The flammability and cage effect of the immiscible alloy polycarbonate/polylactic acid

We have studied the flammability and "cage effect" of the immiscible alloy, PC (polycarbonate) /PLA (polylactic acid). Alloys whose compositions of PC and PLA were 60:40 and 30:70 by weight, respectively, were processed. The heat release rates of the alloys during the horizontal position test were similar to that of PLA. On the other hand, the flammability of the alloy was completely different from the values for PC and PLA in the vertical position test. In order to analyze the phenomena, we conducted thermal degradation tests conducted and obtained two-step degradation curves. The major scission products of the alloys were bisphenol-A originating from PC and acetaldehyde originating from PLA. The ratio of the scission products changed proportionately to the ratio of PC and PLA. These data suggested that the combustibility of PC/PLA alloy increases more than the values of PC and PLA individually due to the cage effect, by which PC protects the PLA drip from the alloy.