Physical and Mechanical Properties of Particleboard Made from Palm Tree Prunings

Article Physical and Mechanical Properties of Particleboard Made from Palm Tree Prunings Clara-Eugenia Ferrández-García 1, Antonio Ferrández-García 1,*, Manuel Ferrández-Villena 1, Juan Fernando Hidalgo-Cordero 2, Teresa García-Ortuño 1 and María-Teresa Ferrández-García 1 1 Department of Engineering, Universidad Miguel Hernández, Carretera de Beniel, Km. 3,2, 03312 Orihuela, Alicante, Spain; [email protected] (C.-E.F.-G.); [email protected] (M.F.-V.); [email protected] (T.G.-O.); [email protected] (M.-T.F.-G.) 2 Construction Unit, Department of Agroforestry Engineering, Universidad Politécnica de Madrid, ETSI Montes, Avda. Ramiro de Maeztu S/N, 28040 Madrid, Spain; [email protected] * Correspondence: [email protected]; Tel.: +34-68-095-7181 Received: 30 October 2018; Accepted: 3 December 2018; Published: 5 December 2018 Abstract: Palm trees are very fast-growing species. Their management produces annually a large amount of biomass that traditionally has been either disposed of at dumping sites or has been burnt onsite. This paper presents an experimental study to obtain particleboard using this biomass in a low energy process (short pressing time and low pressing temperature), using particles of different sizes from the rachis (midrib) of the three palm species most representative of urban gardening in Spain: canary palm (Phoenix canariensis hort. ex Chabaud), date palm (Phoenix dactylifera L.) and washingtonia palm (Washingtonia robusta H. Wendl). Their physical and mechanical properties were tested, and the feasibility of their use as a construction material was evaluated. The results showed that the manufactured particleboard had similar performance to conventional wood particleboard and good thermal insulation properties. Boards made with the canary species showed better mechanical performance. The properties of the particleboard depended on the particle size and species. The use of the pruning waste of palm trees to produce durable materials such as particleboard could be beneficial to the environment since it is a method of carbon fixation, helping to decrease atmospheric pollution and reducing the amount of waste that ends in dumping sites. Keywords: thermal conductivity; palm rachis; biomass; hot pressing; Phoenix canariensis; Phoenix dactylifera; Washingtonia robusta 1. Introduction Climate change is a real long-term problem that requires a multidisciplinary global approach. One of the proposed strategies for responding to this issue is mitigation, understood as actions to limit the emission of greenhouse gases by capturing and storing atmospheric carbon dioxide (CO2) in sinks such as forests [1]. The appropriate management of carbon sinks is needed in order to conserve and expand their size in a socio-economically sustainable manner. One manner of storing carbon is by transforming the biomass produced within forests into wood-based products. A few studies have been performed to assess the carbon flux through the life cycle of wood panels: Wang et al. [2] conducted a study to assess the contribution of the wood-based panels to CO2 emissions and removal in different panels in China. They estimated the CO2 emissions through panel production and the CO2 stored during their useful lives, concluding that the wood-based industry can potentially contribute to climate change mitigation. Rivela et al. [3] studied the life cycle of particleboard and created a database to identify and characterize the manufacture of particleboard. They reported that environmental, Forests 2018, 9, 755; doi:10.3390/f9120755 www.mdpi.com/journal/forests Forests 2018, 9, 755 2 of 14 economic and social considerations strengthened the hypothesis that the use of forest residues in particleboard manufacture is more sustainable than their use as fuel. In the south-east of Spain, palm trees are extensively used in urban landscaping, as in most of the countries surrounding the Mediterranean Sea. Among the different species, the most abundant are: Phoenix dactylifera L. (hereafter called date palm), Phoenix canariensis hort. ex Chabaud (canary palm), and Washingtonia robusta H. Wendl (washingtonia palm). Apart from their ornamental use, the date palm can also be found in groves in the Alicante province, in two cities (Elche and Orihuela) forming a unique forest ecosystem. Some palm species can live from 150 to 300 hundred years. As part of their management, they are pruned to remove old leaves (fronds) and inflorescences at least once a year, producing a large amount of biomass that has traditionally been disposed of either at dumping sites or has been burnt onsite. Palm trees are a very fast-growing species. Their management produces an annual average dry mass of 49.34 kg/tree from Phoenix canariensis [4], 72.26 kg/tree from Phoenix dactylifera [4], and 35.70 kg/tree from Washingtonia robusta [5]. This biomass is classified as urban waste according to the European list of waste [6]. Several studies have been conducted focusing on the manufacturing of building materials using different palm residues. Particleboard with synthetic adhesives and different manufacturing procedures have been studied using fibers or chips of date palm [7–15], washingtonia palm [5,16–18], and canary palm [19–21]. Other studies have been performed using date palm pruning waste as a reinforcement in concrete [22–24], in gypsum [25], and in the manufacturing of different composites [25–27]. Most of these works were aimed at the use of palm pruning waste to produce thermal insulating materials [18,21,22,25,28–30]. These investigations showed different results depending on the palm species and the part of the plant used (generally the leaves or trunk). The particle size and production parameters can also affect the physical and mechanical properties of the resulting materials. Particleboard is made by applying pressure and heat to particles of wood or other lignocellulosic biomass with the addition of an adhesive. The temperature in the hot press varies with the type of adhesive employed. For urea–formaldehyde (UF) the hardening occurs at 90 ◦C, but to shorten this process, temperatures over 200 ◦C are employed. Times of 3 to 4 min for a 20 mm thick particleboard are required when using UF at 180 ◦C. The majority of the world’s production of particleboard is made of wood with densities ranging from 0.60 to 0.80 g/cm3. Most of these are three-layered, with outer layers made of finer particles and a central section composed of coarser and cheaper chips, which improves the strength, stiffness, and appearance. In general, 9% and 12% of UF is needed to bond the particles of the core and the particles of the outer layers, respectively [31]. Although it is possible to manufacture particleboard from almost all types of wood, those with a specific weight smaller than 0.60 g/cm3 are more suitable, since denser woods present difficulties when cutting [31]. The utilization of hard wood causes wear to chippers and other tools and requires higher pressures at the hot press [32]. However, the use of soft woods results in lower strength [33]. Several authors have studied the influence of different manufacturing parameters for particleboard. Of these parameters, Nemli et al. [34] studied the humidity of the mat, the amount of resin, the addition of wood powder, and the pressing time. Boonstra et al. [35] studied steam pretreatments at 200 ◦C and 210 ◦C. Han et al. [36] studied the press speed and the humidity of the raw material. Abdalla et al. [37] studied the density of the boards. Blanchet et al. [38] studied the amount of wood particles and UF (12%, 14% and 16%) in the outer layers (12%, 14% and 16%) and in the core (8%). Ashori et al. [9] studied the amount of UF (9%, 10% and 16%) in single-layer particleboards with 4, 5 and 6 min in the hot press, respectively. Wang et al. [39] studied the different adhesives in the board industry and their optimization. Current investigations are aimed at obtaining a new generation of biocomposites with a wide range of materials, such as plastics, plaster, cement, metal, glass and lignocellulosic residues. The aim of this study was to obtain particleboard using a low energy process (short pressing time and low pressing temperature), using particles of different sizes from the rachis (midrib) (Figure1) of Forests 2019, 10 FOR PEER REVIEW 3 Forests 2018, 9, 755 3 of 14 mechanical properties were tested, and the feasibility of their use as a construction material was evaluated. the three mostForests representative2019, 10 FOR PEER REVIEW palm species in urban gardening in Spain. Their physical and mechanical3 properties were tested, and the feasibility of their use as a construction material was evaluated. mechanical properties were tested, and the feasibility of their use as a construction material was evaluated. FigureFigure 1. Frond1. Frond and and rachis of of a palma palm tree. tree. 2. Materials and Methods 2. Materials and Methods The raw material used was the rachis of the fronds of three different palm species—date, canary, The raw and washingtoniamaterial used palm—that was the the were rachis rachis kindly of of suppliedthe the fron fronds byds the of of municipality three three different different of the Sanpalm palm Anton species—date, species—date, palm grove canary, canary, and washingtonia in Orihuela, palm—that Alicante (Spain). were These kindly rachises supplied were obtained by the by municipality trimming the leaflets of the from San theAnton fronds. palm grove in Orihuela,They Alicante had an initial (Spain). moisture These content rachises of 73% were and obtainedwere air dried by trimmingfor 8 months the to leafletsan approximate from the fronds. in Orihuela,moisture Alicante content (Spain). of 8%. TheseParticles rachises were obtained were obtainedusing a laboratory-scale by trimming ring-knife the leaflets chipper, from after the fronds. They had which an initial they were moisture sieved using content a horizontal of 73% screen and wereshaker airwith dried sieves forof 8, 8 4, months 2, 1 and 0.25 to anmm approximate to moisture contentcontentremove oversize of of 8%.

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