SLAP 2012. 23-26 Septiembre de 2012, Bogotá D.C., Colombia. 1 Influence of coupling agents on melt rheological properties of wood flour polypropylene composites Matheus Poletto 1,2* , Janaína Junges 1 , Ademir J. Zattera 1 , Ruth M. C. Santana 2 1: Laboratório de Polímeros, Universidade de Caxias do Sul. Caxias do Sul, Brasil 2: Escola de Engenharia, Universidade Federal do Rio Grande do Sul. Porto Alegre, Brasil * matheus.poletto@hotmail.com Abstract Melt rheological properties and activation energy to flow of wood flour reinforced polypropylene composites were studied by using a melt flow indexer in a temperatura range of 180-220°C. The addition of wood flour into the polymer matrix reduces the melt flow index probably due the restrictions imposed by the wood particles to polymer flow. Coupling agents tend to increase the melt viscosity, but wall slip effects may interfere in the measured values. The dependence of melt viscosity obeyed the Arrhenius-Eyring expression, and the activation energy values of the composites developed were higher than polymer matrix. Keywords: Wood, Polypropylene, Coupling agent, Rheological properties, Flow activation energy. Section: Nanomaterials, nanocomposites and other polymeric composites 1 INTRODUCTION The use of lignocellulosic materials for reinforced polymeric composites is of great interest due to the inherent advantages of lignocellulosic reinforcements (González-Sánchez et. al, 2011, Li et. al, 2004). These reinforcements show low density, low abrasion of processing equipment, reduced health hazard and in addition are renewable and biodegradable (Li et. al, 2004, Poletto et. al, 2011). Due to such advantages lignocellulosic-reinforced thermoplastic composites materials are an emerging research and development area and the object of several applications in the automotive, construction and aerospace industries (González-Sánchez et. al, 2011, Li et. al, 2004). However the use of lignocellulosic fibers in polymeric composites shows some drawbacks such as degradation at relatively low temperatures and low compatibility between the hydrophilic character of the polar lignocellulosic filler and hydrophobic character of the non-polar polymer matrix (Poletto et. al, 2011). Maleic anhydride-grafted thermoplastic polymers are the most common coupling agent used to improve the interfacial adhesion between lignocellulosic fillers and a thermoplastic polymer matrix (Sain et. al, 2005, Yuan et.al, 2008). Nevertheless, some coupling agents may provide some lubrication effects during processing. The manufacture of end products using thermoplastic composites requires their melting and flow through the plastic processing equipments such as extruders and injection molding machines (González-Sánchez et. al, 2011, Li et. al, 2004). In order to obtain end products with a good performance a suitable engineering design of the polymer processing unit operations involved requires as well as the choice of adequate processing parameters (González-Sánchez et. al, 2011). Wood flour particle size, wood flour content and coupling agent treatment influence on the rheological properties of wood flour composites (Adhikary et. al, 2011). Using capillary rheometry Li and Wolcott studied the rheology of high-density polyethylene (HDPE)/maple flour/MAPE/lubricant composite with varied wood flour content and particle size (Li and Wolcott, 2006). It was reported that wood flour content, rather than particle size changed the melt viscosity significantly and MAPE acts was a lubricant in HDPE/maple composites. For this purpose, the knowledge about the melt flow behavior of these composites used in several polymer processing operations is necessary. In order to better understand such behavior, the aim of this work was evaluated the influence of two coupling agents from renewable and nonrenewable source on the melt flow index and flow activation energy of wood flour polypropylene composites. 1.1 Theoretical background An understanding of the mechanism of the polymer flow process in relation to the nature and composition of the material can be elucidated by a study of the temperature dependence of shear viscosity (Shenoy, 1999). The Arrhenius-Eyring equation is used to express the temperature dependence of shear viscosity, as can be seen in equation 1: