Evaluation of Fatigue Life of Recycled Opaque PET from Household Milk Bottle Wastes

Abstract

Polyethylene terephthalate (PET) is among the most used thermoplastic polymers in large scale manufacturing. Opaque PET is increasingly used in milk bottles to save weight and to bring a glossy white aspect due to TiO2 nanoparticles. The recyclability of opaque PET is an issue: whereas the recycling channels are well established for transparent PET, the presence of opaque PET in household wastes weakens those channels: opaque bottles cannot be mixed with transparent ones because the resulting blend is not transparent anymore. Many research efforts focus on the possibility to turn opaque PET into resources, as one key to a more circular economy. A recent study has demonstrated the improvement of the mechanical properties of recycled PET through reactive extrusion. In the present work, the lifespan of recycled opaque PET has been evaluated throughout tensile–tensile fatigue loading cycles at various steps of the recycling process: The specimens are obtained from flakes after grinding PET wastes (F-r-OPET), from a subsequent homogenization step (r-OPET-hom) and after reactive extrusion (Rex-r-OPET). Virgin PET is also considered as a comparison. First, tensile tests monitored by digital image correlation have been carried out to obtain the elastic modulus and ultimate tensile stress of each type of PET. The fatigue properties of reactive REx-r-OPET increase, probably associated with the rise of cross-linking and branching rates. The fatigue lifespan increases with the macromolecular weight. The fracture surface analysis of specimens brings new insight regarding the factors governing the fatigue behavior and the damaging mode of recycled PET. TiO2 nanoparticles act as stress concentrators, contributing to void formation at multiple sites and thus promoting the fracture process. Finally, the fatigue life of REx-r-OPET is comparable to those of virgin PET. Upcycling opaque PET by reactive extrusion may be a relevant new route to absorb some of the growing amounts of PET worldwide.

Polyethylene Terephthalate (PET) Recycled by Catalytic Glycolysis: A Bridge toward Circular Economy Principles

“…Given the predominance of transparent PET in single-use beverage bottles and the variety of available recycling methods for PET waste, this review primarily focuses on transparent PET. Hence, PET's popularity as a packaging material stems from several properties, such as transparency, food safety, cleanliness, impact strength, UV resistance, durability, costeffectiveness, and barrier properties [13,24,25]. However, the increase in the world market volume over recent years (from 19 million metric tons in 2015 to approximately 25 million metric tons in 2022), as detailed in Figure 3, has had a detrimental effect on the environment.…”

“…In 2020, 7297.7 kilotons of PET were consumed worldwide, with just 23% recycled, 35% incinerated, and 44% landfilled or disposed into the environment, according to a study conducted across 12 global regions (41 countries that, together, manufacture over 95% of the world's PET) [29]. Also, through partial decomposition, PET-derived microplastics indeed become Hence, PET's popularity as a packaging material stems from several properties, such as transparency, food safety, cleanliness, impact strength, UV resistance, durability, costeffectiveness, and barrier properties [13,24,25]. However, the increase in the world market volume over recent years (from 19 million metric tons in 2015 to approximately 25 million metric tons in 2022), as detailed in Figure 3, has had a detrimental effect on the environment.…”

“…Consequently, instead of degrading, plastic debris accumulates in landfills or in the natural environment, causing serious problems to living organisms [ 6 , 12 ]. It was estimated that 12 million tons of plastic waste is dumped into the ocean annually, which is roughly the same as one dumpster truck every minute [ 13 ]. The most well-known example is the Great Pacific Garbage Patch, which is thought to contain 80,000 tons of plastic and 1.8 trillion plastic particles floating in the open ocean [ 14 ].…”

Strategies for Exploiting Milk Protein Properties in Making Films and Coatings for Food Packaging: A Review

“…Above all, the production of biodegradable packaging materials based on natural biopolymers is being prioritized, with these biopolymers being obtained from renewable sources or by-products of different origins [ 8 , 9 ]. Biopolymers derived from by-products or waste are already available and sometimes underutilized resources, and their use reduces disposal costs [ 10 ]. Biopolymers such as proteins, polysaccharides and lipids, with the aid of some additives, appear to be promising raw materials [ 11 , 12 ].…”

Effect of Strain Rates and Heat Exposure on Polyamide (PA12) Processed via Selective Laser Sintering

“…Several polymers fall into the category of thermoplastics, either amorphous or semi-crystalline, with a wide range of mechanical properties [ 1 ]. These materials can be recycled multiple times as they are not subject to thermal degradation [ 2 ] and can be reused for the manufacture of new components [ 2 , 3 , 4 , 5 ]. Moreover, thermoplastic polymers can be processed using 3D printing [ 6 ], i.e., one of the most attractive manufacturing technologies since it allows the fabrication of complex parts in a fairly simple way.…”