【Paper】
Degradation of Biodegradable Plastics in Incineration Ash
Makiko Doi*, Kazuhiko Fukatsu* and Masataka Hanashima**
* Faculty of Environmental & Symbiotic Sciences, Prefectural University of Kumamoto
** Fukuoka Research Center for Recycling Systems
† Correspondence should be addressed to Makiko Doi:
Faculty of Environmental & Symbiotic Sciences, Prefectural University of Kumamoto
（3-1-100 Tsukide, Kumamoto City, 862-8502 Japan）

Abstract
In order to study the degradation of biodegradable plastics, 8×2.5cm2 samples of five kinds of plastic sheets（PBSA, PLA, PHB/V, PCL, PBS）were buried with two types of mixed solid waste
（A: Incineration ash＋crushed waste, B: A＋compost）. Samples of each kind of solid waste were kept in 350mL pots at 25 and 37℃. The degradation rate was measured by the reduction in area and the plastic was examined using SEM. We made six findings.（1）Two types of degradation processes were observed: hole expansion aided by bacteria and crack formation caused by alkalis in the incineration ash.（2）Hole-expansion type degradation was promoted by increasing the temperature from 25 to 37℃ or by adding compost to the ash.（3）The degradation rate of the biodegradable plastics in ash with a low organic content was similar to that in normal soil.（4）Degradability could be ranked from high to low as PBSA＞PHB/V＞PCL＞PBS＞PLA.（5）When microorganisms did not affect the biodegradable plastics, alkalis produced cracks in the plastics.（6）PBSA and PCL probably increase microbial activity in mixed solid waste.

Key words: biodegradable plastics, degradability, landfill, incineration ash, microorganisms