The effect of chipping method on the geometry of particles produced from date palm frond

Abstract

The aim of this research was to study the effect of chipping method on geometry of particles obtained from date palm frond as a lignocellulose residue. For this purpose, date palm fronds were chipped with four different equipment: chipper-flaker, chipper-hammer mill, flaker-hammer mill, and chipper-flaker-hammer mill. The geometry of the particle including particle size, particle size distribution, shape, and aspect ratio were investigated. The results showed that maximum weight percentage (more than 40%) was related to the particles sizes of +30/-40 mesh for all chipping methods and more than 50% of all generated particles had a needle shape. In the chipper-hammer mill method, both the weight percentage of useable particles in particleboard and the particle percentage of the rectangle or nearly rectangle particle were higher. Thus, the chipper-hammer mill method was judged to be the best method.

Full Article

The Effect of Chipping Method on the Geometry of Particles Produced from Date Palm Frond

Neda Eghtedarnejad, Saeed Kazemi Najafi,* and Ali Shalbafan

The aim of this research was to study the effect of chipping method on geometry of particles obtained from date palm frond as a lignocellulose residue. For this purpose, date palm fronds were chipped with four different equipment: chipper-flaker, chipper-hammer mill, flaker-hammer mill, and chipper-flaker-hammer mill. The geometry of the particle including particle size, particle size distribution, shape, and aspect ratio were investigated. The results showed that maximum weight percentage (more than 40%) was related to the particles sizes of +30/-40 mesh for all chipping methods and more than 50% of all generated particles had a needle shape. In the chipper-hammer mill method, both the weight percentage of useable particles in particleboard and the particle percentage of the rectangle or nearly rectangle particle were higher. Thus, the chipper-hammer mill method was judged to be the best method.

Keywords: Chipping method; Particles geometry; Date palm; Frond; Particleboard

Contact information: Department of Wood and Paper Sciences and Technology, Faculty of Natural Resources, Tarbiat Modares University, Tehran, Iran; *Corresponding author: skazemi@modares.ac.ir

INTRODUCTION

The shortage of the raw wood materials has become one of the biggest challenges for wood-based panels (WBP) industries in recent years (Yang et al. 2003). Material efficiency, reuse, recycling of wood, production of lightweight wood-based products, and use of non-wooden lignocellulosic raw materials including agricultural residue are important options for dealing with the aforementioned challenges (Shalbafan et al. 2018). Therefore, many studies have focused on the utilization of underutilized wood resources and alternative materials for application in these industries (Khedari et al. 2003; Ashori and Nourbakhsh 2008; Guler et al. 2008; Al-Oqla et al. 2014; Cosereanu et al. 2015).

Agricultural residues have a great potential to compensate for the wood shortages in WBP industries. Agricultural residues are inexpensive resources that are available in large quantities. Among various agricultural lignocellulosic residues, date palm shows high potential for particleboard manufacturing.

The date palm (Phoenix dactylifera) is a tropical and subtropical species with a lifetime of 150 to 300 years (Hegazy and Aref 2010; Ferrandez-Garcia et al. 2018). This species grows in arid and semi-arid regions of the world (Fig. 1), including southeast Asia, Middle East, North Africa, and some parts of central and southern America (Hosseinkhani et al. 2014; Alfaro-Viquez et al. 2018).

In phytology, the date palm frond consists of two main parts: rachis and leaflets (Zayed et al. 2014; Saadaoui et al. 2013). Large amounts of renewable and lignocellulose residues are produced in cultivating areas due to the annual pruning of date palm fronds (Hegazy and Ahmed 2015). In most areas, these residues are traditionally burned or landfilled. This process causes serious threats to the environment and human health (Usman et al. 2015). These residues have great potential for wood substituting in wood-based panels such as particleboard, oriented strand board, cement board, and wood plastic composites (Rangavar and Hoseiny Fard 2015; Elaieb et al. 2018).

Fig. 1. Date palm global distribution (Shabani et al. 2014)

The date palm cultivation area in Iran is listed as 230,423 ha. In every hectare, approximately 156 date palms are planted. Each date palm produces nearly 49.3 kg of residue during annual pruning (Sajdak et al. 2014). Therefore, it is estimated that 980,000 tons of date palm pruning are annually produced throughout the country.

In recent years, the production of agro-based panels using agricultural residues instead of wood has come into focus. The industrial production of particleboard using date palm fronds has been considered in Iran, and two factories have been established, but the mechanical and physical properties of the products are low and do not meet the national and international standards (such as EN 312-2) limits.

An important problem inhibiting the use date palm fronds in the particleboard industry is the production of particles with inappropriate geometry. Many fine particles are generated during the conventional chipping process. Thus, it can be concluded that improper equipment is being used for chipping the fronds. Particle geometry, including particle shape and particle size, is an important parameter affecting the particleboard properties. Particle geometry determines the contact area for adhesive action which, accordingly, influences the physical and mechanical properties and machining of the particleboard panels (Sackey et al. 2008).

Particle geometry is directly influenced by the chipping method. Different chipping methods and machines are used in particleboard industries. Drum chippers are used for chipping logs and tree trunks and branches of small diameter

‬‬‬‬ A shortage of raw materials resources for WBPs industries, especially particleboard in Iran, has increased in recent years. As mentioned above, a considerable amount of date palm fronds is annually available in Iran. Thus, palm date residues (fronds) can be an important resource for particleboard industries. There has been no comprehensive study on the possibility of using date palm frond in manufacturing of particleboard, and the production of particles with desirable geometry is one of the most important stages prior to particleboard production. Therefore, this study considered the effects of different chipping methods on the particle geometry of date palm fronds. The fronds were chipped using four different methods, and the geometry of generated particles was analyzed.

EXPERIMENTAL

Preparation of the Date Palm Fronds

About 500 date palm fronds (Mazafati cultivar) were collected from a farm in the south of Iran after pruning (Fig. 2). The length of the fronds was 1 to 6 m. All fronds were air-dried to reach a homogeneous moisture content before further processing. The moisture content of the fronds was 7 ± 1% before chipping. The fronds were cut into 200 mm and 300 mm pieces before feeding into the chipper and flaker, respectively (Fig. 3). Groups of 15 to 20 fronds were fed into the chipper machine (Fig. 3a).

Fig. 2. Palm date pruning and frond collecting

Chipping Process

Frond chipping operations were performed using four different chipping methods, including a chipper-flaker, chipper-hammer mill, flaker-hammer mill, and chipper-flaker-hammer mill with three different types of machines. The chipping machines were industrial, and chipping was performed in particleboard factories. The chipper was a drum chipper (PHT 240*850*9, Pallmann, Zweibrücken, Germany). The flaker was a knife ring flaker (PZKR 8-300, Pallmann). Finally, four types of particles were obtained. The fixed factors in the chipping process were date palm cultivar, time of pruning, and the moisture content of the raw material. The blades of the chipping machine were replaced before the process. The particles were dried to reach a moisture content of 2% prior to further analysis.

Investigation of Particle Geometry

Particle size and particle size distribution are the major factors determining the mechanical and physical properties of particleboard (Juliana et al. 2012). The particle size and particle size distribution were determined by screening 100 g of each type of particles using a vibrating machine and sieves of 8-, 10-, 18-, 30-, 40-, 50-, 60-, and 100-mesh. Crossed-openings in the mentioned sieves were respectively 2.38- 2- 1- 0.59- 0.40- 0.29-0.25 and 0.14 mm. A laboratory vibratory shaker was used for particle size analysis. The particles were sieved for 10 min. The weight percentage of the remaining particles on each sieve was determined. Three different samples were analyzed for each type of particles.

To determine particle shape, a Dino-Lite digital microscope (Hsinchu, Taiwan) connecting to an image analyzer was used to measure the widths, thickness, and lengths of the particles. For this purpose, 20 particles from each fraction of 8, 10, 18, 30, 40 and 50 mesh (totally 120 particles for each chipping method) were randomly selected, and the mean values of aspect ratio for each fraction of each chipping method have been reported. The aspect ratios of the particles were determined as the ratio of the length to the width of particles. The particle shape analysis was carried out according to Juliana et al. (2012). In total, 6 main shape of particles were identified, and the numbers of particles in each shape were determined.

Fig. 3. The size of date palm fronds for feeding into the chipper (a) and knife-ring flaker (b)

Finally the particles were divided in two fractions of coarse and fine, and their aspect ratio and slenderness ratio (the ratio of length to thickness) resulting from each method were determined.

RESULTS AND DISCUSSION

Particle Size Analysis

The images of particles generated from four different chipping methods before and after screening (for size analyzing) are presented in Figs. 4 to 7. The four types of particles were clearly different in shape and size.