Differential scanning calorimetry study of linseed oil cured with metal catalysts

Differential scanning calorimetry (DSC) has been used to study the autoxidative curing process of linseed oil catalyzed by conventional metal driers and two metal sol-gel precursors, Ti(Oi-Pr)(2)(acac)(2) and Ti(Oi-Pr)(4), at elevated temperatures. Linseed oil resins with a range of 0-5.0 wt.% metal sol-gel precursor and 0-9.0 wt.% zirconium drier have been investigated by both dynamic and isothermal methods. The onset, peak and end temperatures of the reaction exotherms were observed as a function of metal catalyst type and content. The Borchardt and Daniels kinetics method was used to quantify the heat of reaction of the dynamic DSC scans. The indention hardness of the resultant coatings in the DSC sample pans was measured as an indication of crosslink density. The inclusion of small quantities of metal catalyst (0-5.0 wt.% titanium alkoxide, 0-2.0 wt.% zirconium drier) caused the reaction exotherm to broaden and shift to lower temperatures. At higher metal catalyst content (> 5.0 wt.% Ti(Oi-Pr)(2)(acac)(2) or 5.0 wt.% Ti(Oi-Pr)(4)) the reaction exotherms became imperceptible. Overall, as the metal catalyst content was increased, the heat of reaction decreased while indention hardness increased. The effects of the two sol-gel precursors on the reaction exotherms were similar to the effects of conventional driers. Combinations of conventional driers were also studied.