Modification of Eucalyptus Pulp Fiber Using Silane Coupling Agents With Aliphatic Side Chains of Different Length Rafael Farinassi Mendes, 1 Lourival Marin Mendes, 2 Juliano Elvis de Oliveira, 1 Holmer Savastano Junior, 3 Gregory Glenn, 4 Gustavo Henrique Denzin Tonoli 2 1 Engineering Department, Federal University of Lavras/UFLA, 37200-000, Lavras, Minas Gerais, Brazil 2 Department of Forest Sciences, Federal University of Lavras/UFLA, 37200-000, Lavras, Minas Gerais, Brazil 3 Department of Bio-systems Engineering, Faculdade de Zootecnia e Engenharia de Alimentos, Universidade de S ~ ao Paulo (USP), Avenida Duque de Caxias Norte, 225, Pirassununga, S ~ ao Paulo 13635-900, Brazil 4 Bioproducts Research Unit, WRRC, ARS-USDA, Albany, California 94710 The objective of this work was to evaluate the effect of three silane coupling agents with different aliphatic chain lengths on the hydrophobicity of eucalyptus pulp fiber. The three silanes coupling agents used (isobutyltrimethoxysi- lane, methyltrimethoxysilane, and n-octyltriethoxysilane [OTES]) were each tested at three concentrations. Scanning electron microscopy coupled with energy dis- persive spectroscopy revealed that the silane coupling agents markedly increased the Si content of the treated fibers. The Si distribution was not completely homogenous but was abundant in the treated samples. The treated fibers had higher contact angles for water and lower moisture adsorption than the control. Of the coupling agents tested, OTES treated fibers had the highest moisture resistance. This was likely due to the greater chain length of the aliphatic side group coupled to OTES. The use of silane coupling agents with alkyl side chains could improve the functional properties of pulp fiber and increase its compatibility with hydrophobic polymers. POLYM. ENG. SCI., 55:1273– 1280, 2015. V C 2015 Society of Plastics Engineers INTRODUCTION The use of plant fibers in developing new and inexpensive reinforced composite materials has been recently emphasized [1–3]. Composites made with plant fibers have outstanding mechanical properties and they address current environmental concerns by increasing the renewable content of materials. Plant fibers are widely available from wood, crop commod- ities, and crop residues. Some examples of the abundant and common plant fiber sources include wheat straw [4], cotton [5], sugar-cane bagasse [6], bamboo [7, 8], sisal [9], coconut [10], soybean [11], banana plant residues [12], hemp [13], and wood [14, 15]. Plant fibers have several attractive properties such as their low density, high specific strength, non-abrasiveness, non- corrosive nature, ease of separation, and their broad availability at a low cost [3–16]. In addition, they are completely renewable and can be found with a range in length, aspect ratio, and mor- phology. All these properties make them useful for many appli- cations such as in polymer composites or fiber-reinforced cement products [16–20]. In spite of their useful properties, broader use of plant fibers is limited by their hydrophilic nature. Most commodity poly- mers are hydrophobic and are not compatible with plant fibers [21]. In the case of fiber-cement products, fibers within the cement matrix can shrink and swell when exposed to moisture. This can result in a loss of adhesion between the cement matrix and the fiber surface and, consequently, a loss of strength and durability in fiber-cement composites [22, 23]. Surface modification of plant fibers has been used to improve the adhesion between fibers and hydrophobic matrices. Vinyl monomers, anhydrides, isocyanates, and silanes are among the chemicals used for chemical modification of plant fibers. Modification of glass fibers with silanes is a well-known practice for improving the strength of glass fiber composites [24]. Silanes are prepared with a nonhydrolyzable organic radi- cal that improves compatibility of glass fibers with organic res- ins and polymers and improves bonding. Silanes contain hydroxyl groups that form by hydrolysis. The silanes chemi- cally bond to the surface of glass fibers by condensation of hydroxyl groups on the glass fiber surface and the silane com- ponent. A similar condensation reaction is believed to occur between the hydroxyl groups of silanes and the cellulose com- ponent of plant fibers. Studies that optimized conditions of time, temperature, concentration and pH for chemically modify- ing the surface of the cellulose fibers with silanes have been reported [25–33]. Since silanes can be prepared with a range of hydrophobic groups, they should be able to improve water resistance and promote better adhesion between cellulose and hydrophobic matrices. However, despite the encouraging results of earlier studies, there is still a lack of information on the most effective silanes, the impact of the different alkyl side groups comprised of different chain lengths, and their optimum concentration. The objective of the this work was to evaluate the effect of different concentrations of silanes containing alkyl side groups of different chain length on the chemical properties, water contact angle, and moisture adsorption (MA) of treated eucalyptus pulp fiber. EXPERIMENTAL Materials Conventional eucalyptus (hybrid: Eucalyptus urophylla x Eucalyptus grandis) bleached kraft pulp was obtained from S~ ao Paulo, Brazil. Eucalyptus kraft pulp fiber was chosen because it is abundantly available, inexpensive, and free of lignin and other Correspondence to: Rafael Mendes; e-mail:rafaelfarinassi@gmail.com Contract grant sponsor: Brazilian Research Council (CNPq) and the Research Foundation of Minas Gerais (FAPEMIG). DOI 10.1002/pen.24065 Published online in Wiley Online Library (wileyonlinelibrary.com). V C 2015 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—2015