The Physical Characterization and Terminal Velocities of Aluminium, Iron and Plastic Bottle Caps in a Water Environment

Abstract

Aluminium, iron and plastic are materials which are extensively used at both industry and individual levels. However, significant amounts of aluminium, iron and plastic end up in the environment. Specifically, bottle caps made of these materials are often thrown away, with or without bottles, and appear among the common plastic debris entering the world’s oceans and beaches. More than 20 million bottle caps and lids have been identified during beach-cleaning campaigns over the last 30 years. To recover bottle caps from the shores, conventional technologies can be used. In this paper, the physical properties of used metal and plastic bottle caps were examined and related to the settling and rising velocities of the caps, as well as their drag coefficients and hydrodynamic modes in water environments, with respect to gravity separation. The sample contained aluminium, iron, high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP) bottle caps. The findings revealed that the density differences between the bottle caps resulted in the terminal settling velocities of aluminium and iron particles, which were significantly higher than the rising velocities of the plastic caps. The results allowed us to design a flowsheet for bottle cap recovery from beach coasts in order to reduce environmental impact and produce add-on plastic and metal products.

Special Issue “Feature Papers in Recycling 2021”

“…In [1], the physical properties of metal and plastic bottle caps were studied, via SEM and FTIR spectroscopy analyses. The results show that metal caps are mainly made of iron and aluminum, while plastic caps were made by polyethylene (high-density HDPE and lowdensity LDPE), with a few particles of polypropylene (PP).…”

Perspectives on Thermochemical Recycling of End-of-Life Plastic Wastes to Alternative Fuels

“…Nevertheless, more study is needed to validate the amounts of plastic exposure that constitutes a human health hazard. Some feasible techniques for the removal of microplastics from the environment include physical sorption (adsorption on algae), filtration (membrane separation), chemical methods (coagulation and agglomeration) and biological removal (biodegradation and ingestion by clams) [ 11 , 12 ].…”

From Bottle Caps to Frisbee—A Case Study on Mechanical Recycling of Plastic Waste towards a Circular Economy

“…Such streams are commonly used as recycled content in specific injection-molded PE-HD transport packaging applications (e.g., beer crates). Moreover, caps are often discarded separately from the bottles, which increases their likelihood of entering mixed waste streams or being released into the environment, including landfills and oceans, hence drastically reducing their recycling potential [ 15 , 22 ]. For instance, in a beach cleanup tour of the coastline in the Netherlands conducted by the North Sea Foundation in 2016, over ten thousand plastic beverage bottle caps were collected [ 21 ].…”