In my second week on plastic waste, I would first summarise the life cycle of plastic bags from its construction, using an improvised and basic flowchart seen in Figure 5.
Plastics are very widely used in products and production processes, such as in the form of packaging, textiles, in automotive parts, and paints. They are formed from long chains of organic polymeric molecules, with the most widely-used synthetic polymer being polyethylene (PE). Generally, polyethylene bags are made using plastic pellets which are subjected to high pressure, melted in a hopper, and extracted through a vertical tube to form a long continuous plastic film of desired thickness. Individual bags are then created by cutting and heat-sealing the bags.
Within PE, there are three types of molecules used for plastic bags: linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE) and high-density polyethylene (HDPE). Generally, the higher the density, the greater the molecular weight and the stronger the resulting plastic bag. These three uses account for a combined 38% of global plastic production.
Figure 6. Different types of plastics and their uses (Source: UNEP on Twitter)
Figure 6 shows the different PE types and their typical uses in plastic bagging. Although the image may indicate that LDPE forms the bulk of marine plastic litter given their lightweight properties, over the course of my research I conclude that thickness of the bags in consideration of impacts - the thinner the plastic bag, the lower its quality and the lower its re-usability. Subsequently, some of these lightweight plastic bags may make their way to water bodies from land-based sources such as beach litter and their buoyancy encourages ocean-driven surface transport. Over time, the plastic waste undergoes fragmentation when subject to UV-radiation and warm temperatures as they traverse the oceans, and may form microplastics (defined as plastic particles <5mm in size) which can stay in the ocean for thousands of years.
Within PE, there are three types of molecules used for plastic bags: linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE) and high-density polyethylene (HDPE). Generally, the higher the density, the greater the molecular weight and the stronger the resulting plastic bag. These three uses account for a combined 38% of global plastic production.
Figure 6 shows the different PE types and their typical uses in plastic bagging. Although the image may indicate that LDPE forms the bulk of marine plastic litter given their lightweight properties, over the course of my research I conclude that thickness of the bags in consideration of impacts - the thinner the plastic bag, the lower its quality and the lower its re-usability. Subsequently, some of these lightweight plastic bags may make their way to water bodies from land-based sources such as beach litter and their buoyancy encourages ocean-driven surface transport. Over time, the plastic waste undergoes fragmentation when subject to UV-radiation and warm temperatures as they traverse the oceans, and may form microplastics (defined as plastic particles <5mm in size) which can stay in the ocean for thousands of years.
This knowledge would later be helpful in assisting our understanding on the adverse effects (ecological, environmental and social costs) of marine plastic litter in our oceans. See you!
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