Vera Kovačević

Molecular and Morphological Characterization of Immiscible SAN/EPDM Blends Filled by Nano Filler

The compatibilizing effect of nano sized calcium carbonate filler on immiscible blends of styrene-co-acrylonitrile/ethylene propylene diene (SAN/EPDM) was examined. The surface energy of the calcium carbonate was modified by stearic acid. The compatibility of SAN/EPDM blends was studied by following the glass transition temperature T g by DSC. SEM was used to observe the blend morphology and the X-ray analyzer was used to detect the calcium from filler in samples. Mechanical properties of the blends were determined, and related to changes of polymer-filler interactions and morphology. The results suggest that the morphology of the SAN/EPDM blends studied was affected by the reduction of surface energy of the filler.

Role of the polyurethane component in the adhesive composition on the hydrolytic stability of the adhesive

Abstract In polyurethanes based on linear polyol, isocyanate and a chain extender, the physical morphology of adhesive seems to play an important role in its overall strength characteristics. The aim of this paper is to examine how the morphology and phase separation of such polyurethane components affect the adhesive properties before and after hydrolysis. It is shown that effective microphase separation and the development of hydrogen-bonded structures, as well as hydrolytic events in the hard segment domains, depend strongly on the adhesive composition. The influence of the environment on polyurethane adhesives can be countered by proper selection of the polyurethane component.

Influence of filler surface pre-treatment on the mechanical properties of composites

Abstract Poly(vinyl acetate) (PVAc) composites in the form of films were prepared with CaC03 fillers of different specific surface area. The fillers were commercially surface-treated with stearic acid. Acid-base interactions were found to exert a dominant influence on calcite dispersions in the PVAc matrix. The mechanical properties of these composites varied with the acid-base forces acting at matrix/filler contacts. The relationship between interfacial interaction and composite mechanical properties was analysed by an equation describing the composition dependence of the tensile stress. Attention is focused on the elongation at break and the tensile strength, where the effect of surface conditioning becomes important. Mechanical property modifications are functions not only of the quantity of filler added, but also of the dispersion quality and adhesion at polymer/filler interfaces.

Tensile properties of calcium carbonate-reinforced poly(vinyl acetate)

In certain applications, a reinforced composite is used as an adhesive layer. In this study, the bulk mechanical behaviour of composite films based on a poly(vinyl acetate) (PVAc) matrix and various calcium carbonate (CaCO3) fillers was investigated. The interactions depend on the morphology and chemical structure of the filler and the polymer matrix. The polar natures of both PVAc and CaCO3 have a strong influence because of acid-base interactions. The tensile properties of PVAc/CaCO3 composites showed an increase in strength at break with increased filler concentration. The interactions can be modified by surface pretreatment of CaCO3 with stearic acid, which lowers the surface interaction and changes the degree of filler dispersion in the PVAc matrix. Micrographs confirmed the tendency of small CaCO3 particles to agglomerate and as a consequence, discontinuity of the composite film is observed. An effective surface treatment reduced the particle agglomeration tendency, which improved the film elongatio...

Mechanical properties of adhesive thin films

In this paper, a poly(vinyl acetate) (PVAc) adhesive in the form of a film was considered to be a composite. Its mechanical properties changed with filler addition owing to the interactions at the polymer/filler interface. The experimental results were fitted with various theoretical and empirical equations that describe the dependence of mechanical properties on filler volume fraction. In this way, the coefficients calculated from the mostly empirically broadened equations for the case of adhesion between the matrix and filler gave the opportunity to determine the interactions between the PVAc matrix and various fillers quantitatively.

Effect of calcium carbonate particle size and surface pretreatment on polyurethane composite Part I: interface and mechanical properties

Abstract In the present paper, the changes at interface between calcium carbonate (CaCO3) and polyurethane (PU) matrix in correlation to the mechanical and morphological properties were investigated. The effect of the untreated CaCO3 microfillers versus nanofillers and/or selected silane pretreatment of nanofiller surface were followed. Correlation between the calculated adhesion parameters i.e. interfacial free energy, thermodynamic reversible work of adhesion and coefficient of wetting, based on the measured surface free energies of pure components using the contact angle method, and composite properties was made. The lower surface free energy of the micro CaCO3 filler than the surface energy of the unmodified and silane modified nanofillers resulted in lower work of adhesion for PU/micro CaCO3 than for the PU/nano CaCO3 composites. These results implied weaker interactions in PU/micro CaCO3 than in the PU/nano CaCO3 composites followed by the lower tensile strength and failure at the interface.

Investigation of the Influence of Fillers on the Properties of Poly(vinyl acetate) Adhesives

The properties of poly(vinyl acetate) compositions prepared as potential wood adhesives were investigated. The paper presents the results of the influence of various kinds of inorganic fillers based on calcium carbonate and alumino-silicate and an organic filler, starch, on the adhesive composition properties. The comparison among rheological behavior of the adhesive dispersions concerning the specific role of fillers were made. Mechanical and relaxation properties of the adhesive films could reveal the effect of filler characteristics on the polymer matrix. The significant influences of particle size distribution and specific surface area on the poly(vinyl acetate) adhesive composition were determined, along with other filler characteristics.

Morphology and failure in nanocomposites. Part II: surface investigation

Polymer composites filled with calcium carbonate (CaCO3) nanofillers (<100 nm), and kaolin filler of layered structure, both well suited to create nanocomposites, were analysed. The aim of this study was to investigate the influence of surface properties of the filler and matrix on the adhesion parameters at the interface in composites. The inverse gas chromatography, contact angle and capillary measurements were used for the surface characterization of filler and matrix. Although these methods are based on different assumptions, we found the same trends in the effects of filler surface treatment and/or matrix chemical structure on the changes in the dispersive and polar components of the surface energy. The energetics of the filler and matrix was varied in order to investigate the work of adhesion, interfacial energy and coefficient of spreading, and their influence on the composite properties. We found that the surface treatment of calcium carbonate filler lowered the filler surface energy and the work of adhesion in the composite with poly (vinyl acetate) matrix. The mechanical, thermal and morphological properties of the composite with treated CaCO3, measured in the first part of this paper, indicated a weak and thin interphase. In the composite with kaolin filler the higher interaction with the polyacrylate copolymer matrix based on styrene as compared to the one based on methyl methacrylate, was confirmed by the higher work of adhesion in the interphase, resulting in a stronger reinforcing of the composite.

Silane pre-treatment of calcium carbonate nanofillers for polyurethane composites

Abstract In this work we have investigated the effects of CaCO3 nanofiller pretreatment on the properties of polyurethane (PU) composites prepared by a mixing procedure. The aim was to enhance interactions at the matrix/filler interface and to improve the distribution of the filler in the polyurethane matrix. CaCO3 nanofiller was treated with two different functional trialkoxysilanes, viz. γ-aminopropyltriethoxysilane (AMPTES) and γ-glycidoxypropyltrimethoxysilane (GPTMS). Fourier transform IR spectroscopy of the pre-treated CaCO3 surface indicates that AMPTES formed a high-molecular-weight ladder-type structure on the CaCO3 surface, while GPTMS was adsorbed in the form of a lower-molecular-weight oligomeric structure. Increased ultimate tensile strength and elongation were obtained for PU + CaCO3 nanocomposites with silane pre-treated filler. This can be explained as the consequence of better stress transfer through the composite, observed on scanning electron micrographs, due to an improved adhesion between PU matrix and silane-treated fillers. The reinforcement effect is more pronounced for PU composites with aminosilane-treated CaCO3 filler in comparison to filler treated with glycidoxysilane.

Effect of preparation on morphology-properties relationships in SAN/EPDM/PCC composites

Mechanical and morphological properties of composites containing styrene—acrylonitrile (SAN) copolymer, ethylene— propylene—diene (EPDM) polymer, and different types of precipitated calcium carbonate (PCC) were investigated and their properties were analyzed in regard to PCC surface properties and the way of sample preparation (with or without use of a masterbatch (MB)). Contact angles of test liquids on PCC samples were measured in order to determine surface free energies of filler and to predict strength of filler—polymer interactions. Filler—polymer interactions play a significant role in determining preferential localization of the filler in the composite. The tensile and impact strength results of the composites without the MB show much higher values than composites prepared with the MB. Significant decrease of tensile strength is observed for the samples prepared with the MB due to change in morphology, which is elongated dispersed EPDM particles in SAN matrix, compared to the samples prepared without the MB that have droplet morphology.