Valorisation of Posidonia oceanica Sea Balls (Egagropili) as a Potential Source of Reinforcement Agents in Protein-Based Biocomposites

Abstract

Nanocrystalline cellulose (NC) and a lignin-containing fraction (LF) were obtained from egagropili, the so called sea balls produced from rhizome and stem fragments of Posidonia oceanica that accumulate in large amounts along the coastal beaches in the form of tightly packed and dry materials of various dimensions. Both egagropili fractions have been shown to be able to improve the physicochemical properties of biodegradable films prepared from protein concentrates derived from hemp oilseed cakes. These materials, manufactured with a biodegradable industrial by-product and grafted with equally biodegradable waste-derived additives, exhibited an acceptable resistance with a still high flexibility, as well as they showed an effective barrier activity against water vapor and gases (O₂ and CO₂). Furthermore, both NC and LF decreased film moisture content, swelling ability and solubility, thus indicating that both additives were able to improve water resistance of the hydrocolloid films. The exploitation of egagropili, actually considered only an undesirable waste to be disposed, as a renewable source of reinforcing agents to blend with different kinds of polymers is suggested.

Keywords: Posidonia oceanica; egagropili; lignin; nanocrystalline cellulose; protein-based biocomposites.

Figure 1

Posidonia oceanica rhizomes and stems (A) from which ball shaped dry materials called egagropili (B) origin and accumulate along the costal beach (C).

Figure 2

Scheme of the extraction procedure of nanocrystalline cellulose and lignin containing fraction from egagropili.

Figure 3

SEM images of both grinded egagropili fibers (A) and egagropili nanocrystalline cellulose (B).

Figure 4

Tensile strength, elongation at break, Young’s module and thickness of hemp protein-based films derived from film forming solutions prepared at pH 9 and containing increasing amounts of egagropili nanocrystalline cellulose (NC). Different small letters a–d indicate significant differences among the values reported in each column (p < 0.05). Further experimental details are given in text.

Figure 5

Tensile strength (TS), elongation at break (EB), Young’s module (YM) and thickness of hemp protein-based films derived from film forming solutions (FFSs) prepared at pH 12 and containing increasing concentrations of egagropili lignin fraction (LF). Different small letters a–d indicate significant differences among the values reported in each column (p < 0.05). Further experimental details are given in text.

Figure 6

Moisture content, solubility and swelling ratio of hemp protein-based films prepared with film forming solutions containing increasing amounts of either nanocrystalline cellulose (NC) or lignin fraction (LF) and prepared at pH 9 and 12, respectively. Different small letters a–d indicate significant differences among the values reported in each column (p < 0.05). Further experimental details are given in text.

Figure 7

Gas and water vapor permeability of hemp protein-based films prepared with film forming solutions containing increasing amounts of either nanocrystalline cellulose (NC) or lignin fraction (LF) and prepared at pH 9 and 12, respectively. Different small letters a–d indicate significant differences among the values reported in each column (p < 0.05). Further experimental details are given in text.

Figure 8

Images of hemp protein films (A), and of their SEM cross-sections (B, magnification 8000×) and surfaces (C, magnification 8000×), containing 50% glycerol and prepared in the absence (1) and presence of either 6% egagropili nanocristalline cellulose (2) or lignin fraction (3). Further experimental details are given in the text.