Fully biobased epoxy resins from ring opening polymerization of epoxidized pennycress (Thlaspi arvense L.) oil with itaconic and citric acids

Abstract

Fully biobased thermosetting epoxy resins were efficiently synthesized from non-edible field pennycress (Thlaspi arvense L.) oil following a two-step sequence in which the oil was epoxidized by in situ-generated performic acid and then cured with citric and itaconic acids. Ring opening polymerization reactions were self-catalyzed, solvent-free, and conducted at 120 °C for 5 – 25 h. Analogous polymers were prepared from epoxidized soybean oil to serve as reference comparisons. The influence of comonomer combination and curing time on properties of the resulting elastomeric, ductile, thermally stable (DTG > 379 °C), hydrophobic (contact angle > 70 °) epoxy resins is reported. Crosslink density, storage modulus at the glass transition temperature (6.8 – 14.4 MPa), tensile strength (0.3 – 1.1 MPa), and gel content (87 – 96%) increased with cure time. Citrate-based polymers had higher crosslink densities (317 mol m−3) than itaconate-based polymers (164 – 279 mol m−3) due to the greater functionality of citric acid versus itaconic acid, which resulted in higher glass transitions (> 21 °C), tensile strengths (> 0.6 MPa), and storage moduli in the rubbery state (> 2.6 MPa). Finally, the lower oxirane content of EPO versus ESO resulted in lower crosslink density, storage modulus, tensile strength, and elongation at break. Overall, the epoxy networks had promising thermal, mechanical, and viscoelastic properties that were tunable by selection of appropriate comonomer combinations and curing times.