Challenges and Opportunities for Recycled Polyethylene Fishing Nets: Towards a Circular Economy

Plastic waste generation has become an important problem that critically affects marine and oceans environments. Fishing nets gear usually have a relatively short lifespan, and are abandoned, discarded and lost, what makes them one of the largest generators of ocean plastic waste. Recycled polyolefin resins from fishing nets (rFN), especially from polyethylene (PE), have poor properties due to the presence of contaminants and/or excessive degradation after its lifetime. These reasons limit the use of these recycled resins. This work aims to study the incorporation of recycled fishing nets PE-made to different grades of virgin PE, in order to evaluate the potential use of these rFN in the development of new products. The recovered fishing nets have been fully characterized to evaluate its properties after the collection and recycling process. Then, different PE virgin resins have been mechanically blended with the recovered fishing nets at different recycling contents to study its feasibility for fishing nets or packaging applications. Critical mechanical properties for these applications, as the elongation at break, impact strength or environmental stress cracking resistance have been deeply evaluated. Results show important limitations for the manufacture of fibers from recycled PE fishing nets due to the presence of inorganic particles from the marine environment, which restricts the use of rFN for its original application. However, it is proved that a proper selection of PE raw resins, to be used in the blending process, allows other possible applications, such as non-food contact bottles, which open up new ways for using the fishing nets recyclates, in line with the objectives pursued by the Circular Economy of Plastics.

Difference in polypropylene fragmentation mechanism between marine and terrestrial regions

Two kinds of marine polypropylene (M1-PP and M2-PP) and one land PP (L-PP) samples were collected from two beaches and land in Japan, respectively, to study the fragmentation mechanisms. Delamination was observed on both M1-PP and M2-PP surfaces. Moreover, there was no delamination but an abrasion patch structure on the surface of L-PP. The delamination was studied using an advanced oxidation process-degraded PP as the marine PP model. The number and shape of cracks varied with an increase in degradation time. The fluctuations in the values and ratios of the carbonyl index as well as the weight change ratio were due to repeated oxidation and delamination. We found that the delamination behavior depends on the oxidation state. Poly(oxyethylene)8 octylphenyl ether (POE8) surfactant treatment caused the delamination to speed up, which is a typical characteristic of polyolefin environmental stress cracking (ESC). These results reveal that delamination is based on ESC.Article Highlights Two kinds of marine and one land polypropylene (PP) samples were collected from two beaches and land, respectively, to study the fragmentation mechanisms. Delamination was observed on both of marine PP surfaces. Moreover, there was no delamination but an abrasion patch structure on the land PP surface. We found that the delamination was based on environmental stress cracking mechanism by employing a marine PP model.

Application of short-term methods to estimate the environmental stress cracking resistance of recycled HDPE

Environmental stress cracking is a serious problem for polyethylene because it can cause failure without any visible warning due to the slow crack growth accelerated by aggressive agents. Tie molecules and entanglements are the main macromolecular characteristic increasing environmental stress cracking resistance, thus in this work mechanical and thermal properties governed by those macromolecular characteristics are determined by performing simple tests executable in the industrial laboratories for quality control on recycled high-density polyethylene. The mutual relation between the determined properties confirms their dependence on the investigated macromolecular characteristics and allows to predict in a comparative way the expected environmental stress cracking. The mechanical properties related to the environmental stress cracking resistance are the strain hardening modulus and the natural draw ratio. The strain hardening modulus is an intrinsic property that measure the disentanglement capability of the inter-lamellar links and the natural draw ratio is a highly sensitive parameter to the macromolecular network strength via the intercrystalline tie molecules. Since the measurement of these properties according to the standard ISO 18,488 requires a temperature chamber not often available in the industrial laboratories, the tensile test was performed also at room temperature and displacement rate 0.5 mm/min; a proportionality between the data obtained at different test condition emerged. The thermal property related to the environmental stress cracking resistance is the stepwise isothermal segregation ratio that state the chain fraction that generates a high rate of tie molecules responsible of environmental stress cracking resistance.