In-situ polyurethane/polyacrylate microemulsion formation: the effects of acrylic content in wood coating application

In-situ surfactant-free emulsion polymerization was utilized to prepare polyacrylate/polyurethane (PUA) microemulsions in the absence of surfactant and organic solvent. For this purpose, PUA with higher acrylate content was successfully prepared, with the aim to reduce the coating cost. The dynamic light scattering results showed that the particle size of PUA microemulsion displayed a unimodal distribution and the particle size was ranged from 33 to 61 nm. In comparison with PUA prepared with conventional miniemulsion polymerization, the particle size distribution coefficient dropped by one order. Atomic force microscopy, together with thermogravimetric analyzer, demonstrated good compatibility and interaction between PU and acrylic components, and no phase separation was detected even at 58 wt% acrylic content. With the incorporation of acrylic component, the thermal stability and maximum stress were improved. The maximum stress greatly increased from 4.6 to 30.9 MPa, and the maximum stress of in-situ PUA was nearly three times larger than that of PUA prepared by miniemulsion polymerization. The effects of acrylic content on water resistance, pencil hardness, adhesion, and impact strength of wood coating were evaluated. With increasing the acrylic content, the water resistance and pencil hardness increased, though the impact strength of in-situ PUA films was slightly reduced.