Polyacid-Regulated Acidolysis–Association Balance Enables Scalable Conversion of Cassava Starch into Thermoplastic Composite Films

Abstract The conversion of native starch into high-performance thermoplastic starch (TPS) remains a longstanding challenge. Here, a series of structurally distinct polyacids was used as regulators to shift TPS formation along an acidolysis–association balance during thermoplastic extrusion. Polyacids reduced melt viscosity and enhanced shear-thinning behavior, and participated in extensive hydrogen-bonding interactions with starch chains, partially reconstructing the native starch network and promoting a more homogeneous melt structure. Maleic acid drove an acidolysis-dominated mode for molecular-weight reduction and structural disintegration of starch, whereas tannic acid promoted a phenolic association-dominated pathway through multivalent hydrogen bonding. Saturated carboxylic acids occupied an intermediate position in the acidolysis–association balance, with succinic acid providing a favorable combination of controlled disassembly, matrix homogenization, and film performance. This balanced TPS structure further translated into a poly(butylene adipate-co-terephthalate) blends as a compatible starch phase, enabling stable blown-film extrusion with high strength (15.03 MPa) and elongation (942.33%). These findings establish the acidolysis–association balance as a structure-guided framework for designing processable TPS and starch/polyester biodegradable films.