Mechanism of Film Formation of Acrylic Core-Shell Latex

Proper core-shell structure endows latex film with excellent performance. The mechanism of film formation of a core-shell latex is more complicated compared to normal latex due to its unique structure. And the film formation of core-shell latex is influenced by monomer, core-shell ratio, structure etc. In this paper, film formation process of acrylic and styrene-acrylic core-shell latex was studied. The influence of latex structure on film formation and film performance was discussed.P(St-co-BA)/P(MMA-co-BA) core-shell latex and PMMA/PBA core-shell latex were synthesized by two-step semi-continuous emulsion polymerization under starving conditions. As confirmed by TEM, The synthesized latex has a core-shell structure. By weight analytical method the drying rate curve of an acylic core-shell latex was established, results show that either solid content, film forming aid or core-shell ratio has an impact on drying rate. Either film formation process or film morphology of normal latex and core-shell latex was studied by means of TEM and AFM. The influence of latex structure and core-shell ratio on film morphology and performance was discussed, the results revealed that the film formation process of an core-shell latex is similar to that of a normal latex. When drying the shell of a core-shell latex was deformed while its core maintained its initial shape. It is easier for a core-shell latex to deform and interdiffuse to form a smooth film when the core-shell ratio was less than 2/3, the smaller the core-shell ratio is, the easier for a core-shell latex to form a film. In addition, a core-shell latex was tending to form a compact film with better performance compared to a latex blend. To study the effect of film forming aid, a series research work was carried out. Results showed that the smaller the distribution coefficient of a film forming aid is, the better effect it has. Meanwhile the better the compatibility between a film forming aid and a latex polymer is, the worse it inflicts on the emulsion stability. Furthermore, the adding way of a film forming aid also influenced the emulsion stability. By means of Goh model, the diffusion coefficient of the latex polymer was calculated, result showed that the diffusion coefficient added as the content of the film forming aid increased.