https://doi.org/10.15255/KUI.2004.018
Published: Kem. Ind. 54 (1) (2005) 1–9
Paper reference number: KUI-18/2004
Paper type: Original scientific paper
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Nanocomposite Poly(vinyl acetate) and Polyurethane Materials

S. Lučić Blagojević, V. Kovačević, M. Leskovac and D. Vrsaljko

Abstract

In this paper results of the calcium carbonate nanofillers and microfillers addition, as well as influence of the filler surface pre-treatment with stearate and with γ-aminopropyltrietoxysilane (AMPTES) on the properties of the poly(vinyl acetate) and polyurethane composite films respectively, are presented. The results indicate that morphology, failure and mechanical properties differ significantly depending on the type of fillers i.e. on the size on the filler particles and filler surface pre-treatment. In the PVAc matrix the microfiller particles are distributed in the PVAc polymer matrix as the separated particles (Fig. 1A), that suppose the small amount of matrix under their influence in comparison to the great amount under the influence of nanoparticles distributed as "a net" in PVAc polymer matrix (Fig. 1C). The strong aggregation of the nanofillers primary particles, that cause the non-homogeneous filler dispersion in polymer matrix, could be a problem to nanocomposites preparation by simple mixing procedure. However, the micrographs of the PVAc and PU nanocomposites indicate that, despite of the filler aggregation, the stress transfer from the matrix/filler interface to the matrix occurs. The results of the tensile strength of PVAc (Fig. 3A) and PU (Fig. 3B) composites with micro and nanofillers indicate higher reinforcement in corresponding nanocomposites. The failure that prevailed in PVAc microcomposite, is dewetting at the interface (Fig. 1B), but cohesive failure in relevant nanocomposite (Fig. 1D). The similar behaviour is noticed in PU composites filled with CaCO3 micro and nanofiller. The filler surface pre-treatment influences the changes of surface free energy and the parameters of adhesion at the polymer/filler interface. The surface modification of the calcium carbonate nanofillers caused the changes in the morphology and failure of the PVAc/CaCO3 nanocomposites. By lowering the CaCO3 surface free energy, due to the stearate surface modification, the interactions at the interface become weaker and dewetting occurs (Fig. 4), that result in composite weakening. The all micrographs of the PU nanocomposites, filled with CaCO3 nanofillers untreated and treated one comparatively with stearate and silane coupling agents (AMPTES), indicate more homogeneous characteristic "net-like" distribution of nanocomposites. However, some signs of dewetting noticed at the micrograph of PU composites, filled with stearate pretreated nanofiller result in composite weaking (Fig. 7A). On the contrary, the more cohesive failure in PU composites with AMPTES silane pre-treated CaCO3 nanofiller is followed by the significant increase of composite strength (Fig. 7B) due to increased interactions and work of adhesion at the interface. The homogeneous nanofillers dispersion in polymer matrix and increased interactions between matrix and fillers, that could be improved by relevant filler surface pre-treatment, result in significant improvement of composite properties in comparison to the corresponding microcomposites.

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Keywords

PVAc and PU nanocomposites, calcium carbonate filler, adhesion at the interface, composite morphology, composite failure, mechanical properties