Holzforschung, Vol. 64, pp. 595–601, 2010 • Copyright  by Walter de Gruyter • Berlin • New York. DOI 10.1515/HF.2010.073 2010/005 Article in press - uncorrected proof Surface properties of eucalyptus pulp fibres as reinforcement of cement-based composites Gustavo Henrique Denzin Tonoli 1, *, Alessandra Etuko Feuzicana de Souza Almeida 2 , Marcelo Assumpca ˜o Pereira-da-Silva 3,4 , Alexandre Bassa 5 , ¸ Danilo Oyakawa 5 and Holmer Savastano Jr 2 1 Department of Structural Engineering, Escola de Engenharia de Sa ˜o Carlos, Universidade de Sa ˜o Paulo, Sa ˜o Carlos, Sa ˜o Paulo, Brazil 2 Department of Food Engineering, Faculdade de Zootecnia e Engenharia de Alimentos, Universidade de Sa ˜o Paulo (USP), Pirassununga, Sa ˜o Paulo, Brazil 3 Department of Physics and Materials Science, Instituto de Fı ´sica de Sa ˜o Carlos, Universidade de Sa ˜o Paulo, Sa ˜o Carlos, Sa ˜o Paulo, Brazil 4 Centro Universita ´rio Central Paulista – UNICEP, Sa ˜o Carlos, Sa ˜o Paulo, Brazil 5 Centro de Desenvolvimento Tecnolo ´gico de Celulose (CDTC), Votorantim Celulose e Papel, Jacareı ´, Sa ˜o Paulo, Brazil *Corresponding author. Department of Structural Engineering, Escola de Engenharia de Sa ˜o Carlos, Universidade de Sa ˜o Paulo, Avenida Trabalhador Sa ˜o Carlense, 400, 13566-590, Sa ˜o Carlos, Sa ˜o Paulo, Brazil E-mail: gustavotonoli@yahoo.com.br Abstract The objective of the present work is to evaluate the effects of the surface properties of unrefined eucalyptus pulp fibres concerning their performance in cement-based composites. The influence of the fibre surface on the microstructure of fibre-cement composites was evaluated after accelerated age- ing cycles, which simulate natural weathering. The surface of unbleached pulp is a thin layer that is rich in cellulose, lignin, hemicelluloses, and extractives. Such a layer acts as a physical and chemical barrier to the penetration of low molecular components of cement. The unbleached fibres are less hydrophilic than the bleached ones. Bleaching removes the amorphous lignin and extractives from the surface and renders it more permeable to liquids. Atomic force micros- copy (AFM) helps in understanding the fibre-cement inter- face. Bleaching improved the fibre-cement interfacial bonding, whereas fibres in the unbleached pulp were less susceptible to the re-precipitation of cement hydration prod- ucts into the fibre cavities (lumens). Therefore, unbleached fibres can improve the long-term performance of the fibre- cement composite owing to their delayed mineralization. Keywords: atomic force microscopy; cellulose fibre; cement; contact angle; fibre-cement; surface energy. Introduction Cellulose fibres are widely available and are convenient materials for brittle matrix reinforcement, such as in fibre- cement applications. The main drawback of cellulose fibres in a cementitious matrix is their low durability and also the insufficient compatibility between both phases (Agopyan et al. 2005). The high alkalinity of the pore water from the cementitious matrix weakens the cellulose and accelerates the mineralization phenomenon, as proposed by Bentur and Akers (1989) and Tole ˆdo Filho et al. (2000). As a conse- quence, the strength of the composite decreases in the long- term. The severe degradation of weather exposed composites can also be attributed to interfacial damages owing to con- tinuous volume changes of the porous and hydrophilic cel- lulose fibres inside the cement matrix (John et al. 1998). Mohr et al. (2006) reported that the chemical composition of virgin cellulose pulps significantly affects the mechanisms of mineralization of the fibres within cement-based compos- ites. Lignins are amorphous, three dimensionally cross-linked polymers, which have good solubility in alkaline media. Lig- nin removal occurs mainly during pulping but a more com- plete extraction of lignin is called bleaching. Bleaching also affects the chain length of cellulose and hemicelluloses as well as the bulk cell wall structure and the surface (Paavi- lainen 2001). Mohr et al. (2006) reported that lignin and wood extractives protect the fibre from mineralization phe- nomena. Thus, pulp bleaching makes the cellulose chain more susceptible to degradation, which could lead to impor- tant consequences for the durability of the fibres in the fibre- cement composite. Although the microstructure and macroscopic effects of vegetable fibre and fibre-cement are well described in the literature, few studies are devoted to the complex issue con- cerning the chemical and morphological organization of the fibre surface and mineralization of fibres. The objective of the present work is to investigate the effect of the surface properties of unrefined eucalyptus kraft fibres on their per- formance in cement-based composites. Materials and methods Materials Conventional unrefined unbleached and bleached eucalyptus kraft pulps were investigated. The bleaching sequence consisted of oxy- gen (O), ozone (Z), acid (A), chlorine dioxide (D), and hydrogen peroxide (P) stages. Kappa number detection: according to the SCAN C 1:77 (1977) standard. Calculation of the total residual Author's Copy Author's Copy Author's Copy Author's Copy