Strategies and Methodologies for Improving Toughness of Starch Films

Abstract

Starch films have attracted increasing attention due to their biodegradability, edibility, and potential use as animal feed from post-products. Applications of starch-based films include food packaging, coating, and medicine capsules. However, a major drawback of starch-based films is their brittleness, particularly under dry conditions, caused by starch retrogradation and the instability of plasticizers. To address this challenge, various strategies and methodologies have been developed, including plasticization, chemical modification, and physical reinforcement. This review covers fundamental aspects, such as the microstructures, phase transitions, and compatibility of starch, as well as application-oriented techniques, including processing methods, plasticizer selection, and chemical modifications. Plasticizers play a crucial role in developing starch-based materials, as they mitigate brittleness and improve processability. Given the abundance of hydroxyl groups in starch, the plasticizers used must also contain hydroxyl or polar groups for compatibility. Chemical modification, such as esterification and etherification, effectively prevents starch recrystallization. Reinforcements, particularly with nanocellulose, significantly improved the mechanical properties of starch film. Drawing upon both the literature and our expertise, this review not only summarizes the advancements in this field but also identifies the limitations of current technologies and outlines promising research directions for future development.

Keywords: modification; phase transition; plasticizer; reinforcement; starch; toughness.

Figure 1

Schematic representation of hierarchical starch structures [12].

Figure 2

Scheme of starch granule structures [27].

Figure 3

Schematic representation of the phase transitions of starch during thermal processing and aging [94]. (A) native starch structure; (B) gelatinization; (C) cooling and gel formation and (D) retrogradation.

Figure 4

Chemical modification on starch. Cross-linking modification with (1) CS₂, (2) POCl₃, Na₃P₃O₉, (3) epichlorohydrin, and (4) C₆H₅O(COOH)₃; oxidation modification with (5) O₃ and HIO₄; grafting modification with (6) acrylamide with possible initiators; etherification modification with (7) C₃H₆O, (8) CH₂ClCOONa, and (9) C₂H₅Cl; acid hydrolysis with (10) HCl, TFA, and HNO₃; esterification modification with (11) Na₂HPO₄ and (12) CH₃COOH [139].

Figure 5

(a,b) Schematic summary of condensing reaction [142].