Investigating the Structure–Property−Processing Relationship of Polycaprolactone-Based 3D Printed Self-Healing Polymer Blends

Research into the 3D printing of self-healing polymers has increased; however, the understanding regarding the relationship between 3D printing (3DP) parameters, material composition, and their impact on resulting material properties remains limited. In this work, we examine how material composition affects the 3DP, thermal, mechanical, and self-healing properties of an extrinsically self-healing resin system based on linear polycaprolactone (PCL) as a healing agent. The polymer system is based on 2-phenoxyethyl acrylate (POEA) and 1,6-hexanediol dimethacrylate (HDDMA) with up to 25 wt % PCL. Upon mixing, the POEA monomer and PCL remain homogeneous at room temperature. Polymerization-induced phase separation (PIPS) occurs following irradiation; this is reflected in photo-DSC analyses and polarized optical microscopy. DSC analyses showed an insensitivity of the glass transition temperature to PCL concentration and an increase in the melting enthalpy that scales with PCL content, further supporting phase separation post polymerization. The addition of PCL also yielded enhanced mechanical properties; for example, a 281% increase in tensile strength was observed when comparing a 20 wt % PCL blend to that of pure POEA. Likewise, self-healing properties improved with PCL content, exhibiting >90% healing efficiency based on toughness for the 20 wt % PCL blend. The incorporation of PCL was found to impact the dimensions and curling of printed specimens, which can be attributed to the presence of phase-separated PCL. A validation matrix was used to determine a balanced print time for 0 and 20 wt % PCL blends; it was found that PCL reduced the required exposure time for printing, resulting in faster prints of similar dimensional precision. Finally, the ability to 3D print various complex geometries using a conventional MSLA printer was demonstrated for the 20 wt % PCL blend. Further understanding of the relationship between 3DP processing, material composition, and material properties will enable highly engineered products capable of applications in biomedical, soft robotics, and aerospace.