate from 22.5 to 300 mm/s led to reduced crystal sizes of PLA, from 17.1 to 9.0 nm, and PBAT, from 17.6 to 12.3 nm. However, increasing the annealing time enlarged the crystals of both polyesters, especially PLA. The crystallinity of biaxially oriented films determined from PLA increased with stretching rate and annealing time, from 6 up to 34%. The increased ordered structure and crystallinity of PLA/TPS/PBAT films led to improved tensile strength and oxygen barrier property, approximately twofold and tenfold, respectively, when biaxial stretching was performed at a stretching rate of 150 mm/s and annealing time of 60 s.