Laboratory composting of extruded poly(lactic acid) sheets.
Composting of extruded poly(lactic acid) (PLA) in combination with pre-composted yard waste in a laboratory composting system was studied. Yard waste and PLA mixtures containing 0%, 10%, or 30% PLA (dry weight basis) were placed in composting vessels for four weeks. Exhaust gases were analyzed for carbon dioxide concentration twice per week. After the first week, significantly greater (P < 0.05) amounts of carbon dioxide were generated in vessels with 10% or 30% PLA than in control (0% PLA) vessels. Data indicated that microbial degradation of PLA occurred. There was no significant difference (P > 0.05) in carbon dioxide emission between 10% and 30% PLA mixtures. Compost pH dropped (from 6.0 to 4.0) after 4 weeks of composting for 30% PLA, but remained unchanged (6.3) for 0% or 10% PLA. Most likely, in the case of 30% PLA, substantial chemical hydrolysis and lactic acid generation lowered the compost pH. The lowered pH likely suppressed microbial activity, thus explaining the lack of difference in carbon dioxide emissions between 10% and 30% PLA mixtures. Gel permeation chromatography showed a notable decrease in PLA molecular weight as a result of composting. It was demonstrated that PLA can be efficiently composted when added in small amounts (<30% by weight) to pre-composted yard waste.
Ghorpade
V M
VM
Hill's Pet Nutrition, Science and Technology Center, Topeka, KS 66617, USA.
Gennadios
A
A
Hanna
M A
MA
D001673:Biodegradation, Environmental; D002245:Carbon Dioxide / Q000378:metabolism; D002850:Chromatography, Gel; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D019344:Lactic Acid / Q000378:metabolism*; D011091:Polyesters; D011108:Polymers / Q000378:metabolism*; D013997:Time Factors; D018505:Waste Management / Q000295:instrumentation* / Q000379:methods*
D011091:Polyesters; D011108:Polymers; D002245:Carbon Dioxide; D019344:Lactic Acid; C033616:poly(lactide)