**4.2 The evaluated clones show potential for cellulose pulp in central-western Brazil**

Despite the large variation observed in wood properties, it is possible to affirm that all *Eucalyptus* clones presented quality as raw material to make paper and good pulping performance. The alkali charge values found in the literature for approximate target kappa are lower than those presented in this study [40, 41]. However, Gomide et al. [42] cites alkali percentages between 20.1 and 23.7% for kappa ±18 in assessing 75 wood samples of *Eucalyptus* clones from different Brazilian regions, thus evidencing the great variability existing for this technological parameter depending on the genotype and the environmental influences on growth. These high alkali charges required can be due to relatively high extractive content presented by genotypes (see **Table 1**), which increases the active alkali demand for pulping the wood to a given kappa number [43, 44].

Increasing pulp yield is a major goal of a chemical process, being related to the reduction of residual effective alkali (REA) at the end of cooking [45]. In this sense, higher value of consumed alkali represents better kraft pulping performance. Although the five *Eucalyptus* clones showed similar yield values, the same was not observed for the consumed alkali and residual effective alkali rates. According to Ribeiro et al. [45], the REA varies between 4 and 18 g L−1 considering different mills, while the range of 7–9 g L−1 is more common. Given this, the result is that the clones B and D reached high values for this parameter. Segura et al. [46] presented consumed alkali values on different levels of kappa number around 35–45 g L−1 for *E. grandis* x *E. urophylla* at 6 years old, thus corroborating the results presented herein. For *Eucalyptus* trees grown in southeastern Brazil, Gouvêa et al. [40] mentions pulp yield values from 50.3–52.9%, and Ferreira et al. [47] relates pulp yield values between 50 and 55% for *Eucalyptus* commercial clones at seven-nine years old. Similar results were reported by other authors [48].

The pulping yield directly influences the wood specific consumption - WSC, which in this work, was obtained taking into account only the yield in each pulping, disregarding the losses in the subsequent processes. Segura et al. [46] emphasizes that the basic density, which is an associated key property to wood specific consumption, has an important role in pulping costs and the densest materials present lowest wood specific consumption, reducing the wood and process costs. At the same time, higher densities may imply in low permeability of the wood by the liquor, thereby requiring high chemical usage and energy [49]. This is why density values within a medium range which configure a high proportion of wood in balance with good efficiency in the pulping process is given importance.

The best performance of clone E (*E. grandis* x *E. urophylla*) in terms of mean annual increment of pulp is due the high wood productivity (see **Table 1**, mean annual volume increment), which emphasizes the relevance of this attribute in assessing potential on a large scale. Clone C (*Eucalyptus camaldulensis* x *E. tereticornis*) presented the greatest disadvantage for this parameter. Clone B (*E. grandis* x *Eucalyptus pellita*) presented satisfactory growth in contrast with relatively inferior pulping performance and displayed less dense wood associated to wider fibers and lumen.

As can be seen, variations in the wood properties act dynamically on raw material quality and technological performance of *Eucalyptus* spp. clones. The magnitude of changes in the wood properties in response to the site did not evidence negative impacts on the pulping process efficiency of *Eucalyptus* clones at 4 years in comparison with the literature, except for alkaline charge. With respect to large-scale pulp production, there is a strong influence of growth potential and adaptive capacity of different hybrids. In this sense, the *E. grandis* x *E. urophylla* hybrid having highest wood volume stands out. Finally, the genetic material choice determined by factors which are related to environmental conditions, together with an assessment on the particular parameters related to end-use, as guided by the present study, plays a very important role in efficient breeding selection. However, it is important to emphasize that other traits should be explored in considering the overall assessment of the kraft pulp potential of a wood, such as the cellulose and lignin composition and fiber morphological and handsheet properties.
