Synthesis and characterization of unsaturated lactic acid based thermoset bio-resins

Abstract

Bio-based thermoset resins have been synthesized using lactic acid oligomers, which were functionalized with carbon–carbon double bonds, in order to allow their crosslinking by a free radical mechanism. Two different resin structures were synthesized. One resin was composed of an allyl alcohol terminated lactic acid oligomer, which was end-functionalized with methacrylic anhydride (MLA resin). The second resin was a mixture of the same allyl alcohol-lactic acid oligomer, and penthaerythritol. This mixture was end-functionalized with methacrylic anhydride, in order to get a methacrylate functionalized lactic acid oligomer, and methacrylate functionalized penthaerythritol (PMLA resin). The synthesized resins were characterized using FT-IR, 1H NMR and 13C NMR spectroscopy, differential scanning calorimetry as well as dynamic mechanical analysis to confirm the resin structure and reactivity. The flow viscosities were also measured in order to evaluate the suitability of the resins to be used as a matrix in composite applications. The results showed that the PMLA resin has better mechanical, thermal and rheological properties than the MLA resin, and both had properties which were comparable with a commercial unsaturated polyester resin. The high biobased content of 90% and the high glass transition temperature at 100°C for the PMLA resin makes it an attractive candidate for composite applications where crude oil based unsaturated polyester resins are normally used.