2:45 PM - 3:00 PM
[MIS09-05] The fragmentation properties of foamed polystyrene under coastal simulation over time
Keywords:Foamed polystyrene, Pot mill, Particle counter, Size distribution, Surface abrasion, Shape properties
Microplastics are mainly generated on beaches in marine environments, where they are exposed to seawater, sunlight (solar ultraviolet rays), and mixed with sand. During storms, sand is flung up by the waves and mixes with plastics, causing the plastics to fragment into small pieces. Some studies have conducted fragmentation experiments by mixing plastic, sand, and water. Song et al. (2017) found that the unique “foamed” structure of foamed polystyrene, consisting of thin layers, is more susceptible to fragmentation than bulk plastics such as polyethylene and polypropylene. However, these previous studies did not investigate the temporal variation in the number or the size distribution of particles produced.
This study focused on foamed polystyrene and conducted an experiment to fragment it using a pot mill (AS ONE Co.). The fracture mode of foamed polystyrene was estimated by analyzing the temporal variation of the number of foamed polystyrene produced and its size distributions. To simulate a real beach, the experiment combined beach sand, ultrapure water, and foamed polystyrene spherules (virgin, with a diameter of 5 mm). The quantities of sand, ultrapure water, and foamed polystyrene spherules, as well as the milling speed, were consistent in all cases. However, the milling time varied in six cases: 6 hours, 12 hours, 1 day, 2 days, 3 days, and 5 days. The foamed polystyrene produced was passed through a 109 μm stainless steel mesh. The residences on the mesh were analyzed using software connected to a stereoscopic microscope. The particle sizes that passed through the mesh were analyzed using a particle counter (HIAC 9703+, Beckman Coulter, Inc.). The foamed polystyrene particles produced larger than 5 µm were analyzed.
The number of foamed polystyrene pieces produced increased as the size decreased. In the smallest size category (5−10 μm), there were 103 to 104 pieces per μm per pellet. As the size decreased, the number of particles produced increased exponentially. In the double logarithmic graph, where the horizontal axis represents size and the vertical axis represents number, the values were approximated with straight lines in all cases. The slope of the regression line decreased as the milling time increased. When the milling time was less than one day, all the foamed polystyrene pieces produced were smaller than 150 µm. On the other hand, foamed polystyrene pieces larger than 150 µm were produced after one day, and their quantity increased significantly when the duration exceeded three days. The fracture mode of foamed polystyrene changed as the milling time was varied.
In the future, the surface conditions and internal structures of the foamed polystyrene produced in this study will be observed using a laser microscope, field emission scanning electron microscopy (FE-SEM), and X-ray computed tomography (X-ray CT). Based on the observation results, the fragmentation process will be estimated, considering the factors that influence the change in fracture mode. Furthermore, conducting an analysis of beached foamed polystyrene using the same methods and comparing it with the foamed polystyrene produced in this study will demonstrate the validity of the fragmentation experiments and their applicability to the actual marine environment.
This study focused on foamed polystyrene and conducted an experiment to fragment it using a pot mill (AS ONE Co.). The fracture mode of foamed polystyrene was estimated by analyzing the temporal variation of the number of foamed polystyrene produced and its size distributions. To simulate a real beach, the experiment combined beach sand, ultrapure water, and foamed polystyrene spherules (virgin, with a diameter of 5 mm). The quantities of sand, ultrapure water, and foamed polystyrene spherules, as well as the milling speed, were consistent in all cases. However, the milling time varied in six cases: 6 hours, 12 hours, 1 day, 2 days, 3 days, and 5 days. The foamed polystyrene produced was passed through a 109 μm stainless steel mesh. The residences on the mesh were analyzed using software connected to a stereoscopic microscope. The particle sizes that passed through the mesh were analyzed using a particle counter (HIAC 9703+, Beckman Coulter, Inc.). The foamed polystyrene particles produced larger than 5 µm were analyzed.
The number of foamed polystyrene pieces produced increased as the size decreased. In the smallest size category (5−10 μm), there were 103 to 104 pieces per μm per pellet. As the size decreased, the number of particles produced increased exponentially. In the double logarithmic graph, where the horizontal axis represents size and the vertical axis represents number, the values were approximated with straight lines in all cases. The slope of the regression line decreased as the milling time increased. When the milling time was less than one day, all the foamed polystyrene pieces produced were smaller than 150 µm. On the other hand, foamed polystyrene pieces larger than 150 µm were produced after one day, and their quantity increased significantly when the duration exceeded three days. The fracture mode of foamed polystyrene changed as the milling time was varied.
In the future, the surface conditions and internal structures of the foamed polystyrene produced in this study will be observed using a laser microscope, field emission scanning electron microscopy (FE-SEM), and X-ray computed tomography (X-ray CT). Based on the observation results, the fragmentation process will be estimated, considering the factors that influence the change in fracture mode. Furthermore, conducting an analysis of beached foamed polystyrene using the same methods and comparing it with the foamed polystyrene produced in this study will demonstrate the validity of the fragmentation experiments and their applicability to the actual marine environment.