Novel Waterborne Polyurethanes Containing Short Fluoroalkyl Chains: Synthesis, Characterization And Their Applications On Cotton Fabrics

Fluorocarbons especially those with long perfluoroalkyl chains (C_nF_2n+1), n=6-10) are widely used as the most important class of water and oil repellent finishing agents for textiles due to their optimum performance in lowering the surface free energy and improving both hydrophobicity and oleophobicity. In recent years, the fluorocarbons containing long perfluoroalkyl chains are facing the problems such as the persistence, bioaccumulation, and/or toxicity in the environment. The use of perfluorooctyl contained surfactants such as PFOS and PFOA have been restricted in the international community. Sooner or later, fluorocarbons with long perfluoroalkyl chains will face the same problems. So it is important to find the alternatives to replace the present long perfluoroalkyl-contained fluorocarbons. As reported that compounds with short perfluoroalkyl group (C_nF_2n+1, n≤4) can be decomposed in the environment with low toxicity. Based on the ring-opening polymerization of oxetanes, we designed two novel polyether diols containing short fluoroalkyl side chains. These polyether diols were introduce into polyurethane skeletons to form two novel waterborne polyurethanes containing short fluoroalkyl chains, which were applied on cotton fabrics as the water and oil repellent finishing agent.Starting from tribromoneopentylglycol, the readily available cheap material, we obtained the bromo-substituted oxetane. Using the phase transfer catalyst TBAB, this oxetane was reacted with hexafluoroisopropanoi and pentafluoropropanol separately to form two novel short fluoroalkyl containing oxetanes FOX1 and FOX2 with the yields of 54% and 78% respectively. In the presence of BF₃·Et₂O and neopentylglycol, FOX1 and FOX2 were polymerized to give two novel fluorinated polyether diols PFOX1 and PFOX2 respectively. The molecule weights of the two polyether diols were 3298 and 2629 measured by gel-permeation chromatography. These fluorinated polyether diols were then condensed with diisocyanate IPDI (isophorone diisocyanate) to form waterborne polyurethanes FPU1 and FPU2, their structures were confirmed by FT-IR spectra.The FPU emulsion, of which solid content was about 30%, was diluted with water to form 4 wt %, 8 wt %, 12 wt % emulsions, and these emulsions were applied on cotton fabrics by pad-dry-cure process. The treated cotton fabrics possessed moderate water repellent properties, but no obvious oil repellent properties. In the contact-angle test, the FPU1 treated cotton fabrics had a contact angle of 130°, while the contact angle of FPU2 treated fabrics reached 146°. The other tests have been done to examine the application efficiency, such as white index, wrinkle recovery angle, tear and tensile strength. According to all the test results, we found that FPU2 containing pentafluoropropyl group showed better properties than FPU1.