Co-authors​ :

 Laura SIMONINI (ITALY), Markus KAKKONEN , Royson DSOUZA (FINLAND), Haroon MAHMOOD (ITALY), Olli TANHUANPÄÄ , Mikko KANERVA (FINLAND), Essi SARLIN (FINLAND), Pasi KALLIO , Andrea DORIGATO , Alessandro PEGORETTI (ITALY) 

In this work, a continuous poly(ε-caprolactone) (PCL) coating for glass fibers (GF) was developed and characterized for interfacial self-healing applications. The coating was deposited in accordance to the fluid coating theory, where a fluid is forced to coat a solid while this last is in movement. PCL was dissolved in a mixture of dimethylformamide (DMF) and tetrahydrofuran (THF) and stirred up to obtain a homogeneous liquid solution. The viscosity of the solution was carefully controlled by a Brookfield viscometer, in order to optimize the deposition process by just controlling the coating speed. Scanning electron microscopy (SEM) showed that a well-applied coating gradually formed on the surface of the fibers as a function of the coating speed, without discontinuities nor irregularities. Atomic force microscopy (AFM) showed that the coating improved the surface roughness of the fibers, which contributed in the mechanical interlocking component of adhesion. Microdebonding tests were conducted on epoxy/glass microcomposites to evaluate the efficiency of the coating for interfacial adhesion and self-healing. The results from these tests were particularly promising. It was established that the poly(ε-caprolactone) coating contributed significantly in the enhancement of the fiber/matrix interfacial adhesion achieving an increase of up to 16% of the interfacial shear strength (IFSS), and allowed the complete interface reparation (100%) upon first thermal healing (performed at 80°C for 30 min). This ability to autonomously repair and restore the integrity of the material has significant implications for the durability and longevity of composite structures in various applications. However, while the initial healing process demonstrated impressive results, there was a marginal decrease in self-efficiency after three consecutive healing cycles. This finding suggested that, although the poly(ε-caprolactone) coating exhibited robust self-healing capabilities, there were factors that influenced the adhesion measurements. In particular, a progressive modification of the meniscus shape of the epoxy microdroplets was observed upon consecutive healings, which compromised the actual stress state distribution at the contact point between epoxy and blades during microdebonding. Hence, a numerical model was developed to understand the debonding and healing mechanisms occurring at the fiber/matrix interface, in order to explain the decreasing trend in efficiency for subsequent healing processes.