The relationship between nanosilica dispersion degree and the tensile properties of polyurethane nanocomposites
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ORIGINAL CONTRIBUTION
The relationship between nanosilica dispersion degree and the tensile properties of polyurethane nanocomposites Leonel M. Chiacchiarelli & Ivan Puri & Debora Puglia & José M. Kenny & Luigi Torre
Received: 11 April 2013 / Revised: 21 May 2013 / Accepted: 18 June 2013 # Springer-Verlag Berlin Heidelberg 2013
Abstract The tensile properties and structure of silica-based polyurethane (PU) nanocomposites were parametrically studied as a function of silica type and weight concentration, polyol OH number, and mixing methods. The variation of the silica functionalization groups (from silanols to silazanes) had a relevant effect on dispersion. An elevated interparticle distance of the silica agglomerates improved substantially the tensile strength (from 44.3 to 82.8 MPa) and strain to failure (from 3.0 to 7.95) while maintaining elastic modulus (from 2.08 to 2.31 GPa) with respect to the neat PU matrix. Polyol’s with different OH numbers have shown to dramatically modify the silica dispersion degree by the modification of the stability of the colloidal dispersion. An increase of its value deteriorated dispersion and the tensile properties of the nanocomposites. The effect of three dispersion methods (ultrasonic dispersion, high shear mixing, and tip sonication) has shown to have a relative effect on the reduction of agglomerate size and the interparticle distance. High power sonication methods were more effective in reducing agglomerate size in contrast to shear methods. Classical theories of colloidal dispersion (Derjaguin, Landau, Verwey, and Overbeek) have been able to explain the correlation between the silica aggregation state and the final tensile properties of the nanocomposite.
L. M. Chiacchiarelli : I. Puri : D. Puglia : J. M. Kenny : L. Torre (*) Civil and Environmental Engineering Department, University of Perugia, Strada di Pentima 4, 05100 Terni, Italy e-mail: [email protected] J. M. Kenny Institute of Polymer Science and Technology, CSIC, Juan de la Cierva 3, 28006 Madrid, Spain
Keywords Silica nanocomposites . Thermoset polyurethane . Polyol OH number . Dispersion method
Introduction The development of silica-based nanocomposites has been intensified in the last 20 years. The extremely high interfacial area of the silica nanoparticles have attracted the scientific community to investigate their insertion into epoxy, phenolic, polyester, polyurethane and other polymeric matrix systems. Even though substantial research has been performed, there is no general agreement in the structure and properties relationships for those newly developed nanocomposites. Research associated to silica polyurethane nanocomposites has been extensive [1–21]. This is mainly because of the enormous flexibility of polyurethanes (PU), with formulations than can be used for thermosets, thermoplastics, elastomers, coatings, foams, and other applications [22–24]. In addition, the biphasic microstructure of polyurethanes (hard and soft segments) also diversifies the scene. Hence, it can be inferred that a general
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