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Polymers
Special Issues
Recycling and Resource Recovery from Polymers II
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Recycling and Resource Recovery from Polymers II

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 (10 February 2023) | Viewed by 76439

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Dr. Sheila Devasahayam

E-Mail Website
Guest Editor
Senior Lecturer, WASM: Minerals, Energy and Chemical Engineering, Curtin University, Curtin, Australia
Interests: energy and emission reductions in process metallurgy, pelletisation, decarbonising cement and iron ore reduction; biomass and waste utilisation in process metallurgy, dewatering, carbon reforming, polymers for carbon reduction; polymers for sustainable materials processing; recycling
Special Issues, Collections and Topics in MDPI journals
Dr. Laurence Dyer

E-Mail Website
Guest Editor
Department of Mining Engineering and Metallurgical Engineering, Western Australian School of Mines, Curtin University, Curtin, Australia
Interests: rare earth dissolution and recovery; extractability of Ni and Cu; lithium minerals

Special Issue Information

Dear Colleagues,

Following the success of the Special Issue of Polymers, "Recycling and Resource Recovery from Polymers", we are delighted to reopen this Special Issue, now entitled "Recycling and Resource Recovery from Polymers II".

About 90% of the 300 million tonnes of plastics produced each year is not recycled and disposed of in landfills, posing significant environmental concerns. By 2030, 104 Mt of waste plastics are projected to enter landfill, causing a 50% increase in CO2 emissions from the plastic life cycle and a three-fold CO2 increase caused by plastic incineration due to poor waste management. A zero-waste approach conserves natural resources and reduces pollution from extraction, manufacturing and disposal. The vision for a new circular economy for plastics initiative is supported by three key actions: eliminate, innovate, and circulate. This Special Issue will focus on current and future research concernign the repurposing of plastics at the end of their life for various applications.

Dr. Sheila Devasahayam
Dr. Laurence Dyer
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.

Keywords

  • circular economy/plastics economy
  • energy recovery
  • monomer recovery
  • hydrogen energy systems
  • emissions reduction
  • carbon capture
  • carbon conversion reactions
  • gasification
  • novel cataslysts
  • feedstock recycling
  • sustainable materials processing (e.g., iron and steel industry)
  • polymer wastes in geopolymer concrete (construction, built materials)
  • process modelling
  • economic analysis

Published Papers (20 papers)

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Research

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27 pages, 15825 KiB  
Article
Chloride Permeability Coefficient Prediction of Rubber Concrete Based on the Improved Machine Learning Technical: Modelling and Performance Evaluation
by Xiaoyu Huang, Shuai Wang, Tong Lu, Houmin Li, Keyang Wu and Weichao Deng
Polymers 2023, 15(2), 308; https://0-doi-org.brum.beds.ac.uk/10.3390/polym15020308 - 07 Jan 2023
Cited by 3 | Viewed by 1223
Abstract
The addition of rubber to concrete improves resistance to chloride ion attacks. Therefore, rapidly determining the chloride permeability coefficient (DCI) of rubber concrete (RC) can contribute to promotion in coastal areas. Most current methods for determining DCI of RC [...] Read more.
The addition of rubber to concrete improves resistance to chloride ion attacks. Therefore, rapidly determining the chloride permeability coefficient (DCI) of rubber concrete (RC) can contribute to promotion in coastal areas. Most current methods for determining DCI of RC are traditional, which cannot account for multi-factorial effects and suffer from low prediction accuracy. Machine learning (ML) techniques have good non-linear learning capabilities and can consider the effects of multiple factors compared with traditional methods. However, ML models easily fall into the local optimum due to their parameters’ influence. Therefore, a mixed whale optimization algorithm (MWOA) was developed in this paper to optimize ML models. The main strategies are to introduce Tent mapping to expand the search range of the algorithm, to use an adaptive t-distribution dimension-by-dimensional variation strategy to perturb the optimal fitness individual to thereby improve the algorithm’s ability to jump out of the local optimum, and to introduce adaptive weights and adaptive probability threshold values to enhance the adaptive capacity of the algorithm. For this purpose, data were collected from the published literature. Three machine learning models, Extreme Learning Machine (ELM), Random Forest (RF), and Elman Neural Network (ELMAN), were built to predict the DCI of RC, and the three models were optimized using MWOA. The calculations show that the MWOA is effective with the optimized ELM, RF, and ELMAN models improving the prediction accuracy by 54.4%, 62.9%, and 36.4% compared with the initial model. The MWOA-ELM model was found to be the optimal model after a comparative analysis. The accuracy of the multiple linear regression model (MRL) and the traditional mathematical model is calculated to be 87.15% and 85.03%, which is lower than that of the MWOA-ELM model. This indicates that the ML model that is optimized using the improved whale optimization algorithm has better predictive ability than traditional models, providing a new option for predicting the DCI of RC. Full article
(This article belongs to the Special Issue Recycling and Resource Recovery from Polymers II)
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11 pages, 2651 KiB  
Article
Thermal and Mechanical Degradation of Recycled Polylactic Acid Filaments for Three-Dimensional Printing Applications
by Dongoh Lee, Younghun Lee, Inwhan Kim, Kyungjun Hwang and Namsu Kim
Polymers 2022, 14(24), 5385; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14245385 - 09 Dec 2022
Cited by 5 | Viewed by 2529
Abstract
The recycling of filaments used in three-dimensional (3D) printing systems not only mitigates the environmental issues associated with conventional 3D printing approaches but also simultaneously reduces manufacturing costs. This study investigates the effects of successive recycling of polylactic acid (PLA) filaments, which were [...] Read more.
The recycling of filaments used in three-dimensional (3D) printing systems not only mitigates the environmental issues associated with conventional 3D printing approaches but also simultaneously reduces manufacturing costs. This study investigates the effects of successive recycling of polylactic acid (PLA) filaments, which were used in the printing process, on the mechanical properties of recycled filaments and printed objects. The mechanical strengths of the printed PLA and the adhesion strengths between 3D-printed beads were evaluated via the tensile testing of the horizontally and vertically fabricated specimens. Gel permeation chromatography analysis revealed a reduction in the molecular weight of the polymer as a result of recycling, leading to a decrease in the mechanical strength of the 3D-printed product. Additionally, scanning electron microscopy images of the cutting plane showed that the fabricated beads were broken in the case of the horizontally fabricated specimen, whereas in the case of the vertically fabricated samples, the adhesion between the beads was weak. These findings indicate that the mechanical strength in the in-plane and out-of-plane directions must be improved by increasing the mechanical strength of the bead itself as well as the adhesion strength of the beads. Full article
(This article belongs to the Special Issue Recycling and Resource Recovery from Polymers II)
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12 pages, 4068 KiB  
Article
Upcycling Different Particle Sizes and Contents of Pine Branches into Particleboard
by Anita Wronka and Grzegorz Kowaluk
Polymers 2022, 14(21), 4559; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14214559 - 27 Oct 2022
Cited by 8 | Viewed by 1404
Abstract
A growing world population means that demand for wood-based materials such as particleboard is constantly increasing. In recent years, wood prices have reached record highs, so a good alternative can be the utilization of branches, which can reduce the cost of raw materials [...] Read more.
A growing world population means that demand for wood-based materials such as particleboard is constantly increasing. In recent years, wood prices have reached record highs, so a good alternative can be the utilization of branches, which can reduce the cost of raw materials for particleboard production. The goal of the study was to confirm the feasibility of using an alternative raw material in the form of Pinus sylvestris L. pine branches for the production of three-layer particleboard. Characterization of the alternative raw material was also carried out, and the bulk density was determined. As part of the research, six variants of particleboard, 0%, 5%, 10%, 25%, and 50%, w/w, and two variants where the first one had the face layer made of branch particles and the core layer made of industrial particles, and the reverse variant (all produced panels were three-layer) were produced and then their physical and mechanical properties were studied. The results show that even if the bulk density of branch particles is significantly higher than industrial material, the internal bond and water absorption rises as branch particle content increases. In the case of bending strength and modulus of elasticity, these were decreased with a branch particle content increase. The conducted tests confirmed the possibility of using the raw material, which was usually used as fuel or mulch, to produce particleboards even in 50% content. The present solution also contributes to the positive phenomenon of carbon storage, due to incorporating the branches’ biomass into panels rather than burning it. Further research should be focused on the modification of particle production from branches to obtain lower bulk density and to reach fraction shares closer to industrial particles. Furthermore, the chemical characterization of the pine branch particles (cellulose and lignin content, extractives content, pH value) would provide valuable data about this potential alternative raw material. Full article
(This article belongs to the Special Issue Recycling and Resource Recovery from Polymers II)
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16 pages, 2410 KiB  
Article
Investigation of Recycled and Coextruded PLA Filament for Additive Manufacturing
by Jana Sasse, Lukas Pelzer, Malte Schön, Tala Ghaddar and Christian Hopmann
Polymers 2022, 14(12), 2407; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14122407 - 14 Jun 2022
Cited by 9 | Viewed by 2305
Abstract
Polylactide acid (PLA) is one of the most used plastics in extrusion-based additive manufacturing (AM). Although it is bio-based and in theory biodegradable, its recyclability for fused filament fabrication (FFF) is limited due to material degradation. To better understand the material’s recyclability, blends [...] Read more.
Polylactide acid (PLA) is one of the most used plastics in extrusion-based additive manufacturing (AM). Although it is bio-based and in theory biodegradable, its recyclability for fused filament fabrication (FFF) is limited due to material degradation. To better understand the material’s recyclability, blends with different contents of recycled PLA (rPLA) are investigated alongside a coextruded filament comprised of a core layer with high rPLA content and a skin layer from virgin PLA. The goal was to determine whether this coextrusion approach is more efficient than blending rPLA with virgin PLA. Different filaments were extruded and subsequently used to manufacture samples using FFF. While the strength of the individual strands did not decrease significantly, layer adhesion decreased by up to 67%. The coextruded filament was found to be more brittle than its monoextruded counterparts. Additionally, no continuous weld line could be formed between the layers of coextruded material, leading to a decreased tensile strength. However, the coextruded filament proved to be able to save on master batch and colorants, as the outer layer of the filament has the most impact on the part’s coloring. Therefore, switching to a coextruded filament could provide economical savings on master batch material. Full article
(This article belongs to the Special Issue Recycling and Resource Recovery from Polymers II)
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18 pages, 1599 KiB  
Article
Simulation and Modelling of Hydrogen Production from Waste Plastics: Technoeconomic Analysis
by Ali A. Al-Qadri, Usama Ahmed, Abdul Gani Abdul Jameel, Umer Zahid, Muhammad Usman and Nabeel Ahmad
Polymers 2022, 14(10), 2056; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14102056 - 18 May 2022
Cited by 19 | Viewed by 5061
Abstract
The global energy demand is expected to increase by 30% within the next two decades. Plastic thermochemical recycling is a potential alternative to meet this tremendous demand because of its availability and high heating value. Polypropylene (PP) and polyethylene (PE) are considered in [...] Read more.
The global energy demand is expected to increase by 30% within the next two decades. Plastic thermochemical recycling is a potential alternative to meet this tremendous demand because of its availability and high heating value. Polypropylene (PP) and polyethylene (PE) are considered in this study because of their substantial worldwide availability in the category of plastic wastes. Two cases were modeled to produce hydrogen from the waste plastics using Aspen Plus®. Case 1 is the base design containing three main processes (plastic gasification, syngas conversion, and acid gas removal), where the results were validated with the literature. On the other hand, case 2 integrates the plastic gasification with steam methane reforming (SMR) to enhance the overall hydrogen production. The two cases were then analyzed in terms of syngas heating values, hydrogen production rates, energy efficiency, greenhouse gas emissions, and process economics. The results reveal that case 2 produces 5.6% more hydrogen than case 1. The overall process efficiency was enhanced by 4.13%. Case 2 reduces the CO2 specific emissions by 4.0% and lowers the hydrogen production cost by 29%. This substantial reduction in the H2 production cost confirms the dominance of the integrated model over the standalone plastic gasification model. Full article
(This article belongs to the Special Issue Recycling and Resource Recovery from Polymers II)
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11 pages, 3714 KiB  
Article
Fabrication of Recycled Polycarbonate Fibre for Thermal Signature Reduction in Camouflage Textiles
by Asril Soekoco, Ateeq Ur Rehman, Ajisetia Fauzi, Hamdi Tasya, Purnama Diandra, Islami Tasa, Nugraha and Brian Yuliarto
Polymers 2022, 14(10), 1972; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14101972 - 12 May 2022
Cited by 3 | Viewed by 1822
Abstract
Thermal signature reduction in camouflage textiles is a vital requirement to protect soldiers from detection by thermal imaging equipment in low-light conditions. Thermal signature reduction can be achieved by decreasing the surface temperature of the subject by using a low thermally conductive material, [...] Read more.
Thermal signature reduction in camouflage textiles is a vital requirement to protect soldiers from detection by thermal imaging equipment in low-light conditions. Thermal signature reduction can be achieved by decreasing the surface temperature of the subject by using a low thermally conductive material, such as polycarbonate, which contains bisphenol A. Polycarbonate is a hard type of plastic that generally ends up in dumps and landfills. Accordingly, there is a large amount of polycarbonate waste that needs to be managed to reduce its drawbacks to the environment. Polycarbonate waste has great potential to be used as a material for recycled fibre by the melt spinning method. In this research, polycarbonate roofing-sheet waste was extruded using a 2 mm diameter of spinnerette and a 14 mm barrel diameter in a 265 °C temperature process by using a lab-scale melt spinning machine at various plunger and take-up speeds. The fibres were then inserted into 1 × 1 rib-stitch knitted fabric made by Nm 15 polyacrylic commercial yarns, which were manufactured by a flat knitting machine. The results showed that applying recycled polycarbonate fibre as a fibre insertion in polyacrylic knitted fabric reduced the emitted infrared and thermal signature of the fabric. Full article
(This article belongs to the Special Issue Recycling and Resource Recovery from Polymers II)
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25 pages, 2551 KiB  
Article
Multilayer Packaging in a Circular Economy
by Jannick Schmidt, Laura Grau, Maximilian Auer, Roman Maletz and Jörg Woidasky
Polymers 2022, 14(9), 1825; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14091825 - 29 Apr 2022
Cited by 24 | Viewed by 8334
Abstract
Sorting multilayer packaging is still a major challenge in the recycling of post-consumer plastic waste. In a 2019 Germany-wide field study with 248 participants, lightweight packaging (LWP) was randomly selected and analyzed by infrared spectrometry to identify multilayer packaging in the LWP stream. [...] Read more.
Sorting multilayer packaging is still a major challenge in the recycling of post-consumer plastic waste. In a 2019 Germany-wide field study with 248 participants, lightweight packaging (LWP) was randomly selected and analyzed by infrared spectrometry to identify multilayer packaging in the LWP stream. Further investigations of the multilayer packaging using infrared spectrometry and microscopy were able to determine specific multilayer characteristics such as typical layer numbers, average layer thicknesses, the polymers of the outer and inner layers, and typical multilayer structures for specific packaged goods. This dataset shows that multilayer packaging is mainly selected according to the task to be fulfilled, with practically no concern for its end-of-life recycling properties. The speed of innovation in recycling processes does not keep up with packaging material innovations. Full article
(This article belongs to the Special Issue Recycling and Resource Recovery from Polymers II)
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14 pages, 2675 KiB  
Article
Pulverization of Waste Polyvinyl Chloride (PVC) Film by Low Temperature Heat Treatment and Properties of Pulverized Product for Blast Furnace Injection as Alternative Fuel
by Guang Wang, Sixian Liu, Hongqiang Zhang, Jingsong Wang and Qingguo Xue
Polymers 2022, 14(9), 1689; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14091689 - 21 Apr 2022
Cited by 3 | Viewed by 2136
Abstract
Recycling of waste plastics is of great significance for human society. The pulverization of waste film plastics is a key technical link in the development of collaborative utilization of waste plastics in the steel industry. In this study, waste polyvinyl chloride film plastics [...] Read more.
Recycling of waste plastics is of great significance for human society. The pulverization of waste film plastics is a key technical link in the development of collaborative utilization of waste plastics in the steel industry. In this study, waste polyvinyl chloride film plastics were first heated at different temperatures; then the de-chlorination ratio pulverization and the properties of the pulverized products closely related to blast furnace injection, such as powdery properties, combustion and explosiveness, were further analyzed. The weight loss ratio increased significantly with an increase in temperature and was not obvious between 370 °C and 400 °C. The highest de-chlorination ratio was approximately 84% at 370 °C, and the relative chlorine content in the product was 9%. The crushing performance of heat-treated polyvinyl chloride film increased with increasing temperature. Before 370 °C, there were more pores in the samples, and the surface of the sample seemed to be damaged with the temperature was further increased. The pulverized polyvinyl chloride had better fluidity and strong jet flow compared to industrial injection coals. At the same time, compared with other carbonaceous materials, it also exhibited better combustion performances. The pulverized polyvinyl chloride belonged to non explosiveness substance despite its high volatile content. The obtained results demonstrated that the pulverized polyvinyl chloride obtained under the present conditions could be used for blast furnace injection to some extent. Full article
(This article belongs to the Special Issue Recycling and Resource Recovery from Polymers II)
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8 pages, 16577 KiB  
Communication
A Magic Filter Filled with Waste Plastic Shavings, Loofah, and Iron Shavings for Wastewater Treatment
by Zengrui Pan, Jianlong Sheng, Chong Qiu, Hongtang Wei, Qianjin Yang, Jinbo Pan and Jun Li
Polymers 2022, 14(7), 1410; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14071410 - 30 Mar 2022
Cited by 6 | Viewed by 1809
Abstract
Integrated sewage treatment equipment has been widely used, but the commonly used fillers for wastewater treatment are not suitable in rural areas due to their price and performance issues. In this study, an integrated magic filter filled with waste fillers was proposed and [...] Read more.
Integrated sewage treatment equipment has been widely used, but the commonly used fillers for wastewater treatment are not suitable in rural areas due to their price and performance issues. In this study, an integrated magic filter filled with waste fillers was proposed and established for wastewater treatment. The filter was composed of functional modules and an equipment room, and the fillers in each module can be taken out separately and changed arbitrarily according to the needs of specific treatment conditions. The fillers used include waste plastic shavings, loofah, and waste iron shavings, generated during the processing of plastic, crop, and steel. At the same time, a 91 d experiment was performed for real wastewater treatment, and a satisfactory removal performance was obtained, with average removal rates of COD, TP, NH4+-N, TN, and SS being 83.3%, 89.6%, 93.8%, 74.7%, and 94.0%, respectively. Through microscope observation, a large number of microorganisms were attached to the surface of the fillers, which was conducive to the simultaneous removal of nitrogen and phosphorus. The micro-electrolysis of waste iron shavings can produce Fe2+ and Fe3+, which would combine with PO43− to form Fe3(PO4)2 and FePO4 precipitates, enhancing the removal of phosphorus. In addition, the filled fillers have an excellent physical filtering effect, which can reduce the effluent SS. The magic filter achieves both the recycling of wastes and the treatment of wastewater. Full article
(This article belongs to the Special Issue Recycling and Resource Recovery from Polymers II)
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14 pages, 5303 KiB  
Article
Towards Circular Economy by the Valorization of Different Waste Subproducts through Their Incorporation in Composite Materials: Ground Tire Rubber and Chicken Feathers
by Xavier Colom, Javier Cañavate and Fernando Carrillo-Navarrete
Polymers 2022, 14(6), 1090; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14061090 - 09 Mar 2022
Cited by 4 | Viewed by 1794
Abstract
Incorporation of residua into polymeric composites can be a successful approach to creating materials suitable for specific applications promoting a circular economy approach. Elastomeric (Ground Tire Rubber or GTR) and biogenic (chicken feathers or CFs) wastes were used to prepare polymeric composites in [...] Read more.
Incorporation of residua into polymeric composites can be a successful approach to creating materials suitable for specific applications promoting a circular economy approach. Elastomeric (Ground Tire Rubber or GTR) and biogenic (chicken feathers or CFs) wastes were used to prepare polymeric composites in order to evaluate the tensile, acoustic and structural differences between both reinforcements. High-density polyethylene (HDPE), polypropylene (PP) and ethylene vinyl acetate (EVA) polymeric matrices were used. EVA matrix defines better compatibility with both reinforcement materials (GTR and CFs) than polyolefin matrices (HDPE and PP) as it has been corroborated by Fourier transform infrared spectroscopy (FTIR), termogravimetric analysis (TGA) and scanning electron microscopy (SEM). In addition, composites reinforced with GTR showed better acoustic properties than composites reinforced with CFs, due to the morphology of the reinforcing particles. Full article
(This article belongs to the Special Issue Recycling and Resource Recovery from Polymers II)
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12 pages, 2189 KiB  
Article
Sustainable Cellulose-Aluminum-Plastic Composites from Beverage Cartons Scraps and Recycled Polyethylene
by Irene Bonadies, Roberta Capuano, Roberto Avolio, Rachele Castaldo, Mariacristina Cocca, Gennaro Gentile and Maria Emanuela Errico
Polymers 2022, 14(4), 807; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14040807 - 19 Feb 2022
Cited by 4 | Viewed by 2690
Abstract
The sustainable management of multilayer paper/plastic waste is a technological challenge due to its composite nature. In this paper, a mechanical recycling approach for multilayer cartons (MC) is reported, illustrating the realization of thermoplastic composites based on recycled polyethylene and an amount of [...] Read more.
The sustainable management of multilayer paper/plastic waste is a technological challenge due to its composite nature. In this paper, a mechanical recycling approach for multilayer cartons (MC) is reported, illustrating the realization of thermoplastic composites based on recycled polyethylene and an amount of milled MC ranging from 20 to 90 wt%. The effect of composition of the composites on the morphology and on thermal, mechanical, and water absorption behavior was investigated and rationalized, demonstrating that above 80 wt% of MC, the fibrous nature of the filler dominates the overall properties of the materials. A maleated polyethylene was also used as a coupling agent and its effectiveness in improving mechanical parameters of composites up to 60 wt% of MC was highlighted. Full article
(This article belongs to the Special Issue Recycling and Resource Recovery from Polymers II)
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18 pages, 3367 KiB  
Article
Oil Production by Pyrolysis of Real Plastic Waste
by Laura Fulgencio-Medrano, Sara García-Fernández, Asier Asueta, Alexander Lopez-Urionabarrenechea, Borja B. Perez-Martinez and José María Arandes
Polymers 2022, 14(3), 553; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14030553 - 29 Jan 2022
Cited by 14 | Viewed by 9212
Abstract
The aim of this paper is for the production of oils processed in refineries to come from the pyrolysis of real waste from the high plastic content rejected by the recycling industry of the Basque Country (Spain). Concretely, the rejected waste streams were [...] Read more.
The aim of this paper is for the production of oils processed in refineries to come from the pyrolysis of real waste from the high plastic content rejected by the recycling industry of the Basque Country (Spain). Concretely, the rejected waste streams were collected from (1) a light packaging waste sorting plant, (2) the paper recycling industry, and (3) a waste treatment plant of electrical and electronic equipment (WEEE). The influence of pre-treatments (mechanical separation operations) and temperature on the yield and quality of the liquid fraction were evaluated. In order to study the pre-treatment effect, the samples were pyrolyzed at 460 °C for 1 h. As pre-treatments concentrate on the suitable fraction for pyrolysis and reduce the undesirable materials (metals, PVC, PET, inorganics, cellulosic materials), they improve the yield to liquid products and considerably reduce the halogen content. The sample with the highest polyolefin content achieved the highest liquid yield (70.6 wt.% at 460 °C) and the lowest chlorine content (160 ppm) among the investigated samples and, therefore, was the most suitable liquid to use as refinery feedstock. The effect of temperature on the pyrolysis of this sample was studied in the range of 430–490 °C. As the temperature increased the liquid yield increased and solid yield decreased, indicating that the conversion was maximized. At 490 °C, the pyrolysis oil with the highest calorific value (44.3 MJ kg−1) and paraffinic content (65% area), the lowest chlorine content (128 ppm) and more than 50 wt.% of diesel was obtained. Full article
(This article belongs to the Special Issue Recycling and Resource Recovery from Polymers II)
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14 pages, 4472 KiB  
Article
Development of Oil and Gas Stimulation Fluids Based on Polymers and Recycled Produced Water
by Mustafa AlKhowaildi, Bassam Tawabini, Muhammad Shahzad Kamal, Mohamed Mahmoud, Murtada Saleh Aljawad and Mohammed Bataweel
Polymers 2021, 13(22), 4017; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13224017 - 20 Nov 2021
Cited by 4 | Viewed by 2070
Abstract
Freshwater scarcity is a highly pressing and accelerating issue facing our planet. Therefore, there is a great incentive to develop sustainable solutions by reusing wastewater or produced water (PW), especially in places where it is generated abundantly. PW represents the water produced as [...] Read more.
Freshwater scarcity is a highly pressing and accelerating issue facing our planet. Therefore, there is a great incentive to develop sustainable solutions by reusing wastewater or produced water (PW), especially in places where it is generated abundantly. PW represents the water produced as a by-product during oil and gas extraction operations in the petroleum industry. It is the largest wastewater stream within the industry, with hundreds of millions of produced water barrels per day worldwide. This research investigates a reuse opportunity for PW to replace freshwater utilization in well stimulation applications. Introducing an environmentally friendly chelating agent (GLDA) allowed formulating a PW-based fluid system that has similar rheological properties in fresh water. This work aims at evaluating the rheological properties of the developed stimulation fluid. The thickening profile of the fluid was controlled by chelation chemistry and varying different design parameters. The experiments were carried out using a high-pressure, high-temperature (HPHT) viscometer. Variables such as polymer concentration and pH have a great impact on the viscosity, while temperature and concentration of the chelating agents are shown to control the thickening profile, as well as its stability and breakage behaviors. Furthermore, 50 pptg of carboxymethyl hydroxypropyl guar (CMHPG) polymer in 20 wt.% chelating solution was shown to sustain 172 cP viscosity for nearly 2.5 h at 150 °F and 100 S−1 shear rate. The newly developed fluid system, solely based on polymer, chelating agent, and PW, showed great rheological capabilities to replace the conventional stimulation fluids based on fresh water. The newly developed fluid can also have economic value realization due to fewer additives, compared with conventional fluids. Full article
(This article belongs to the Special Issue Recycling and Resource Recovery from Polymers II)
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11 pages, 10492 KiB  
Article
Functionalization of Graphene Oxide with Polysilicone: Synthesis, Characterization, and Its Flame Retardancy in Epoxy Resin
by Jiangbo Wang
Polymers 2021, 13(21), 3857; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13213857 - 08 Nov 2021
Cited by 3 | Viewed by 1839
Abstract
A novel polysilicone flame retardant (PMDA) has been synthesized and covalently grafted onto the surfaces of graphene oxide (GO) to obtain GO-PMDA. The chemical structure and morphology of GO-PMDA was characterized and confirmed by the Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectrometer [...] Read more.
A novel polysilicone flame retardant (PMDA) has been synthesized and covalently grafted onto the surfaces of graphene oxide (GO) to obtain GO-PMDA. The chemical structure and morphology of GO-PMDA was characterized and confirmed by the Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectrometer (XPS), atomic force microscope (AFM), and thermogravimetric analysis (TGA). The results of dynamic mechanical analysis (DMA) indicated that the grafting of PMDA improved the dispersion and solubility of GO sheets in the epoxy resin (EP) matrix. The TGA and cone calorimeter measurements showed that compared with the GO, GO-PMDA could significantly improve the thermal stability and flame retardancy of EP. In comparison to pure EP, the peak heat release rate (pHRR) and total heat release (THR) of EP/GO-PMDA were reduced by 30.5% and 10.0% respectively. This greatly enhanced the flame retardancy of EP which was mainly attributed to the synergistic effect of GO-PMDA. Polysilicone can create a stable silica layer on the char surface of EP, which reinforces the barrier effect of graphene. Full article
(This article belongs to the Special Issue Recycling and Resource Recovery from Polymers II)
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Review

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29 pages, 3340 KiB  
Review
Current Prospects for Plastic Waste Treatment
by Damayanti Damayanti, Desi Riana Saputri, David Septian Sumanto Marpaung, Fauzi Yusupandi, Andri Sanjaya, Yusril Mahendra Simbolon, Wulan Asmarani, Maria Ulfa and Ho-Shing Wu
Polymers 2022, 14(15), 3133; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14153133 - 31 Jul 2022
Cited by 37 | Viewed by 11095
Abstract
The excessive amount of global plastic produced over the past century, together with poor waste management, has raised concerns about environmental sustainability. Plastic recycling has become a practical approach for diminishing plastic waste and maintaining sustainability among plastic waste management methods. Chemical and [...] Read more.
The excessive amount of global plastic produced over the past century, together with poor waste management, has raised concerns about environmental sustainability. Plastic recycling has become a practical approach for diminishing plastic waste and maintaining sustainability among plastic waste management methods. Chemical and mechanical recycling are the typical approaches to recycling plastic waste, with a simple process, low cost, environmentally friendly process, and potential profitability. Several plastic materials, such as polypropylene, polystyrene, polyvinyl chloride, high-density polyethylene, low-density polyethylene, and polyurethanes, can be recycled with chemical and mechanical recycling approaches. Nevertheless, due to plastic waste’s varying physical and chemical properties, plastic waste separation becomes a challenge. Hence, a reliable and effective plastic waste separation technology is critical for increasing plastic waste’s value and recycling rate. Integrating recycling and plastic waste separation technologies would be an efficient method for reducing the accumulation of environmental contaminants produced by plastic waste, especially in industrial uses. This review addresses recent advances in plastic waste recycling technology, mainly with chemical recycling. The article also discusses the current recycling technology for various plastic materials. Full article
(This article belongs to the Special Issue Recycling and Resource Recovery from Polymers II)
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13 pages, 449 KiB  
Review
Thermocatalytic Conversion of Plastics into Liquid Fuels over Clays
by Evgeniy S. Seliverstov, Lyubov V. Furda and Olga E. Lebedeva
Polymers 2022, 14(10), 2115; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14102115 - 23 May 2022
Cited by 5 | Viewed by 2789
Abstract
Recycling polymer waste is a great challenge in the context of the growing use of plastics. Given the non-renewability of fossil fuels, the task of processing plastic waste into liquid fuels seems to be a promising one. Thermocatalytic conversion is one of the [...] Read more.
Recycling polymer waste is a great challenge in the context of the growing use of plastics. Given the non-renewability of fossil fuels, the task of processing plastic waste into liquid fuels seems to be a promising one. Thermocatalytic conversion is one of the methods that allows obtaining liquid products of the required hydrocarbon range. Clays and clay minerals can be distinguished among possible environmentally friendly, cheap, and common catalysts. The moderate acidity and the presence of both Lewis and Brønsted acid sites on the surface of clays favor heavier hydrocarbons in liquid products of reactions occurring in their pores. Liquids produced with the use of clays are often reported as being in the gasoline and diesel range. In this review, the comprehensive information on the thermocatalytic conversion of plastics over clays obtained during the last two decades was summarized. The main experimental parameters for catalytic conversion of plastics according to the articles’ analysis, were the reaction temperature, the acidity of modified catalysts, and the catalyst-to-plastic ratio. The best clay catalysts observed were the following: bentonite/spent fluid cracking catalyst for high-density polyethylene (HDPE); acid-restructured montmorillonite for medium-density polyethylene (MDPE); neat kaolin powder for low-density polyethylene (LDPE); Ni/acid-washed bentonite clay for polypropylene (PP); neat kaolin for polystyrene (PS); Fe-restructured natural clay for a mixture of polyethylene, PP, PS, polyvinyl chloride (PVC), and polyethylene terephthalate (PET). The main problem in using natural clays and clay minerals as catalysts is their heterogeneous composition, which can vary even within the same deposit. The serpentine group is of interest in studying its catalytic properties as fairly common clay minerals. Full article
(This article belongs to the Special Issue Recycling and Resource Recovery from Polymers II)
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22 pages, 5948 KiB  
Review
Review of Soil Quality Improvement Using Biopolymers from Leather Waste
by Daniela Simina Stefan, Magdalena Bosomoiu, Annette Madelene Dancila and Mircea Stefan
Polymers 2022, 14(9), 1928; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14091928 - 09 May 2022
Cited by 5 | Viewed by 2621
Abstract
This paper reviews the advantages and disadvantages of the use of fertilizers obtained from leather waste, to ameliorate the agricultural soil quality. The use of leather waste (hides and skins) as raw materials to obtain biopolymer-based fertilizers is an excellent example of a [...] Read more.
This paper reviews the advantages and disadvantages of the use of fertilizers obtained from leather waste, to ameliorate the agricultural soil quality. The use of leather waste (hides and skins) as raw materials to obtain biopolymer-based fertilizers is an excellent example of a circular economy. This allows the recovery of a large quantity of the tanning agent in the case of tanned wastes, as well as the valorization of significant quantities of waste that would be otherwise disposed of by landfilling. The composition of organic biopolymers obtained from leather waste is a rich source of macronutrients (nitrogen, calcium, magnesium, sodium, potassium), and micronutrients (boron, chloride, copper, iron, manganese, molybdenum, nickel and zinc), necessary to improve the composition of agricultural soils, and to remediate the degraded soils. This enhances plant growth ensuring better crops. The nutrient release tests have demonstrated that, by using the biofertilizers with collagen or with collagen cross-linked with synthetic polymers, the nutrient release can be controlled and slowed. In this case, the loss of nutrients by leaching into the inferior layers of the soil and ground water is minimized, avoiding groundwater contamination, especially with nitrate. Full article
(This article belongs to the Special Issue Recycling and Resource Recovery from Polymers II)
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25 pages, 1857 KiB  
Review
Valorization of Spent Coffee Grounds as Precursors for Biopolymers and Composite Production
by Anne Shayene Campos de Bomfim, Daniel Magalhães de Oliveira, Herman Jacobus Cornelis Voorwald, Kelly Cristina Coelho de Carvalho Benini, Marie-Josée Dumont and Denis Rodrigue
Polymers 2022, 14(3), 437; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14030437 - 22 Jan 2022
Cited by 25 | Viewed by 9182
Abstract
Spent coffee grounds (SCG) are a current subject in many works since coffee is the second most consumed beverage worldwide; however, coffee generates a high amount of waste (SCG) and can cause environmental problems if not discarded properly. Therefore, several studies on SCG [...] Read more.
Spent coffee grounds (SCG) are a current subject in many works since coffee is the second most consumed beverage worldwide; however, coffee generates a high amount of waste (SCG) and can cause environmental problems if not discarded properly. Therefore, several studies on SCG valorization have been published, highlighting its waste as a valuable resource for different applications, such as biofuel, energy, biopolymer precursors, and composite production. This review provides an overview of the works using SCG as biopolymer precursors and for polymer composite production. SCG are rich in carbohydrates, lipids, proteins, and minerals. In particular, carbohydrates (polysaccharides) can be extracted and fermented to synthesize lactic acid, succinic acid, or polyhydroxyalkanoate (PHA). On the other hand, it is possible to extract the coffee oil and to synthesize PHA from lipids. Moreover, SCG have been successfully used as a filler for composite production using different polymer matrices. The results show the reasonable mechanical, thermal, and rheological properties of SCG to support their applications, from food packaging to the automotive industry. Full article
(This article belongs to the Special Issue Recycling and Resource Recovery from Polymers II)
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21 pages, 4908 KiB  
Review
Composite Polymers from Leather Waste to Produce Smart Fertilizers
by Daniela Simina Stefan, Magdalena Bosomoiu, Rodica Roxana Constantinescu and Madalina Ignat
Polymers 2021, 13(24), 4351; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13244351 - 12 Dec 2021
Cited by 10 | Viewed by 4640
Abstract
The leather industry is facing important environmental issues related to waste disposal. The waste generated during the tanning process is an important resource of protein (mainly collagen) which can be extracted and reused in different applications (e.g., medical, agricultural, leather industry). On the [...] Read more.
The leather industry is facing important environmental issues related to waste disposal. The waste generated during the tanning process is an important resource of protein (mainly collagen) which can be extracted and reused in different applications (e.g., medical, agricultural, leather industry). On the other side, the utilization of chemical fertilizers must be decreased because of the negative effects associated to an extensive use of conventional chemical fertilizers. This review presents current research trends, challenges and future perspectives with respect to the use of hide waste to produce composite polymers that are further transformed in smart fertilizers. Hide waste contains mostly protein (collagen that is a natural polymer), that is extracted to be used in the cross-linking with water soluble copolymers to obtain the hydrogels which are further valorised as smart fertilizers. Smart fertilizers are a new class of fertilizers which allow the controlled release of the nutrients in synchronization with the plant’s demands. Characteristics of hide and leather wastes are pointed out. The fabrication methods of smart fertilizers and the mechanisms for the nutrients release are extensively discussed. This novel method is in agreement with the circular economy concepts and solves, on one side, the problem of hide waste disposal, and on the other side produces smart fertilizers that can successfully replace conventional chemical fertilizers. Full article
(This article belongs to the Special Issue Recycling and Resource Recovery from Polymers II)
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1 pages, 161 KiB  
Correction
Correction: Devasahayam, S. Decarbonising the Portland and Other Cements—Via Simultaneous Feedstock Recycling and Carbon Conversions Sans External Catalysts. Polymers 2021, 13, 2462
by Sheila Devasahayam
Polymers 2022, 14(2), 281; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14020281 - 11 Jan 2022
Cited by 2 | Viewed by 707
Abstract
The author wishes to make the following correction to the above paper [...] Full article
(This article belongs to the Special Issue Recycling and Resource Recovery from Polymers II)
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