Construction of Core‐Shell Acrylate Emulsions Based on Keto‐Hydrazide Self‐Crosslinking Mechanism and Their Impact on the Barrier Properties of Paper Substrates

ABSTRACT To address the limited water resistance and barrier properties of traditional acrylate paper coatings caused by the lack of a chemical crosslinking network, a core‐shell keto‐hydrazide‐modified aqueous acrylate emulsion was synthesized in this study. This was achieved via semi‐continuous seeded emulsion polymerization by introducing a diacetone acrylamide (DAAM) and adipic dihydrazide (ADH) self‐crosslinking system. Furthermore, the effects of emulsifier type/dosage, reaction temperature, and the content of functional monomers on the emulsion polymerization kinetics and colloidal stability were systematically investigated. The results demonstrated that under the optimal synthesis conditions—specifically, an OP‐10 to SDS mass ratio of 1:2, a total emulsifier dosage of 4%, a reaction temperature of 85°C, and a DAAM dosage of 4%—the monomer conversion reached 95.32% with a low coagulum content of 0.162%, and the emulsion exhibited excellent storage and chemical stability. Fourier transform infrared (FT‐IR) spectroscopy and transmission electron microscopy (TEM) confirmed the formation of a C N covalent crosslinking structure and the successful construction of a core‐shell morphology. Furthermore, coating performance tests revealed that the keto‐hydrazide crosslinking effectively reduced the surface free energy of the system and restricted the swelling of polymer segments. At a DAAM content of 4%, the static water contact angle of the coated paper increased to 137.7°, and the Kit rating for oil resistance reached 11. Additionally, the water vapor transmission rate (WVTR) exhibited a significant reduction of 40.38% compared to the uncoated base paper. By combining the Flory‐Huggins theory and the free volume model, the microscopic physical mechanism was elucidated: the crosslinking network provides an elastic retractive force to resist solvent penetration, while simultaneously increasing the tortuosity of the diffusion paths to hinder the transport of water molecules. This study provides a quantitative model and an engineering foundation for the design of high‐barrier, eco‐friendly, waterborne paper‐based packaging materials.