Effect of Zeolite Filler on the Thermal Degradation Kinetics of Polypropylene H. Pehlivan, D. Balko ¨se, S. U ¨ lku ¨ , F. Tıhmınlıog ˘lu Chemical Engineering Department, I ˙ zmir Institute of Technology, Urla, I ˙ zmir, Turkey, 35430 Received 18 November 2004; accepted 15 June 2005 DOI 10.1002/app.23105 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: In this study, the thermal degradation be- havior of polypropylene (PP) and PP–zeolite composites was investigated. Clinoptilolite, a natural zeolitic tuff, was used as the filler material in composites. The effects of both pure clinoptilolite and silver-ion-exchanged clinoptilolite on the thermal degradation kinetics of the PP composites was studied with differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Polymer degradation was evaluated with DSC at heating rates of 5, 10, and 20°C/ min from room temperature to 500°C. The silver concentra- tion (4.36, 27.85, and 183.8 mg of Ag/g of zeolite) was the selected parameter under consideration. From the DSC curves, we observed that the heat of degradation values of the composites containing 2– 6% silver-exchanged zeolite (321–390 kJ/kg) were larger than that of the pure PP (258 kJ/kg). From the DSC results, we confirmed that the PP– zeolite composites can be used at higher temperatures than the pure PP polymer because of its higher thermal stability. The thermal decomposition activation energies of the com- posites were calculated with both the Kissinger and Ozawa models. The values predicted from these two equations were in close agreement. From the TGA curves, we found that zeolite addition into the PP matrix slowed the decomposi- tion reaction; however, silver-exchanged zeolite addition into the matrix accelerated the reaction. The higher the silver concentration was, the lower were the thermal decomposi- tion activation energies we obtained. As a result, PP was much more susceptible to thermal decomposition in the presence of silver-exchanged zeolite. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 143–148, 2006 Key words: composites; degradation; kinetics (polym.); poly(propylene) (PP); zeolites INTRODUCTION Composites with desired properties can be achieved by the incorporation of fillers into a polymer matrix to suit various applications. Glass fibers, carbon fibers, and particulate fillers can be used as reinforcing ma- terials. The primary advantages of polymeric compos- ites are increases in stiffness, strength, and dimen- sional stability; reduced permeability to gases and liquids; and reduced cost. Polypropylene (PP) is among the most widely exploited thermoplastic poly- mers and is of increasing practical importance because of its good comprehensive use, light weight (0.9 g/cc), chemical resistance, low cost, ease of processing, and good recycling properties. It has various applications, including food packaging, medical delivery systems, carpets, fibers, protective coatings, and applications in the automobile, electrical, and furniture industries, depending on these properties. The properties of the composite materials are affected by the chemical prop- erties of the components and the nature of the inter- action between the phases. 1 Different types of zeolite minerals, either natural (e.g., clinoptilolite, mordenite, chabazite) or syn- thetic (e.g., A type, X type, Y type), have been used as particulate fillers. 2–4 All commercial zeolites owe their value to one of the following properties: ion exchange, adsorption, or catalysis. They have un- usual crystalline structures that give them unique chemical properties. For instance, in 1 g of natural zeolite, channels can provide up to several hun- dreds of square meters of surface area on which chemical reactions can take place. Natural zeolite can also absorb up to 30% of its dry weight in gases, such as nitrogen or ammonia. Studies have reported on the removal of lead, silver, and cadmium by clinoptilolite in the presence of com- peting concentrations of calcium, magnesium, and so- dium via ion-exchange processes. 5 Silver zeolites are of great importance because of their potential uses as germicidal, bactericidal, antifungal, and antiseptic components in different compositions. 6–8 Silver salts appear to meet the requirements to as antiseptic agents. The modification of an inorganic compound by the addition of silver is attractive because silver Correspondence to: F. Tıhmınlıog ˘ lu (fundatihminlioglu@iyte. edu.tr). Contract grant sponsor: Technical and Scientific Research Council of Turkey; contract grant number: MI ˙ SAG 129. Contract grant sponsor: Government Planning Institute; contract grant number: 120290 K. Journal of Applied Polymer Science, Vol. 101, 143–148 (2006) © 2006 Wiley Periodicals, Inc.