Tuning wettability and mechanical property of polylactide composite films with in-situ nanofibrils of poly(butylene adipate-co-terephthalate)

The poor hydrophobicity and toughness of polylactide (PLA) films make it difficult to meet the requirements of barrier, printing and moisture-proof material. How to improve the two drawbacks of PLA simultaneously is a daunting challenge at present. In this work, we introduce poly (butylene adipate-co-terephthalate) (PBAT) as a second flexible phase into PLA matrix and concomitantly impose intensive elongational flow by two-stage drawing. Under the elongational flow field, the PLA/PBAT film can form the oriented structure combining in-situ nanofibrils with oriented lamellae, exhibiting excellent stiffness-toughness balance. Then surface treatment via moderate alkaline etching makes the micro/nano structure expose on the surface, which can effectively improve the hydrophobicity of the surface. We further investigates the influence of blend composition, drawing ratio and etching time on the oriented structure, mechanical and wetting properties. It is found that the PLA/PBAT film with the weight ratio of 70/30, low draw ratio of 2.7 and etching time of 24 h has the optimal properties, which possesses Young's modulus of 2.53 GPa, yield strength of 51.9 MPa, elongation of break of 131.8% and water contact angle of 131.8 degrees. It is noteworthy that the film can mainly keep original mechanical after surface treatment. This work could offer a facile and effective method to fabricate the green PLA based film with good mechanical properties and hydrophobicity in a large scale.