Non-fluorine oil repellency: To what extent can it substitute perfluoroalkyl substances?

Oil-repellency of fabric is essentially based on perfluoroalkyl substances (PFAS, or called perfluorochemicals (PFCs)). However, plans to phase out the use of these chemicals, even those short-chain ones (C4-C6), have been announced because they accumulate in the human body and are extremely persistent in the environment. It is urgent to develop non-fluorine surface chemistry for oil-repellent fabric finishing. Here, we report the non-fluorine oil repellency of brush-like polydimethylsiloxane (PDMS) coating (g-PDMS), and the comparison of its oil repellency with that of a common PFAS crosslink polysiloxane coating (C4-PFAS). A catalyst-free, solvent-free chemical vapor deposition (CVD) process was used to prepare the g-PDMS coating. For smooth glass, g-PDMS coating exhibits ultralow contact angle hysteresis (∆θ) for various oils (1.3–7.3°), while the ∆θ of C4-PFAS coating is much higher (30.7–49.7°). For fabrics, g-PDMS and C4-PFAS achieved almost the same contact angles to castor oil (~134°). According to GB/T 19977-2014 standard, the oil repellency of coated fabrics was rated Grade 5 for both g-PDMS and C4-PFAS. Therefore, the non-fluorine oil repellency of g-PDMS is able to meet the basic requirement of oil-repellent fabric finishing, and it is expected that the oil repellency can be further improved by the rational design on surface topography.