110
7 Molten Salt Conversion of Plastics into Highly Conductive …
birds, fish and other organisms, and eventually by mankind who eat these creatures,
creating a serious global environmental crisis and waste management. In fact, marine
plastic pollution is a key transboundary environmental crisis affecting biodiversity,
marine industrial sectors, coastal communities, posing potential food security and
human health risks. The current trend results in a global used plastic accumulation
of about 12,000 million tons in 20 years time [3–10]. It should be mentioned that the
natural degradation of PET plastics takes a long time, probably over the course of
several hundreds of years [11], and therefore, their recycling or conversion is vital.
Currently, the utilization of waste plastics in various applications is an active
research stream. For instance, Naga et al. [12] studied the effect of PET waste plastic
materials on improving the performance and properties of asphalt pavements. They
found that the addition of PET has a positive impact in both reducing the penetration and increasing the softening point of asphalt binders, reducing their temperature
susceptibility. This can be an advantage for asphalt pavements in hot climates. The
resultant asphalt mixtures also exhibited a higher Marshall stiffness modulus, indirect tensile strength and rutting stiffness. However, the loss of stability was observed
when PET is employed. Louzada et al. [13] studied the application of waste PET
in geotechnical engineering and found that fine crushed PET may improve the load
capacity of soil. As another example, Marques et al. [14] utilized PET waste to produce fire-resistant polyurethane boards. In these applications, PET is either directly
employed with no chemical change in its structure or converted into a different
polymer material. In contrast, chemical depolymerization methods have also been
considered to manage PET waste through the production of new chemicals [15].
A viable approach toward the utilization of PET waste is based on the extraction
of hydrogen and/or carbon content of PET. Being hydrocarbons, plastics have high
caloric values [16], and therefore, are widely considered as a potential feedstock
for producing fuels such as H 2 and syngas [17–20]. In this regard, biodegradation
of PET waste using various microorganisms is an interesting approach leading to
the preparation of useful fuels such as methane [21]. PET can also be considered
as a precursor material to prepare nanostructured carbon materials. In the following
sections, a brief discussion on the thermochemical characteristics of PET is presented.
Then, the conversion of PET into carbonaceous materials is discussed.
7.1 Structural Characterization of PET
PET can possess mobile or rigid amorphous phases as well as crystalline structures
[22], and as such it can be characterized by X-ray diffraction (XRD).
The XRD analysis was performed on pieces of a PET water bottle, and the pattern
obtained is shown in Fig. 7.1a. The broad single peak and the diffused nature of the
profile indicate the presence of disorder in the amorphous PET structure. However,
PET with different degrees of crystallinity can be fabricated by annealing of the
material at different temperatures [23].
7 Molten Salt Conversion of Plastics into Highly Conductive …
birds, fish and other organisms, and eventually by mankind who eat these creatures,
creating a serious global environmental crisis and waste management. In fact, marine
plastic pollution is a key transboundary environmental crisis affecting biodiversity,
marine industrial sectors, coastal communities, posing potential food security and
human health risks. The current trend results in a global used plastic accumulation
of about 12,000 million tons in 20 years time [3–10]. It should be mentioned that the
natural degradation of PET plastics takes a long time, probably over the course of
several hundreds of years [11], and therefore, their recycling or conversion is vital.
Currently, the utilization of waste plastics in various applications is an active
research stream. For instance, Naga et al. [12] studied the effect of PET waste plastic
materials on improving the performance and properties of asphalt pavements. They
found that the addition of PET has a positive impact in both reducing the penetration and increasing the softening point of asphalt binders, reducing their temperature
susceptibility. This can be an advantage for asphalt pavements in hot climates. The
resultant asphalt mixtures also exhibited a higher Marshall stiffness modulus, indirect tensile strength and rutting stiffness. However, the loss of stability was observed
when PET is employed. Louzada et al. [13] studied the application of waste PET
in geotechnical engineering and found that fine crushed PET may improve the load
capacity of soil. As another example, Marques et al. [14] utilized PET waste to produce fire-resistant polyurethane boards. In these applications, PET is either directly
employed with no chemical change in its structure or converted into a different
polymer material. In contrast, chemical depolymerization methods have also been
considered to manage PET waste through the production of new chemicals [15].
A viable approach toward the utilization of PET waste is based on the extraction
of hydrogen and/or carbon content of PET. Being hydrocarbons, plastics have high
caloric values [16], and therefore, are widely considered as a potential feedstock
for producing fuels such as H 2 and syngas [17–20]. In this regard, biodegradation
of PET waste using various microorganisms is an interesting approach leading to
the preparation of useful fuels such as methane [21]. PET can also be considered
as a precursor material to prepare nanostructured carbon materials. In the following
sections, a brief discussion on the thermochemical characteristics of PET is presented.
Then, the conversion of PET into carbonaceous materials is discussed.
7.1 Structural Characterization of PET
PET can possess mobile or rigid amorphous phases as well as crystalline structures
[22], and as such it can be characterized by X-ray diffraction (XRD).
The XRD analysis was performed on pieces of a PET water bottle, and the pattern
obtained is shown in Fig. 7.1a. The broad single peak and the diffused nature of the
profile indicate the presence of disorder in the amorphous PET structure. However,
PET with different degrees of crystallinity can be fabricated by annealing of the
material at different temperatures [23].