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Polymer Waste Recycling and Management II

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A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Circular and Green Polymer Science".

Deadline for manuscript submissions: closed (29 February 2024) | Viewed by 25247

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Dr. Cristina Cazan

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Product Design and Environment Faculty, Product Design, Mechatronics and Environment Department, Transilvania University of Brasov, Brasov, Romania
Interests: waste management; polymeric waste; solid waste processing; ecological recycling technology; bioenergy-biomass; life-cycle assessment; composite materials; materials synthesis and processing; materials characterization; surface and interface science; biotechnology; sustainable technology development; environmental assessment
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Dr. Mihaela Cosnita

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Centre Product Design for Sustainable Development, Transilvania University of Brasov, Eroilor 29, 500036 Brasov, Romania
Interests: recycling; waste tyre rubber; rubber–PET–HDPE–wood composites; CaO nanoparticles; wood sawdust; mechanical properties
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Solid waste treatment is a significant problem nowadays. Millions of solid waste items are produced worldwide annually. They are often disposed of in landfills, but this is both an ecologically and economically unacceptable way. A sustainable alternative is the use of wastes as secondary materials for the manufacture of different types of products. Special emphasis is placed on the recycling of polymeric waste and on their management with respect to the principle of waste hierarchy: minimization/prevention, collection, separation, identification, recovery by recycling, biological recovery, energy recovery by incineration, and storage in ecological landfills.

The aim of this Special Issue is to publish original articles, critical reviews, research notes, analyses, and case studies on topics and short communications relating to innovation processes, waste management, and methodologies concerning the reutilization and recycling of polymeric wastes.

Subject Areas:

innovation processes, tools, and methodologies for polymeric waste recycling across the industry (such as paper, wood, plastic, elastomers, PV modules, etc.);
strategies and processes for the recovery, recycling, and reuse of polymer-based materials;
design and processing of recyclable polymer blends and composites;
synthesis and characterization of intrinsically recyclable polymer-based materials;
circular economy;
life-cycle assessment and management of resources, materials, and products to improve the resource efficiency and productivity, conserve resources, and reduce waste;
societal, economic, and technological change for improved recovery and reuse of materials.

Dr. Cristina Cazan
Dr. Mihaela Cosnita
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (10 papers)

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Research

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20 pages, 11339 KiB

Open AccessArticle

Polymer Waste Recycling of Injection Molding Purges with Softening for Cutting with Fresnel Solar Collector—A Real Problem Linked to Sustainability and the Circular Economy

by Ma. Guadalupe Plaza, Maria Luisa Mendoza López, José de Jesús Pérez Bueno, Joaquín Pérez Meneses and Alejandra Xochitl Maldonado Pérez

Polymers 2024, 16(7), 1012; https://0-doi-org.brum.beds.ac.uk/10.3390/polym16071012 - 08 Apr 2024

Viewed by 542

Abstract

A plastic injection waste known as “purge” cannot be reintegrated into the recycling chain due to its shape, size, and composition. Grinding these cannot be carried out with traditional mills due to significant variations in size and shape. This work proposes a process and the design of a device that operates with solar energy to cut the purges without exceeding the degradation temperature. The size reduction allows reprocessing, revalorization, and handling. The purges are mixtures of processed polymers, so their characterization information is unavailable. Some characterizations were conducted before the design of the process and after the cut of the purges. Some of the most representative purges in a recycling company were evaluated. The flame test determines that all material mixtures retain thermoplasticity. The hardness (Shore D) presented changes in four of the purges being assessed, with results in a range of 59–71 before softening and 60–68 after softening. Young’s modulus was analyzed by the impulse excitation technique (IET), which was 2.38–3.95 GPa before softening and 1.7–4.28 after softening. The feasibility of cutting purges at their softening temperature was evaluated. This was achieved in all the purges evaluated at 250–280 °C. FTIR allowed for corroboration of no significant change in the purges after softening. The five types of purges evaluated were polypropylene-ABS, polycarbonate-ABS-polypropylene, yellow nylon 66, acetal, and black nylon 66 with fillers, and all were easily cut at their softening temperature, allowing their manipulation in subsequent process steps. Full article

(This article belongs to the Special Issue Polymer Waste Recycling and Management II)

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15 pages, 12236 KiB

Open AccessArticle

The Effect of Various Ti6Al4V Powders on the Behavior of Particle-Reinforced Polyester Matrix Composites

by Erdoğan Teke, Elif Alyamaç Seydibeyoğlu and Mehmet Özgür Seydibeyoğlu

Polymers 2023, 15(13), 2904; https://0-doi-org.brum.beds.ac.uk/10.3390/polym15132904 - 30 Jun 2023

Viewed by 757

Abstract

In this study, recycled and commercial Ti6Al4V powder was added to polyester composites at various filling ratios by weight fraction. Three weight fractions of Ti6Al4V particles, 0%, 5%, and 10%, were chosen for study. By examining the mechanical and microstructural properties of polyester composites, the effects of the Ti6Al4V powder proportion by weight fraction and particle size parameters were investigated. With the filler loading, a 39% increase in the tensile strength of the composites was achieved. A minor decrease in flexural strength was observed at 5% filler weight fraction. The addition of the recycled Ti6Al4V powder to the polyester matrix slightly reduced the thermal conductivity of the composite over that of the neat polymer. However, the incorporation of the commercial Ti6Al4V powder fillers in the polyester matrix considerably increased the thermal conductivity of the composites, suggesting several potential uses. The presence of high levels of oxygen in the powder led to reduced thermal conductivity of the composites due to the reduction in phonon scattering. Full article

(This article belongs to the Special Issue Polymer Waste Recycling and Management II)

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15 pages, 10939 KiB

Open AccessArticle

3D-Printed PLA Molds for Natural Composites: Mechanical Properties of Green Wax-Based Composites

by Mihai Alin Pop, Mihaela Cosnita, Cătălin Croitoru, Sebastian Marian Zaharia, Simona Matei and Cosmin Spîrchez

Polymers 2023, 15(11), 2487; https://0-doi-org.brum.beds.ac.uk/10.3390/polym15112487 - 28 May 2023

Cited by 2 | Viewed by 1936

Abstract

The first part of this paper is dedicated to obtaining 3D-printed molds using poly lactic acid (PLA) incorporating specific patterns, which have the potential to serve as the foundation for sound-absorbing panels for various industries and aviation. The molding production process was utilized to create all-natural environmentally friendly composites. These composites mainly comprise paper, beeswax, and fir resin, including automotive function as the matrices and binders. In addition, fillers, such as fir needles, rice flour, and Equisetum arvense (horsetail) powder, were added in varying amounts to achieve the desired properties. The mechanical properties of the resulting green composites, including impact and compressive strength, as well as maximum bending force value, were evaluated. The morphology and internal structure of the fractured samples were analyzed using scanning electron microscopy (SEM) and an optical microscopy. The highest impact strength was measured for the composites with beeswax, fir needles, recyclable paper, and beeswax fir resin and recyclable paper, 19.42 and 19.32 kJ/m², respectively, while the highest compressive strength was 4 MPa for the beeswax and horsetail-based green composite. Natural-material-based composites exhibited 60% higher mechanical performance compared to similar commercial products used in the automotive industry. Full article

(This article belongs to the Special Issue Polymer Waste Recycling and Management II)

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16 pages, 5877 KiB

Open AccessArticle

Study and Characterization of Regenerated Hard Foam Prepared by Polyol Hydrolysis of Waste Polyurethane

by Xiaohua Gu, Xiaoyao Wang, Xinyu Guo, Siwen Liu, Qi Li and Yan Liu

Polymers 2023, 15(6), 1445; https://0-doi-org.brum.beds.ac.uk/10.3390/polym15061445 - 14 Mar 2023

Cited by 3 | Viewed by 1557

Abstract

In this paper, four different kinds of diols were used for the alcoholysis of waste thermoplastic polyurethane elastomers. The recycled polyether polyols were used to prepare regenerated thermosetting polyurethane rigid foam through one-step foaming. We used four different kinds of alcoholysis agents, according to different proportions of the complex, and we combined them with an alkali metal catalyst (KOH) to trigger the catalytic cleavage of the carbamate bonds in the waste polyurethane elastomers. The effects of the different types and different chain lengths of the alcoholysis agents on the degradation of the waste polyurethane elastomers and the preparation of regenerated polyurethane rigid foam were studied. Based on the viscosity, GPC, FT-IR, foaming time and compression strength, water absorption, TG, apparent density, and thermal conductivity of the recycled polyurethane foam, eight groups of optimal components were selected and discussed. The results showed that the viscosity of the recovered biodegradable materials was between 485 and 1200 mPa·s. The hard foam of the regenerated polyurethane was prepared using biodegradable materials instead of commercially available polyether polyols, and its compressive strength was between 0.131 and 0.176 MPa. The water absorption rate ranged from 0.7265 to 1.9923%. The apparent density of the foam was between 0.0303 and 0.0403 kg/m³. The thermal conductivity ranged from 0.0151 to 0.0202 W/(m·K). A large number of experimental results showed that the degradation of the waste polyurethane elastomers by the alcoholysis agents was successful. The thermoplastic polyurethane elastomers can not only be reconstructed, but they can also be degraded by alcoholysis to produce regenerated polyurethane rigid foam. Full article

(This article belongs to the Special Issue Polymer Waste Recycling and Management II)

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12 pages, 2318 KiB

Open AccessArticle

One-Pot Tandem Alcoholysis-Hydrogenation of Polylactic Acid to 1,2-Propanediol

by Jialin Xu, Kuo Zhou, Linlin Qin, Zaiming Tan, Shijing Huang, Peigao Duan and Shimin Kang

Polymers 2023, 15(2), 413; https://0-doi-org.brum.beds.ac.uk/10.3390/polym15020413 - 12 Jan 2023

Viewed by 1831

Abstract

The chemical recycling of end-of-life polylactic acid (PLA) plays roles in mitigating environmental pressure and developing circular economy. In this regard, one-pot tandem alcoholysis and hydrogenation of PLA was carried out to produce 1,2-propanediol, which is a bulk chemical in polymer chemistry. In more detail, the commercially available Raney Co was employed as the catalyst, and transformation was conducted in ethanol, which acted as nucleophilic reagent and solvent. Single-factor analysis and Box–Behnken design were used to optimize the reaction conditions. Under the optimized condition, three kinds of PLA materials were subjected to degradation. Additionally, 74.8 ± 5.5%, 76.5 ± 6.2%, and 71.4 ± 5.7% of 1,2-propanediol was yielded from PLA powder, particle, and straws, respectively, which provided a recycle protocol to convert polylactic acid waste into value-added chemicals. Full article

(This article belongs to the Special Issue Polymer Waste Recycling and Management II)

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19 pages, 2626 KiB

Open AccessArticle

The Preservative Action of Protein Hydrolysates from Legume Seed Waste on Fresh Meat Steak at 4 °C: Limiting Unwanted Microbial and Chemical Fluctuations

by Eman T. Abou Sayed-Ahmed, Karima Bel Hadj Salah, Rasha M. El-Mekkawy, Nourhan A. Rabie, Mada F. Ashkan, Soha A. Alamoudi, Mohammed H. Alruhaili, Soad K. Al Jaouni, Mohammed S. Almuhayawi, Samy Selim, Ahmed M. Saad and Mohammad Namir

Polymers 2022, 14(15), 3188; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14153188 - 04 Aug 2022

Cited by 1 | Viewed by 1823

Abstract

Valorizing agricultural wastes to preserve food or to produce functional food is a general trend regarding the global food shortage. Therefore, natural preservatives were developed from the seed waste of the cluster bean and the common bean to extend the shelf life of fresh buffalo meat steak and boost its quality via immersion in high-solubility peptides, cluster bean protein hydrolysate (CBH), and kidney bean protein hydrolysate (RCH). The CBH and the RCH were successfully obtained after 60 min of pepsin hydrolysis with a hydrolysis degree of 27–30%. The SDS-PAGE electropherogram showed that at 60 min of pepsin hydrolysis, the CBH bands disappeared, and RCH (11–48 kD bands) nearly disappeared, assuring the high solubility of the obtained hydrolysates. The CBH and the RCH have considerable antioxidant activity compared to ascorbic acid, antimicrobial activity against tested microorganisms compared to antibiotics, and significant functional properties. The CBH and the RCH (500 µg/mL) successfully scavenged 93 or 89% of DPPH radicals. During the 30-day cold storage (4 °C), the quality of treated and untreated fresh meat steaks was monitored. Protein hydrolysates (500 g/g) inhibited lipid oxidation by 130–153% compared to the control and nisin and eliminated 31–55% of the bacterial load. The CBH and the RCH (500 µg/g) significantly enhanced meat redness (a* values). The protein maintained 80–90% of the steak’s flavor and color (p < 0.05). In addition, it increased the juiciness of the steak. CBH and RCH are ways to valorize wastes that can be safely incorporated into novel foods. Full article

(This article belongs to the Special Issue Polymer Waste Recycling and Management II)

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12 pages, 1894 KiB

Open AccessArticle

The Dependence of the Properties of Recycled PET Electrospun Mats on the Origin of the Material Used for Their Fabrication

by Ewa Kijeńska-Gawrońska, Katarzyna Wiercińska and Monika Bil

Polymers 2022, 14(14), 2881; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14142881 - 16 Jul 2022

Cited by 2 | Viewed by 1585

Abstract

Plastic materials are one of the significant components of construction materials omnipresent in all areas of the industry and everyday life. One of these plastics is polyethylene terephthalate (PET). Due to its processing properties, with a simultaneous low production cost, PET has been used in many industrial applications, including the production of various types of bottles. Moreover, the high consumption of PET bottles causes the accumulation of large amounts of their waste and necessitates finding an effective way to recycle them. Electrospinning is a well-known non-complicated method for the fabrication of nonwovens from polymers and composites, which can be utilized in many fields due to their outstanding properties. In addition, it might be a promising technique for the recycling of plastic materials. Therefore, in this study, the electrospinning approach for the recycling of two types of PET bottle wastes—bottles made of virgin PET and bottles made of recycled PET (PET bottles) has been utilized, and a comparison of the properties of the obtained materials have been performed. The fibers with diameters of 1.62 ± 0.22, 1.64 ± 0.18, and 1.89 ± 0.19 have been produced from solutions made of virgin PET granulate, PET bottles, and PET bottles made of recycled bottles, respectively. Obtained fibers underwent morphological observation using a scanning electron microscope. Physico-chemical properties using FTIR, gel chromatography, and differential scanning calorimetry have been evaluated, and mechanical properties of obtained mats have been investigated. Cytotoxicity tests using the L929 mouse fibroblast cell line revealed no cytotoxicity for all tested materials. Full article

(This article belongs to the Special Issue Polymer Waste Recycling and Management II)

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15 pages, 10556 KiB

Open AccessArticle

Recycled Poly(Ethylene Terephthalate) from Waste Textiles with Improved Thermal and Rheological Properties by Chain Extension

by Wen-Jun Wu, Xiao-Li Sun, Qinghua Chen and Qingrong Qian

Polymers 2022, 14(3), 510; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14030510 - 27 Jan 2022

Cited by 15 | Viewed by 3665

Abstract

Annual production of textile fibers is continuing to rise and the substantial discharge of undegradable waste polyester fibers can cause serious environmental and even health problems. Thus, the recycling and reuse of recycled poly(ethylene terephthalate) from waste textiles (rPET-F) is highly desirable but still challenging. Here, five chain extenders with a different number of epoxy groups per molecules were used to blend with discarded PET fibers and improve its viscosity and quality loss in the recycling process. The molecule weight, thermal properties, rheological properties and macromolecular architecture of modified r-PET were investigated. It was found that all modified rPET-F samples show higher viscosities and better thermal properties. rPET-F modified by difunctional EXOP molecules show linear structure and improved rheological properties. rPET-F modified by polyfunctional commercial ADR and synthesized copolymers exhibit a long chain branched structure and better crystallization. This study reveals a deeper understanding of the chain extension and opens an avenue for the recycling of PET textiles. Full article

(This article belongs to the Special Issue Polymer Waste Recycling and Management II)

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30 pages, 3787 KiB

Open AccessReview

Insights into Anthropogenic Micro- and Nanoplastic Accumulation in Drinking Water Sources and Their Potential Effects on Human Health

by Maria Râpă, Raluca Nicoleta Darie-Niță, Ecaterina Matei, Andra-Mihaela Predescu, Andrei-Constantin Berbecaru and Cristian Predescu

Polymers 2023, 15(11), 2425; https://0-doi-org.brum.beds.ac.uk/10.3390/polym15112425 - 23 May 2023

Cited by 5 | Viewed by 3007

Abstract

Anthropogenic microplastics (MPs) and nanoplastics (NPs) are ubiquitous pollutants found in aquatic, food, soil and air environments. Recently, drinking water for human consumption has been considered a significant pathway for ingestion of such plastic pollutants. Most of the analytical methods developed for detection [...] Read more.

μ

m, but new analytical approaches are required to identify NPs below 1

μ

m. This review aims to evaluate the most recent information on the release of MPs and NPs in water sources intended for human consumption, specifically tap water and commercial bottled water. The potential effects on human health of dermal exposure, inhalation, and ingestion of these particles were examined. Emerging technologies used to remove MPs and/or NPs from drinking water sources and their advantages and limitations were also assessed. The main findings showed that the MPs with sizes > 10

μ

m were completely removed from drinking water treatment plants (DWTPs). The smallest NP identified using pyrolysis–gas chromatography–mass spectrometry (Pyr-GC/MS) had a diameter of 58 nm. Contamination with MPs/NPs can occur during the distribution of tap water to consumers, as well as when opening and closing screw caps of bottled water or when using recycled plastic or glass bottles for drinking water. In conclusion, this comprehensive study emphasizes the importance of a unified approach to detect MPs and NPs in drinking water, as well as raising the awareness of regulators, policymakers and the public about the impact of these pollutants, which pose a human health risk. Full article

(This article belongs to the Special Issue Polymer Waste Recycling and Management II)

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30 pages, 5877 KiB

Open AccessReview

Sustainable Reuse of Waste Tire Textile Fibers (WTTF) as Reinforcements

by Ali Fazli and Denis Rodrigue

Polymers 2022, 14(19), 3933; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14193933 - 20 Sep 2022

Cited by 6 | Viewed by 7373

Abstract

Waste tire textile fibers (WTTF), as a by-product (10–15% by weight of tires) of end-of-life tires (ELT) mechanical recycling (grinding), are classified as hazardous wastes and traditionally burnt (thermal recycling) or buried (landfilling), leading to several environmental and ecological issues. Thus, WTTF still represent an important challenge in today’s material recycling streams. It is vital to provide practical and economical solutions to convert WTTF into a source of inexpensive and valuable raw materials. In recent years, tire textile fibers have attracted significant attention to be used as a promising substitute to the commonly used natural/synthetic reinforcement fibers in geotechnical engineering applications, construction/civil structures, insulation materials, and polymer composites. However, the results available in the literature are limited, and practical aspects such as fiber contamination (~65% rubber particles) remain unsolved, limiting WTTF as an inexpensive reinforcement. This study provides a comprehensive review on WTTF treatments to separate rubber and impurities and discusses potential applications in expansive soils, cement and concrete, asphalt mixtures, rubber aerogels and polymer composites. Full article

(This article belongs to the Special Issue Polymer Waste Recycling and Management II)

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