Mechanical properties of titanium dioxide-filled polystyrene microcomposites Thomas P. Selvin a , Joseph Kuruvilla b , Thomas Sabu a, * a School of Chemical Sciences, Mahatma Gandhi University, Priyadarsini Hills P.O., Kottayam, Kerala 686560, India b St. Berchman’s College, Changanacherry, Kottayam, Kerala, India Received 2 April 2003; accepted 30 April 2003 Abstract Microcomposites of polystyrene with different loading of titanium dioxide fillers were prepared by melt mixing in a brabender plasticorder at a rotor speed of 60 rpm. The mechanical properties of the composites such as tensile behaviour, impact strength and flexural behaviour were studied as a function of filler loading. The tensile moduli of the composites were increased with titanium dioxide content. Tensile strength first showed an increase followed by a decrease at higher loading. To improve adhesion between the filler and the matrix an amino silane coupling agent has been used. The composites with coupling agent showed enhanced mechanical properties. In order to understand the filler dispersion and filler/matrix interaction, the fracture surfaces were examined under SEM. Finally, experimental results were compared with theoretical predictions. D 2003 Elsevier B.V. All rights reserved. Keywords: Polystyrene; Microcomposites; Mechanical properties; Particulate fillers; Titanium dioxide 1. Introduction An important attribute of polymers is the ability to modify their inherent physical properties by the addition of fillers while retaining their characteristic processing ease. Polymers can be coloured, made stronger, stiffer, electron- ically conductive, magnetically permeable, flame retardant, harder, and more wear resistant by the incorporation of various additives. Most of these modifications are made by the addition of inorganic fillers to the polymer. These fillers, present in varying degrees, also affect the basic mechanical properties of the polymer. In many cases, the changes in the mechanical properties of the filled polymer can be predicted from basic principles. In other cases, the property changes must be experimentally measured, because there is not much sufficient knowledge about the polymer – filler interactions to calculate the effect of filler concentration on property changes. By principle, polymer composite is a combined material created by the assembly of two or more components, viz., selected filler or reinforcing agent and a compatible matrix in order to obtain specific characteristics and properties. The components offer often the properties that neither constitu- ent has. The components of a composite do not merge completely into each other but nevertheless they do act in concert and are divided generally by direct boundaries. These components as well as the interface between them can usually be physically identified, and it is this behavior and properties of the interface that generally control prop- erties of the composite. The properties of a composite cannot be achieved by any of the components acting alone. For obtaining the optimal properties in composites, their components have to be chosen so as to have sharply different but complimentary properties [1–8]. There is a large body of literature that discusses the mechanical property behaviour of filled polymer systems [9–14]. These reports reveal that the modulus is the easiest mechanical property to estimate, because it is a bulk property that depends primarily on the geometry, modulus, particle size distribution and concentration of the filler. The tensile strength of a filled polymer is more difficult to predict because it depends strongly on local polymer – filler interactions as well as the above factors. A number of in- vestigators have shown that two general tensile strength – 0167-577X/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0167-577X(03)00470-1 * Corresponding author. Tel.: +91-481-2730003, +91-481-2731036; fax: +91-481-561190. E-mail address: sabut@vsnl.com (T. Sabu). www.elsevier.com/locate/matlet Materials Letters 58 (2004) 281 – 289