Study On The Film-forming Process Of Waterborne Polyurethane Based On The Apparent Fluorescence Lifetime Of Excimer

In recent years,relevant state departments have become more and more stringent in the management of VOC.Compared with solvent-based polyurethane,water-based polyurethane is more environmentally friendly and has many excellent properties.Waterborne polyurethane has therefore become a new type of green material and is used in many fields.Researchers have done a lot of work on the synthesis and modification of water-based polyurethane,but there are few studies on the film formation of water-based polyurethane,and many water-based polyurethane products achieve their performance through film formation,which makes The research on waterborne polyurethane film formation has become very important.There are two methods to study the IPD process of dispersion film formation,one is small angle neutron diffraction(SANS)and the other is fluorescent probe.Both have their own advantages and disadvantages.Among them,small-angle neutron diffraction is only suitable for the study of the film-forming process of small particle size dispersions.However,most of the dispersion particle sizes used in industry are beyond its scope of application,so this method is The actual meaning is limited.The fluorescent probe method is more commonly used in the study of the film formation process of aqueous polymer dispersions.This method can be used to study the IPD process of polymer dispersions of various particle sizes.Specifically,it can be divided into resonance energy transfer method and excimer method.The disadvantage of the resonance energy transfer method is that it needs to synthesize two kinds of D and A labeled dispersions,and the process is complicated.A more practical and simple method to study the dispersion IPD process is the fluorescence probe method based on Excimer.In this paper,firstly,a fluorescent chain extender of dihydroxypropyl pyrene butyrate was synthesized,and the fluorescent chain extender was characterized by carbon NMR and liquid mass spectrometry.A fluorescently labeled waterborne polyurethane with a concentration gradient was prepared.In the experiment,we did find that the apparent fluorescence lifetime of the excimer is related to the fluorescence concentration,and the linearity and sensitivity are much higher than the double fluorescence of the excimer.On the basis of theory and experiment,we have established a new method based on the apparent fluorescence lifetime of excimer to study the IPD process of polymer dispersion film formation.This method has not been reported in the literature.The labeled waterborne polyurethane with a fluorescent chain extender accounting for 5%of the formula mass is selected as the next research object.By modifying the waterborne polyurethane,a series of waterborne polyurethanes are prepared.The fluorescent labeled waterborne polyurethane and the unlabeled waterborne polyurethane with similar structure are based on the quality 1:10 mixed film formation.As the IPD process progresses,the fluorescently labeled dispersion molecular chains diffuse into the non-labeled particles.As a result of molecular chain diffusion,the concentration of fluorescent probes inside the labeled particles decreases,and the number of excimer formations decreases.The emission peak of the excimer decreases,and the apparent fluorescence lifetime of the excimer becomes shorter.In order to explore the important influence of particle size,soft segment content,film forming temperature,and degree of crosslinking on the fusion of molecular chains between particles in the film forming process,the following work has been mainly done:(1)Preparation and characterization of dihydroxypropyl pyrene butyrateThe reaction of pyrene butyrate and 3-chloro-1,2-propanediol under the catalysis of quaternary ammonium salt to produce dihydroxypropyl pyrene butyrate was characterized by carbon nuclear magnetic resonance spectroscopy and liquid-mass spectrometry.(2)Derivation of the relationship between the fusion depth between particles and the fluorescence lifetime during the formation of waterborne polyurethane filmsUsing dihydroxypropyl pyrene butyrate as the fluorescent chain extender,the synthetic fluorescent chain extender accounts for 1%-5% of the total mass of the labeled waterborne polyurethane.Characterized by Fourier infrared spectrometer and Malvern particle size.Fluorescence lifetime test was performed on it,and it was found that the apparent fluorescence lifetime of the excimer was related to the fluorescence concentration.The higher the concentration,the longer the lifetime.The origin software was used to linearly fit the fluorescence lifetime and the concentration of fluorescent substance,and the fitted linear equation was y=13.89x+1.83.It can be seen that the linear relationship between the fluorescence lifetime ? and the concentration of the fluorescent chain extender Cpy is good.Through formula derivation,the relationship between the fusion depth between particles and the fluorescence lifetime during water-based polyurethane film formation is established,which lays the foundation for calculating the particle fusion depth during water-based polyurethane film formation.(3)Research on the factors affecting the fusion of particles during the formation of waterborne polyurethane filmsA group of water-based polyurethane containing 5% of the total weight of the formula is mixed with a series of water-based polyurethanes of similar structure to form a film.The fluorescence lifetime of the mixed film is tested and the fluorescence lifetime is analyzed.Calculate the particle fusion depth.The study found that the particle size,soft segment content,cross-linking degree,and film forming temperature have important effects on the mutual fusion of particles during the film forming process.