PRODUCTION OF ACRYLIC-CASEIN HYBRID LATICES BY EMULSION POLYMERIZATION

M.L. PICCHIO; N. FIGUEROA; R.J. MINARI; V.D. GONZALEZ; M.C.G. PASSEGGI(H); J.R. VEGA; M.J. BARANDIARAN; L.M. GUGLIOTTA

Cancun

Conferencia; Polymer Reaction Engineering VIII; 2012

Engineering Conferences International (ECI)

Natural proteins -such as caseins- were widely used for long time in paper coatings, adhesives, glues, and paint binders, because of their reduced environmental impact, high degradability, good stained acceptance, finishing glazed aspect and good paper penetrability. However, casein films present a low wet rub resistance, are susceptible to microbial attack, and exhibit poor mechanical properties (brittleness). For these reasons, caseins have been replaced in many applications by synthetic polymers, which provide better mechanical properties though resigning the good penetration and adhesion to polar substrates, and the low environmental impact typically offer by natural products. In this work the synthesis of hybrid acrylic-casein latices is considered with the aim of improving the properties of the natural substance by incorporating acrylates as a second synthetic material. An adequate balance between the application properties of caseins and acrylic polymers is achieved when they form a compatible system; and for this reason, the extent of casein incorporation to the acrylics (casein degree of grafting, CDG), is a key variable to develop a successful polymerization strategy. Several kinetic results are presented after evaluating different polymerization conditions, initiator type and concentrations, casein contents, and monomer formulations. The use of hydroperoxide initiators (instead of thermal initiators) allows the initiation of the polymerization on the protein amino groups, and therefore the casein incorporation becomes increased. Also, the kinetic emulsion polymerization is affected at high casein concentration, giving place to a constant hybrid particle nucleation up to the end of the reaction. AFM and TEM were employed to observe the core-shell particles and the nanostructure films; and an ad-hoc analytical procedure was proposed to evaluate the CDG.