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Fig. 14 XRD patterns of the residual calcium alginate from (a) commercial alginate fi bres (CA) and (b) kelp alginate fi bres (KA) after thermal treatment at 200, 400, 600, and 800 °C.
Fig. 13 (a) Thermogravimetric (TG) and (b) DTG curves of calcium alginate fi bres and paper composites.
degradation temperature of calcium carbonate compared to KA bres. This occurs because it might take more energy to break the bonds in the polymer chains in CA bres than in KA bres. 3.4.4. Inorganic particle formation. The thermal degrada- tion of the calcium alginate bres was found to vary with the temperature applied to the tube in the furnace at 200, 400, 600, and 800 °C and the residual ash was analysed by XRD to clarify the formation of inorganic particles at elevated temperatures, as shown in Fig. 14. Calcium alginate bres from commercial alginate (CAF) did not show any signi cant peaks even when heated at 400 °C (CA400). The calcium alginate bres from kelp alginate (KAF) exhibited peaks at = 27.3°, 29.4°, 32.3°, 45.5°, and 56.6° in 2 q , similarly to KA200. In the case of KA400, the XRD pattern of a CaCO 3 powder shows 2 q peaks at 23.1°, 29.4°, 36.0°, 39.5°, and 43.3°, 41 indicating that calcium carbonate started to form in CA600 with two small peaks that appeared at 28.1° and 38.4°, representing the formation of Ca(OH) 2 and CaO, respec- tively. 42 In the case of KA 600, two small peaks were also observed at 28.1° and 38.4°, indicating the formation of Ca(OH) 2 andCaO, respectively. In the CA800 sample, in total ve additional peaks appeared at 18.0°, 47.0°, and 51.0° (Ca(OH) 2 ) 41 and at 32.3° and 55.7° (CaO). In the case of KA800, there were also additional peaks found as in CA800. The presence of CaCO 3 and CaO pro- cessed at high temperatures was exhibited by the XRD patterns of the calcium alginate bres in the residual char. The presence of CaCO 3 in the composites e ffi ciently increased the heat resistance
3.4.3 Thermal properties. The thermal stabilities (TGA and DTG) of the samples were analysed and are shown in Fig. 13a and b. Calcium alginate exhibited three stages of thermal decomposition; dehydration at 82 – 155 °C in the rst stage, loss of the abundant hydroxyl groups on the calcium alginate at 220 – 300 °C in the second stage at a maximum temperature of 280 °C, and calcium carbonate decomposition at 628 – 800 °C in the nal stage. Plain paper without alginate bres exhibited two-step decomposition between 50 and 100 °C due to dehydration and decomposition of the chemical structure of cellulose (glycosidic bonds) starting at 250 °C. The composite paper containing calcium alginate bres exhibited notable di ff erences compared to the original paper. KA25 showed a small peak at 621 °C, whereas CA25 showed a peak at 710 °C, indicating calcium carbonate decomposition. On the other hand, KA50 and KA75 showed a more pronounced peak at 625 °C, while CA50 and CA75 showed a peak indicating the decomposition of calcium carbonate at 715 °C. 39 It is because calcium alginate is a substance that is naturally ame- retardant, and it produces inorganic particles while it burns, and the inorganic particles could act as a barrier or insulating the surface, slow down the production of combustible gases, and prevent further decomposition. 40 From these results, it can be seen that the composite with CA bres added had a higher
RSC Sustainability , 2025, 3 , 599 – 610 | 607
© 2025 The Author(s). Published by the Royal Society of Chemistry
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