Preparation, Emulsion Stability and Preliminary Demoulding Evaluation of a Wax-Free Water-Based Soybean Oil-Mineral Oil Concrete Release Agent

Water-based, wax-free release agents are attractive for concrete formwork, yet their emulsification window and demoulding behaviour remain poorly defined. This work prepared a soybean-oil/naphthenic-oil emulsion and evaluated its stability and pull-off performance. OP-10/Span-80 blends produced a visually stable soybean-oil emulsion in a narrow hydrophilic–lipophilic balance (HLB) window, with only trace or small separation within 1 h across a calculated HLB interval of 12.15–12.31 at an assumed OP-10 HLB of 14.5 (11.3–12.3 across the reported range). The high-non-volatile-content naphthenic-oil emulsion containing 1.00 wt% sodium benzoate (MH2+) showed no visible phase boundary after centrifugation at 7000 rpm for 6 min and only a thin re-emulsifiable surface layer after 20 d, whereas the sodium-benzoate-free emulsion separated into three phases. At 1.57–1.59 micrometres, the 1:3 blend of the soybean-oil emulsion and MH2+ gave a pull-off force of 7.92 N, comparable to EP6 (7.963 N at 1.50 micrometres) and lower than MH2+ (11.63 N) and the soybean-oil emulsion (55.26 N), and produced visually more uniform demoulded surfaces. The blend force increased to 73.68 N at 1.05 micrometres, indicating that sufficient coating is essential. The 1:3 blend is therefore a promising low-force, wax-free water-based release agent at sufficient coating, providing a basis for coating optimization and field validation.