3D printing with citronella- incorporated resins: exploring printability and essential oil retention in hardened materials

Abstract

This study investigates the incorporation of citronella essential oil into water-washable UV-curable resin to fabricate 3D-printed materials and evaluates the combination of both oil and resin. Formulations with 0%, 5%, 10%, and 15% (v/v) citronella oil were analyzed for curing kinetics under UV exposure (405 nm source, exposure times 15–210 s), chemical structure, thermal stability, thermal transitions, mechanical performance, and insect repellency. GC-MS analysis identified the oil's volatile terpenoid composition, predominantly geraniol (28.79%), citronellal (24.33%), and citronellol (16.49%), which governed all observed properties. Results showed that higher oil loadings delayed UV-curing and reduced final mass due to terpene volatilization. A concentration-dependent reduction in initial thermal stability was observed, while the main polymer degradation temperature remained largely unchanged. FTIR confirmed physical encapsulation via non-covalent interactions, and DSC revealed a plasticization effect, indicated by a decrease in glass transition temperature (Tg) from 133 °C to 128 °C. Mechanical testing showed a trade-off, with oil reducing tensile strength and modulus but enhancing ductility up to 10% loading, beyond which phase separation caused property deterioration. Repellency assays against Musca domestica confirmed strong bioactivity, with the 15% formulation sustaining significant efficacy after 10 days. These findings underscore a critical compromise between material performance and functionality, establishing an optimal formulation window of 5–10% citronella oil for developing durable, insect-repellent 3D-printed products for agricultural and consumer applications.