**2.2 Fiber morphology and basic wood density**

Blocks of approximately 1 cm3 were sampled along the radius for fiber measurements from the pith to bark. Block samples were macerated with acetic acid and hydrogen peroxide, stained with Safranin and assembled in microscope slides. Images were obtained using a Zeiss Axio Scope A1 microscope and a digital camera (Canon A640). The length, diameter, wall thickness, and lumen width of fibers were

### *Arid Environment - Perspectives, Challenges and Management*


*MAIvol–mean annual volume increment; VA–vessels area; SL–soluble lignin; TL–total lignin; HOL–holocellulose; EXT– extractive contents.*

### **Table 1.**

*Species, productivity, vessels area and chemical composition of wood of the five selected* Eucalyptus *elite-clones.*

**Figure 2.** *Sampling process and respective analysis of the Eucalyptus clones wood.*

measured using the Image Pro-Plus Software (version 5.0) program as recommended by International Association of Wood Anatomists (IAWA) [21].

Next, relationships were established between individual fiber dimensions and quality indices to evaluate the wood morphological properties for paper purposes, such as the Runkel ratio, wall proportion, flexibility coefficient, slenderness ratio and Luce's shape factor. These indices were analyzed according to the categories established by Barrichelo and Brito [22] and Foelkel et al. [23], and calculated according to the following equations:

$$\text{Runkel\\_ratio}(\text{RR}) = 2w \mid d \tag{1}$$

$$\text{Wall\ proportion} \left(\text{WP}\right) = \left(\text{2x} \land \text{D}\right) \times \text{100} \tag{2}$$

*Wood Quality and Pulping Process Efficiency of Elite* Eucalyptus *spp. Clones Field-Grown… DOI: http://dx.doi.org/10.5772/intechopen.106341*

$$\text{Flexibility coefficient} \left( \text{FC} \right) = d \left( \text{D} \right) \tag{3}$$

$$\text{Slenderness ratio} \left( \text{SR} \right) = \text{L} / \text{D} \tag{4}$$

$$\text{Luce'}\\\\
\text{shape factor} \left(\text{LSF}\right) = \left(\text{D}^2 - d^2\right) / \left(\text{D}^2 + d^2\right) \tag{5}$$

In which: w is the cell wall thickness, D is the fiber diameter, d is the fiber lumen width, and L is the fiber length.

The basic wood density was determined according to ASTM D2395–17 using wood wedges (approximately 1/4) obtained from each disk.

## **2.3 Pulping process**

All pulping processes were performed in triplicate in a rotating digester containing eight capsules with capacity of 10 L. An alkaline curve with four active alkali levels was performed under fixed kraft pulping conditions for each genotype (**Table 2**). The alkali levels were selected from previous tests in order to determine the dosage of active alkali (AA) required to obtain a kappa number 18.0 ± 0.5. The analysis of residual alkali in black liquor was performed according to SCAN-N 2:88 modified. Pulp yields and consumed alkali (difference between applied and residual alkali) were calculated, and the pulps' kappa number was determined according to TAPPI T 236 om-99. The other calculated parameters were wood specific consumption [24] and mean annual pulp increment [15], according to the following equations:

$$WSC = \frac{1}{BD \times PY} \times 0.9\tag{6}$$

in which: WSC = wood specific consumption (m3 t−1); BD = basic density (g cm−3); PY = pulp yield (in decimal).

$$\text{MAI} \text{pul} \text{p} = \frac{\text{MAI} \text{vol} \times \text{BD} \propto \text{PY}}{1111} \tag{7}$$

in which: MAIpulp = mean annual increment of pulp (t h−1 yr−1); MAIvol = mean annual increment of volume (m3 h−1 yr−1); BD = basic density (kg m−3); PY = pulp yield (%).


**Table 2.** *Kraft pulping conditions.*
