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Recycling and Utilization of Waste Polymer

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A special issue of Sustainability (ISSN 2071-1050). This special issue belongs to the section "Waste and Recycling".

Deadline for manuscript submissions: closed (20 July 2023) | Viewed by 14040

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Special Issue Editors

Dr. Shuangqiao Yang

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Guest Editor

State Key Laboratory of Polymer Materials Engineering, Polymer Research Institute of Sichuan University, Chengdu 610065, China
Interests: sustainability; recycling plastic; sustainable materials; e-waste; wood-plastic composites; thermal conductivity materials

Dr. Qingye Li

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Guest Editor

College of Food Science, Sichuan Agricultural University, Ya’an 625014, China
Interests: sustainability; recycling plastic; sustainable materials; wood-plastic composites; thermal conductivity materials
Special Issues, Collections and Topics in MDPI journals

Dr. Dong Tian

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Guest Editor

Institute of Ecological and Environmental Sciences, Sichuan Agricultural University, Chengdu 611130, China
Interests: biomass wastes valorization, lignin and cellulose materials, eco-friendly materials

Special Issue Information

Dear Colleagues,

Polymer materials, such as plastics, rubber, and synthetic fibers, have excellent properties, including low density, easy processing, high performance, and multi-functionality, and they are widely used in various fields. However, the emergence of a large number of polymer wastes has posed serious challenges to people. Statistics show that approximately 8.3×10⁹ t of plastic products have been produced globally, with a waste amount of about 6.3×10⁹ t until 2015, while only 9% of this has been recycled. The environmental consequences of polymer solid waste are visible in the ever-increasing levels of global plastic pollution both on land and in the oceans. However, although there are important economic and environmental incentives for polymer recycling, end-of-life treatment options for polymer solid waste are in practice quite limited. Presorting of plastics before recycling is costly and time intensive, recycling requires large amounts of energy and often leads to low-quality polymers, and current technologies cannot be applied to many polymeric materials. For the prevention and control of waste polymer, it is essential to achieve the high-value utilization of waste polymer and improving scientific and technological innovation of plastic recycling. Recent research points the way toward compatibilization of mixed plastic wastes to avoid the need for sorting, chemical recycling methods with lower energy requirements and expanding recycling technologies to traditionally nonrecyclable polymers.

This Special Issue aims to explore the new recycling approaches for successfully recycling and utilization of waste polymer in terms of:

Strategies for recycling mixed or contaminated polymer and minimizing the need for sorting through compatibilizer design;
Improving chemical recycling efficiency and selectivity through catalyst development such as new low-energy catalysts; and
Expanding recycling beyond thermoplastics;

Dr. Shuangqiao Yang
Dr. Qingye Li
Dr. Dong Tian
Guest Editors

Manuscript Submission Information

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Keywords

environmental pollution
waste polymer
recycling
utilization
mechanical recycling
chemical recycling

Published Papers (7 papers)

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Research

23 pages, 8795 KiB

Open AccessArticle

Compaction Effort Evaluation of Crumb Rubber Modified Hot Mix Asphalt

by Dlzar Bakr Qadr and Aso Faiz Talabany

Sustainability 2023, 15(10), 7839; https://doi.org/10.3390/su15107839 - 10 May 2023

Cited by 1 | Viewed by 1234

Abstract

The primary goal of this study was to obtain the same performance from an asphalt mixture made using a Marshall impact hammer (MIH) as from asphalt made using a Superpave gyratory compactor (SGC). This was due to the expense of Superpave equipment compared with Marshall equipment. A wet process was used to blend the CR with PG 70-16 asphalt. A crushed stone aggregate was used with a 19 mm nominal maximum aggregate size, and the samples were prepared using an SGC and an MIH. The results show that nine percent CR was determined to be the optimum crumb-rubber content (OCRC). In addition, the SGC provided excellent performance in Marshall stability, density, tensile strength, and compressive strength at different numbers of blows and gyrations compared with the MIH. Moreover, the MIH required approximately 21, 21, 18, and 24 extra blows to obtain the same stability, density, tensile strength, and compressive strength, respectively, as the SGC at the design number of gyrations (N_design). Furthermore, modified mixtures at the OCRC increased the compressive strength in the range from 16 to 48 percent and had higher values on the index of retained strength than unmodified mixtures. As a result, they provided mixtures with less susceptibility to moisture damage. The significance of this study is that asphalt that performed the same as Superpave samples was obtained using only Marshall equipment. Full article

(This article belongs to the Special Issue Recycling and Utilization of Waste Polymer)

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15 pages, 8981 KiB

Open AccessArticle

Solid-State Shear Milling for Recycling Aluminum–Plastic Packaging Waste: A Sustainable Solution for Mixed Plastic Waste

by Baojie Wei, Liang Li, Shiyu Ding, Ning Chen, Shibing Bai and Shuangqiao Yang

Sustainability 2023, 15(7), 6144; https://doi.org/10.3390/su15076144 - 03 Apr 2023

Viewed by 1702

Abstract

The application of paper–aluminum–plastic packaging has been widely adopted in various fields such as the food and medical industries, owing to its exceptional preservation and obstruction properties. Nonetheless, the recycling process for paper and aluminum from this packaging type typically involves water pulping and solvent separation. The resulting residual waste, commonly known as multi-plastic waste (PMW), poses significant challenges in terms of separation and recycling. In this research article, we propose a solution for the recycling of PMW using solid-state shear milling (S³M). This process utilizes powerful three-dimensional shear force to achieve pulverization and excellent dispersion of multicomponent polymers, all while maintaining ambient temperature conditions. The thermoplastic processability of milled PMW powder was improved. The results indicate that a significant reduction in the the average particle size of PMW from 700 μm to 226 μm after 10 milling cycles, as evidenced by both a particle size analyzer and SEM. Furthermore, S³M processing leads to a good dispersion of PMW domains, as confirmed by the reduction in domain size from 9.64 μm to 2.65 μm. DSC and DMA reveal excellent compatibility between the components of the composite, resulting in improved mechanical properties such as tensile stress (from 14.03 MPa to 22.02 MPa) and unnotched impact strength (from 3.26 KJ/m² to 4.82 KJ/m²). The findings suggest that S³M technology could be an effective and sustainable method for recycling PMW without any separation process, with promising industrial application. Full article

(This article belongs to the Special Issue Recycling and Utilization of Waste Polymer)

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16 pages, 2384 KiB

Open AccessArticle

Influence of a Multifunctional Epoxy Additive on the Performance of Polyamide 6 and PET Post-Consumed Blends during Processing

by Anna Raffaela de Matos Costa, Mariana Alves Henrique, Carlos Bruno Barreto Luna, Laura Hecker de Carvalho and Yêda Medeiros Bastos de Almeida

Sustainability 2022, 14(24), 16658; https://doi.org/10.3390/su142416658 - 12 Dec 2022

Cited by 5 | Viewed by 1435

Abstract

In this study, a commercial chain extender (Polyad PR 002) in concentrations of 0.5, 1.0, and 1.5% w/w was used as a compatibilizer in post-consumed PET/PA6 blends (25/75, 50/50 e 75/25) processed in a laboratory mixer. The degradation rate, phase miscibility, chemical interaction, crystallization, and melting behavior, as well as the thermal stability of the mixtures, were analyzed by torque rheometry, scanning electron microscopy (SEM), FTIR spectroscopy, differential scanning calorimetry (DSC), and thermogravimetry (TGA), respectively. The results showed that the addition of 1% chain extender was sufficient to increase the melt viscosity of the PET-rich mixtures and 1.5% for the PA6-rich samples. Clearly, adding Polyad PR 002 to PET/PA6 blends improves polymer compatibility; for the 25%PET/75%PA6 blend with 1.5% PR 002, complete miscibility was observed, indicating a new compatible blend formation, revealing a chemical reaction between the systems, and proving the synergism between them. This chain extender did not affect the thermal stability of the blends, and the low contents employed reduced the crystallization rate of the blends investigated. Full article

(This article belongs to the Special Issue Recycling and Utilization of Waste Polymer)

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28 pages, 9250 KiB

Open AccessArticle

Catalytic Pyrolysis Process to Produce Styrene from Waste Expanded Polystyrene Using a Semi-Batch Rotary Reactor

by Gerardo Pérez-Bravo, José Luis Contreras-Larios, Jorge Francisco Rodríguez, Beatriz Zeifert-Soares, Deyanira Angeles-Beltrán, Ricardo López-Medina, Tamara Vázquez-Rodríguez and José Salmones-Blasquez

Sustainability 2022, 14(22), 14914; https://doi.org/10.3390/su142214914 - 11 Nov 2022

Cited by 2 | Viewed by 1489

Abstract

Thermal and catalytic pyrolysis of waste expanded polystyrene (WEPS) was studied to obtain mainly styrene monomer, which can be recycled in the polystyrene industry. Initially, preliminary experiments were carried out in a static semi-batch glass reactor with basic catalysts and without catalysts, using toluene as solvent at 250 °C, determining their styrene yields to select the best catalyst. MgO turned out to be the best catalyst due to its stability and cost. This catalyst was characterized by XRD, BET area, SEM-EDS, Raman spectroscopy, UV–VIS, and TGA. The kinetic equation for WEPS pyrolysis in the glass reactor was determined as a first-order reaction. The heat of reaction, the Gibbs free energy change, and the entropy change were calculated. Finally, WEPS pyrolysis experiments were carried out using a rotating semi-batch steel reactor, at higher temperatures and without using solvents, evaluating the styrene yield and its performance for its possible industrial application. In this reaction, the activity remained almost constant after four catalyst regenerations. The best styrene yield was 94 wt%, which could be one of the highest reported in the literature. This result may be associated with the back-mixing obtained in the rotary reactor, in contrast to the performance observed in the static glass reactor. Full article

(This article belongs to the Special Issue Recycling and Utilization of Waste Polymer)

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12 pages, 2484 KiB

Open AccessArticle

Effects of Heating Rate and Temperature on the Yield of Thermal Pyrolysis of a Random Waste Plastic Mixture

by José Manuel Riesco-Avila, James R. Vera-Rozo, David A. Rodríguez-Valderrama, Diana M. Pardo-Cely and Bladimir Ramón-Valencia

Sustainability 2022, 14(15), 9026; https://doi.org/10.3390/su14159026 - 23 Jul 2022

Cited by 4 | Viewed by 2185

Abstract

Effects of heating rate and temperature on thermal-pyrolytic yield of a plastic-waste mixture were studied in a semi-batch reactor. The temperature in the range of 380–460 °C and heating rates of 10, 19, and 28 °C/min were evaluated through an experimental multi-level design. The results show that higher temperatures or lower residence time reduce the yield of pyrolytic oil at the expense of increasing the yield of gaseous products. The maximum liquid yield was 69%, obtained at 410 °C and a heating rate of 10 °C/min. The composition of pyrolytic oil covers a wide range of hydrocarbons; thus, a fractionation is necessary before using it as fuel in internal combustion engines. The fractionation process yielded 21.12 wt% of light fraction (gasoline-like), 56.52 wt% of medium fraction (diesel-like), and 22.36 wt% of heavy fraction (heavy diesel-like). The light fraction has an octane index and caloric value within the range of the typical gasoline values. On the other hand, the cetane index and caloric value of the medium fraction meet the requirements of the standards for diesel. Full article

(This article belongs to the Special Issue Recycling and Utilization of Waste Polymer)

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25 pages, 8111 KiB

Open AccessArticle

From Waste to Potential Reuse: Mixtures of Polypropylene/Recycled Copolymer Polypropylene from Industrial Containers: Seeking Sustainable Materials

by Carlos Bruno Barreto Luna, Wallisson Alves da Silva, Edcleide Maria Araújo, Lara Júlia Medeiros Dantas da Silva, João Baptista da Costa Agra de Melo and Renate Maria Ramos Wellen

Sustainability 2022, 14(11), 6509; https://doi.org/10.3390/su14116509 - 26 May 2022

Cited by 4 | Viewed by 1996

Abstract

This work investigated the effect of thermo-oxidation aging in blends of copolymer polypropylene (PPc)/recycled copolymer polypropylene (PPcr) from industrial container waste, coded as PPc/PPcr blends. All compounds were melt extruded, and the injection molded specimens were characterized by mechanical properties (tensile and impact), Fourier-transform infrared spectroscopy (FTIR), melt flow index (MFI), contact angle, heat deflection temperature (HDT), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). FTIR spectra presented bands related to the hydroperoxides and carbonyl groups, as resulted from thermo-oxidation aging. The contact angle decreased upon a thermo-oxidation aging influence, corroborating the FTIR spectra. PPcr presented higher MFI as a consequence of reprocessing. Impact strength and elongation at break were quite sensible to the thermo-oxidation aging influence and were progressively reduced upon increased time, whereas tensile strength, elastic modulus, and HDT only slightly changed. SEM images of PPc presented a higher quantity of pulled-out particles, resulted from a lower interaction between phases, i.e., polypropylene and ethylene/propylene. From the impact strength and toughness data, proper dissipation energy mechanisms were found in PPc/PPcr blends. Summing up, using PPcr contributed to minimize properties’ losses, which may be related to the stabilizer agents, whereas the described results presented great potential for the PP market, while contributing to the sustainable environment. Full article

(This article belongs to the Special Issue Recycling and Utilization of Waste Polymer)

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15 pages, 7322 KiB

Open AccessEditor’s ChoiceArticle

Mechanical and Durability Assessment of Recycled Waste Plastic (Resin8 & PET) Eco-Aggregate Concrete

by Adewumi John Babafemi, Nina Sirba, Suvash Chandra Paul and Md Jihad Miah

Sustainability 2022, 14(9), 5725; https://doi.org/10.3390/su14095725 - 09 May 2022

Cited by 19 | Viewed by 3358

Abstract

The massive amount of plastic waste in our natural environment is a global concern. In this study, recycling plastic waste to partially replace natural sand in concrete is investigated. The performance of Resin8, a unique combination of all types of plastics and Polyethylene Terephthalate (PET) in concrete, has also been investigated. Replacement contents of 5%, 10%, and 15% for sand by volume were performed. The concrete mixes incorporating recycled plastic waste were tested against a reference concrete mix without plastic. The workability, compressive strength, tensile strength, oxygen permeability index (OPI), and effect of temperature were assessed. Scanning Electron Microscopy (SEM) analysis was conducted on the plastics and plastic concretes, pre- and post-temperature exposure. PET at a replacement content of 10% slightly increased the compressive strength by 2.4%. Regarding the OPI test, all the mixes incorporating recycled plastic waste are classified as “good”. When exposed to a temperature of 250 °C, no significant change in compressive strength was observed for the concrete mixes incorporating Resin8 at a replacement content of 15%, and the mixes incorporating PET at a replacement content of 5%, 10%, and 15%. It was clear from the results that both Resin8 and PET are suitable as a partial replacement for sand in concrete. Full article

(This article belongs to the Special Issue Recycling and Utilization of Waste Polymer)

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