Preparation of hydrophobic block copolymer PCL-b-PFPE: The microsphere-coated fabrics via direct electrostatic spraying and its super-hydrophobicity

In this study, the perfluoropolyether carboxylic acid (PFPE-COOH) was used to react with polycaprolactone (PCL) to synthesise the hydrophobic block copolymer PCL-b-PFPE. The esterification reaction was performed successfully with the terminated hydroxyl group in the PCL-OH after activation of PFPE-COOH with N, N′ -dicyclohexyl carbon diimide. The PCL-b-PFPE was dissolved in various solvents to prepare microspheres using electrostatic spraying technology, and the flow rate, voltage, temperature and humidity parameters were optimised. The findings demonstrated that the solvent and ambient humidity had a substantial influence on the microspheres' surface morphology. Through smooth surface morphology, chloroform (CF) single solvent formed an ideal microsphere and DMF/CF mixed solvent produced a 'pit' surface morphology. Furthermore, the surface roughness of microspheres increases with an increase in humidity. The static contact angles of electrostatic spraying polyester fabric were 147.1° ± 1.8°, 150.9° ± 1.5°, 156.3° ± 2.6° and 155.9° ± 3.3°, under 20 %, 40 %, 60 % and 80 % humidity, respectively. The findings demonstrated that during the electrostatic spraying, the PFPE chain's introduction into PCL helped construct the secondary rough morphology on the microsphere surface and substantially enhanced the hydrophobicity of coatings, providing the finished polyester fabric super-hydrophobicity. The PCL-b-PFPE microspheres were directly sprayed and coated with the developed spray solution via electrostatic spraying. The water contact angle of the finished polyester fabric was found to be ≥140°, which provided hydrophobicity after 5 cycles of laundry. Following the sandpaper abrasion and adhesion tests, the contact angle of the fabrics coated with the microspheres remained ≥145°, indicating a good mechanical stability.