Preparation Of Water-borne Coatings Employed On The Lower Surface Energy Substrates Through Complexation Of Polymer Latexes

On the principle of environmental protection, energy saving and efficiency, it is important to develop water-borne coatings employed on low surface energy substrates. In this study, two component latexes with chemically complementarystructure, containing OH groups and (H3C)C-O- groups respectively, were prepared through emulsion polymerization. The complex latexes were obtained by mixing two component latexes with different proportions. The structure and properties of the component latexes and the complex latexes, as well as the coatings obtained form the component latexes and the complex latexes were studied. In addition, the cohesive action of latexes on the substrates was probed.The observations of the structure and morphology of the particles of the two component latexes by transmitting electron microscope (TEM) show that, thesize of particles of the latex containing -C-OH groups is smaller than that ofparticles of the latex containing(H3C-)C-O- groups, and that the shape of particlesof the former is more regular than that of particles of the latter. The properties of the obtained polymer latexes and the complex latexes were investigated by means of surface tension, contact angle and viscosity measurements. The results indicate that the interactions between functional groups of the latex particles decrease thecontent of bare -C-OH groups, resulting in a decrease of the surface tension ofthe complex latexes, and that the wettability of the complex latexes on suchsubstrates as polyethylene, polyester and glass are better than that of the component latexes on the same substrates, and that the viscosities of the complex latexes can be higher or lower than that of the component latexes, depending greatly on interparticle interactions and interactions between the latex particles and the continuous phase.The structure of coatings obtained from the latexes was analyzed by X-ray photoelectron spectroscopy (XPS), scanning probe microscope (SPM) and infrared spectrum (IR). The outcomes show that, polysiloxane enrichment on the surface of coatings obtained from the complex latexes is lower than that on the surface of coatings obtained from the component latexes, and that the latexparticles of coatings obtained from the complex latexes are interlinked, hencethere are more -C-O- groups on the surface of coatings obtained from thecomplex latexes, and that the stretching peak of -OH and > C=O groups move to lower wave-number directions. Using the method of harmonic equation, the values of the surface energy of the coatings were obtained by measurement of the contact angles of the H2O and CH2I2 on the coatings. The surface energy of the tested coatings is lower than 35mN/m. For the certain latex, the surface energy of the coatings formed on the polyethylene substrate is higher than that of the costings formed on the glass substrate. The effects of interaction of interparticles with complementary structure on the mechanical properties and water-resistibility of the coatings obtained from the latexes were investigated by tensile strength and water-absorption measurements. The water-resistibility of the coatings obtained from the complex latexes is better than that of the coatings obtained from the component latexes. The interaction of latex particles with chemically complementary structure may improve the tensile strength of coatings obtained from the complex latexes and maintain the higher elongation at break at the same time.