Extrusion and characterization of recycled polyethylene terephthalate (rPET) filaments compounded with chain extender and impact modifiers for material-extrusion additive manufacturing

Abstract

The continuous growth of annual production and consumption of polyethylene terephthalate (PET) is coined with increasing waste that leaks into the environment, landfills and oceans as microplastics and nano plastics fragments. Upcycling the recycled PET to make a feedstock for the fast-growing material-extrusion additive manufacturing (MEX-AM) technology can contribute to the solution and supports the concept of sustainable materials. In this work, extrudable filaments comprising recycled polyethylene terephthalate (rPET) with low-cost additives, such as pyromellitic dianhydride (PMDA) as a chain extender, styrene-ethylene-butylene-styrene terpolymer functionalized with maleic anhydride (SEBS-g-MA), a thermal modifier and toughening agent, ethylene-ethyl acrylate-glycidyl methacrylate terpolymer (E-EA-GMA), a functional reactive elastomeric impact modifier and ethylene-ethyl-acrylate (EEA), a non-reactive elastomeric impact modifier, have been fabricated using the twin-screw extruder. The optimum extrusion process parameters for producing uniform filaments of different rPET compounded formulations have been identified, this includes the extrusion die temperature of 280 °C and the screw speed of 150 ± 3 rpm. The compounded filaments are then printed into standard ASTM test specimens for thermal characterization and mechanical characterization, including glass transition and melting temperatures, crystallinity and crystallization temperature, tensile strength, tensile modulus, ductility, flexural strength, and Izod impact energy. Furthermore, the melt flow index for the filaments was measured. More significantly, the experimental data showed that compounding rPET with such additives in the reactive twin-screw extrusion process results in uniform filaments that display advantageous thermal and mechanical properties and can be used as a feedstock in the MEX-AM technology. This study suggests that compounding the recycled PET pellets with low-cost additives while extruding them into filaments for MEX-AM offers excellent potential to make high-value-added customized products from a sustainable polymer feedstock, such as prototyping, tooling, testing components or end-use internal components for small machines and cars.

Evaluation of PET recyclability and characterization of modified reprocessed‐PET for industrial application

“…Rashwan et al explained that only one degradation peak is found around 420 C, indicating that the additives did not negatively impact the decomposition temperatures. 49…”

Prospects of sustainable polymers

“…Therefore, Rashwan et al demonstrated the utilization of recycled PET (rPET) as sustainable value-added material feedstock for material-extrusion additive manufacturing technology. For this, rPET was compounded with low-cost additives such as pyromellitic dianhydride (PMDA, a chain extender), maleic anhydride-functionalized styrene-ethylene-butylene-styrene terpolymer (MA-g-SEBS, a thermal modifier/toughening agent), ethylene-ethyl acrylate-glycidyl methacrylate terpolymer (E-EA-GMA, a reactive elastomeric impact modifier), and ethylene-ethyl-acrylate (EEA, non-reactive elastomeric impact modifier), and extruded into filaments using twin-screw extruder for potential application in prototyping, tooling and testing parts, or end-use internal parts of small machines and cars 10 . In another approach, Verma et al .…”

Mechanical Performance of Recycled 3D Printed Sustainable Polymer-Based Composites: A Literature Review

“…Polyethylene Terephthalate (PET) Easy Packaging, textiles, electronic cables, water bottles [32][33][34][35][36][37][38][39][40] High-Density Polyethylene (HDPE) Easy Pipes, chemicals packaging, fuel tanks, bumpers [41][42][43][44][45][46] Polyvinyl Chloride (PVC) Moderate Bags, medical equipment, pipes [47] Low PET is usually used in AM by employing material extrusion (MEX) processes such as fused filament fabrication (FFF), but several challenges have emerged due to its shrinkage and warpage issues caused by high fusion temperatures and lack of control of crystallinity, water absorption (leading to molecular weight reduction) and weak interfacial bonding between layers [32][33][34][35]. PET is mainly used for water and food packaging and the waste-tofeedstock process consists of label removal, water cleaning and drying, and granulation or shredding into flakes or pellets before sterilization.…”

“…PET is mainly used for water and food packaging and the waste-tofeedstock process consists of label removal, water cleaning and drying, and granulation or shredding into flakes or pellets before sterilization. Single-or twin-screw extruders are commonly used for feedstock production [36][37][38][39][40]. Polyethylenes (HDPE and LDPE) are used as well in the same industry, with HDPE providing a high strength-to-density ratio and being employed for blow-molded water bottles.…”

“…Recycled PET has been utilized for AM, but due to shrinkage, weak interfacial adhesion and warping, the insertion of stabilizers and reinforcements is vital for sustainable 3D printing [45]. The addition of pyromellitic dianhydride (PMDA) or other chain extenders helps improve viscosity [35,37,88]. Recycled carbons (fibers, biochar) used as reinforcement have been shown to help limit shrinkage issues and improve thermal stability and dimensional accuracy [38,89].…”