Addition of Halloysite to Room Temperature Intrinsic Self-Healing Polyurethanes for Enhancing Their Mechanical Properties

Room temperature self-healing polyurethanes (PUs) generally showed limited mechanical properties. In order to improve the mechanical properties of PUs without sacrificing their self-healing ability, in this study, different amounts of halloysite clay filler were added. Thus, intrinsically self-healing PUs were synthesized using polycar-bonate diol polyol, aliphatic diisocyanate, 1,4-butanediol, and different amounts (0.5–10 wt.%) of thermally treated halloysite. The structural, thermal, viscoelastic, and me-chanical properties of the resulting PU/halloysite composites were evaluated. All hal-loysite-filled PUs retained room-temperature self-healing capability, while exhibiting improved mechanical strength. PU with 0.5 wt.% halloysite (E0.5) showed the most balanced performance, with well-dispersed halloysite nanotubes intercalated within the soft segments, enhancing chain mobility and soft segment ordering. Higher hal-loysite loadings (1–3 wt.%) led to increased mechanical properties but also some round clay particles agglomeration and surface migration; this led to limited halloysite–PU matrix interactions. The addition of more than 3 wt.% halloysite did not result in fur-ther improvements of mechanical properties. The findings of this study provided new insight into the filler–polymer interaction mechanism and establish a foundation for the design of multifunctional PUs with both autonomous self-repair and enhanced mechanical performance.