Flame retardant PLA system containing lignin
Lignin is an amorphous aromatic high polymer that widely exists in plants. After the aromatic structure of lignin is decomposed, it has a high carbon residue rate. It exists in the plant cell wall, and together with cellulose and hemicellulose, it constitutes the basic skeleton of the plant.
During the combustion process of lignin, old bonds are broken and new bonds are formed. The pyrolysis process of lignin can be roughly divided into the following three stages:
The first stage is free water volatilization;
The second stage starts from about 120 ℃, the weak bonds around the benzene ring are broken and the volatile components are recombined; ·
In the third stage, when the temperature reaches 800 ℃, the benzene ring is cracked, volatilized and polymerized into polynuclear aromatic compounds. With the further increase of temperature, the new aromatic compounds undergo polycondensation and carbonization. It shows that lignin has high char-forming ability at high temperature, and almost no char-forming during ordinary combustion.
However, its structure contains a variety of functional groups, such as methoxy, alcoholic hydroxyl, phenolic hydroxyl, benzene, aldehyde, carbonyl, etc., which provide abundant active sites for further chemical modification, which is beneficial to improve its flame retardant properties. The combination of lignin and other flame retardants such as metal hydroxides and phosphorus-based compounds can further improve the flame retardant effect.
A large number of experiments show that modified lignin can significantly improve the flame retardant modification of PLA. Mainly due to the unique aromatic structure and high carbonization ability of lignin.
