Preparation and properties of alginate based flame-retardant epoxy resin materials

Copper alginate (CA) and manganese alginate (MA) were prepared from the polysaccharide biomass sodium alginate, and these two alginates were introduced to epoxy resin (EP) to improve the flame retardancy. The limiting oxygen index (LOI), vertical combustion (UL-94), cone calorimetry (CCT), and thermogravimetric analysis (TGA) have been employed to analyze the impacts of alginates on the flame retardancy, thermal stability, and char formation characteristics of EP. Compared to pure EP, when 20 wt% of CA or MA was added, the LOI was increased by 5.6% and 6.7%, respectively, and no melt drops appeared. Because of alginates having catalytic carbonization effects, the residual char of EP composites containing CA or MA increased significantly, 5.53% and 9.56%, respectively. The peak heat release rate (PHRR) and total heat release (THR) of the EP composite containing CA or MA were drastically reduced. PHRR is reduced by 38.9% and 33%, while THR is decreased by 27% and 31%, respectively. In addition, total smoke production was reduced by approximately 17% and 30%, respectively. The scanning electron microscope (SEM) tests of the residual char revealed that EP containing CA or MA had a stronger charcoal-forming ability, and their charcoal layers had a more homogeneous and compact microstructures. Briefly, alginate, CA, or MA can effectively promote the catalytic carbonization of EP matrix in the condensed phase, and the flame-retardant properties of the EP resin are improved.