Investigation of the Curing Behavior of Orange Oil-Based Epoxy Resins With Different Hardeners

In biogenic base resins with various hardeners, part of the epoxidized linseed oil was replaced with increasing proportions of 5–25% by weight of orange oil, limonene, limonene epoxide, and limonene dioxide. The temperature development while curing, foam formation, and final hardness depended on the oxygen content of the limonene derivative used. Orange oils and limonene slowed the curing process down. The resulting hardness of the biobased epoxies decreased for all samples when adding 0–25% by weight. After six weeks of curing, Shore A 40–70 was achieved compared to Shore A 80–90 of the unmodified systems. Epoxidation of limonene to (+)-limonene-1,2-epoxide increased the reactivity. Here too, the achievable Shore hardness A decreased linearly to 60–85 with increasing addition of limonene epoxide. A replacement of 5% of the epoxidized linseed oil was possible without significant loss of material hardness. With limonene dioxide, the resins heated 75–85% faster than samples without the additive. As the proportion increased, all sample variants foamed, at maximum temperatures of up to 122°C. The suitability as a surface sealant for floor coatings was determined visually and through mechanical tests. Limonene dioxide improved flow and gloss, but the resin systems became more brittle and showed less adhesion to the floor surface. The resins were resistant to UV weathering. Due to the short gelling time, the resins should preferably be processed using the spray process.