Waterborne Polyurethanes Containing Fluoroalkyl Chains: Synthesis, Characterization And Their Application On Cotton Fabrics

With the improvement of people's living standard,demand for the functional textiles has increased rapidly.Fluorocarbons especially those with long perfluoroalkyl chains(C_nF_2n+1-,n≥8) 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.However,fluorocarbons containing long perfluoroalkyl chains can degrade into perfluorooctyl-sulfonyl(PFOS) and perfluorooctyl(PFOA) type compounds which accumulate in natural environment and are toxic to human beings.Their applications are restricted in the international community.Thus,it is significant to find alternatives to replace the present long perfluoroalkyl-contained fluorocarbons.On the basis of ring-opening polymerization of oxetane,we designed a series of polyether diols containing short fluoroalkyl side chains(C_nF_2n+1-,n≤6),these polyether diols were introduced into the polyurethane skeletons to form novel waterborne polyurethanes containing short fluoroalkyl chains,which were applied on cotton fabrics as the water and oil repellent finishing agent.Starting from cheap tribromoneopentylglycol,3,3-dibromomethyloxetane was obtained via cyclization.Using the phase transfer catalyst TBAB,this oxetane was reacted with trifluoroethanol,heptafluorobutanol or tridecafluorooctan-1-ol separately to form 3-bromomethyl-3-fluoroalkyloxetanes(FOBX1-3) by controlling the molar ratio of 3,3-dibromomethyloxetane to fluoro alcohol.In the presence of BF₃·Et₂O and neopentylglycol, FOBX1-3 were polymerized to give novel fluorinated polyether diois PFOBX1-6 respectively. These fluorinated polyether diols were then condensed with IPDI(isophorone diisocyanate) to form waterborne polyurethanes FPUs.Their structures and thermal stabilities were studied by FT-IR spectra and thermogravimetric analysis(TGA) respectively.The FPU emulsion was diluted with water to form 4,6,8 and 10 wt%emulsions,and these emulsions were applied on cotton fabrics by pad-dry-cure process.The surface composition and morphology changes of the treated cotton fibers were analyzed by X-Ray photoelectron spectroscopy(XPS),Scanning Electron Microscopy(SEM) and Atomic Force Microscopy(AFM). Cotton fabrics treated with CFPU1 had a contact angle of 136°for water,contact angel for fabric treated with CFPU2 reached 142°,and 147°for both fabrics treated with CFPU3 and AFPU3.As CFPU1 and CFPU2 contained relatively short fluoroalkyl side chains,the treated cotton fabrics had no obvious oil repellent properties.Surfaces treated with CFPU3 showed Grade 3 repellent property with n-hexadecane.Contact angle could reach 95°.Fabrics treated with AFPU3 had grade 1 repellent property,the contact angle for nujor droplet was 126°.