Castor-oil-based UV-curable hybrid coatings with self-healing, recyclability, removability, and hydrophobicity

Restrained by the irreversibility of the permanently cross-linked networks formed by double bonds, UV-curable thermosets with self-healing and reprocessing properties especially those derived from renewable feedstocks are highly desired for practical applications. In this work, repairable, recyclable, removable, and hydrophobic UV-curable polyurethane coatings derived from renewable castor oil were constructed by the employment of dynamic hindered urea bonds (HUBs). The resulting UV-curable materials not only showed high biobased contents (45.1%–47.6%), but also exhibited good thermal, mechanical, coating, and hydrophobic performance (a Tg of 67.0–77.8 °C, a tensile strength up to 16.6 MPa, a pencil hardness of 3H–5H, a flexibility of 2 mm, a water contact angle of 90.8–105.9°, etc.). Furthermore, due to the rapid dissociation or exchange of HUBs and intramolecular hydrogen bonds, the resulting UV-curable coatings exhibited excellent repairability, weldability, recyclability, and removability at moderate temperatures. For instance, the selected sample (PU-Si2) demonstrated a scratch healing efficiency up to 97.0% at 140 °C for 60 min and a welding efficiency (tensile strength) of 91.3% at 120 °C for 60 min. In particular, the UV-cured PU-Si2 sample could be physically recycled at least 4 times with enhanced performance in tensile properties, and the resulting PU-Si2 coatings were easily removed or recycled by using low-toxicity organic solvents like ethyl acetate and dimethylformamide.