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New Frontiers in Recycling and Reuse of Plastic Wastes

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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Environmental Sciences".

Deadline for manuscript submissions: closed (10 August 2022) | Viewed by 22153

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Special Issue Editors

Prof. Dr. Francesco Ciardelli

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Guest Editor

SPIN‐PET srl and University of Pisa, Pisa, Italy
Interests: polyolefins; catalytic polymerization; structure-controlled polymers; composites and nanocomposites; reactive extrusion; polymer recovery; natural and synthetic plastic polymers; optoelectronic polymers

Prof. Dr. Francesco Picchioni

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Guest Editor

Department of Chemical Engineering, University of Groningen, Groningen, The Netherlands
Interests: recycling; thermally reversible networks; product engineering; polymers processing; structure–property relationship
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Special Issue Information

Dear Colleagues,

We would like to warmly invite you to submit a manuscript for this Special Issue of the journal Applied Sciences on the recycling and reuse of plastic waste.

Recycling can be considered as the opposite approach versus biodegradation for the disposal of plastic waste. Indeed, recycling requests a long-lasting duration of the starting properties, whereas biodegradation implies a short material life, as similar as possible to the use duration of the plastics item. However, it is necessary to consider how bioplastics, when fully rolled out, ultimately affect the recycling of conventional plastics. The plastic recycling process begins with sorting the various items by their resin content. There are seven different plastic recycling symbols marked on the bottoms of plastic containers. The recycling mill sorts the used plastics by these symbols and may perform an additional sorting based on the color of the plastic. Once sorted, the plastics are chopped up into small pieces and chunks. These pieces are then cleaned to further remove debris like paper labels, residue from what was inside the plastic, dirt, dust, and other small contaminants. The cleaned plastic pieces are melted down and compressed into tiny pellets called nurdles. Once in this state, the recycled plastic pellets are now ready to reuse and fashion into new and completely different products, as recycled plastic is hardly ever used to create the same or an identical plastic item of its former self.

In this Special Issue, we aim at providing our readers with an exhaustive overview of recent developments on the general topic of polymer product recycling. Novel technologies and scientific results focused on the recycling of different polymeric materials constitute a pivotal cornerstone toward a truly circular economy. Attention paid to the most popular commodity polymeric materials (e.g., polyolefins, PVC, polyesters, rubbers, PS) as well as novel approaches for specialties constitute the man focus of the present issue. Additionally, the development of novel fundamental concepts involving the re-definition of basic processing steps (i.e., design for recycling) is of high interest. In addition to new technological and scientific progresses in the field, review papers on related subjects as well as opinions are certainly welcome. Moreover, in order to dovetail the intrinsic multidisciplinary character of the subject, we would be particularly pleased to receive contributions at the interface between science and technology and the surrounding policy and societal aspects. This might include recent developments in LCA studies as well as other assessment methods for the embedding of new technologies into the correct societal and industrial context.

Prof. Dr. Francesco Ciardelli
Prof. Dr. Francesco Picchioni
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. Applied Sciences 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 2400 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

Plastics recycling
Bioplastics recycling
Selection of postconsumer polymers
Postindustrial polymer recovery
Circular economy
Polyolefins
Polyesters
PVC
Rubbers
Specialty and commodity products
Design for recycling
Waste as raw material
LCAs and other assessment methods
Combination of waste streams (composites and blends)

Published Papers (7 papers)

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Research

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14 pages, 2503 KiB

Open AccessArticle

The Effect of Molecular Weight on the (Re)-Processability and Material Properties of Bio-Based, Thermoreversibly Cross-Linked Polyesters

by Martijn Beljaars, Arjen J. Kamphuis, Hero J. Heeres, Antonius A. Broekhuis and Francesco Picchioni

Appl. Sci. 2022, 12(14), 7287; https://0-doi-org.brum.beds.ac.uk/10.3390/app12147287 - 20 Jul 2022

Cited by 1 | Viewed by 1272

Abstract

A (partially) bio-based short-chain polyester is prepared through interfacial polycondensation of furan-functionalized diphenolic acid with terephthalic chloride. The furan groups along the backbone of the obtained polyester are able to form a covalent network (PE-fur/Bism) with various ratios of 1,1′-(methylenedi-4,1-phenylene)bismaleimide via the thermoreversible Diels–Alder (DA) reaction. Several techniques have been employed to characterize the polyester network, including ¹H-NMR, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA). The polyester base polymer displays a glass transition temperature of 115 °C, whereas the temperatures at which the retro-Diels–Alder (rDA) reaction takes place lie above 130 °C for the various polyester/bismaleimide networks. Excellent thermoreversibility and recyclability of the polyester resin have been shown through DSC and DMTA measurements. Full article

(This article belongs to the Special Issue New Frontiers in Recycling and Reuse of Plastic Wastes)

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18 pages, 5068 KiB

Open AccessArticle

Reactive Extrusion Grafting of Glycidyl Methacrylate onto Low-Density and Recycled Polyethylene Using Supercritical Carbon Dioxide

by Frederique A. Versteeg, Benedicta B. Benita, Jesse A. Jongstra and Francesco Picchioni

Appl. Sci. 2022, 12(6), 3022; https://0-doi-org.brum.beds.ac.uk/10.3390/app12063022 - 16 Mar 2022

Viewed by 2037

Abstract

Glycidyl methacrylate (GMA) was grafted onto (recycled) polyethylene (PE) to design a new adhesive with better mechanical properties compared to non-grafted PE. The effects of the amount of GMA, the amount of dicumyl peroxide (DCP) and the use of supercritical carbon dioxide (scCO₂) in a reactive extrusion (REX) were evaluated based on the grafting degree and efficiency of the grafted samples. Generally speaking, higher amounts of GMA led to higher functionalization degrees (FD), whereas higher amounts of DCP resulted in a lower FD due to the occurrence of more unfavorable side reactions. The influence of scCO₂ showed different outcomes for the two substrates used. Higher FDs were obtained for the low-density polyethylene (LDPE) samples while, by contrast, lower FDs were obtained for the recycled polyethylene (RPE) samples when using scCO₂. Additionally, adjusting the screw speed and the temperature profile of the extruder to the half-life time of the radical initiator appeared to have the highest positive impact on the FD. According to the tensile tests, all the grafted samples can withstand higher stress levels, especially the grafted RPE, compared to the non-grafted samples. Full article

(This article belongs to the Special Issue New Frontiers in Recycling and Reuse of Plastic Wastes)

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15 pages, 4677 KiB

Open AccessArticle

Bio-Based Aromatic Polyesters Reversibly Crosslinked via the Diels–Alder Reaction

by Martijn Beljaars, Hero J. Heeres, Antonius A. Broekhuis and Francesco Picchioni

Appl. Sci. 2022, 12(5), 2461; https://0-doi-org.brum.beds.ac.uk/10.3390/app12052461 - 26 Feb 2022

Cited by 7 | Viewed by 1755

Abstract

Diphenolic acid is functionalized with furfuryl amine and subsequently incorporated in a (partly) bio-based polyester through interfacial polycondensation with terepthalic chloride. The furan groups present in the resulting polyester are able to form a thermoreversible covalent network with different bismaleimide moieties via the Diels–Alder (DA) reaction. Our analysis of the polymer network by ¹H-NMR clearly shows the formation of both possible stereoisomers (endo and exo) from the Diels–Alder coordination of furan and maleimide. Furthermore, it was found that these isomers can be reversibly interchanged at temperatures below the reported retro Diels–Alder reaction temperature, a phenomenon often claimed but, until present, never directly observed, for thermally reversible polymeric systems. Finally, a proof of principle for reversibility and recyclability is shown. Full article

(This article belongs to the Special Issue New Frontiers in Recycling and Reuse of Plastic Wastes)

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20 pages, 3261 KiB

Open AccessArticle

Integrated User-Oriented Service for 3D Printing Environments with Recycled Material from Maritime Plastic Waste

by Julio Garrido, Diego Silva, Bruno Portela and Blanca Lekube

Appl. Sci. 2021, 11(9), 3787; https://0-doi-org.brum.beds.ac.uk/10.3390/app11093787 - 22 Apr 2021

Cited by 1 | Viewed by 3871

Abstract

Plastic waste is a major concern for marine environment care, and many researchers and projects face the problem from different points of view. The European CircularSeas project aims to encourage the development of greener maritime industries through the combination of principles of Circular Economy, plastic recycling and 3D printing. However, while 3D printing has shown its benefits for conventional industry environments, the first issue discussed in this paper is whether 3D printing technology can also bring benefits to the maritime-port sector, where parts manufacturing, new prototyping trends and even product customization have not traditionally been major business issues. A secondary issue is how 3D printing and this specific user scenario could accommodate recycled plastic in a Circular Economy strategy in a feasible way. In an attempt to address both of these issues, the paper reviews some particularities of 3D printing open technologies and proposes a new integrated and user-oriented 3D printing framework, independent of hardware and adaptable to non-standard recycled plastic raw material from marine waste. Full article

(This article belongs to the Special Issue New Frontiers in Recycling and Reuse of Plastic Wastes)

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25 pages, 7463 KiB

Open AccessArticle

Design of an Atypical Construction of Equipment for Additive Manufacturing with a Conceptual Solution of a Printhead Intended for the Use of Recycled Plastic Materials

by Jakub Kaščak, Štefan Gašpár, Ján Paško, Lucia Knapčíková, Jozef Husár, Petr Baron and Jozef Török

Appl. Sci. 2021, 11(7), 2928; https://0-doi-org.brum.beds.ac.uk/10.3390/app11072928 - 25 Mar 2021

Cited by 17 | Viewed by 2704

Abstract

This article presents the variability of Fused deposition modelling (FDM) technology and the possibilities of its use in the design and implementation of a prototype atypical device. The assumptions of the behaviour of individual components and subsystems of the design result from an extensive application of the finite element method and motion analysis of subsystems and various parts of the structure. The use of this method to such an extent accelerated the design process and its implementation. The proposal itself reflects the current state of this technology and its focus is on improving sustainable development. As is generally known, great efforts are currently being made to reduce plastic waste volume and its environmental burden. The proposed concept is modified to replace the final treatment of the top layers of the models, called “ironing” by non-planar layering of material. At the same time, it points out the advantages of this method in reducing energy requirements and the time required to produce models. The conclusion is a conceptual design of a printhead for a proposed prototype, designed to use recycled FDM, intending to streamline the possibility of recycling with little serial and piece production. This process thus closes the circle of opportunities published by us, which in the future can contribute to the optimisation of this technology towards increasing the efficiency of resource use, reduction of energy demands and environmental burden. Full article

(This article belongs to the Special Issue New Frontiers in Recycling and Reuse of Plastic Wastes)

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9 pages, 2279 KiB

Open AccessCommunication

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

by Patchiya Phanthong, Yusuke Miyoshi and Shigeru Yao

Appl. Sci. 2021, 11(4), 1707; https://0-doi-org.brum.beds.ac.uk/10.3390/app11041707 - 14 Feb 2021

Cited by 2 | Viewed by 2314

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. Full article

(This article belongs to the Special Issue New Frontiers in Recycling and Reuse of Plastic Wastes)

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Review

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17 pages, 2265 KiB

Open AccessReview

LCA Practices of Plastics and Their Recycling: A Critical Review

by Timothy M. Kousemaker, Gerald H. Jonker and Antonis I. Vakis

Appl. Sci. 2021, 11(8), 3305; https://0-doi-org.brum.beds.ac.uk/10.3390/app11083305 - 07 Apr 2021

Cited by 19 | Viewed by 7216

Abstract

In a bid to help address the environmental footprints associated with products and services, life cycle assessment (LCA) applications have become increasingly popular throughout the years. This review summarizes some important methodological developments in recent years, such as the advent of dynamic LCA, as well as highlighting recent LCA applications in the context of plastics/recycling with a focus on their methodological choices. Furthermore, this review aims to offer a set of possible research lines to improve the gap between LCA and decision-making (policy). It was found that the majority of reviewed papers are mostly conservative in their methodological practice, employing mostly static analyses and making little use of other methods. In order to bridge the gap between LCA and policy, it is suggested to broaden system boundaries through the integration of dynamic modelling methods, incorporating interactions between fore- and background systems, and including behavioral components where relevant. In addition, advanced sampling routines to further explore and assess the policy space are recommended. This is of paramount importance when dealing with recycling processes as the molecules/polymers constituting the output of those processes have to be benchmarked in terms of costs and, crucially, their sustainability character against virgin ones. Full article

(This article belongs to the Special Issue New Frontiers in Recycling and Reuse of Plastic Wastes)

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