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3.3.2 Tensile strength of single calcium alginate bres. The average tensile strengths of a single bre of commercial algi- nates, kelp calcium alginates, and sargassum calcium alginates are compared in Fig. 9. The results of this study indicate that the tensile strengths of commercial alginate bres and kelp calcium alginate bres were higher than that of the sargassum calcium alginate bres. The lower tensile strength of the Sargassum calcium algi- nate bres is attributed to the lower viscosity of sodium alginate obtained from S. polycystum , as compared to the other two sources. The higher viscosity suggesting a higher molecular weight of the alginate composed of long poly- saccharide chains generally leads to stronger bres. 37 On the other hand, a lower viscosity would result in weak bres because a low viscosity material is typically more uid, presumably having an impact on the bonding that occurs during the formation of the bres. Based on these results, the commercial and kelp calcium alginate bres were chosen for further experiments. 3.4 Characterization of paper composites 3.4.1 FESEM. Fig. 10 shows the FESEM images of the morphology of the paper, calcium alginate bres and paper composites. The calcium alginate bres (Fig. 10e) display a larger bre size in comparison to the pulp bres, as observed in the HBKP sample (Fig. 10a) with the same magni cation. While the calcium alginate bres are bonded, their structure appears weaker compared to the pulp bres, which are smaller and more uniform. 3.4.2 Tensile index. Fig. 11 shows the tensile index of a paper composite consisting of pulp bres mixed with and without alginate bres obtained from L. japonica and commercial alginate. The tensile strength results showed that the formulations CA25, KA25, CA50, and KA50 exhibited an improvement in the tensile index compared to CA75 and KA75. However, the tensile strength with the addition of alginate bres was still lower than that of the control (paper containing only pulp bres). This is also con rmed by other studies clari- fying that the mechanical strengths of a cotton/alginate
Fig. 11 Tensile index of calcium alginate-containing wood pulp sheets.
Fig. 12 SEM image before fracture and after fracture of HBKP (a and c) and KA75 (b and d).
composite decreased with increasing alginate content. 38 As can be seen from the fracture, interaction among calcium alginate bres is not particularly strong, as shown in Fig. 12.
Fig. 10 SEM images of (a) HBKP, paper composites containing commercial alginate (CA) fi bres: (b) 25%, (c) 50%, and (d) 75%, (e) calcium alginate fi bres, and paper composites containing kelp alginate (KA) fi bres: (f) 25%, (g) 50% and (h) 75%.
606 | RSC Sustainability , 2025, 3 , 599 – 610
© 2025 The Author(s). Published by the Royal Society of Chemistry
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