Study On Modification Of Polyacrylate Emulsion

With the development of economy, more and more attention has paid to the environmental protection. The emission of volatile organic compounds (VOC) in the coating industry is becoming one of the most serious pollution in the world. Therefore, studies of waterbased coating with low VOC and nontoxicity have attracted considerable attention in the last decades. Polyacrylate (PA) is an important coating polymer due to its excellent photostability, weather fastness, chemical stability and good adhesive property. However, polyacrylate emulsion has some disadvantages such as low hardness, slowly drying speed, poor water-resistance, poor film-forming in low temperature, becoming pastiness in high temperature and so on, which has already limited its application in waterbased coating. So the research of waterbased polyacrylate emulsion with excellent properties has been an important topic to be solved eagerly.In this thesis, from the point of molecular structure modification, nanocomposite modification and design of latex particle, a series of polyacrylate emulsions with excellent performance were synthesized via emulsion polymerization. The main results are as follows:1. The aqueous ambient self-crosslinking polyacrylate emulsion (AACPA) was synthesized via pre-emulsified and semi-continuous seeded emulsion polymerization by using methyl methacrylate (MMA), butyl acrylate (BA), acrylic acid (AA) and diacetone acrylamide (DAAM) as monomers and adipic acid dihydrazide (ADH) as a crosslinker. As a comparison, conventional polyacrylate emulsion (CPA) was also prepared. The results of FTIR analysis and cross-linking degree test showed that crosslinking reaction between crosslinker (ADH) and functional monomer (DAAM) can been occurred at room temperature, as a result the ambient self-crosslinking polyacrylate emulsion has been prepared successfully.2. The particle size, structure and morphology of these two kinds of polyacrylate emulsions, as well as the glass transition temperature and the mechanical property of their latex films were investigated. Transmission Electron Microscopy (TEM) showed that the morphology of latex particle was less affected by the introducing of the self-crosslinking system. The result of Dynamic Light Scattering (DLS) indicated the particle size of AACPA emulsion became smaller and its particle size distribution got narrower. Differential Scanning Calorimetry (DSC) showed that Tg of AACPA latex film was higher than that of uncrosslinked CPA latex film. In addition, from the result of the tensile test, it can be seen that the mechanical properties of polyacrylate latex films had been greatly improved by the introduction of cross-linked system. Moreover, water resistance of AACPA latex film has also been improved.3. The silane coupling agent y-MPTES has been used as reagents for the chemical modification of inorganic clay Laponite platelets. The structure of y-MPTES modified inorganic clay Laponite was qualitatively determined by means of FTIR,29Si and13C solid-state NMR spectroscopies. Quantitative data (grafted amount) were also obtained by means of elemental and thermogravimetric analysis. The results showed that y-MPTES has been grafted on the surface of inorganic clay platelets, which also provided a reactive methacryloyl group that can be reacted with vinyl monomers.4. Poly(St-co-BA)/MPTES-Laponite nanocomposite emulsion was synthesized by using styrene (St) and butyl acrylate (BA) as monomers and MPTES modified Laponite clay platelets as seed. By the DLS analysis, the particle size of the emulsion was small and its distribution was narrow. DSC and TG showed that the nanocomposite polyacrylate latex films had excellent thermal properties, such as high Tg and the maximum thermal decomposition temperature (Tmax) increased more than ten degrees. By testing the contact angle and water absorption, it is proved that water resistance of the latex film was improved. In addition, the latex film showed excellent mechanical properties. When the content of MPTES-Laponite in the film was5%, the tensile strength of latex films can be increased by3times, and when the content of clay increased to10%, the tensile strength of latex films can increase nearly4times.5. Since Laponite is a cationic exchanger, organic cations can be electrostatically adsorbed onto its surface. Laponite clay particles was functionalized by ion exchange with a free radical initiator2,2-azobis(2-methylpropionamidine) hydrochloride (AIBA). The amount of AIBA adsorption on clay surface was determined by UV-Vis spectrophotometer (UV), EA and TG. In addition, the crystallization of modified clay AIBA-Laponite was analyzed by XRD, the result indicated that the regularly stacking structure of layers was formed after AIBA adsorbed on the clay.6. A series of polyacrylate emulsions with core-shell structure were prepared using AIBA-Laponite as initiator which based on St and BA as core monomer and MMA, BA and EHA as shell monomers. While the corresponding emulsion was synthesized using AIBA as initiator. TEM observation showed that latex particles with core-shell structure were successfully obtained. DSC analysis revealed that Tg of the latex films with hard-core soft-shell structure had been improved using AIBA-Laponite as initiator. TG indicated Tmax of latex film has also been increased. Thus, by the introduction of clay particles, the thermal properties of latex films had been improved greatly.