Flame Retardant PLA System Containing Cyclodextrin
Cyclodextrin (CD) is a cyclic oligosaccharide formed by the action of amylase, containing a large number of hydroxyl structures. Its carbonization process includes ring opening, followed by chemical evolution similar to cellulose, losing the glucose structure and hydroxyl groups, Form carbonyl, aromatic and other structures.
Common CDs are mainly divided into three categories: α-CD, β-CD, and γ-CD. Among them, β-CD is widely used in flame-retardant PLA, polypropylene (PP) and other polymers due to its excellent carbon-forming properties, thermal stability and low cost.
In the first stage of the thermal degradation process of cyclodextrin, physical dehydration occurs at about 40 °C to remove the crystal water in β CD;
In the second stage, thermal decomposition and carbonization begin to occur at 260 °C, generating carbon dioxide gas and carbon residue;
In the third stage, when the temperature reaches 400 °C, the residual carbon undergoes slow thermal degradation. In addition to the polyhydroxyl structure that can be used for carbonization,
β-CD also contains more active primary and secondary hydroxyl groups, which can be modified by esterification, cross-linking and chemical modification to improve its flame retardant properties.
βCD is widely used in medical, food and environmental fields due to its more active hydroxyl groups and special annular cavity structure. When used as a flame retardant, its application in the field of flame retardant PLA is still in its infancy due to its large amount of addition and poor compatibility with the matrix.
The experimental results show that when the ratio of APP to PCD is 25%: 5%, the flame retardant effect is the best. Compared with pure PLA (limiting oxygen index is 19.7%), PLA/30% APP-PCD (5:1) The limiting oxygen index increased to 42.6 %, the carbon residue rate increased from 1.2 % to 71.5 %, and the RPHRR and HTHR decreased by 56 % and 84 %, respectively, because the material could form a smooth and dense carbon layer during the combustion process.
