Abstract
The increasing amount of marine plastic waste poses challenges including, not only the collection, but also the subsequent recyclability of the plastic. An artificial accelerated weathering procedure was developed, which modelled the marine environment and investigated the recyclability of weathered and non-weathered PET. Marine conditions were simulated for poly(ethylene terephthalate) (PET) bottle material and high-density polyethylene (HDPE) cap material. It consisted of 2520 h cyclical weathering, alternating the sample between a salt spray and a Xenon-chamber—this corresponds to roughly 3–4 years on the surface of an ocean.It was proved that the molecular weight of PET is a function of weathering time and can be described mathematically. Microscopic examination of the surface of the PET bottles and HDPE caps proved that these surfaces were damaged. After weathering, manufacturing tests were performed on the PET material by extrusion, injection moulding, 3D printing and thermoforming. Quantitative comparison between products manufactured by the same technology was performed in order to compare the qualities of products made from original PET, non-weathered PET waste, which was the example of classical recycling, and weathered PET. In the case of products made from weathered PET, certain mechanical and optical properties (e.g. impact strength and transparency) were significantly impaired compared to the original PET and the recycled, non-weathered PET. Certain other properties (e.g. strength and rigidity) did not change significantly. It was proved that the samples from weathered plastic material can be successfully recycled mechanically and used to manufacture plastic products.
Highlights
The function can be modelled with an exponential proportional rate decrease function (Eq (2)). (In Fig. 2 the function is shown with the dashed grey trend line): IVðtÞ 1⁄4 IV0 À IVD;1ð1 À exp ðÀktÞÞ; ð2Þ
The detailed statistical analyses can be found in Supplementary Material
These results indicate that the weathered sample became considerably darker and its colour shifted towards red and yellow, in samples made from non-weathered PET or original PET, but their strain is still over 200%, which is enough for being applied in injection moulded products
Summary
The population of the world is constantly increasing; at the moment it is 7.7 billion (United Nations, 2019). It is predicted that Earth cannot support more than 10 billion people if the current trends continue (Kin et al, 2019; Taagepera, 2014; United Nations, 2019). It has been estimated that 6789 million metric tons of non-fiber plastics were produced between 1950 and 2017, and production is growing every year (Geyer et al, 2017; NovaInstitut, 2015). Much of the plastic is used for packaging, which becomes waste very quickly. Between 1950 and 2015, about 6300 million metric tons of primary and secondary (recycled)
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