DOI 10.1515/hf-2013-0211 Holzforschung 2014; 68(8): 981–986 Vladimir Eliodoro Costa*, Marcos Antônio de Rezende and Valdemir Antônio Rodrigues Conversion between basic density and apparent density at any moisture content in Eucalyptus grandis Abstract: Wood basic density (BD) is related to other wood characteristics and its determination is important in for- est inventory, though BD must be differentiated from the apparent density (AD), which relates to the moisture con- tent (MC) of wood. The aim of this study is to demonstrate a reliable conversion from BD to AD for any MC of Euca- lyptus grandis wood based on two exponential and linear models that relate volumetric shrinkage to MC. To this end, wood specimens were submitted to drying and the volumetric shrinkage was determined as a function of MC. The two models proved to be efficient in the conversion of BD to AD and vice versa. Keywords: apparent density, basic density, density con- version, Eucalyptus grandis, specific gravity, wood *Corresponding author: Vladimir Eliodoro Costa, Instituto de Biociências, UNESP – Universidade Estadual Paulista, Campus Botucatu, Departamento de Física e Biofísica, Botucatu-SP, CEP 18618970, Brazil, e-mail: vladimir@ibb.unesp.br Marcos Antônio de Rezende: Instituto de Biociências, Universidade Estadual Paulista, Campus Botucatu, Departamento de Física e Biofísica, Brazil Valdemir Antônio Rodrigues: Faculdade de Ciências Agronômicas, Universidade Estadual Paulista, Campus Botucatu, Departamento de Ciência Florestal, Brazil Introduction The production and demand for wood products is growing worldwide. Various eucalyptus species are among the most cultivated trees in forest plantations for produc- tion of cellulose, paper, plywood and sawn wood (FAO 2012; ITTO 2012). Wood density is an important property because of its relation to many other physical and mechan- ical characteristics (Chave et al. 2006; Crous et al. 2009; Forest Products Laboratory 2010; Santini et al. 2012) and it is dependent upon the moisture content (MC) (Forest Products Laboratory 2010). In this context, one speaks about the apparent density (AD) of wood as a porous and hygroscopic material. The AD at a certain MC is different from the basic density (BD), which is related to dry wood. Through the course of drying, the apparent mass of wood varies linearly with MC but not with its apparent volume (AV). This non-linear behaviour of the AV is related to the fibre saturation point (FSP) at approx. 30% MC (Berry and Roderick 2005). The MC max is inversely proportional to the BD (Skaar 1988). The volumetric shrinkage (V shr ) of wood is inversely proportional to the MC (Almeida et al. 2008). For MC below FSP, the relationship is linear but above FSP it is not (Rezende 2003; Almeida et al. 2008). Rezende (2003) proposed an exponential model to better describe this relationship. The % V shr is directly proportional to BD (Newlin and Wilson 1919; Stamm 1964; Rezende 2003). Not all methods for determination of wood density involve calculating the BD (Simpson 1993; Koch et al. 1998; Passialis 1998; Bergsten et al. 2001; ASTM 2008; Chan et al. 2010; Forest Products Laboratory 2010; Dvinskikh et al. 2011; Kothiyal and Raturi 2011; Mäkipää and Linkosalo 2011; Wei et al. 2011; Alves et al. 2012). Frequently, specimens with 12% MC are tested for density. In the pulping industry, the wood is filled into digesters with an MC of approx. 50%. There is a need in industrial practice to convert BD into AD and vice versa. If the BD is 500 kg m -3 , the AD can be between 600 and 1175 kg m -3 (Forest Products Laboratory 2010). The existing equations for this type of conversions are valid either for MC< FSP or MC> FSP (Simpson 1993; ASTM 2008). An additional problem is the relationship between the dry mass and volume at the MC of the sample. The aim of the present study is to develop a single expres- sion for the conversion between the BD and AD at any MC considering the volumetric shrinkage based on the species Eucalyptus grandis. Materials and methods Abbreviations AD apparent density (kg m -3 ) AD 12 apparent density (kg m -3 ) with 12% MC AD dry dry apparent density (kg m -3 ) with zero MC AD green green apparent density (kg m -3 ) with MC max BD basic density (kg m -3 ) CH commercial height of the tree Brought to you by | New York University Bobst Library Technical Services Authenticated Download Date | 5/20/15 9:45 PM