Flame retardant PLA system containing chitosan
CS) is prepared by deacetylation of chitin, which has the advantages of reproducibility and good biocompatibility.
CS is a kind of positively charged natural amino polysaccharide, which can be directly used as a char-forming agent for flame retardant PLA composites. It will undergo a ring-opening reaction at high temperature and self-aggregate in the matrix to form an aromatic ring cross-linked structure, that is, in the condensed phase. The carbon layer is formed in the matrix, which is beneficial to inhibit the heat exchange in the matrix.
At the same time, the amino group in CS is released into the gas phase in the form of NH3 during thermal decomposition, which can dilute the concentration of combustible gas on the one hand, and promote the formation of an expanded carbon layer on the other hand. The expanded carbon layer has better properties than ordinary carbon layers. protective matrix effect. Usually, CS and acid source (such as APP) are used to form an intumescent flame retardant system, and the products generated by the acid source during the thermal decomposition process can promote the dehydration and carbonization of chitosan. In addition, due to the more active groups in its structure, it can also be modified to optimize its flame retardant properties.
APP has a good flame retardant effect in PLA. The researchers used APP as the core, cationic CS and anionic alginic acid (AA) as the shell, and prepared the core-shell flame retardant APP@CS@AA nBL by LBL technology (BL represents double-layer, n represents the number of double-layer layers, 1BL is composed of a pair of CS@AA), it was melt-blended with PLA to prepare flame retardant materials, compared with pure PLA, the RPHRR of the composites decreased significantly, when the number of layers was only When it is 3BL, the limiting oxygen index of the material increases to 30.6 %, and the carbon residue rate increases from 1.5 % (pure PLA) to 13.2 %.
This is because CS and AA can be used as carbon sources to form an IFR system with APP, and since both CS and AA have polyhydroxyl structure, the phosphoric acid and polyphosphate released during thermal decomposition of APP promote the dehydration and carbonization of CS and AA, and the carbon The layer becomes dense and continuous, effectively preventing the escape of combustible gas and inhibiting the exchange of thermal oxygen, thereby improving the flame retardant properties of the material. In addition to the above-mentioned intumescent flame retardant system, CS modified system has higher thermal stability and better thermal and mass barrier effect than ordinary carbon layer, which inhibits the spread of heat and combustible gas.
