Toward a Long-Chain Perfluoroalkyl Replacement: Water and Oil Repellency of Polyethylene Terephthalate (PET) Films Modified with Perfluoropolyether-Based Polyesters

Abstract

Original perfluoropolyethers (PFPE)-based oligomeric polyesters (FOPs) of different macromolecular architecture were synthesized via polycondensation as low surface energy additives to engineering thermoplastics. The oligomers do not contain long-chain perfluoroalkyl segments, which are known to yield environmentally unsafe perfluoroalkyl carboxylic acids. To improve the compatibility of the materials with polyethylene terephthalate (PET) we introduced isophthalate segments into the polyesters and targeted the synthesis of lower molecular weight oligomeric macromolecules. The surface properties such as morphology, composition, and wettability of PET/FOP films fabricated from solution were investigated using atomic force microscopy, X-ray photoelectron spectroscopy, and contact angle measurements. It was demonstrated that FOPs, when added to PET film, readily migrate to the film surface and bring significant water and oil repellency to the thermoplastic boundary. We have established that the wettability of PET/FOP films depends on three main parameters: (i) end-groups of fluorinated polyesters, (ii) the concentration of fluorinated polyesters in the films, and (iii) equilibration via annealing. The most effective water/oil repellency FOP has two CF-PFPE-tails. The addition of this oligomeric polyester to PET allows (even at relatively low concentrations) reaching a level of oil repellency and surface energy comparable to that of polytetrafluorethylene (PTFE/Teflon). Therefore, the materials can be considered suitable replacements for additives containing long-chain perfluoroalkyl substances.

Towards a Long-Chain Perfluoroalkyl Replacement: Water and Oil Repellent Perfluoropolyether-Based Polyurethane Oligomers

“…To this end, perfluoropolyether derived (co)polymers and cross-linked materials have been shown in our previous works and that of others to have the ability to serve as hydrophobic/lyophobic materials and interfaces [20][21][22][23][25][26][27][28][29][30][31][32][33][34][35][36][37]. In particular, we have found that when PFPE-based triblock polyesters [20,21,37] or methacrylic molecular brushes [36] are added to engineering thermoplastic (PET, nylon 6, or polymethyl methacrylate) films, they readily migrate to the film surface, imparting significant water and oil repellency to the thermoplastic boundary. Specifically, the macromolecular additives populated the boundary with PFPE segments terminated with C 4 F 9 -perfluoroalkyl moiety, which cannot yield unsafe long-chain perfluoroalkyl carboxylic acids.…”

“…The surface energy values estimated from the contact angle of hexadecane are close, but to some extent different from the ones obtained by the Owens-Wendt method utilizing both WCA and HDCA. We associate this difference with the differences in the size of the wetting liquids, which plays a significant role in the wettability of polymer surfaces [20,21,36]. Based on molecular weight and chemical structure, the size of water molecule is about an order of magnitude smaller than that of hexadecane.…”

“…PFPEs are macromolecules possessing -CF 2 -, -CF 2 -CF 2 -, and -CF(CF 3 ) -CF 2 -molecular fragments in their Polymers 2021, 13, 1128 2 of 12 backbone that are separated by oxygen atoms. Currently, PFPEs are considered as potentially safer replacements for LCPFAs [3,[19][20][21]. PFPEs have numerous advantages, such as high chemical inertness and radiation resistance, low surface tension (20-22 mN/m) [22], nonflammability, low toxicity, optical transparency, and low volatility [22][23][24].…”

Fluorinated Metal–Organic Coatings with Selective Wettability

“…Lower surface tension liquids (e.g., oil) will wet better than higher surface tension liquids (e.g., water) for most surfaces. − This phenomenon largely explains the challenge in creating surfaces with both water affinity and oil repellence properties . Nevertheless, achieving simultaneous controlled surface affinity − and repellence to various liquids is important for engineering advanced materials and holds promise and broad interest for a wide range of wetting-related applications such as self-cleaning, chemical sensing, and membrane separations. − Externally induced wetting, through, e.g., shear and strain − or by combining surface active additives (e.g., chromophores), − can initiate responsive wettability. − However, externally induced wetting strategies do not lead to selective wetting without the application of external stimuli/energy or super-repellence to conventional wetting oils, in air or under water (e.g., droplet bouncing). Therefore, to date, a mechanistic understanding of selective wetting is largely unexplored.…”

Comparison of Branched and Linear Perfluoropolyether Chains Functionalization on Hydrophobic, Morphological and Conductive Properties of Multi-Walled Carbon Nanotubes

“…Perfluoropolyethers (PFPEs) are liquid fluoropolymers embodying supplementary properties such as high gas permeability and high molecular mobility in addition to those of fluorinated materials [ 27 ]. PFPE-functionalization can be performed by employing several functional PFPE reagents, but the majority of them contains hydrogenated spacers lack the same thermal and chemical stability of fluoromaterials [ 28 , 31 , 32 ]. To this aim, PFPE peroxides are advantageous reagents since their thermolysis generates highly reactive perfluorinated radicals, which are able to bond directly with MW-CNTs sidewall without employing detrimental spacers [ 33 ].…”