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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 (15 December 2022) | Viewed by 23626

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Dr. Jesús-María García-Martínez

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Polymer Engineering Group (GIP), Polymer Science and Technology Institute (ICTP), Spanish Council for Scientific Research (CSIC), 28006 Madrid, Spain
Interests: polymers and environment; heterogeneous materials based on polymers; polyolefins; interfacial agents; interphase; interface; functionalization; plastic wastes; blends; composites
Special Issues, Collections and Topics in MDPI journals

Dr. Emilia P. Collar

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Dear Colleagues,

In the early 1980s, the first global environmental crisis took place with an emphasis on the role played by the presence of plastics in the huge solid waste streams of big cities. It was clear then (and now) that the best environmental management practices required solid scientific and technical knowledge (most times under technical standards). Thus, these plastics, once at the end of their useful life, now have their materials (polymers and additives) coalesced into a circular economy strategy conjugated with the non-steady scenarios of the other key sectors of the economy, industry, society, and policy. Thus, a twofold perspective, applied and academic, to link tandem polymers and the environment has led, forty years later, to a wide polymer research field devoted to the continuous improvement of the environmental performance of polymer and polymer-based materials. This strategy comprises all the steps in the polymer management chain, from the raw materials to the polymers themselves, many of which come from classical and/or renewable sources (so-called bioplastics). There is this a need to improve the processability, ultimate properties, and performance through friendly environment additives; the recyclability of the materials; and innovative processes that will allow for better mechanical and/or energy recovery, including chemical recycling. Therefore, this Special Issue welcomes all works related to this frontrunner polymer R&D area.

Dr. Jesús-María García-Martínez
Dr. Emilia P. Collar
Guest Editors

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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

plastics and circular economy
bioplastics
biocomposites
ecofriendly blends
additives and plastics performance
ecofriendly additives
plastic wastes and recycling
plastic wastes valorization routes
Life Cycle Assessment (LCA)
standardization and legal frameworks

Published Papers (11 papers)

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Editorial

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4 pages, 205 KiB

Open AccessEditorial

Polymers and the Environment: Some Current Feature Trends

by Jesús-María García-Martínez and Emilia P. Collar

Polymers 2023, 15(9), 2093; https://doi.org/10.3390/polym15092093 - 27 Apr 2023

Cited by 3 | Viewed by 2971

Abstract

In the early 1980s, the first global environmental crisis occurred with an emphasis on the role of plastics in big cities’ massive solid waste streams [...] Full article

(This article belongs to the Special Issue Polymers and the Environment)

Research

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22 pages, 4148 KiB

Open AccessArticle

Evaluation of the Physical and Shape Memory Properties of Fully Biodegradable Poly(lactic acid) (PLA)/Poly(butylene adipate terephthalate) (PBAT) Blends

by Marica Bianchi, Andrea Dorigato, Marco Morreale and Alessandro Pegoretti

Polymers 2023, 15(4), 881; https://doi.org/10.3390/polym15040881 - 10 Feb 2023

Cited by 7 | Viewed by 2363

Abstract

Biodegradable polymers have recently become popular; in particular, blends of poly(lactic acid) (PLA) and poly(butylene adipate terephthalate) (PBAT) have recently attracted significant attention due to their potential application in the packaging field. However, there is little information about the thermomechanical properties of these blends and especially the effect induced by the addition of PBAT on the shape memory properties of PLA. This work, therefore, aims at producing and investigating the microstructural, thermomechanical and shape memory properties of PLA/PBAT blends prepared by melt compounding. More specifically, PLA and PBAT were melt-blended in a wide range of relative concentrations (from 85/15 to 25/75 wt%). A microstructural investigation was carried out, evidencing the immiscibility and the low interfacial adhesion between the PLA and PBAT phases. The immiscibility was also confirmed by differential scanning calorimetry (DSC). A thermogravimetric analysis (TGA) revealed that the addition of PBAT slightly improved the thermal stability of PLA. The stiffness and strength of the blends decreased with the PBAT amount, while the elongation at break remained comparable to that of neat PLA up to a PBAT content of 45 wt%, while a significant increment in ductility was observed only for higher PBAT concentrations. The shape memory performance of PLA was impaired by the addition of PBAT, probably due to the low interfacial adhesion observed in the blends. These results constitute a basis for future research on these innovative biodegradable polymer blends, and their physical properties might be further enhanced by adding suitable compatibilizers. Full article

(This article belongs to the Special Issue Polymers and the Environment)

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11 pages, 1227 KiB

Open AccessArticle

Effect of Innovative Bio-Based Plastics on Early Growth of Higher Plants

by Ewa Liwarska-Bizukojc

Polymers 2023, 15(2), 438; https://doi.org/10.3390/polym15020438 - 13 Jan 2023

Cited by 3 | Viewed by 1219

Abstract

Plastic particles are widespread in the environment including the terrestrial ecosystems. They may change the physicochemical properties of soil and subsequently affect plant growth. In recent decades, traditional, petroleum-derived plastics have been increasingly replaced by more environmentally friendly bio-based plastics. Due to the growing role of bio-based plastics it is necessary to thoroughly study their impact on the biotic part of ecosystems. This work aimed for the assessment of the effect of five innovative bio-based plastics of different chemical composition and application on the early growth of higher plants (sorghum, cress and mustard). Each bio-based plastic was tested individually. It was found that the early stages of growth of monocotyledonous plants were usually not affected by any of plastic materials studied. At the same time, the presence of some kinds of bio-based plastics contributed to the inhibition of root growth and stimulation of shoot growth of dicotyledonous plants. Two PLA-based plastics inhibited root growth of dicotyledonous plants more strongly than other plastic materials; however, the reduction of root length did not exceed 22% compared to the control runs. PBS-based plastic contributed to the stimulation of shoot growth of higher plants (sorghum, cress and mustard) at the concentrations from 0.02 to 0.095% w/w. In the case of cress shoots exposed to this plastic the hormetic effect was observed. Lepidium sativum turned out to be the most sensitive plant to the presence of bio-based plastic particles in the soil. Thus, it should be included in the assessment of the effect of bio-based plastics on plant growth. Full article

(This article belongs to the Special Issue Polymers and the Environment)

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19 pages, 3070 KiB

Open AccessArticle

Plasticized Mechanical Recycled PLA Films Reinforced with Microbial Cellulose Particles Obtained from Kombucha Fermented in Yerba Mate Waste

by Ángel Agüero, Esther Corral Perianes, Sara Soledad Abarca de las Muelas, Diego Lascano, María del Mar de la Fuente García-Soto, Mercedes Ana Peltzer, Rafael Balart and Marina Patricia Arrieta

Polymers 2023, 15(2), 285; https://doi.org/10.3390/polym15020285 - 05 Jan 2023

Cited by 7 | Viewed by 2245

Abstract

In this study, yerba mate waste (YMW) was used to produce a kombucha beverage, and the obtained microbial cellulose produced as a byproduct (KMW) was used to reinforce a mechanically recycled poly(lactic acid) (r-PLA) matrix. Microbial cellulosic particles were also produced in pristine yerba mate for comparison (KMN). To simulate the revalorization of the industrial PLA products rejected during the production line, PLA was subjected to three extrusion cycles, and the resultant pellets (r3-PLA) were then plasticized with 15 wt.% of acetyl tributyl citrate ester (ATBC) to obtain optically transparent and flexible films by the solvent casting method. The plasticized r3-PLA-ATBC matrix was then loaded with KMW and KMN in 1 and 3 wt.%. The use of plasticizer allowed a good dispersion of microbial cellulose particles into the r3-PLA matrix, allowing us to obtain flexible and transparent films which showed good structural and mechanical performance. Additionally, the obtained films showed antioxidant properties, as was proven by release analyses conducted in direct contact with a fatty food simulant. The results suggest the potential interest of these recycled and biobased materials, which are obtained from the revalorization of food waste, for their industrial application in food packaging and agricultural films. Full article

(This article belongs to the Special Issue Polymers and the Environment)

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24 pages, 12894 KiB

Open AccessArticle

Optimizing Polymer Costs and Efficiency in Alkali–Polymer Oilfield Applications

by Rafael E. Hincapie, Ante Borovina, Torsten Clemens, Eugen Hoffmann, Muhammad Tahir, Leena Nurmi, Sirkku Hanski, Jonas Wegner and Alyssia Janczak

Polymers 2022, 14(24), 5508; https://doi.org/10.3390/polym14245508 - 15 Dec 2022

Cited by 3 | Viewed by 1343

Abstract

In this work, we present various evaluations that are key prior field applications. The workflow combines laboratory approaches to optimize the usage of polymers in combination with alkali to improve project economics. We show that the performance of AP floods can be optimized by making use of lower polymer viscosities during injection but increasing polymer viscosities in the reservoir owing to “aging” of the polymers at high pH. Furthermore, AP conditions enable the reduction of polymer retention in the reservoir, decreasing the utility factors (kg polymers injected/incremental bbl. produced). We used aged polymer solutions to mimic the conditions deep in the reservoir and compared the displacement efficiencies and the polymer adsorption of non-aged and aged polymer solutions. The aging experiments showed that polymer hydrolysis increases at high pH, leading to 60% higher viscosity in AP conditions. Micromodel experiments in two-layer chips depicted insights into the displacement, with reproducible recoveries of 80% in the high-permeability zone and 15% in the low-permeability zone. The adsorption for real rock using 8 TH RSB brine was measured to be approximately half of that in the case of Berea: 27 µg/g vs. 48 µg/g, respectively. The IFT values obtained for the AP lead to very low values, reaching 0.006 mN/m, while for the alkali, they reach only 0.44 mN/m. The two-phase experiments confirmed that lower-concentration polymer solutions aged in alkali show the same displacement efficiency as non-aged polymers with higher concentrations. Reducing the polymer concentration leads to a decrease in EqUF by 40%. If alkali–polymer is injected immediately without a prior polymer slug, then the economics are improved by 37% compared with the polymer case. Hence, significant cost savings can be realized capitalizing on the fast aging in the reservoir. Due to the low polymer retention in AP floods, fewer polymers are consumed than in conventional polymer floods, significantly decreasing the utility factor. Full article

(This article belongs to the Special Issue Polymers and the Environment)

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20 pages, 5971 KiB

Open AccessArticle

Diverted from Landfill: Reuse of Single-Use Plastic Packaging Waste

by Kit O’Rourke, Christian Wurzer, James Murray, Adrian Doyle, Keith Doyle, Chris Griffin, Bernd Christensen, Conchúr M. Ó Brádaigh and Dipa Ray

Polymers 2022, 14(24), 5485; https://doi.org/10.3390/polym14245485 - 15 Dec 2022

Cited by 5 | Viewed by 2226

Abstract

Low-density polyethylene (LDPE) based packaging films mostly end up in landfill after single-use as they are not commonly recycled due to their flexible nature, low strength and low cost. Additionally, the necessity to separate and sort different plastic waste streams is the most costly step in plastics recycling, and is a major barrier to increasing recycling rates. This cost can be reduced through using waste mixed plastics (wMP) as a raw material. This research investigates the properties of PE-based wMP coming from film packaging wastes that constitutes different grades of PE with traces of polypropylene (PP). Their properties are compared with segregated individual recycled polyolefins and virgin LDPE. The plastic plaques are produced directly from the wMP shreds as well as after extruding the wMP shreds into a more uniform material. The effect of different material forms and processing conditions on the mechanical properties are investigated. The results of the investigation show that measured properties of the wMP fall well within the range of properties of various grades of virgin polyethylene, indicating the maximum possible variations between different batches. Addition of an intermediate processing step of extrusion before compression moulding is found to have no effect on the tensile properties but results in a noticeably different failure behaviour. The wMP does not show any thermal degradation during processing that was confirmed by thermogravimetric analysis. The results give a scientific insight into the adoption of wMP in real world products that can divert them from landfill creating a more circular economy. Full article

(This article belongs to the Special Issue Polymers and the Environment)

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16 pages, 3771 KiB

Open AccessArticle

Influence of Stabilization Additive on Rheological, Thermal and Mechanical Properties of Recycled Polypropylene

by Mohor Mihelčič, Alen Oseli, Miroslav Huskić and Lidija Slemenik Perše

Polymers 2022, 14(24), 5438; https://doi.org/10.3390/polym14245438 - 12 Dec 2022

Cited by 6 | Viewed by 1985

Abstract

To decrease the amount of plastic waste, the use of recycling techniques become a necessity. However, numerous recycling cycles result in the mechanical, thermal, and chemical degradation of the polymer, which leads to an inefficient use of recycled polymers for the production of plastic products. In this study, the effects of recycling and the improvement of polymer performance with the incorporation of an additive into recycled polypropylene was studied by spectroscopic, rheological, optical, and mechanical characterization techniques. The results showed that after 20 recycling steps of mechanical processing of polypropylene, the main degradation processes of polypropylene are chain scission of polymer chains and oxidation, which can be improved by the addition of a stabilizing additive. It was shown that a small amount of an additive significantly improves the properties of the recycled polypropylene up to the 20th reprocessing cycle. The use of an additive improves the rheological properties of the recycled melt, surface properties, and time-dependent mechanical properties of solid polypropylene since it was shown that the additive acts as a hardener and additionally crosslinks the recycled polymer chains. Full article

(This article belongs to the Special Issue Polymers and the Environment)

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16 pages, 1813 KiB

Open AccessArticle

Implications of the Circular Economy in the Context of Plastic Recycling: The Case Study of Opaque PET

by Noel León Albiter, Orlando Santana Pérez, Magali Klotz, Kishore Ganesan, Félix Carrasco, Sylvie Dagréou, Maria Lluïsa Maspoch and César Valderrama

Polymers 2022, 14(21), 4639; https://doi.org/10.3390/polym14214639 - 31 Oct 2022

Cited by 2 | Viewed by 1921

Abstract

The use of recycled opaque PET (r-O-PET, with TiO₂) as a reinforcement for the recycled polypropylene matrix (r-PP) was evaluated through the life cycle assessment according to different scenarios corresponding to two different recycled blends and considered two virgin raw plastic material as reference materials when comparing the environmental performance of the proposed treatments. The results indicate that the environmental performance was quite different for each blend, since the additional extrusion process required in scenario 2 (blend with TiO₂) causes all impact categories analysed to report higher values when compared with scenario 1 (blend without TiO₂). The stage that contributes the most corresponds to the different extrusion processes included in both recycling blends, representing at least 80% of the total for global warming. Compared with virgin raw materials, the blend with TiO₂ showed better performance in all the impact categories analysed in comparison with virgin PA66, while the blend without TiO₂ showed the opposite trend when compared to PP. Furthermore, the fact that the upcycling treatment was carried out on a pilot scale provides room for improvement when implemented on a full scale. It is worth noting the high energy consumption of the treatment processes and their associated cost, in addition to the market cost of virgin raw materials, however, when considering the environmental cost of raw materials, it is observed that when substituting virgin materials PP and PA66 for the blends evaluated in this study results in a reduction of the environmental price of up to 2.5 times. Full article

(This article belongs to the Special Issue Polymers and the Environment)

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15 pages, 4867 KiB

Open AccessArticle

Fractional Calculus Approach to Reproduce Material Viscoelastic Behavior, including the Time–Temperature Superposition Phenomenon

by Andrea Genovese, Flavio Farroni and Aleksandr Sakhnevych

Polymers 2022, 14(20), 4412; https://doi.org/10.3390/polym14204412 - 19 Oct 2022

Cited by 6 | Viewed by 1649

Abstract

The design of modern products and processes cannot prescind from the usage of viscoelastic materials that provide extreme design freedoms at relatively low cost. Correct and reliable modeling of these materials allows effective use that involves the design, maintenance, and monitoring phase and the possibility of reuse and recycling. Fractional models are becoming more and more popular in the reproduction of viscoelastic phenomena because of their capability to describe the behavior of such materials using a limited number of parameters with an acceptable accuracy over a vast range of excitation frequencies. A particularly reliable model parametrization procedure, using the poles–zeros formulation, allows researchers to considerably reduce the computational cost of the calibration process and avoid convergence issues typically occurring for rheological models. The aim of the presented work is to demonstrate that the poles–zeros identification methodology can be employed not only to identify the viscoelastic master curves but also the material parameters characterizing the time–temperature superposition phenomenon. The proposed technique, starting from the data concerning the isothermal experimental curves, makes use of the fractional derivative generalized model to reconstruct the master curves in the frequency domain and correctly identify the coefficients of the WLF function. To validate the methodology, three different viscoelastic materials have been employed, highlighting the potential of the material parameters’ global identification. Furthermore, the paper points out a further possibility to employ only a limited number of the experimental curves to feed the identification methodology and predict the complete viscoelastic material behavior. Full article

(This article belongs to the Special Issue Polymers and the Environment)

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Review

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18 pages, 1463 KiB

Open AccessReview

Sustainable Materials Containing Biochar Particles: A Review

by Giulia Infurna, Gabriele Caruso and Nadka Tz. Dintcheva

Polymers 2023, 15(2), 343; https://doi.org/10.3390/polym15020343 - 09 Jan 2023

Cited by 11 | Viewed by 2112

Abstract

The conversion of polymer waste, food waste, and biomasses through thermochemical decomposition to fuels, syngas, and solid phase, named char/biochar particles, gives a second life to these waste materials, and this process has been widely investigated in the last two decades. The main thermochemical decomposition processes that have been explored are slow, fast, and flash pyrolysis, torrefaction, gasification, and hydrothermal liquefaction, which produce char/biochar particles that differ in their chemical and physical properties, i.e., their carbon-content, CHNOS compositions, porosity, and adsorption ability. Currently, the main proposed applications of the char/biochar particles are in the agricultural sector as fertilizers for soil retirement and water treatment, as well as use as high adsorption particles. Therefore, according to recently published papers, char/biochar particles could be successfully considered for the formulation of sustainable polymer and biopolymer-based composites. Additionally, in the last decade, these particles have also been proposed as suitable fillers for asphalts. Based on these findings, the current review gives a critical overview that highlights the advantages in using these novel particles as suitable additives and fillers, and at the same time, it shows some drawbacks in their use. Adding char/biochar particles in polymers and biopolymers significantly increases their elastic modulus, tensile strength, and flame and oxygen resistance, although composite ductility is significantly penalized. Unfortunately, due to the dark color of the char/biochar particles, all composites show brown-black coloration, and this issue limits the applications. Full article

(This article belongs to the Special Issue Polymers and the Environment)

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15 pages, 4913 KiB

Open AccessReview

Preparation and Applications of Green Thermoplastic and Thermosetting Nanocomposites Based on Nanolignin

by Debora Puglia, Francesca Luzi and Luigi Torre

Polymers 2022, 14(24), 5470; https://doi.org/10.3390/polym14245470 - 14 Dec 2022

Cited by 3 | Viewed by 2109

Abstract

The development of bio-based materials is of great importance in the present environmental circumstances; hence, research has greatly advanced in the valorization of lignin from lignocellulosic wastes. Lignin is a natural polymer with a crosslinked structure, valuable antiradical activity, unique thermal- and UV-absorption properties, and biodegradability, which justify its use in several prospective and useful application sectors. The active functionalities of lignin promote its use as a valuable material to be adopted in the composite and nanocomposites arenas, being useful and suitable for consideration both for the synthesis of matrices and as a nanofiller. The aim of this review is to summarize, after a brief introduction on the need for alternative green solutions to petroleum-based plastics, the synthesis methods for bio-based and/or biodegradable thermoplastic and thermosetting nanocomposites, along with the application of lignin nanoparticles in all green polymeric matrices, thus generating responsiveness towards the sustainable use of this valuable product in the environment. Full article

(This article belongs to the Special Issue Polymers and the Environment)

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