Tailored UV-curable acrylated linseed oil-based alkyds: Optimizing crosslinking and coating performance through functionalization and reactive diluent design

This study outlines a safer and greener pathway for the synthesis of UV-curable acrylated linseed oil-based alkyds (ALO-A), introducing enhancement in bio-based coating performance while addressing environmental and industrial challenges. Building upon conventional methods, our optimized process integrates acrylic functionality directly into the alkyd backbone through an improved reaction pathway, offering a significant advancement in resin synthesis. This method eliminates halogenated reagents, reduces the need for excess acrylic acid, and supports rapid, VOC-free UV curing. To investigate the impact of acrylate functionality on coating properties, two strategies were employed: adjusting the number of acrylic groups integrated into the alkyd backbone and incorporating reactive diluents. Two ALO-A resins with 2.3 and 1.8 mmol of acrylic groups/g resin, determined by 1H NMR, were synthesized. ALO-A resins were mixed with bio-based isobornyl acrylate (IBOA), tripropylene glycol diacrylate (TPGDA), or trimethylolpropane trimethacrylate (TMPTMA) in various ratios. Real-time photorheology demonstrated that higher acrylate functionality in ALO-A together with reactive diluents lowered the gel point to 3.0 s. The acrylate functionality led to a 2.2-fold difference in coating hardness, reaching a maximum pendulum hardness of 103 s. The incorporation of reactive diluents further enhanced hardness, achieving up to 2.9-fold with lower-functionality ALO-A and 1.7-fold with higher-functionality ALO-A (max. 174 s). Indentation tests revealed exceptional flexibility, showing up to 7.4 mm in Erichsen cupping. Adjusting the reagent ratio during ALO-A synthesis and incorporating reactive diluents offer two effective strategies for precise control over the mechanical performance of coatings. The comparison of these approaches highlights advancements in UVcurable coating design.