Surface adhesion and physical properties of modified TPS and PBAT multilayer film

Starch-based materials are susceptible to moisture, leading to sticking and instability. Coating with hydrophobic biodegradable materials improves their stability. This research produced multilayer biodegradable packaging based on thermoplastic cassava starch (TPS) blended with poly(butylene adipate-co-terephthalate) (PBAT). TPS/PBAT mixtures were produced via blown film extrusion before coating with PBAT solution. Different TPS content (up to 80 %) and types of modified cassava starch namely native starch (NS), hydroxypropylated starch (HS), acetylated starch (AS), and octenyl-succinated starch (OS) were investigated for micro and chemical structure, delamination, and PBAT coating deposition on TPS/PBAT multilayer film. IR spectra of the peak at 3300 cm⁻¹ (O-H stretching of TPS) was absent after coating, suggesting reduced TPS content on the film surface, while 1717 cm⁻¹ (CO from carbonyl groups of PBAT), became sharper, indicating that PBAT deposition covered the film surface. The X-ray diffractogram showed a 2θ peak located at 24.4° (starch crystallinity) in the coated NS film; however, the peak was absent in coated HS, AS, and OS films because bulky chemical-grafted modified starch prevented molecular arrangement. Hydrophilic NS showed delamination and film substrate swelling after 60 s of direct contact with a sessile drop of water, indicating poor affinity. Hydrophobic-modified AS and OS significantly improved affinity with the PBAT coating layer giving a higher contact angle (105–112°), preventing delamination and substrate swelling and indicating increased water resistance. AS and OS (60 %) had higher shrinkage (23.78 % and 47.33 %) and a thicker coating layer (11.51 and 10.35 µm) due to greater polymer-solvent interaction. Hydrophobic-modified starch successfully improved the interaction between film layers and increased PBAT deposition.