Influence of carboxyl content on the rheological properties and printability of oxidized starch for 3D printing applications.

With the rapid development of 3D printing technology, the development of starch gels based on 3D printing with excellent printing properties has attracted great attention. This study successfully prepared four types of oxidized starch (OMS) with varying carboxyl group contents (0.203 %, 0.612 %, 1.043 %, and 1.278 %) by controlling the amount of sodium hypochlorite. Rheological analysis of these OMS gels revealed typical shear-thinning behavior and excellent structural recovery during heating shear across various concentrations. As the concentration of OMS increased, key parameters such as consistency index (K), storage modulus (G'), yield stress (τ), and flow stress (τ) also increased, signifying enhanced molecular chain entanglement and densification with reduced digestibility. Conversely, at a constant concentration, increasing carboxyl group content led to decreased K, G', τ, and τ values due to molecular chain degradation, resulting in diminished aggregation and increased network pore size. Notably, OMS gels demonstrated favorable printability within a specific range of G' (4314.0-6690.0 Pa), τ (1254.8-2697.5 Pa), and τ (822.3-2296.3 Pa). Meanwhile, oxidized starch (OMS2 and OMS3) gels exhibited exceptional printability, attributed to appropriate molecular chain length and carboxyl content, which promoted sufficient physical crosslinking. These findings provided theoretical insights and foundational data for developing 3D printable starch-based materials.