PLA system containing cellulose flame retardant
Cellulose is a cell wall component. In simple terms, cellulose is a linear macromolecule composed of glucose molecules connected by β 1,4 glycosidic bonds. The molecular formula is (C6H10O5) (n where n is the degree of polymerization). Widely distributed, mainly in the cell walls of higher plants and bacteria, algae and fungi.
Thermal degradation process of cellulose
In the first stage, physical dehydration occurs under low temperature conditions, and the crystal water in the cellulose is removed;
In the second stage, chemical dehydration occurs at about 150 °C to generate water and dehydrated cellulose. The generation of water is conducive to accelerating the hydrolysis of glycosidic bonds and promoting the degradation of cellulose; as the temperature increases;
In the third stage, thermal decomposition and carbonization reactions occur from 240 °C, resulting in liquid product tar and carbon-containing intermediate products, while dehydrated cellulose further reacts to generate carbon monoxide, carbon dioxide, and water vapor;
In the fourth stage, aromatization and cross-linking of carbon occurs above 400 °C to form coke residue.
It is worth noting that under high temperature conditions, the reaction tends to form tar and inhibit coke formation. However, abundant modification technologies are beneficial to improve the flame retardant properties of cellulose at high temperature. Cellulose can be hydrolyzed by inorganic acid to form cellulose with low degree of polymerization and a certain degree of crystallinity, called microcrystalline cellulose (MCC). In addition, cellulose can also be hydrolyzed to form nanocrystalline cellulose (NCC). The physical properties of MCC and NCC are significantly different, and NCC has the characteristics of high crystallinity. In recent years, MCC and NCC have also been used to flame retardant PLA.
Cellulose containing a large number of natural hydroxyl structures has potentially good carbon-forming properties, but has poor thermal stability and cannot meet the processing requirements of PLA. Therefore, the flame retardant system is still in the basic research stage and has not been industrialized.
