Quality-determination of recycled plastic packaging waste by identification of contaminants by GC--MS after microwave assisted extraction (MAE)

摘要

The quality of recycled resins of high density polyethylene (HDPE) and polypropylene (PP) separated from mixed solid waste (MSW) were studied by analyzing the tentative low molecular weight contaminants. For that purpose a microwave assisted extraction (MAE) technique was developed using MDPE and two aromatic antioxidants (Irganox 10l0 and Irgafos 168) as models. A 50:50 mixture of cyclohexane and isopropanol gave high recovery yields; 97/100 for Irgafos 168 and 93/100 for Irganox 1010 and short extraction times. Limonene, isopropylester of myristic and palmitic acids were examples of products identified in recycled HDPE. These compounds are typically fragrance and flavor constituents. In addition alcohols, esters, ketones were identified. Most of the substances are constituents of the packaging fillings at their first usage. But the possibility that contaminants may have entered the material by contact with other plastics is not excluded. The major category of compounds identified already in the virgin material is composed of aliphatic hydrocarbons (e.g. pentadecane, hexadecaned, 1-hexadenene), branched alkanes, branched alkenes and others. The same kind of compounds were also identified in the recycled materials at a similar concentration as in virgin ones. Virgin and recycled polyethylene contain also ethylbenzene and o-, m- and p-xylenes, where o-xylene had the largest peak of the four. The aromatic hydrocarbons are probably parts of additives, which degraded during extraction and sample preparation procedures. Aromatic hydrocarbons without functional groups, such as ethylbenzene and xylenes are considered highly toxic, but the height and area of their peaks suggest low concentrations. The concentration of these hazardous contaminants in the recycled resin is, however, approximately five times higher in recycled material, estimated by a comparison of the peak areas. Ethylbenzene and o-, m- and p-xylenes, o-xylene having the largest peak of the four were also identified in virgin and recycled polypropylene resins.