Sugar/sugar alcohol with glycerol as co‐plasticizers for high‐content starch/PBAT blown films: from fine structure to physicochemical properties

BACKGROUND Glycerol is a well‐known plasticizer for starch‐based materials, but it easily migrates during starch retrogradation, thereby deteriorating the films' properties. We hypothesized that the performance of high‐content starch/poly(butylene adipate‐co‐terephthalate) (PBAT) films could be enhanced by using sugar/sugar alcohol (glucose, sucrose and sorbitol) as natural, green and edible co‐plasticizers with glycerol. RESULTS The employment of co‐plasticizers reduced the melt fluidity of the blends, established intermolecular hydrogen bonds with starch and resulted in a brittle film structure. The presence of sucrose contributed to the formation of more B‐type starch crystals. Glucose and sucrose promoted the conversion of bound water to entrapped water, while sorbitol contributed to more bound water. The co‐plasticizers enhanced films' thermal stability, moisture permeability (from 3.61 to 3.72 × 10 −11 g m m −2 s −1 Pa −1 ), and oxygen barrier (from 12.84 to 8.74 × 10 −13 cm 3 cm cm −2 s −1 Pa −1 ). Glucose/glycerol co‐plasticized film had the maximum tensile strength (10.12 MPa), and sucrose/glycerol co‐plasticized film showed the highest Young's modulus (380.31 MPa). CONCLUSION Sorbitol with linear structure and the lowest melting point exhibited a plasticizing capacity similar to glycerol. The molecular structure (linear or cyclic), hydroxyl group proportion and melting point of the sugar/sugar alcohol were the key factors to regulate the fine structure and properties of starch/PBAT films.