**1. Introduction**

Seaweeds or marine macroalgae are plant-like organisms which are in general live attached to rocks or other substrata in coastal territories. This aquatic flowering plant grows at the bottom of the sea and consists of about 60 species. A total of 42 countries worldwide are involved in the commercialization of seaweeds and it is reported that the entire area coverage of this plant approaches a value of about 177,000 km<sup>2</sup> [1]. Indonesia produces 800,000 tons/year dried seaweed, which corresponds to almost the half of the world's production, and approximately the 85% of that figure is exported [2]. Seaweed is widely used for industrial purposes such as in cosmetics, medicine, food and beverages, ink and paper [3,4]. Seaweed can also be manufactured artificially with different levels of viscosity and can be used as industrial adhesives, known as hydrocolloids [5]. Seaweeds are important habitats for various microorganisms living in the sea, however, they are considered to be a waste material, since many leaves break away after their growing season, settle on the sea shores and decay; furthermore, their appearance becomes an eyesore. It is reported that a moderately wide belt of *Possidonia oceanica* seagrass may deliver more than 125 kg of dry material per square meter of the coastline annually [6,7].

*Possidonia oceanica* is a lignocellulosic material that can be found on the shores of the Mediterranean Sea, covering approximately 40,000 km2 of the seabed, and can be found in the form of seagrass balls and leaves [8]. The former has a fibrous form and comes

**Citation:** Rammou, E.; Mitani, A.; Ntalos, G.; Koutsianitis, D.; Taghiyari, H.R.; Papadopoulos, A.N. The Potential Use of Seaweed (*Posidonia oceanica*) as an Alternative Lignocellulosic Raw Material for Wood Composites Manufacture. *Coatings* **2021**, *11*, 69. https:// doi.org/10.3390/coatings11010069

Received: 22 December 2020 Accepted: 7 January 2021 Published: 8 January 2021

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from the rhizome of the plant and the latter comes from the living leaves. Seagrass has been investigated mainly because it was considered as a potential insulation material for buildings [6,7]. In addition, seagrass balls have been incorporated as a reinforcing agent in the manufacture of polyethylene composites [9,10]. Bettaieb et al. [11,12] examined the chemical and morphological characteristics of *Possidonia oceanica* leaves and concluded that they exhibited encouraging perspectives as nano-fillers for polymer matrices. Garcia et al. [13] studied the physical and mechanical properties of fiberboards made from *Possidonia oceanica* fibers and concluded that can be considered as an alternative to the conventional fiberboards. Similar observations were reported by Alamsjah et al. [14].

Although there is intense research into *Possidonia oceanica* fibers, the leaves have received far less attention. Saval et al. [15] manufactured cement-bonded particleboards from *Possidonia oceanica* leaves and outlined the possibility of their application in construction. Liew et al. [16] studied the physico-mechanical properties of particleboard made from seaweed adhesive and tapioca starch flour. They found that increasing the amount of tapioca starch flour in the seaweed adhesive resulted in improved mechanical properties. Kuqo et al. [17] made particleboards from *Possidonia oceanica* leaves and used isocyanate resin as a binder. They reported that seagrass leaves are propitious for application in construction and furniture industries.

A big challenge in composites industry is the availability of cheap raw lignocellulosic materials, potential candidates to replace slow growing trees, in order to minimize the production cost. A variety of plants were studied and tested worldwide in composites manufacturing, including vine stalks [18], topinambur stalks [19], cotton stalks [20,21], bamboo chips [22], canola straws [23], reed stem [24], date palms [25], oil palms and poppy husks [26], rice and wheat straw [27,28], stalks from cotton [29], camelthorn [30], and even chicken feathers [31,32]. This laboratory has extensive experience in the utilization of various lignocellulosic materials for composites manufacture, including vine prunings [33], castor stalks [34], bamboo and coconut chips [35,36], flax and banana chips [37,38] and cotton stalks [39]. As a consequence, the objective of this paper was to investigate the technical feasibility of manufacturing particleboards from seaweed leaves (*Possidonia oceanica).* The use of such materials may benefit both socioeconomic and environmental development since these leaves settle on the seashores and decay.

#### **2. Materials and Methods**

#### *2.1. Raw Material*

*Possidonia oceanica* (PO) leaves were collected from the coastline of Volos, central Greece. Their size varied from 8 to 10 mm in width and 50 to 150 mm in length. The leaves were washed and rinsed with distilled water in order to eliminate sand and other contaminations. After that, they were dried at room temperature for about two months. In their dried form, they have a brown appearance (Figure 1). Their moisture content, absolute density and pH were 118%, 0.35 kg/m3 and 8.2, respectively. The leaves were dried at 105 ◦C to 6.5–7% moisture content. Industrially produced wood chips comprising of predominantly mixed softwoods were supplied by a local plant. The wood chips were first screened through a mesh with 5 mm apertures to remove oversized particles, and they were then put through a mesh with 1 mm apertures to remove undersized (dust) particles.

After screening, the chips were dried to 6.5–7% moisture content. The boards were manufactured from particles dried to this moisture content.

#### *2.2. Board Manufacture and Testing*

A urea-formaldehyde resin (UF) (200–400 cP in viscosity, 47 s of gel time, and 1.277 kg/m<sup>3</sup> in density), 7% as a percentage of the oven dry weight of raw material, was applied for single layer board manufacture. Mattresses (50 × 50 cm2) were hot pressed at 180 ◦C for 6 min. The specific pressure of the plates was 24 kg/cm<sup>2</sup> (with 200 kgf as the total nominal pressure). The target board thickness was 16 mm and the target density was 0.55 kg/m3. A 2% aqueous solution of ammonium chloride (20% solids content), based on

resin solids, was added to the UF as a hardener before spraying. No water-repelling agent was used in this study. Four types of panel were made, consisting of varying mixtures of wood chips and PO leaves (the percentages of wood to PO leaves were 90:10, 75:25 and 50:50, respectively) and control boards with no PO content were made. Three replicates were made for each board type. The flow diagram of the experimental procedure is depicted in Figure 2.

**Figure 1.** *Possidonia oceanica* (PO) leaves as collected (**a**) and after drying (**b**).

**Figure 2.** The flow diagram of the experimental procedure.
