Influence of oxidative modification of polyhydroxy polymers on the performance of shear thickening polishing slurry

The dispersed phase particles, which form dynamic clusters under high shear, play a key role in determining the rheological properties of shear thickening polishing slurry (STPS). Enhancing the hydrophilicity of dispersed phase particles through chemical modification is a potential method to improve the performance of STPS, and oxidation modification is a commonly used method. However, a clear understanding of how the molecular-level changes induced by oxidation, such as chain scission and introduction of polar groups, jointly control the macroscopic polishing performance remains a challenge, hindering the rational design of high-performance STPS. This study compares two polyhydroxy polymers (P-A/P-B, tapioca starch/ corn starch) and their oxidized derivatives (P-O-A/P-O-B) as dispersed phases to evaluate the impact of oxidation on slurry performance. Comprehensive characterization, including particle size distribution, fourier transform infrared spectroscopy (FTIR), microscopic structure, rheological behavior, dispersion stability and mechanical properties, revealed distinct physicochemical differences between raw and oxidized materials. The results show that P-O-A and P-O-B exhibit obvious particle fragmentation, and the corresponding polishing slurries, due to the molecular chain breakage effect caused by oxidation and the synergistic effect of continuous shear force, exhibit a continuous attenuation trend of polishing force over time. However, oxidized slurries exhibit enhanced anti-sedimentation performance and increased viscosity (from 1339 mPa·s to 1921 mPa·s) due to the introduced polar functional groups (e.g., carboxyl groups). Polishing experiments on titanium alloy (TC4) workpieces showed that oxidized slurries outperform unmodified ones, achieving a higher material removal rate (2.1 times that of unmodified slurry) and lower surface roughness (Sa 21.7 nm), with P-O-B slurry exhibiting superior performance due to its better rheological properties. These findings not only provide an important experimental basis and theoretical reference for understanding the structure-activity relationship between the chemical modification of dispersed phase particles and their polishing performance, but also demonstrate a viable strategy for developing advanced STPS formulations for high-efficiency and high-quality precision machining of difficult-to-machine materials like titanium alloys.