*Article* **Effect of Temperature on the Functionalization Process of Structural Self-Healing Epoxy Resin**

**Luigi Vertuccio 1, Elisa Calabrese 2, Marialuigia Raimondo 2, Michelina Catauro 1, Andrea Sorrentino 3, Carlo Naddeo 2, Raffaele Longo <sup>2</sup> and Liberata Guadagno 2,\***


**Abstract:** This work deals with developing a self-healing resin designed for aeronautical and aerospace applications. The bifunctional epoxy precursor was suitably functionalized to enhance its toughness to realize good compatibilization with a rubber phase dispersed in the hosting epoxy resin. Subsequently, the resulting mixture was loaded with healing molecules. The effect of the temperature on the epoxy precursor's functionalization process was deeply studied. Fourier trans-former infrared (FT-IR) spectroscopy and dynamic mechanical analyses (DMA) evidenced that the highest temperature (160 ◦C) allows for obtaining a bigger amount of rubber phase bonded to the matrix. Elastomeric domains of dimensions lower than 500–600 nanometers were found well distributed in the matrix. Self-healing efficiency evaluated with the tapered double cantilever beam (TDCB) method evidenced a healing efficiency for the system functionalized at 160 ◦C higher than 69% for all the explored fillers. The highest value was detected for the sample with DBA, for which 88% was found. The healing efficiency of the same sample functionalized at 120 ◦C was found to decrease to the value of 52%. These results evidence the relevant role of the amount and distribution of rubber domains into the resin for improving the resin's dynamic properties. The adopted strategy allows for optimizing the self-healing performance.

**Keywords:** self-healing efficiency; functionalization reaction; epoxy resin; mechanical properties
