Pyrolysis mechanisms of typical seaweed polysaccharides

•Different algal polysaccharides consist of different components.•The main pyrolysis products of green and brown algal polysaccharides are different.•Using TG-MS combined with Py-GC/MS, pyrolysis mechanisms can be obtained.•The generation pathway of main products of polysaccharides pyrolysis were revealed.

The pyrolysis mechanisms of typical seaweed polysaccharides were investigated using TG-MS and Py-GC/MS. It was found that Enteromorpha polysaccharides (EN) was mainly composed of glucan, xylan and glucuronide-sulfate-rhamnose, while Sargassum fusiforme (SA) mainly consisted of uronic acid, sulfate group-fucose and polysaccharide galactose. Because of the component differences, it was found that the content of oxygen-containing functional groups and inorganic oxides varies. Meanwhile, three types of sulfur-containing functional groups (sulfonyl groups, sulphates, sulfate) were observed in seaweed polysaccharide. During the pyrolysis process, SO2 was generated because of the cleavage of sulfuric acid group in 4-O-glucuronide-2 sulfate-l-rhamnose. The generation of CO2 was due to the decarboxylation of organic matter. Besides, Py-GC/MS analysis indicated that the main pyrolysis products of EN polysaccharides were furans. The pyrolysis products of SA polysaccharides were mainly ester substances. Thus, the pyrolysis mechanisms as well as the generation pathways of main products of polysaccharides pyrolysis, were revealed.