Study On Reaction Process And Phase Transition Process In Polymer-Water System By Near Infrared Spectroscopy

NIR spectroscopy technology has been widely applied in process analysis as a fast and nondestructive on line technology.Water is a commonly used reaction and dispersing media.However,NIR spectra of components usually overlap seriously and water has strong and broad NIR absorption,which usually covers the useful information.Therefore,it is difficult to analyze water system by NIR spectroscopy.In this paper,NIR spectral analysis technology is used to analyze the change processes of three polymer water systems,focusing on how to extract favorable information from the overlapping NIR absorption in the presence of water.The main contents of this paper are as follows:1.Water soluble phenolic resin is a kind of widely used polymer which is synthesized by phenols and aldehydes in water.The real-time detection of free formaldehyde content in the synthesis process is of great significance to the quality control of resin products.The traditional method is off-line laboratory measurement,which is time-consuming and tedious,and cannot be used for on-line analysis.Therefore,a real-time online detection method of free formaldehyde content during the synthesis of water-soluble phenolic resin was studied.Because the NIR spectra of the reaction system of formaldehyde-phenol alkaline aqueous solution are severely overlapped,the characteristic peak of free formaldehyde cannot be directly used for quantitative analysis.The method of establishing a multivariate correction model of free formaldehyde by partial least squares(PLS)achieved the online detection of free formaldehyde content during the synthesis of phenolic resin.The modeling conditions of free formaldehyde content during polymerization at different temperatures(55,65 and 75?)were studied,and the optimal models have been obtained.However,the establishment of PLS multivariate correction model requires a lot of work and the built model has strict application conditions.In order to solve the above problems,a new method based on the free formaldehyde related characteristic peak extracted by MCR-ALS was proposed to on line real-time detect of the free formaldehyde content in phenolic resin synthesis process.The results of the MCR-ALS method are consistent with those of the chemical titration method,which shows that the results of MCR-ALS method are accurate.Compared with the traditional method of building multivariate correction model,this method does not need modeling so that it is more time-saving and labor-saving,and easy to be popularized in industrial production.2.Self-crosslinking acrylate emulsion has been widely used in waterborne coatings because of its excellent performance.Crosslinking reaction of waterborne self-crosslinking acrylate emulsion in film forming process will affect the film performance.Therefore,it is very important to study the crosslinking reaction process in emulsion forming.In this study,the film formation process of self-crosslinking waterborne acrylate emulsion of diacetone acrylamide(DAAM)and adipic acid aihydrazide(ADH)was studied by NIR spectroscopy combined with second derivative.The position of NIR characteristic absorption peak of NH2 group in ADH was determined.The process of cross-linking reaction during film-forming was discussed according to the change of integral area ratio of the absorption peak of NH2 and the absorption peak of CH group with time,and the physical film forming process was studied by film formation kinetics.Based on the above analysis,it is found that in the first and second stages of film formation,the cross-linking reaction does not occur or the reaction speed is very slow;in the third stage where the latex particles are merged and the polymer molecular chains diffuse with each other,the cross-linking reaction significantly accelerates.3.Thermosensitive hydrogel is composed of two main components,polymer and water.Study on the change of water and polymer during sol gel transformation is helpful to understand the mechanism of thermosensitive hydrogel sol gel transformation.In this study,NIR spectroscopy was used for investigating the change of water and NH bonds in polymer during the sol-gel phase transformation process of the thermosensitive hydrogel of PDMAA22-b-PDAAM70-b-PDMAA22 three block copolymer composed of poly(N,N-two methacrylamide)-b-poly(diacetone acrylamide)-b-poly(N,N-two methacrylamide).The NIR spectra of 20 wt%copolymer water dispersion during heating(30-50?)and cooling(50-30?)process were collected by transmission mode.The NIR spectra of water in the copolymer water system measured at different temperatures were analyzed by difference spectra analysis and PCA analysis,and the change of absorption intensity of second derivative spectra of NH bonds in amide groups with temperature was analyzed.The results show that both the structure of water and the absorption strength of NH bond have a response to the sol-gel transition process,and their temperature response ranges are consistent during the heating process,which can be used to judge the sol-gel transition process.The consistency of the response range of structure of water and NH to sol-gel indicates that water and polymer have a synergistic effect during the sol-gel transition process,and this effect could be mainly due to the change of water solvation effect on the polymer during the transition process.