**3. Properties of oil palm fronds**

The fronds are found around the trunk in two spirals which are left-handed or right-handed. Individual mature frond has rachis, leaflets, and thorns [23]. Oil palm fronds, the aerial part of the oil palm tree comprises two central portions; they are the petiole and the leaflet. The petiole, which is the woody part of the frond, represents more than 70% of the whole frond, whereas the weight of the leaflet is less than 30%. Therefore, the proportion of petiole and leaflet portions, which is determined by the age of the frond at the time of harvest, would be the dominant factor determining the fibre composition of maturing oil palm fronds [24].

The moisture content of oil palm fronds is very high, up to 60% on a wet basis. The leaves are found at the top of the plant arranged like a crown containing 40 or more fronds. Each palm frond has 20 to over 150 pairs of roughly 2.5 cm wide leaflets arranged in two rows along each side of the petiole [25]. The frond lengths decrease from the bottom to the top level of the crown, reaching the length of about 4 m. In a cross-section, the frond shows a triangle shape with the width decreasing from the base to the end of the petiole and from the bottom to the top fronds [23]. A fruiting branch that contains thousands of fruits is held in the axils of the leaves and arranged in a rosette pattern around the crown [26, 27].

#### **3.1 Anatomical characteristics of oil palm fronds**

Anatomical characteristics of oil palm fronds are different from other woody structures in that they have four essential cell elements: parenchyma, vascular bundles, sclerenchyma, and epidermis [17]. Oil palm fronds do not possess cambium, sapwood, heartwood, and growth ring; hence their 'wood' is the primary tissue itself [28]. The fronds are primarily composed of parenchymatous tissues with numerous fibrous strands and vascular bundles. The oil palm fronds consist of a mass of discrete vascular bundles embedded in parenchymatous tissues [29]. The growth and increase of the fronds result from the overall cell division and cell

enlargement in the parenchymatous tissues, together with the enlargement of the fibre of the vascular bundles [30].

Like other monocotyledon plants, oil palm has inner and outer vascular bundles, and the same goes for its fronds. The outer region of living tissues is differentiated into a narrow cortex from the wide central cylinder. **Figure 1** shows the anatomical characteristics of the oil palm fronds. In the cylinder, vascular bundles were found concentrated at the outer and scattered at the inner division. The distribution of the vascular bundles throughout the fronds has become an essential factor influencing the oil palm fronds' anatomical features and physical properties [30]. **Figure 2** shows the oil palm fronds in the transverse section. The morphological of oil palm frond structures presented in **Figures 3**–**5** were observed under high-performance microscopy with different magnification.

The parenchymatous tissues comprise a short chain of polysaccharides, starch, and also a soft structure. However, the fibrous strands are principally dense cellulose which is challenging to degrade. A study found the weight ratio of the parenchymatous tissues on fibre strands in the range 24-29% to 71-76%. The riches of starch discovered in the parenchyma structure are about 55% while 2.4% in the fibre. Then, the lignin content recorded a slightly comparable value, 20% in fibre and 15.7% in the parenchyma [31]. Furthermore, regarding the orientation of

**Figure 1.** *Structure of anatomical characteristics of oil palm fronds.*

**Figure 2.** *Oil palm fronds at the transverse sectional view.*

*Processing and Properties of Oil Palm Fronds Composite Boards from* Elaeis guineensis *DOI: http://dx.doi.org/10.5772/intechopen.98222*

#### **Figure 3.**

*High-performance micrograph of oil palm fronds at the transverse sectional view (0.75 magnification).*

#### **Figure 4.**

*High-performance micrograph of outer part on oil palm fronds at the transverse sectional view (4 magnification).*

#### **Figure 5.**

*High-performance micrograph of inner part on oil palm fronds at transverse sectional view (2 magnification).*

**Figure 6.** *SEM of oil palm fronds at the transverse sectional view (16 magnification).*

vascular bundles over the transverse section, most of the vascular bundles were oriented randomly. **Figure 6** clearly shows the difference in sizes and population of vascular bundles towards the outer to the central part of the oil palm fronds using scanning electron microscopy (SEM).
