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Table 2 Intrinsic viscosity and average molecular weight estimation of sodium alginate samples
Intrinsic viscosity [ h ] (L g − 1 )
w a × 10 5 (gmol − 1 )
R 2
No
Brown seaweed species
Sample name
M
1 2 3 4 5 6 7 8 9
BSAR BSCR USAR USCR BKAR BKCR UKAR UKCR CMAL
0.14 0.07 0.21 0.18 0.17 0.15 0.58 0.38 0.55
0.63 0.34 0.99 0.84 0.79 0.68 2.74 1.89 2.60
0.956 0.984 0.912 0.909 0.936 0.970 0.996 0.954 0.960
S.polycystum
L. japonica
Commercial alginate
Additionally, the puri cation process was found to be one of the factors for the low yield of sodium alginates. Fig. 5 shows that the yield via the calcium route was higher than that via the acid route because calcium ions have a strong a ffi nity for algi- nate molecules, leading to strong bonds between sodium algi- nates and calcium ions. In contrast, the acid route via the addition of an acid, such as sulfuric acid, may cause some degradation of alginate molecules, resulting in a lower yield of sodium alginates. This nding was con rmed by Lim et al. 29 The yield of sodium alginates from Sargassum sp. was higher via the calcium route than the acid route.
3.2 Sodium alginate characterization 3.2.1 Intrinsic viscosity ([ h ]) and molecular weight ( M w a ). The intrinsic viscosity and molecular weight based on the molar mass of sodium alginates from S. polycystum are shown in Table 2 and Fig. 6, ranging from 0.07 to 0.21 L g − 1 and 0.338 to 0.994 × 10 5 gmol − 1 , and the molar mass of sodium alginates from L. japonica ranged from 0.15 to 0.58 dL g − 1 and 0.679 to 2.74 × 10 5 g mol − 1 , and for commercial sodium alginates (CMAL) it was 0.55 L g − 1 . This result also demonstrates a regression coe ffi cient ( R 2 ) greater than 0.9, as shown in Table 2, indicating the accuracy of the outcomes. S. polycystum subjected to various ozonation treatments (bleaching treatment) had intrinsic viscosities ranging from 0.042 to 0.158 dL g − 1 . 30 The polymer chain was shortened during the bleaching process because of the glycosidic bond breakage. The results show that the intrinsic viscosity of sodium alginates from the bleaching process signi cantly decreased due to the bleaching treatment. This led to a decrease in molecular weight. 25,30 The acid route can promote more complete precipitation of sodium alginates, leading to the formation of larger, more
Fig. 6 Speci fi c viscosity ( h
sp ) of sodium alginate samples in 0.1 M NaCl
Fig. 7 FTIR of alginate from commercial, L. japonica , and S. polycystum .
from(a) S. polycystum and (b) L. japonica .
604 | RSC Sustainability , 2025, 3 , 599 – 610
© 2025 The Author(s). Published by the Royal Society of Chemistry
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