2.2. Posidonia oceanica Egagropili in Environmental Decontamination Processes
PO is a natural biomonitor of pollution in the sea as it catches heavy metal ions such as arsenic (As), cadmium (Cd), lead (Pb), and zinc (Zn) present in the water to store them in its organs at concentrations of up to several mg/kg
[21][14]. Additionally, the dried fibrous balls of POEGs have promising features, such as being green adsorbents for cationic pollutants since they are already found in nature as cation-imprinted lignocellulose networks that contain a high presence of salts
[21][14]. The high biosorption properties of POEGs could constitute a new potential way for their valorization and reusing in cleaning systems of blackish water decontamination processes from dyes, phenol compounds, and heavy metals
[10,21][8][14]. According to some scholars, the POEGs’ ability to uptake metals might be due to the porosity of their cell walls, which allow the entrance of small ions, and due to their lignocellulose composition
[22][15]. In the literature, many studies have focused on POEGs’ absorption abilities and their possible applications in diverse decontamination processes. In these investigations, some key parameters of the process have been taken into account, such as the pH of the contaminant solution, the temperature at which the process is performed, the contact time between the solution and the POEGs, the initial concentration of the contaminant, the amount and size of the POEGs, and the enthalpy and entropy of the process. In a recent paper, some POEGs collected in Marsa Matrouh, Egypt (31°21′15″ N, 27°14′14″ E) (
Figure 2) were “activated” by soaking them after pulverization in 1 M acetic acid overnight and then used as an eco-adsorbent for the removal (in 30 min of shaken run) of methylene blue and lead ions (Pb
2+) present in aqueous solutions in concentration ranges from 0.6 to about 2.6 g/L
[21][14]. The initial acetic acid activation method resulted in greatly reducing the presence of some ions, such as barium (B), cadmium (Cd), chromium (Cr), copper (Cu), magnesium (Mg), and zinc (Zn), in the fibers that are naturally present in the collected samples without altering the lignocellulose composition. On the basis of these analyses of the adsorption isotherms and thermodynamic studies, the scholars proposed that the POEG adsorption mechanism of methylene blue, present in water as monomers, dimers, or trimers, might be due to combined electrostatic and physical multi-layer adsorption processes, whereas the lead was chemically adsorbed. The activated fibers were then applied to decontamination of waste blackish waters to remove the methylene blue from Manzala Lake, Egypt, with an efficiency of 91.5–99.9%
[21][14]. The use of POEGs as new bio-sorbents for heavy metals (M) with an oxidation state of II was investigated in another paper using samples collected in Tipaza, Algeria (36°37′4″ N, 2°23′28″ E) (
Figure 2).
2.3. Posidonia oceanica Egagropili in Bioplastic and Biocomposite Preparations
POEG fibers have been widely used to strengthen the matrix of plastics, both of bio-based and oil-based origins. Mirpoor et al.
[2] have exploited both the lignin-carbohydrate (LCC) and the nanocrystalline cellulose (NC) fractions, after extraction from egagropili collected in Poetto (
Figure 2), as reinforcing agents for hydroplastic materials. The two fractions were able to improve the physicochemical properties of biodegradable films obtained from hemp (
Cannabis sativa) oil seedcake protein concentrates. In fact, such materials exhibited a high tensile strength and Young’s modulus; the Young’s modulus increased from around 20 to 45 and to 80 MPa, while the elongation at break was reduced from 300% to 250% and to 120% in the presence of LCC and NC, respectively. They possessed barrier properties towards water vapor, O
2, and CO
2. In addition, both fractions decreased film hydrophilicity, infact, moisture content, solubility, and swelling ratio were lower for the films prepared in the presence of additives. In 2021, the same scholars
[12][16] investigated deeply the LCC fraction obtained from the same POEG samples from a chemical point of view using FT-IR and NMR analyses (see also
Section 1.2). The LCC fraction was water soluble as it contained monosaccharides and exhibited a brownish-to-black color due to certain functional groups, such as phenylpropane-based polymers. Furthermore, it exhibited a remarkable and stable antioxidant activity that was easily released over 6 months when it was used as an additive in hemp protein-based films. On the other hand, in another paper, lignin-containing cellulose micro/nanofibrils (LCM/NF) were also obtained by combining the steam explosion process or twin-screw extrusion (as energy-efficient pretreatments) with a conventional grinding step
[27][17]. The chemical composition of the fibers, collected in Monastir (
Figure 2), before and after pulping, was analyzed. The obtained LCM/NF suspensions were characterized by several techniques, such as morphological and mechanical analysis. It has been shown that if the sulfonation method was coupled with steam explosion or twin-screw extrusion, then it was possible to obtain LCM/NF gels with relatively low viscosity and nano papers with a Young’s modulus of around 5 GPa. Sulfonation was revealed to be an effective pretreatment to lower the energy during grinding, and therefore it can be considered a valid technique to be applied in the field of packaging
[27][17]. POEG fibers, collected in Campello Beach in Alicante, Spain (38°21′00.01″ N, 0°29′00″ W) (
Figure 2), were exploited in the reinforcement phase and in oil-based polymeric matrices, such as the high-density polyethylene (HDPE)
[28][18] samples), and more recently even in polyesters
[28,29][18][19].
2.4. Posidonia oceanica Egagropili in Construction Materials and as Decoration
POEGs have been widely studied in recent years as environmentally friendly materials to be employed in buildings having fire, sound, and water-resistant properties. For example, POEGs have been used in the construction sector as insulating material to reduce the risk of energy source shortages and better manage energy consumption in buildings
[33][20]. In this context, the use of insulating materials is a key factor, as they might provide better thermal comfort, sound insulation, and fire protection
[37][21]. It is worth noting that so far, many of the insulation materials used in the building sector were petroleum derivatives, and they must be replaced with materials derived from renewable natural resources from the perspective of a sustainable bioeconomy
[34][22]. Benjeddou et al.
[35][23] studied the effect of adding POEGs to cement composites and found that the mechanical strength, sound, and thermal diffusivity were all improved. The POEG fibers were able to reduce sound transmission by increasing the fiber volume and, consequently, the air voids in the cement paste. Another study carried out by Jedidi and Abroug
[34][22] reported that the addition of POEG fibers (collected in Monastir, Tunisia;
Figure 2), up to 10%, to the plasters significantly improved their mechanical properties. Thermal conductivity also decreased from 0.35 W/m/K in the absence of fibers to 0.11 W/m/K in the presence of 20% of them.
3. Conclusions
In recent years, POEGs have caught more and more attention as interesting marine-origin raw materials. Due to their structural and physical properties, they have demonstrated that they could be employed in a variety of applications and fields. The whole POEG fiber network constitutes an interesting nutrient that can be supplemented to a medium for both plant and microorganism growth, while their cellulose components have already been used in biotechnological processes to obtain added valuable molecules, such as enzymes and biofuels. Due to their physical and mechanical properties, these fibers could easily constitute the base of newly developed bioplastics and biocomposites, as well as insulating materials for buildings. Moreover, their isolated lignin fractions might be easily used as reinforcement in newly designed biomaterials. The ability of their fibers to adsorb metals and water contaminants also makes POEGs the ideal ecological tools for environmental decontamination.