Effects of Vinyltrimethoxy Silane on Thermal Properties and Dynamic Mechanical Properties of Polypropylene–Wood Flour Composites Rebeca Bouza, 1 Aurora Lasagabaster, 2 Marı ´a Jose ´ Abad, 1 Luis Barral 1 1 Grupo de Polı ´meros, Departamento de Fı ´sica, E.U.P.-Ferrol, Universidad de A Corun ˜a, s/n. 15405 Ferrol; Spain 2 Departamento de Quı ´mica Orga ´nica I. Escuela de Optica, Universidad Complutense de Madrid (UCM), Arcos de Jalo ´n, s/n. 28037 Madrid, Spain Received 26 September 2007; accepted 22 January 2008 DOI 10.1002/app.28159 Published online 15 April 2008 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: The viability of vinyltrimethoxy silane was investigated as a coupling agent for the manufacture of wood–plastic composites (WPC). The effect of silane pre- treatment of the wood flour on the thermal and the dynamic mechanical properties and thermal degradation properties of the composites were studied. Moreover, the effect of orga- nosilane on the properties of composites was compared with the effect of maleated polypropylene (MAPP). DSC studies indicated that the wood flour acts as a PP-nucleating agent, increasing the PP crystallization rate. In general, pretreat- ment with small amounts of silane improved this behavior in all the WPCs studied. Thermal degradation studies of the WPCs indicated that the presence of wood flour delayed degradation of the PP. Silane pretreatment of the wood flour augmented this effect, though without significantly affecting cellulose degradation. Studies of dynamic mechanical prop- erties revealed that the wood flour (at up to 30 wt %) increased storage modulus values with respect to those of pure PP; in WPCs with a higher wood flour amount, there was no additional increase in storage modulus. Pretreatment of the wood flour with silane basically had no effect on the dynamic mechanical properties of the WPC. These results show that with small amounts of vinyltrimethoxy silane similar properties to the MAPP are reached. Ó 2008 Wiley Periodicals, Inc. J Appl Polym Sci 109: 1197–1204, 2008 Key words: wood flour; coupling agent; polypropylene; DMA; morphology; crystallization INTRODUCTION In recent years, agrowastes and agroforest materials have attracted great interest in the reinforced plastics market. 1,2 Fillers of this type are very cheap and readily available. The use of woody materials as reinforcement in thermoplastics offers numerous advantages, including low cost, low density, and rel- atively high strength and stiffness. 3–6 However, the poor compatibility between hydrophilic natural fill- ers and the hydrophobic polymers used as matrix may have adverse effects on the final properties of the composite: the polarity of the filler affects its dis- persion in the nonpolar matrix, 7,8 and poor adhesion may lead to composites with rather poor durability and toughness. 9,10 The use of a coupling agent or ‘‘compatibilizer’’ may improve adhesion between the filler and the matrix, and thus enhance the mechani- cal properties of the composite. The most commonly used coupling agents are the maleated polyole- fins, 9,11,12 isocyanates, 13,14 and various organosi- lanes. 15,16 There have been several studies 17,18 about the use of organosilanes as coupling agents in wood flour (WF) composites, but the effectiveness of a given organosilane depends strongly on its organic group, so that the influence of each organosilane on composite properties needs to be characterized indi- vidually. In this study, a vinyltrimethoxy silane was evaluated as coupling agent for polypropylene (PP)– WF composites. The silane crosslinking reaction takes place in the presence of water. This reaction proceeds over two steps. In the first step, the methoxyl groups are hydrolyzed to hydroxyl groups with production of methanol. The crosslinking takes place in the second step, in which the hydroxyl group is recombined through condensation. 19 The reaction between the silanol groups (SiÀÀOH) and hydroxyl groups of the wood creates covalent bonds, so that the vinyl group may be either chemically bonded to the PP matrix (covalent CÀÀC) or may interact with it through van der Waals forces. The aim of this study was to evaluate and explain the influence of vinyltrimethoxy silane on the ther- mal and dynamic mechanical properties of PP-WF Correspondence to: L. Barral (labpolim@udc.es). Contract grant sponsor: Secretarı ´a Xeral de Investigacio ´n e Desenrolo, Xunta de Galicia; contract grant number: XUGA-PGIDIT05TMT17201PR. Journal of Applied Polymer Science, Vol. 109, 1197–1204 (2008) V V C 2008 Wiley Periodicals, Inc.