Comparative Study on the Effect of Beta-Cyclodextrin and Polypseudorotaxane As Carbon Sources on the Thermal Stability and Flame Retardance of Polylactic Acid

Polypseudorotaxane (PPR) prepared by the inclusion complex between beta-cyclodextrin (beta-CD) and poly(propylene glycol) (PPG) was chosen as a "green" carbon source in intumescent flame retardants (IFRs) and exhibited more effective carbonization and higher degree of graphitic network than that of free beta-CD. Its combination with ammonium polyphosphate (APP) and melamine (MA) presented the most excellent char-forming ability whether in nitrogen or in air atmosphere. After blending IFRs into polylactic acid (PLA), the thermal stability was characterized by thermogravimetric analysis (TGA), and their flammability was assessed by limited oxygen index (LOI), vertical combustion, and cone calorimeter. The higher LOI% value and lower total heat release (THR) of PLA2 (which contains 20 wt% APP/MA/PPR mixtures) revealed that it presented more excellent flame retardance. Besides, the results of scanning electron microscopy (SEM) exhibited the existence of more bubbles in the char residue of PLA2.