3.4.1. SEM analysis
SEM was used to observe the bulk structure of the untreated and pretreated SWBCs. As can be seen in Fig. S3, the pretreated SWBCs show swelling cellulose fragments. Interestingly, a similar observation was found for the untreated SWBC. This finding was slightly different from that reported by Shiddanta et al. [25]. The swelling cellulose fragments of the untreated SWBC were caused by extraction during the production of refined carrageenan, which uses NaOH or KOH. Refined carrageenan extraction was carried out using 5–7% KOH at 60–70 °C for 1–3 h depending on the age of the seaweed materials (personal communication with a contact in the carrageenan industry).