| During the past few decades,polyurethanes(PUs)are among the most versatile polymeric materials which offer a wide range of applications,such as coatings,binders,adhesives,elastomers,packaging materials and for automotive finishes.However,conventional(PUs)products usually contain a significant amount of organic solvents and sometimes even free isocyanate monomers.In the process of construction,the volatilization of a large number of organic solvents brings harm to the environment and human body.Due to the strict environmental legislation and the enhancement of people’s awareness of environmental protection,waterborne polyurethane(WPU)has received much attention due to its zero or low amount of volatile organic compounds(VOCs).However,waterborne polyurethanes have a disadvantage in that the PU films exhibit high hydrophilic properties due to the presence of the hydrophilic carboxylate groups in the main chain,resulting in poorly mechanical properties and water or solvent resistance.The purpose of this paper is to optimize these shortcomings.The experimental basis is from formulations of water proof paint.A series of waterborne polyurethane synthesis was performed using a prepolymer method based on poly(tetramethylene ether glycol)and isophorone diisocyanate.Perfluorinated polyether oil(E10-H)and/or polydimethylsiloxane(PDMS)was then introduced to the system as soft segments,and by changing the contents of E10-H and PDMS,the change with different molecular weight of PDMS and the film-forming temperature to prepare modified waterborne polyurethanes.The structural changes of the materials were characterized by Fourier transform infrared spectroscopy(FTIR),and it confirmed that fluorine and silicone were successfully incorporated into the chain of the WPU polymer.The surface properties of the resultant WPU polymers were characterized by X-ray photoelectron spectroscopy(XPS),contact angle(CA)measurements and water absorption measurements.An improved contact angle,a decrease of the surface free energy,a decrease of water absorption,and a remarkable enrichment of fluorine and silicon at the film-air interface confirmed the surface mobility of the fluorine and silicon moieties,which results from their low surface energy,and as the film-forming temperature increase,the migration ability is obviously improved.However,the XPS data indicated that the ability of these moieties to migrate were mutually inhibited when they were both present in the polymer backbone.Meanwhile,the mechanical properties of the polymer were improved significantly when E10-H or PDMS was introduced into the backbone.A favorable synergistic effect was observed when both silicon and fluorine moieties were included in the polyurethane chain,yielding WPU films with the highest tensile strength(27 MPa).In addition,the effects of molecular weight of PDMS and film forming temperature on tensile strength were investigated.The results show that the tensile strength decreases with the increase of PDMS molecular weight,and increases obviously with the increase of film forming temperature.The tensile strength improve to 40.69 MPa when the film-forming temperature is 60 °C.Cryogenically brittle fractured cross section of samples were observed by scanning electron microscopy(SEM).It was found that a pure polyurethane section is smooth,but with E10-H and PDMS introduce into WPU,the extent of variable phase separation cause by the mobility and incompatibility between the fluorine and silicone moieties and the WPU segment is observed in the matrix of the WPU films. |
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