Synthesis and Performance of PA/EAA Composite Latex for Paper Coating

Poor water resistance and thermal stability of waterborne polymer coatings in paper‐based packaging remain a critical limitation. An in situ composite emulsion system of polyacrylate/ethylene‐acrylic acid copolymer (PA/EAA) was therefore established by synchronously introducing EAA during emulsion polymerization and copolymerizing it with PA monomers, thereby mitigating phase separation inherent to physical blending and achieving close interfacial bonding that enhances emulsion stability and film‐formation properties. Experimental results indicated that composite latex particles exhibited a core–shell morphology, with EAA forming the shell and PA the core. ATR‐FTIR and acetone extraction confirmed hydrogen‐bonded associations and chain‐segment grafting between the two phases. DSC and TGA revealed that EAA significantly improved the thermal resistance of the composite films, and its bimodal thermal‐degradation profile demonstrated complementary thermal‐stability contributions from both phases. Incorporation of EAA markedly enhanced low‐temperature heat‐seal strength, reaching 3.13 N/15 mm at 80°C, although higher EAA contents increased Cobb values and reduced Kit oil resistance ratings. A comprehensive evaluation identified the 35 wt% EAA composite emulsion as achieving the optimal balance among water resistance, thermal stability, and heat‐sealability. Interface optimization and structural synergy afforded by the in situ composite process thus provide an effective route to develop water‐based EAA coatings with superior water resistance and thermal stability.