Comparison between the Mechanical Recycling Behaviour of Amorphous and Semicrystalline Polymers: A Case Study

Abstract

The increase in waste has motivated the adoption of the circular economy concept, which assumes particular relevance in the case of plastic materials. This has led to research of new possibilities for recycling plastics after their end-of-life. To achieve this goal, it is fundamental to understand how the materials’ properties change after recycling. This study aims to evaluate the thermal and mechanical properties of recycled plastics, namely polycarbonate (PC), polystyrene (PS), glass fibre-reinforced polyamide 6 (PA6-GF30), and polyethylene terephthalate (PET). With this purpose, injected samples were mechanically recycled twice and compared through thermal and mechanical tests, such as differential scanning calorimetry, hardness, tensile strength, and the melt flow rate. The results show that the amorphous materials used do not suffer significant changes in their properties but exhibit changes in their optical characteristics. The semicrystalline ones present some modifications. PET is the material that suffers the biggest changes, both in its flowability and mechanical properties. This work demonstrates that the mechanical recycling process may be an interesting possibility for recycling depending on the desired quality of final products, allowing for some materials to maintain comparable thermal and mechanical properties after going through the recycling process.

Optimization in the reprocessing of recycled polyamide 6 reinforced with 30 wt% Glass Fiber (PA6/GF30) using mixture design

“…Fibers chains breaking after reprocessing operations (recycling cycles) causes the fall of the molecular weight of the polymer and eases the flow of the materials, which leads to a high MFI. Similar results were revealed by Costa et al,20 who reported that the melt flow rate (MFR) of PA6-GF30 are significantly increased after recycling. Figure3Bshows that the MFI decreased with the substitution of 50 wt% of the recycled PA6/GF30 composites (N1 or N2) with 50 wt% of the virgin PA6/GF30 composite (N0).…”

“…[8][9][10][11] Mechanical recycling techniques start with cutting, grinding and reprocessing of wastes plastics generated after the end-of-life or during production to produce new component for a wide application. 12,13 Studies on recycling process and its effects on properties have been conducted for a large number of polymers such as polypropylene (PP), 14,15 high density polyethylene (HDPE), 16 low density polyethylene (LDPE), 16,17 polyethylene terephthalate (PET), [18][19][20] polystyrene (PS), [20][21][22] polycarbonate (PC), 20,23 and polyamide 6 (PA6). 20,24,25 PA6 is a semicrystalline thermoplastic polymer that finds extensive use in various engineering applications, especially in the electronic and automobile industries due to its good mechanical properties and ease of processing.…”

“…Mechanical recycling techniques start with cutting, grinding and reprocessing of wastes plastics generated after the end‐of‐life or during production to produce new component for a wide application 12,13 . Studies on recycling process and its effects on properties have been conducted for a large number of polymers such as polypropylene (PP), 14,15 high density polyethylene (HDPE), 16 low density polyethylene (LDPE), 16,17 polyethylene terephthalate (PET), 18–20 polystyrene (PS), 20–22 polycarbonate (PC), 20,23 and polyamide 6 (PA6) 20,24,25 …”

“…12,13 Studies on recycling process and its effects on properties have been conducted for a large number of polymers such as polypropylene (PP), 14,15 high density polyethylene (HDPE), 16 low density polyethylene (LDPE), 16,17 polyethylene terephthalate (PET), [18][19][20] polystyrene (PS), [20][21][22] polycarbonate (PC), 20,23 and polyamide 6 (PA6). 20,24,25 PA6 is a semicrystalline thermoplastic polymer that finds extensive use in various engineering applications, especially in the electronic and automobile industries due to its good mechanical properties and ease of processing. [26][27][28] PA6 can be filled with synthetic fiber (carbon and glass) or inorganic filler (talc, calcium carbonate, and kaolin) in order to improve its properties and to reduce cost.…”

“…PA6 can be filled with synthetic fiber (carbon and glass) or inorganic filler (talc, calcium carbonate, and kaolin) in order to improve its properties and to reduce cost. Several studies focused on the reprocessing of PA6 reinforced with carbon fiber, 29 talc filler, 30 and glass fiber 2,20,31 have been conducted. Kuram et al 2 studied the effects of the number of processing cycles and process parameters on the chemical, thermal and mechanical properties of glass‐fiber reinforced nylon 6 (PA6‐GF) during the injection molding process by using the Taguchi experimental design method.…”