engleski

Influence of nanosilica modification on the properties of polyacrylate emulsions and films

In situ preparation is the best procedure to achieve uniform distribution of nanofillers in polymer matrix, which is one of the most important factors that determine improvement of the properties. For successful in situ polymerization of emulsion it is necessary to achieve conditions in which the polymerization process will occur around nanofiller particles. This can be achieved by using nonionic surfactant, initiator that can adsorb on nanofiller surface or using silane as coupling agent. In this work, the aim was to synthesize stable emulsions by in situ polymerization of butyl acrylate (BA) and methyl methacrylate (MMA) with colloidal nanosilica (0-15 %wt) and to investigate influence of silica addition on the properties of emulsion and films. Emulsion polymerization in presence of nanofiller is very complex since stability is influenced by many factors. In order to investigate influence of concentration and surface modification of colloidal silica filler with particle size 25 nm (K25), in situ emulsion polymerization was optimised for systems with unmodified silica surface and for systems in which silica surface is modified with nonionic emulsifier, octylphenol ethoxylate, cationic initiator 2, 2'-azobis-(amidinopropane dihydrochloride) (AIBA) and 3-methacryloxypropyltrimethoxysilane (MPS). With optimised procedure, polyacrylate/silica emulsions with 0-15 mass % of colloidal silica were prepared. Rheological behavior and particle size distribution of stable emulsions were determined, and particle morphology was analyzed using scanning electron microscope. Mechanical and thermal properties of nanocomposite films prepared from emulsions by casting method were investigated. Results indicate that modification of colloidal silica surface influence on particle size of polyacrylate emulsion. Addition and surface modification of the filler have significant influence on polyacrylate rheological properties. Systems with lower filler concentration are Newtonian fluids and systems with higher filler concentration are pseudoplastic fluids with rheopexy. Addition of colloidal silica regardless of surface modification has no influence on polyacrylate Tg. Results showed that the addition and surface modification of silica, improved thermal stability of polyacrylate matrix. Addition of colloidal silica increases strength at break of PAK matrix and slightly reduces elongation at break of polyacrylate films.

in situ polymerisation; polyacrylate emulsions; colloidal silica; particle size

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