Single agent, double effect: Grafting of soy protein isolate into low-migration self-initiating ultraviolet-curable polyacrylate wood coatings

Abstract

Benzophenone is a hydrogen-capturing small molecule photoinitiator and its migration in ultraviolet curing systems has been identified as a potential issue. In this study, soy protein isolate (SPI) was used as both the reactant and the hydrogen donor of the photoinitiator for free radical polymerization. Benzophenone-containing polyacrylate (PA) molecules were then grafted into SPI to achieve the self-initiation of the light-curing reaction. The SPI-benzophenone structure on the polymer chain formed a large-molecule photoinitiator system, in which bimolecular interactions occurred under UV irradiation to promote the low migration of the photoinitiator. A waterborne polyacrylate resin (PA-AHBP-SPI) suitable for wood coatings was prepared, and the detailed mechanism of reaction process was proposed. It was noticed that the PA-AHBP-SPI composite emulsion exhibited substantial UV absorption at 285 nm, with a maximum molar extinction coefficient of 27,387 L.mol⁻¹.cm⁻¹. The migration rate of the cured film was found to be only 17.68 % after 9 h of soaking in acetonitrile, and it demonstrated markedly low mobility. Under the optimal SPI content (4 g), the absorption of benzophenone photoinitiators is reduced three times to 29.74 %, the UV cure time of the film is reduced to 4.28 s and the tensile strength reaches 9.43 MPa.