Increasing demand for geotextiles and increased environmental awareness have led to searching for new natural fibres that can be used as an alternative to synthetic ones. Coconut fibre appears to be one of the most versatile, but it is still little used in maritime applications and information on its performance is scarce. This study investigates the performance of coconut fibre in the marine environment by assessing three aspects: (i) substrate selectivity in terms of biofouling recruitment, (ii) fibre strength, and (iii) acidification potential. To address these aspects, a suite of field (i) and laboratory (ii and iii) experiments was carried out in collaboration with the Department of Civil Engineering and Architecture - DICAR of the University of Pavia, and the ‘Istituto Nazionale di Oceanografia e di Geofisica Sperimentale’ - OGS in Trieste. A natural coconut fibre, in the form of nonwoven geotextile was used for the analyses. An in-situ experiment of biofouling recruitment (i) was carried out at the ‘Marina del Fezzano’ (SP). The physical-mechanical characterisation of the fibre (ii) was performed by comparing scanning electron microscope (SEM) analysis of untreated fibres (T0) and fibres treated by immersion in the sea for 7 months (T1). Additionally, uniaxial tensile tests were performed both on the geotextile and on the individual T0 and T1 fibres. For both T0 and T1 conditions, the fibres were studied separately according to size category (< 200 μm - fine, 201 - 300 μm - medium, > 301 μm - thick). Finally, the geotextile was subjected to an evaluation of acidification potential in a controlled environment (iii), recreating a marine environment with constant temperature and different fibre concentrations (control - CTRL; low fibre - LF; 2 panels = 392 cm2 / 2 L; high fibre - HF; 4 panels = 784 cm2 / 2 L). As regards the biofouling recruitment experiment (i), a total of 40 species were identified, belonging to the following phyla: Annelida (41.24%), Bryozoa (24.07%), Tunicata (21.42%), of which 72.73% were colonial, Porifera (9.56%), Cnidaria (2.65%), of which 86.67% were colonial, Crustacea (0.53%) and Mollusca (0.53%). Non-Indigenous species were found at lower abundances (23.36%) than native species. As regards tests of fibre strength, SEM analyses revealed a marginally significant effect of condition (T0 - T1) on diameter variation (ANOVA; F (1.54) = 2.996; p = 0.089), which is in contrast to previous studies showing that fibre diameter increases of up to 34%, following water uptake. The fibre traction curves obtained from the uniaxial tensile tests (ii) show an approximately bilinear trend, and the Young's Modulus (GPa) was derived for each set of specimens: fine: T0 (2.391), T1 (1.978); medium: T0 (1.615), T1 (1.173); thick: T0 (1.126), T1 (0.579). The results obtained from the statistical analysis showed a highly significant effect of the size category on the elastic modulus (ANOVA; F2.84 = 30.328; p << 0.001) and a significant effect of the condition: specifically, a reduction in fibre stiffness as the diameter increases and after sea treatment is emphasised. The Young's Modulus (1.65 MPa) was also obtained for the coconut fibre geotextile, which indicates greater elasticity compared to other synthetic materials, such as polypropylene (PP). The pH analyses of fibres kept in tanks at different concentration (iii) revealed highly significant effects of condition (ANOVA; F2.31 = 315.222; p << 0.001) and time (ANOVA, F4.31 = 30.335; p << 0.001). Furthermore, the interaction between the two factors was statistically significant (ANOVA; F8.31 = 3.373; p = 0.010). In conclusion, coconut fibre proves to be a viable alternative to synthetic fibres. However, in order to optimise its performance, further studies would be required.
L’incremento della domanda di geotessili e la maggiore consapevolezza ambientale hanno portato alla necessità di ricercare nuove fibre naturali utilizzabili in alternativa a quelle sintetiche. La fibra di cocco risulta una tra le più comunemente utilizzate in ambito terrestre, ma il suo impiego in ambiente marino è ancora limitato; di conseguenza, le informazioni relative alle sue performance in questo ambiente scarseggiano. Questo studio indaga le prestazioni della fibra di cocco in ambiente marino, valutando tre aspetti: (i) la capacità di reclutamento biofouling del substrato, (ii) la resistenza della fibra ed (iii) il potenziale di acidificazione dell’ambiente. Per investigare questi aspetti, è stata condotta una serie di esperimenti sul campo (i) e in laboratorio (ii e iii), in collaborazione con il Dipartimento di Ingegneria Civile e Architettura - DICAR dell'Università di Pavia e l'Istituto Nazionale di Oceanografia e di Geofisica Sperimentale - OGS di Trieste. Per le analisi è stato utilizzato un geotessile non tessuto in fibra di cocco. Un esperimento in-situ di reclutamento di biofouling (i) è stato effettuato presso il porticciolo turistico di Marina del Fezzano (SP). La caratterizzazione fisico-meccanica della fibra (ii) è avvenuta mediante confronto dell’analisi al microscopio elettronico a scansione (SEM) delle fibre non trattate (T0) e trattate mediante immersione in mare di 7 mesi (T1), in associazione a prove di trazione uniassiale, effettuate sia sul geotessile sia sulle singole fibre T0 e T1. Per ambedue le condizioni T0 e T1, le fibre sono state studiate separatamente in base alla categoria dimensionale (< 200 µm - fini, 201 - 300 μm - medie, > 301 μm - spesse). Infine, il geotessile è stato sottoposto ad una valutazione del potenziale di acidificazione in ambiente controllato (iii), ricreando un ambiente marino a temperatura costante e diverse concentrazioni di fibra (control - CTRL; low fiber - LF; 2 pannelli = 392 cm2 / 2 L; high fiber - HF; 4 pannelli = 784 cm2 / 2 L). Studiando la comunità sessile sono state identificate 40 specie, appartenenti ai seguenti phyla: Annelida (41,24%), Bryozoa (24,07%), Tunicata (21,42%), Porifera (9,56%), Cnidaria (2,65%), Crustacea (0,53%) e Mollusca (0,53%). Le specie non indigene (NIS) sono state riscontrate con abbondanze inferiori (23,36%) rispetto alle specie native. Dalle analisi al SEM (ii), è emerso un effetto marginalmente significativo della condizione (T0 - T1) (ANOVA, F1,54 = 2.996; p = 0,089) sul diametro delle fibre. Dalle prove di trazione uniassiale è stato ricavato il Modulo di Young (GPa) per ogni set di provini: fini: T0 (2,39 ± 0,81), T1 (1,98 ± 0,73); medie: T0 (1,62 ± 0,56), T1 (1,17 ± 0,85); spesse: T0 (1,13 ± 0,60), T1 (0,58 ± 0,27). Dall'analisi statistica è emerso un effetto altamente significativo della categoria dimensionale (ANOVA, F2,84 = 30,328; p << 0,001) ed un effetto significativo della condizione (ANOVA, F1,84 = 11,073; p = 0,001) sul modulo: nello specifico, viene sottolineata una riduzione della rigidezza delle fibre all’aumentare del diametro e dopo il trattamento in mare. Il modulo elastico ricavato dal geotessile risulta pari a 1,65 MPa. Dalla valutazione del potenziale acidificante della fibra sono emersi effetti altamente significativi della condizione (ANOVA, F2,31 = 315,222; p << 0,001) e del tempo (ANOVA, F4,31 = 30,335; p << 0,001) sul pH. Inoltre, l’interazione tra i due fattori è risultata statisticamente significativa (ANOVA, F8,31 = 3,373; p = 0,010): una maggiore concentrazione di fibra influenza maggiormente il pH. La fibra di cocco ha mostrato performance soddisfacenti anche in mare, confermandosi una buon alternativa alle fibre sintetiche anche in questo ambiente. Tuttavia, per ottimizzarne le prestazioni, sarebbe necessario approfondire gli studi in merito.
Studio delle performance tecniche ed ecologiche della fibra di cocco in ambiente marino.
NAZZARI, MIREA
2023/2024
Abstract
Increasing demand for geotextiles and increased environmental awareness have led to searching for new natural fibres that can be used as an alternative to synthetic ones. Coconut fibre appears to be one of the most versatile, but it is still little used in maritime applications and information on its performance is scarce. This study investigates the performance of coconut fibre in the marine environment by assessing three aspects: (i) substrate selectivity in terms of biofouling recruitment, (ii) fibre strength, and (iii) acidification potential. To address these aspects, a suite of field (i) and laboratory (ii and iii) experiments was carried out in collaboration with the Department of Civil Engineering and Architecture - DICAR of the University of Pavia, and the ‘Istituto Nazionale di Oceanografia e di Geofisica Sperimentale’ - OGS in Trieste. A natural coconut fibre, in the form of nonwoven geotextile was used for the analyses. An in-situ experiment of biofouling recruitment (i) was carried out at the ‘Marina del Fezzano’ (SP). The physical-mechanical characterisation of the fibre (ii) was performed by comparing scanning electron microscope (SEM) analysis of untreated fibres (T0) and fibres treated by immersion in the sea for 7 months (T1). Additionally, uniaxial tensile tests were performed both on the geotextile and on the individual T0 and T1 fibres. For both T0 and T1 conditions, the fibres were studied separately according to size category (< 200 μm - fine, 201 - 300 μm - medium, > 301 μm - thick). Finally, the geotextile was subjected to an evaluation of acidification potential in a controlled environment (iii), recreating a marine environment with constant temperature and different fibre concentrations (control - CTRL; low fibre - LF; 2 panels = 392 cm2 / 2 L; high fibre - HF; 4 panels = 784 cm2 / 2 L). As regards the biofouling recruitment experiment (i), a total of 40 species were identified, belonging to the following phyla: Annelida (41.24%), Bryozoa (24.07%), Tunicata (21.42%), of which 72.73% were colonial, Porifera (9.56%), Cnidaria (2.65%), of which 86.67% were colonial, Crustacea (0.53%) and Mollusca (0.53%). Non-Indigenous species were found at lower abundances (23.36%) than native species. As regards tests of fibre strength, SEM analyses revealed a marginally significant effect of condition (T0 - T1) on diameter variation (ANOVA; F (1.54) = 2.996; p = 0.089), which is in contrast to previous studies showing that fibre diameter increases of up to 34%, following water uptake. The fibre traction curves obtained from the uniaxial tensile tests (ii) show an approximately bilinear trend, and the Young's Modulus (GPa) was derived for each set of specimens: fine: T0 (2.391), T1 (1.978); medium: T0 (1.615), T1 (1.173); thick: T0 (1.126), T1 (0.579). The results obtained from the statistical analysis showed a highly significant effect of the size category on the elastic modulus (ANOVA; F2.84 = 30.328; p << 0.001) and a significant effect of the condition: specifically, a reduction in fibre stiffness as the diameter increases and after sea treatment is emphasised. The Young's Modulus (1.65 MPa) was also obtained for the coconut fibre geotextile, which indicates greater elasticity compared to other synthetic materials, such as polypropylene (PP). The pH analyses of fibres kept in tanks at different concentration (iii) revealed highly significant effects of condition (ANOVA; F2.31 = 315.222; p << 0.001) and time (ANOVA, F4.31 = 30.335; p << 0.001). Furthermore, the interaction between the two factors was statistically significant (ANOVA; F8.31 = 3.373; p = 0.010). In conclusion, coconut fibre proves to be a viable alternative to synthetic fibres. However, in order to optimise its performance, further studies would be required.| File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.14239/28560