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 T-g of 67.0-77.8 degrees 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 degrees, 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-Si-2) demonstrated a scratch healing efficiency up to 97.0% at 140 degrees C for 60 min and a welding efficiency (tensile strength) of 91.3% at 120 degrees C for 60 min. In particular, the UV-cured PU-Si-2 sample could be physically recycled at least 4 times with enhanced performance in tensile properties, and the resulting PU-Si-2 coatings were easily removed or recycled by using low-toxicity organic solvents like ethyl acetate and dimethylformamide.

Automated summary

This study constructed repairable, recyclable, removable, and hydrophobic UV curable polyurethane coatings derived from renewable castor oil using dynamic hindered urea bonds (HUBs). The resulting materials showed high biobased contents and exhibited excellent thermal, mechanical, coating, and hydrophobic performance. Due to the rapid dissociation and exchange of bonds, the UV-curable coatings demonstrated outstanding repairability, weldability, recyclability, and removability.