Strategies to enhance compatibility without affecting oxidative curing on waterborne alkyd/acrylic hybrids

GOIKOETXEA, MONIKA; MINARI, ROQUE J; BERISTAIN, ITXASO; PAULIS, MARÍA; BARANDIARAN, MARÍA J.; ASUA, JOSÉ M.

Glasgow

Congreso; MACRO 2010 43rd IUPAC Word Polymer Congress; 2010

IUPAC

Research on hybrid latexes has gained a lot of interest in the last years, because it is an opportunity for developing new products, based on the synergistic effects of the compounds. Particular attention has been paid to alkyd/acrylic hybrid latexes. For many decades, alkyds have been used as binders for coatings, due to advantageous properties such as high gloss, good penetration in wood and the hardness that can be achieved by oxidative curing. However, most of them need to be dissolved in organic solvents to be applied. Due to the stricter environmental legislation, the traditional long oil alkyd will likely disappear in the near future. Further, those resins are based on vegetable oils, a renewable source. Therefore, the use of alkyds is as an opportunity for the reduction of the dependence on the oil-based products. On the other hand, acrylic latexes present quick curing, easy water clean-up and colour retention, among others. However alkyd resins and acrylic polymers are not compatible, and therefore, they are prone to suffer phase separation that results in haziness and lower gloss. The challenge in this kind of materials is to compatibilize them. This requires intimate contact between both materials, which can be achieved by grafting of the acrylic onto the alkyd resin. Miniemulsion polymerization was used for achieving a good compatibilization, because alkyds are present in the polymerization loci and graft alkyd-acrylic copolymer may be formed. This graft copolymer acts as compatibilizer between the pure polyacrylate and the free alkyd that can be present inside the particles. Grafting can occur by radical addition on the alkyd carbon-carbon double bonds and by abstraction of allylic hydrogens. Addition is energetically favoured over abstraction, but this process yields an important reduction of the unsaturated groups of the alkyds, resulting in the deterioration of the autooxidative properties of the alkyds. In this work, routes to improve the compatibility between the alkyd and acrylic in an aqueous dispersion, without affecting alkyd double bonds will be presented. Further, the effect of the increased compatibilization on the particle morphology, which strongly influences the properties of the hybrid materials such as gloss and film homogeneity, will be discussed. In all the cases, 50% solids content acrylic/alkyd (50/50 %wt) hybrid latexes were synthesized.