Linear low density polyethylene (LLDPE) is one of the most widely used plastics, mainly as a packaging film, contributes to the generation of a huge volume of plastic waste. Only 5.8 % of waste LLDPE was recycled in 2014, while the remaining wastes were buried in landfills, posing a huge challenge for solid waste management.
Researchers from Korea Institute of Science and Technology, Korea University of Science and Technology, Konkuk University, Republic of Korea and Georgia Institute of Technology, USA have developed a process to LLDPE to graphitic carbon and demonstrated that it would be possible to convert typical household LLDPE waste products such as cling wrap and poly-gloves into high quality carbon materials. (Choi et al., High performance graphitic carbon from waste polyethylene: thermal oxidation as a stabilization pathway revisited,
Chem. Mater., DOI: 10.1021/acs.chemmater.7b03737).
Thermal oxidation was used as a pre-treatment to modulate the chemical structure of LLDPE. During the thermal oxidative pre-treatment (~330 °C) the ‘non carbonizable’ LLDPE was successfully transformed into an ordered carbon (50% yield). The aliphatic LLPDE chain is reorganized into thermally stable cross-linked polyaromatic moieties with a cyclized ladder structure (Scheme 1), which makes them suitable for carbonization.
Scheme 1 Proposed chemical structural transformation of aliphatic LLDPE chains into cyclized polyaromatic moieties through thermal oxidation
The thermally stable cross-linked polyaromatic moieties, in turn, guides a spontaneous transition into well-stacked polyaromatic carbon structures with a further increase in temperature from 330 to 2400 °C (Scheme 2). The resultant product possesses a high quality graphitic structure that exhibits superior degree of ordering and electrical performance.
Scheme 2 Growth of basic structural unit (BSU) of thermally oxidized LLDPE samples during carbonization and graphitization processes
It is a low-cost production route for graphitic carbon materials, which would find application in energy storage and flexible, printed electronics.
T.S.N. Sankara Narayanan
For more information, the reader may kindly refer: Choi et al., High performance graphitic carbon from waste polyethylene: thermal oxidation as a stabilization pathway revisited, Chem. Mater., DOI: 10.1021/acs.chemmater.7b03737
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