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Title: Thermal degradation of Polyethylene
Authors: Khurram, Malik Jehanzeb
Keywords: Physical Sciences
Issue Date: 2020
Publisher: Gomal University, D.I.Khan.
Abstract: Polymeric waste is increasing very fast and exploring most appropriate technology of recycling is need of the day. Two samples of polyethylene carrying bags "Yaadgar" (Y), a Pakistani, "Econogreen" (E), a Canadian brand and Polyethylene supplied by "Fluka" were investigated. The samples were thermally aged at 80°C in an oven and exposed to accelerated weathering conditions in QUV chamber up to 20 days. In QUV the samples were exposed to UV radiations, high temperature and condensation processes. The analysis was made by employing FT Infrared spectroscopy, Scanning Electron Microscopy, Differential Scanning Calorimetry, X-Ray Diffraction and Thermogravimetric Analysis. The IR spectra concluded that the sample "Y" was high density polyethylene while sample "E" was linear low density polyethylene. A carbonyl peak at 1715 cm-1 for sample "E" was detected after 20 days of aging in an oven and same peak was observed for both the sample in case of QUV chamber. The carbonyl index for "E" was higher than sample “Y” and was increased with aging. It was observed that after 20 days of exposure in an oven or .in QUV chamber the samples "Y" and "E" were converted from "HDPE" to "LLDPE" and "LLDPE" to "LDPE", respectively. The percent crystallinity determined through DSC/XRD was increased with aging and the degradation pattern obtained via SEM indicated that it was instigated at preferential sites in "Y" and in all directions in sample "E". The kinetics of degradation was investigated using thermogravimetric analysis and employing "Flynn-Wall-Ozawa", "Coats-Redfern", "Kissinger" and "Augis-Bennett" equations under nitrogen and air atmosphere. Single degradation step and multiple degradation steps were observed under nitrogen and air atmosphere, respectively. The activation energy obtained by Flynn-Wall-Ozawa method was more consistent than the others. The activation energy of thermal degradation was decreased with the aging. The order of reaction under nitrogen atmosphere varied in this way before exposure (Y = 1.06, E = 1.05) > after oven aging (Y = 1.04, E = 0.87) > after exposure in QUV chamber (Y = 0.93, E = 0.72 ) and under air atmosphere, it was before exposure (Y = 1.51, E = 1.23) < after oven aging (Y = 1.84, E = 2.03) < after exposure in QUV chamber (Y = 2.64, E = 2.65). The aging impact was found severe in QUV chamber due to UV radiations and/or high humidity. Sample "E" was more vulnerable to thermo-oxidative degradation than sample "Y". Keeping in view the variation in activation energy during the thermal degradation, it can be stated that the process followed the formation of di-mer/ tri-mer and then chain scission took place. However, in case of photodegradation, in the presence of oxygen first the formation of carbonyl groups took place which ultimately led to the formation smaller molecule.
Gov't Doc #: 20259
Appears in Collections:PhD Thesis of All Public / Private Sector Universities / DAIs.

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