Production of particleboards from licorice ( Glycyrrhiza glabra ) and European black pine ( Pinus Nigra Arnold ) wood particles

In this study particleboards were manufactured from mixtures of licorice (Glycyrrhiza glabra) and European Black Pine (Pinus nigra Arnold) wood particles at several ratios. The suitability of licorice (Glycyrrhiza glabra) chips for particleboard production was examined. Urea formaldehyde resin was used as a binder in 3-layers particleboards. The manufactured boards were tested according to European (EN) standards. The licorice and European Black Pine wood particles were mixed at ratios 25, 50, 75 and 100% respectively. Produced panels were tested for certain mechanical and physical properties. Experimental results indicated that increase in licorice chips in the mixture generally diminished the mechanical and physical properties. The produced boards can be utilized for general purposes as well as furniture for interior environments and the results obtained showing that licorice could be an alternative raw material for particleboard industry.


INTRODUCTION
In recent years the utilization of agricultural waste and annual fibers for particleboard or other composite board production is going popular.Particleboard is one of the most important products of forest products industry known.Throughout the years, the production coast of particle board has increased while the quality of product reduced.
Agricultural waste materials and annual plants have become alternative raw materials for the production of particleboard or fiber composite materials.While many industries utilise forest products as a raw material and uneconomical use of these resources cause extinction of forest.It is really necessary to find alternative raw material source in order to reduce forest consumption.For this reason it is important to study suitability of annual plants fibres for particleboard production.This will aid protection of environment and as well as development of environmental friendly technologies.The most frequently referred alternative non-wood materials are flax, bagasse, hemp, reed and cereal straws such as rice and  The density of the boards made from licorice and European Black Pine wood chips was 0.70 g/cm 3 .
wheat straw (Younquist et al., 1994).Today, chemical pulp and panel products using wheat straw and other crop residues are being commercially manufactured in a number of countries including Turkey (Copur et al., 2007).There is still an outgoing research interest to find alternative sources of raw materials for composite manufacturing.
The problems of the industrial usage of agricultural residues in particleboard industry refer to the high cost of collecting, transporting, and storing of the residue materials.Some of these problems could be overcome by building local, small scale mills, close to the rural areas.
In Turkey licorice, sunflower, rice, wheat, straw, sugar cane and cotton are produced for vegetable oil fiber or food industries.The waste products of these agricultural plants are consumed for animal feed fertilizer or heat production.
One of the agricultural residues, licorice (GlycyrrhizaglabraL.), is produced by former USSR, Spain, Turkey, Syria, Iraq and Afghanistan.Most of the commercial supply comes from wild sources and only a limited amount is cultivated.In addition to its medicinal use, licorice has been industrially utilized in chocolates, beverages and tobacco (Copur et al, 2007).However, in utilization of licorice fibers, there is almost no literature in the particleboard industry.
Eastern Anatolia in Turkey is covered with licorice plant about 4 million acres.Utilization of licorice in particleboard industry might produce economic benefits and contribute to environmental sustainability.Therefore, this study focuses on the potential use of licorice roots as a source of board making raw material.
The possible utilization of licorice in particleboard industry might produce economic benefits and contribute to environmental sustainability.Therefore, this study focuses on the potential use of licorice roots as a source of panel making raw material.

MATERIALS AND METHODS
Licorice roots obtained from the Mediterranean region of Turkey were cleaned from dust and dirt.Licorice roots and pine wood were coarsely chopped.The particles were sifted by utilizing a horizontal position sieve.3 to 1.5 mm average size particles were used in the core section of particleboard while 1.5 to 0.8 mm average size particles were utilized in the shell layers.
All particles used in this study were dried at 100 to 110°C in a technical oven until 3% MC is reached.Urea formaldehyde (UF) resin is the most common applied on wood panels (Silva et al., 2013).The resin was applied at 9% for the core layer and 11% for the shell layers based on oven dry weight.The properties of the UF resin are given in Table 1.As a hardener, 33% of ammonium chloride solution was used for all of the UF resin boards.Panels with a target density of 0.70 g/cm 3 were manufactured using 0, 25, 50, 75 and 100% licorice chips in the mixture.Experimental design are given in Table 2.The dimensions of the produced particleboards were 50×50×2 cm in pressing and after edge trimming the final dimensions of the particleboards were 47×47×2 cm.The pressing conditions were as follows; press temperature: 150°C; press time: 7 min; pressure: 2.4-2.6 N/mm 2 and production parameters of boards used in this study are shown in Table 3.
Prior to testing, the boards produced were conditioned at 65  5% Relative Humidity (RH) and 20  1°C in according to TS 642-ISO 554 (1997) Hardboard Method.The samples were cut from the experimental boards to determine some physical and mechanical properties in accordance with TS-EN 310 (1999), TS-EN 317 (1999), TS-EN 319 (1999), andTS-EN 312 (2012) standards.Mechanical and physical properties were tested 10 and 20 specimens respectively.
The analysis of variance (ANOVA) was applied using randomized complete design to find out the statistical differences in the physical, mechanical and dimensional properties of the particleboard.A Duncan multiple range test at 5% level of probability was conducted to study the significance of the

RESULTS AND DISCUSSION
Table 4 indicated results for the mechanical properties of the produced particleboard.Results indicated that licorice root ratios used in particleboard production significantly affect modulus of rupture, modulus of elasticity and internal bond of the product.The highest MOR and MOE values of 16.42 and 2582.62N/mm 2 were observed when only pine wood was utilized in the manufacture of the particleboard (E), respectively.On the other hand, the lowest MOR and MOE values of 12.02 and 2142.21N/mm 2 were obtained produced panels with licorice root ratio of 100%.It can be easily seen that mechanical properties of particleboards were reduced with the increase of licorice root ratio in the panels.The standard method TS-EN 312 (2012) recommends a minimum modulus of rupture (MOR) and modulus of elasticity values of 11 and 1600 N/mm 2 for the particleboards manufactured for general propose-use as well as furniture for interior environments respectively.The findings in this study showed that all panel types particleboards met the minimum requirement for MOR and MOE.
In the case of IB, similar to the other mechanical properties, the highest IB value of 0.55 N/mm 2 was observed with the particleboard produced using 100% pine wood.The lowest IB value of 0.33 N/mm 2 was obtained produced panels with licorice ratio of 100%.Figure 1 shows the IB strengths of the particleboards.Particleboards met the IB requirement of 0.35 N/mm 2 for general purpose end-use as well as furniture for interior environments expect for A type.This finding is compatible with previous results reported in literature (Goker et al, 1993, Bektas et al., 2005;Guler et al., 2006).
Table 5 shows the results of ANOVA and Duncan's mean separation tests for water absorption and thickness swelling for 2 and 24 h water immersion times.The highest water absorption (48.25 and 59.69%) and thickness swelling (17.12 and 20.19%) were observed with the particleboard (A) having 100% licorice root in the mixture for 2 and 24 h water immersion times, respectively.A diagram of the effect of two different soaking times on the TS of the boards is shown in Figure 2. Increase in licorice root percentage in the mixture resulted in a higher thickness swelling and water absorption for particleboards produced using licorice root and wood chip mixtures.The observed results indicated that the particleboards (A, B, C, and D) including licorice root in the mixture resulted in higher thickness swelling (more than 14%) required by TS EN 312 (2012) Standard.The values obtained with licorice rootwere found to be comparable with other agricultural residues investigated earlier in the literature: thickness swelling and water absorption values of 17 and 60% for tobacco, 29 and 70% for tea leaves (Kalaycioglu 1992), and 30 and 72% for cotton stalks (Gulerand Ozen, 2004) were reported for 24 h water immersion time, respectively.Utilizing water repellent chemicals, such as paraffin in the production may improve these properties.

Conclusions
This study investigated the possibility of using licorice root and European Black Pinewood mixture to manufacture three-layer particleboards.For this purpose, the mixture of particles produced from licorice root and black pine wood at certain concentrations (0, 25, 50, 75 and 100%) have been used.Five types of panels are produced and their mechanical and physical properties are evaluated.The results indicated that it is possible to produce particleboards from licorice root alone and from the mixture of licorice root and wood chips by using ureaformaldehyde adhesives.The produced boards can be utilized for general purposes as well as furniture for interior environments and the results obtained show that licorice could be an alternative raw material for particleboard industry.Even though increase in the concentration of licorice root particles in composite matrix reduces both the physical and mechanical properties of the particleboard, almost all the studied properties (that is, modulus of rupture, modulus of elasticity, intermal bond strength) of the produced panels comply with the minimum requirements in standards for general grade particleboards with the exception of thickness swelling and water absorption.As there are no hydrophobic additives used in these panels, these properties can be improved by the utilization of hydrophobic materials in the matrix.Overall, this study showed that licorice root could be utilized as a raw material in particleboard production by itself or in combination with European Black Pine wood mixture.

Figure 1 .
Figure 1.The internal bond strength of the particleboards.

Figure 2 .
Figure 2. The effect of two different soaking times on thicknesses swelling of board types.

Table 1 .
Properties of the UF adhesive.
a Urea formaldehyde.

Table 4 .
The mechanical properties of particleboards made from licorice rootand European Black Pine andthe test results of ANOVA and Duncan's mean separation tests.
a , Mean values are the average of 10 specimens; b , minimum value; c , maximum value; d, significance level of 0.01 (for ANOVA); p,s,u,t,v , values having the same letter are not significantly different Duncan test).MOR, Modulus of rapture; MOE, modulus of elasticity; IB, internal bond strength.differences among species using Statistical Analysis System.

Table 5 .
Thickness swelling (TS) and water absorption (WA) test results of ANOVA and Duncan's mean separation tests ofparticleboards produced from licorice root and European Black Pine wood particles.
a Std.