Development of Tensile Properties and Crystalline Conformation of Recycled Polypropylene by Re-Extrusion Using a Twin-Screw Extruder with an Additional Molten Resin Reservoir Unit

Abstract

Plastic mechanical recycling is an attractive method for reducing the amounts of waste plastics. However, the alterations in the mechanical properties (degradation) in recycled plastics is a limitation to the material’s mechanical recycling. In this study, the mechanical recycling was enhanced by the addition of a “molten resin reservoir” unit at the end of the twin-screw extruder. Recycled polypropylene (RPP) obtained from a household was re-extruded with this developed extrusion unit. The tensile properties, type of crystalline, and conformation of polypropylene polymorphs were evaluated and compared for virgin polypropylene (VPP), recycled polypropylene (RPP) without extrusion (RPP-original), and RPP with extrusion by using a new type of extruder (RPP-extrusion). It could be found that the tensile properties of RPP-extrusion were improved, so as to be similar to those of VPP. In addition, the conformation of RPP-extrusion was similar to that of VPP by increasing the ratio between the helix and parallel band. This study succeeded in regenerating the tensile properties and inner structures in recycled PP, which could prolong the used lifetime and decrease the amount of waste from single-use plastic.

Valorization of Polypropylene Waste in the Production of New Materials with Adequate Mechanical and Thermal Properties for Environmental Protection

“…In spectra shown in Figure 6 can be observed the three main spectra regions: 3000–2800 cm −1 , 1500–1250 cm −1 , and 1160–800 cm −1 . The PPW sample displayed characteristic peaks at 997 cm −1 and 975 cm −1 attributed to the crystalline and amorphous structure of PP [ 36 ], 2830 cm −1 related to the symmetrical stretching of CH 2 (amorphous and crystalline phases), and 2900 cm −1 and 2950 cm −1 assigned to the asymmetric stretching bands of CH 2 (amorphous phase) [ 52 ]. The absorption bands at 1461 cm −1 and 1377 cm −1 are the -CH 3 - (symmetric bending), while low intensities of absorption bands are observed at 1159 cm −1 (CH bending, CH 3 rocking, C-C stretching) [ 53 ].…”

“…The X-ray profile in Figure 8 indicates the approximately equal intensities of signals characteristic for crystalline polymers, together with the amorphous character observed for the synthesized block copolymer. The peaks of 2-theta at 16.9°, 18.4°, 25.3°, and 28.6° detected in pure PPW were assigned to the crystalline phase of PP [ 35 ], while the peaks appearing at 21.5° and 23.2° were due to the PE [ 36 , 60 ].…”

“…The irradiation technique could be a method for improving the tensile and flexural properties of recycled PP/microcrystalline cellulose (MCC) composites [ 20 ]. When a molten resin reservoir was added to a twin-screw extruder, the elongation of break and toughness both increased by 77% as compared with the original PP waste [ 36 ]. Another paper reported that the flexural properties, impact strength, and heat deflection temperature (HDT) of kenaf fiber/PP composites with waste expanded PP (EPP) were markedly higher than those with virgin PP.…”

Revolutionary Plastic Mechanical Recycling Process: Regeneration of Mechanical Properties and Lamellar Structures

“…Based on this physical regeneration theory, the creation of a new type of extrusion process was exhibited. Phanthong et al [28] studied the development of mechanical properties and crystalline conformation of recycled polypropylene by re-extrusion using a new type twin-screw extruder. This was the establishment of a new unit which was a blank space added into the end of a twin-screw extruder, namely a "Molten Resin Reservoir: MRR".…”

“…Figure 11. (a) New type of twin-screw extruder with additional MRR unit; (b) schematic image of MRR unitwhich was a blank space connected at the end of screw mixing zone of general extruder[28].…”