Synthesis And Properties Of The Polyacrylate Soap-free Emulsion With A Core-shell Structure

Polycrylate emulsion has widely applied in coatings industry due to its heat-resistance, light-resistance and age-resistance, etc. However, common polyacrylate emulsion has some disadvantages such as poor water-resistance, poor film-forming in low temperature, becoming pastiness in high temperature, polluting environment with emulsifier and so on. So a new polyacrylate emulsion with a core-shell structure was synthesized by the technology of soap-free seeded emulsion polymerization, using oligomer of poly(butyl acrylate/sodium acrylate) (P(BA/AANa)) as an emulsifier. The results showed that the emulsion had higher solid contents, lower viscosity, good storage stability and excellent comprehensive performance of film, which could be used as coatings of degradable snack box. The oligomer was synthesized by using potassium persulfate (KSP) as initiator,butyl acrylate(BA) and acrylic acid (AA) as comonomers. The synthesis conditions of the oligomer were determined by researching the main effects on its performance: monomer/water 1/5; BA/AA 4/6 (mass ratio); reaction temperature 70±1℃; the amount of KPS 0.8%; the amount of dodecyl thioalcohol (DDM) 1.0%; pH value 7-8. The result of surface tension was that 10% of the oligomer was critical micelle concentration(the CMC was 8×10^-2g/ml). On the basis, the effects ( such as core-shell monomer ratio, the amount of oligomer, initiator, AA and crosslinking agent, reaction temperature, the feeding method of shell monomer, etc.) on emulsion and film performance were studied. The reaction conditions of the emulsion were determined: the feeding method of shell monomer was starved semi-continuous; the mass ratio of core-shell monomer 1/1; the amount of oligomer 8%; the amount of KPS 0.8%; reaction temperature 75±1℃. As a result, the emulsion with higher solid contents and lower viscosity was obtained, which didn't delaminate over a half-year period of storage. It could form bright and transparent film in room temperature with good resisting viscidity and adhesive force of 0 grade. The contents of AA, which greatly affected on water-resistance and adhesive force of film, were 2% of gross monomers. A little crosslinking agent divinyl benzene(DVB)in the core could reduce water absorptivity and greatly improve water-resistance. Orthogonal experiments resulted that the film with good water-resistance could resist especially 90 ℃water over one hour. The morphology of emulsion particles was characterized by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), infrared spectroscopy(IR), etc, which indicated that the core-shell particles were uniform in size but bigger than those of the core particles. It also verified that the polymer particles had core-shell structure.