Abstract
The production of low-density binderless bark particleboards (LDBBP) from gelam wood bark (GWB) using a hot pressing method at low temperature (128 °C) and pressure (30 kg × cm-2) was explored by examining their physical properties according to SNI 03-2105-2006 (2006). They were also examined via scanning electron microscope (SEM)-energy dispersive X-ray (EDX) observation. The LDBBPs were manufactured using two types of GWB particles: (1) bark waste that was peeled off of small-diameter trees < 10 cm (A) and, (2) bark that was directly peeled off from a standing tree with an average diameter of 10 cm to 15 cm (B). Results showed that the average values of the physical properties of LDBBP(A) and LDBBP(B) met the SNI 03-2105-2006 (2006) requirements in terms of density, moisture content, and thickness swelling after being immersed for 24 h for particleboard type 24-10 and type 17.5-10.5 with maximum thickness swelling requirement 20%. However, they failed to meet the maximum thickness swelling criterion of 12% for other particleboard types. Subsequent internal morphology observation using SEM indicated the presence of cracks on LDBBP (A), so only LDBBP (B) could be manufactured without delamination. Gelam bark could potentially be used to produce non-adhesive particleboards.
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Pilot Study on Low-density Binderless Bark Particleboards Manufacture from Gelam Wood (Melaleuca sp.) Bark
Eva Oktoberyani Christy,a,* Soemarno,b Sumardi Hadi Sumarlan,c and Agoes Soehardjono d
The production of low-density binderless bark particleboards (LDBBP) from gelam wood bark (GWB) using a hot pressing method at low temperature (128 °C) and pressure (30 kg × cm-2) was explored by examining their physical properties according to SNI 03-2105-2006 (2006). They were also examined via scanning electron microscope (SEM)-energy dispersive X-ray (EDX) observation. The LDBBPs were manufactured using two types of GWB particles: (1) bark waste that was peeled off of small-diameter trees < 10 cm (A) and, (2) bark that was directly peeled off from a standing tree with an average diameter of 10 cm to 15 cm (B). Results showed that the average values of the physical properties of LDBBP(A) and LDBBP(B) met the SNI 03-2105-2006 (2006) requirements in terms of density, moisture content, and thickness swelling after being immersed for 24 h for particleboard type 24-10 and type 17.5-10.5 with maximum thickness swelling requirement 20%. However, they failed to meet the maximum thickness swelling criterion of 12% for other particleboard types. Subsequent internal morphology observation using SEM indicated the presence of cracks on LDBBP (A), so only LDBBP (B) could be manufactured without delamination. Gelam bark could potentially be used to produce non-adhesive particleboards.
Keywords: Gelam wood bark; Waste; Hot pressing; Valorisation, Low-density; Binderless bark particleboards; Physical properties
Contact information: a: Postgraduate Program, Faculty of Agriculture, Brawijaya University, Malang, Indonesia; b: Department of Soil Science, Faculty of Agriculture, Brawijaya University, Malang, Indonesia; c: Department of Agricultural Engineering, Faculty of Agricultural Technology, Brawijaya University, Malang, Indonesia; d: Department of Civil Engineering, Faculty of Engineering, Brawijaya University, Malang, Indonesia; *Corresponding author: eochristy28@gmail.com
INTRODUCTION
The Melaleuca species from the Myrtaceae family is native to Australia and Southeast Asia (Sakasegawa et al. 2003). It is an introduced species in the southern United States and South America (Tran et al. 2013). It is present in several Southeast Asian countries, which include Malaysia, Cambodia, Vietnam, Thailand, and Indonesia (Tran et al. 2013). In Indonesia, Melaleuca sp. is known by the local people as gelam. It grows naturally and is abundant in the Central Kalimantan, South Kalimantan, and South Sumatra coastal peat swamp forests (Supriyati et al. 2015).
Generally, in Indonesia, gelam timbers are used as wooden piles for constructing buildings, bridges, and roads. In addition, they are used as firewood, charcoal, and materials for making fences and chicken coops. The gelam wood used for such purposes is collected by wood gathering communities, one of which is located in the Pulang Pisau area of Central Kalimantan, which is a former target area of the Indonesian government’s Million Hectare Mega Rice Project [Proyek Lahan Gambut Sejuta Hektar]. Moreover, they also collect gelam wood from the Kapuas area, as mentioned by Lasino and Witarso (2014). The transmigration area in Kapuas Regency, Central Kalimantan Province has significant local potential in the form of gelam forest (Melaleuca cajuputi), which covers an area of around 63,800 Ha. Selling gelam wood is the main livelihood of the local people. At the market, particularly at the level of collectors (traders), the number of gelam wood supply reaches no less than 2500 tree trunks per day with a diameter of 6 to 20 cm and length of 4 m (Lasino and Witarso 2014). They sell small-size gelam timbers (Ø < 10 cm) without bark to build fences or chicken coops (Fig. 1d), and the outer bark of the gelam timber with a medium diameter (Ø = 10 cm to 15 cm) is usually peeled off directly from a standing tree and used for roofs or to mend boats. According to Chiang and Wang (1984), Melaleuca has thick bark that is composed of many thin layers that comprises approximately 15% to 20% of the total stem volume. Abundant Melaleuca bark can cause problems when it is disposed of during timber harvesting seasons (Poole and Conover 1979). There are a number of environmental problems in Indonesia due to gelam wood bark (GWB) waste disposal. It renders the river water dirty, black, smelly, and silty, and it narrows the river mouth. In addition, the burning of the waste causes thick smoke that damages public health and disrupts access to public roads. To overcome such environmental problems, GWB waste must be turned into value-added products.
To improve the usage of Melaleuca sp. bark, several studies have been carried out in the context of both environmental and health care, in which bark from renewable, abundant, and inexpensive sources was used as lignocellulosic-biomass. Talib et al. (2014) examined the use of Melaleuca sp. bark as a green corrosion inhibitor, and Luo et al. (2015) studied their use as supercapacitors. Veeramani et al. (2015) studied the use of Melaleuca sp. bark for practical electrochemical vanillin detection, and Xiao et al. (2014) investigated the use of porous carbon materials for hydrogen storage. In addition, Melaleuca sp. bark was used for lithium-sulphur batteries (Zhu et al. 2019), bioethanol (Ahmed et al. 2013a), thermic, hydraulic, and dielectric devices (Roussan 1923), particleboard with urea-formaldehyde adhesive (Purwanto 2015), and high-density bark board without adhesive (Sato 2008). In this study, GWB was made into low-density binderless bark particleboard (LDBBP). There has not been any prior research on the manufacture of low-density binderless particleboards made from GWB.
For the production of bark particleboards without adhesives, Blanchet et al. (2000) and Claude et al. (2008) reported an approach based on particle plasticization (physical consolidation) and extractive polymerization for bark particle self-bonding. Burrows (1960) demonstrated how particleboards made from Douglas-fir bark particles could be manufactured at pressing temperatures below 180 °C with a mat moisture content of 12 to 20%. In particular, the conditions were approximately 138 °C and pressing pressures of 3 MPa without adhesives through the plasticisation mechanism. Such a mechanism may take place because bark is a lignocellulosic material and due to the availability of water as plasticizer. According to Almusawi et al. (2016), some lignocellulosic components with lightweight molecules such as lignin polymers, non-crystalline cellulose, and hemicellulose allow softening at a temperature suitable for producing a plasticized matrix that can connect particles in self-bonding particleboard. Such amorphous polymer softening basically requires a particular temperature and depends on the moisture content. Morsing (2000) mentions that the softening behavior of an amorphous polymer is marked by glass transition temperature (Tg), which is known as softening temperature.
According to Pintiaux et al. (2015), glass transition temperature decreases as moisture content increases. Therefore, this plasticizing effect is considered as an important aspect when determining the right pressing temperature for producing panel products without synthetic adhesives in order to achieve the desired bonding. This is the same as performed by Burrows (1960) when producing a particle board without synthetic adhesives, in which he used a pressing temperature above the softening temperature of Douglas-fir bark, which could result in board properties that are comparable to those of commercial boards. It must be noted that the softening temperature of Douglas-fir bark varies according to the moisture content, as shown by a study by Chow (1980), in which the softening temperatures for materials with moisture content of 0%, 9.7 %, and 14% were 180 °C, 120 °C, and 70 °C, respectively. By applying a suitable pressing temperature, plasticization can take place in amorphous polymers and flow in such a way as to reach a high degree of mechanical contact or closeness (a few microns, at least) between the surface of particles or fibers intended to be adhesive and sufficient contact area, as proposed by Hubbe et al. (2018). Therefore, such mechanical contact becomes one of the critical links that can be recommended for the development of bonding in hot-pressed products by self-bonding or natural adhesives. With respect to the production of LDBBP from GWB, lignin, which is one of the flowable matrix components, is also present in the outer bark of Melaleuca sp. in a moderate amount. It was confirmed by Ahmed et al. (2013b) who report that Melaleuca leucadendron shedding bark contains 47.2 % glucan, 17.4% xylan, 19.13% lignin (determined as acid-insoluble lignin and acid-soluble lignin), and 9.2% extractives. According to Pintiaux et al. (2015), the presence of lignin, albeit at a low level, is beneficial in the production of binderless boards. Therefore, it is recommended that GWB be used as a material for producing non-adhesive particle boards. In this study, a manufacturing process involving low temperature and pressure was carried out to produce LDBBP from GWB.
This pilot study was an initial step to ensure that GWB can be manufactured into LDBBP via the hot pressing process. In order to ensure this, the physical properties of LDBBP were first investigated with an emphasis on thickness swelling (TS) and water absorption (WA) tests. TS is an important parameter for demonstrating the dimensional stability of a composite board product. This is because, according to Mantanis and Papadopoulus (2010), dimensional stability or more exactly the dimensional instability, as the case may be is the main disadvantage of wood-based panels (particle boards, MDF, or OSB) in terms of their final usage. This is related to moisture effect, where Halligan (1970) mentions that moisture effect in a particle board has an important influence on its properties and usages. When a particle board undergoes a change in moisture content, its strength is reduced and its lifespan is shortened, thus limiting its usage for exterior and structural purposes. Besides that, the moisture effect in a material is measured based on TS and WA (Baskaran et al. 2019), particularly TS, which is one of the requirements in various composite board testing standards. One of such standards involving the TS criterion is the Indonesian National Standard (Standard Nasional Indonesia or SNI) 03-2105-2006 (2006) for particle boards which is used in LDBBP testing. Besides that, LDBBP characterization was also carried out by means of SEM-EDX observation. Therefore, the objective of this study was to determine the possibility of manufacturing LDBBP by examining the physical properties and morphology of the resultant boards.
EXPERIMENTAL
Materials
The gelam wood bark in this research was gathered from gelam wood collecting sites in Garung Village of the Pulang Pisau Regency in Central Kalimantan in the form of bark waste that was peeled from Melaleuca viridiflora Sol. Ex Gaertn. trunks with a diameter (Ø) of < 10 cm (Fig. 1b and Fig. 1c). For comparison purposes, samples of gelam bark were taken directly from standing Melaleuca leucadendra (L.) trees with diameters of 10 cm to 15 cm. Both GWB types were then identified by the Indonesian Institute of Science (the Centre for Plant Conservation and Botanical Gardens). In this study, there was no separation between the outer bark and the inner bark. Based on field observations, the gelam bark from the Ø < 10 cm trunk was thin (Fig. 2a), and the bark from the Ø = 14.5 cm trunk had multiple layers with a thickness of approximately 3 cm (Fig. 2b).