Rosin-modified o-cresol novolac based vinyl ester thermosets containing methacrylated lignin model compounds: synthesis, curing and thermo-mechanical analysis

Abstract

In the present research article, a detailed study on the synthesis, characterization, and structure–property correlation study of the vinyl ester resin (AVEOCN) based on the rosin modified o-cresol-formaldehyde epoxy novolac resin has been done. The rosin was condensed with o-cresol formaldehyde novolac resin to obtain the product (AOCN). The AOCN resin was epoxidized and subsequently esterified with methacrylic acid using triphenylphosphine as a catalyst and inhibitor hydroquinone to get vinyl ester resin (AVEOCN) having acid value ~ 7 mg of KOH per gram of solid. The chemical structures were confirmed using FT-IR, 1H-NMR, 13C-NMR, and DEPT-135° spectroscopic techniques, and their number average molecular weights were evaluated using 1H-NMR spectroscopy as well as Gel Permeation Chromatographic technique (GPC). The curing dynamics of synthesized VER with lignin modeled compounds, methacrylated eugenol (ME) and methacrylated guaiacol (MG), and petroleum-based styrene as reactive diluents was studied using Differential Scanning Calorimetry (DSC). The thermal stability analysis and mechanical performance of the VER samples were done using Thermogravimetric analysis (TGA) and Universal Testing Machine (UTM), respectively. Chemical resistance tests of the above VER samples were also assessed via exposing the sample coated panels to the different chemical environments for 90 days and their % weight loss was determined. The surface morphology of exposed samples was also studied using Scanning Electron Microscopy (SEM). The results obtained were compared to VER systems based on petroleum products and epoxy resins systems and the superior performance of rosin-modified VER systems indicate that they are suited for pressing demands for coating applications.