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Open AccessArticle

Graphene Oxide Facilitates Transformation of Waste PET into MOF Nanorods in Ionic Liquids

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Deepa Gangaraju

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Andikkadu Masilamani Shanmugharaj

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Vadahanambi Sridhar

Polymers 2023, 15(11), 2479; https://doi.org/10.3390/polym15112479 - 27 May 2023

Viewed by 360

Abstract

Although though ionic liquids (IL) are rapidly emerging as highly efficient reagents for the depolymerization of waste plastics, their high cost and adverse impact on the environment make the overall process not only expensive but also environmentally harmful. In this manuscript, we report [...] Read more.

Although though ionic liquids (IL) are rapidly emerging as highly efficient reagents for the depolymerization of waste plastics, their high cost and adverse impact on the environment make the overall process not only expensive but also environmentally harmful. In this manuscript, we report that graphene oxide (GO) facilitates the transformation of waste polyethylene terephthalate (PET) to Ni-MOF (metal organic framework) nanorods anchored on reduced graphene oxide (Ni–MOF@rGO) through NMP (N-Methyl-2-pyrrolidone)-based coordination in ionic liquids. Morphological studies using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed mesoporous three-dimensional structures of micrometer-long Ni-MOF nanorods anchored on reduced graphene substrates (Ni–MOF@rGO ), whereas structural studies using XRD and Raman spectra demonstrated the crystallinity of Ni-MOF nanorods. Chemical analysis of Ni–MOF@rGO carried out using X-ray photoelectron spectroscopy demonstrated that nickel moieties exist in an electroactive OH-Ni-OH state, which was further confirmed by nanoscale elemental maps recorded using energy-dispersive X-ray spectroscopy (EDS). The applicability of Ni–MOF@rGO as an electro-catalyst in a urea-enhanced water oxidation reaction (UOR) is reported. Furthermore, the ability of our newly developed NMP-based IL to grow MOF nanocubes on carbon nanotubes and MOF nano-islands on carbon fibers is also reported. Full article

(This article belongs to the Special Issue Advances in Recycling of Polymers)

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Open AccessArticle

Screening the Impact of Surfactants and Reaction Conditions on the De-Inkability of Different Printing Ink Systems for Plastic Packaging

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Polymers 2023, 15(9), 2220; https://doi.org/10.3390/polym15092220 - 08 May 2023

Viewed by 1012

Abstract

One of the major applications (40% in Europe) of plastic is packaging, which is often printed to display required information and to deliver an attractive aesthetic for marketing purposes. However, printing ink can cause contamination in the mechanical recycling process. To mitigate this [...] Read more.

One of the major applications (40% in Europe) of plastic is packaging, which is often printed to display required information and to deliver an attractive aesthetic for marketing purposes. However, printing ink can cause contamination in the mechanical recycling process. To mitigate this issue, the use of surfactants in an alkaline washing process, known as de-inking, has been employed to remove printing ink and improve the quality of recyclates. Despite the existence of this technology, there are currently no data linking the de-inking efficiency with typical printing ink compositions. Additionally, it is necessary to investigate the de-inking process under the process parameters of existing recycling plants, including temperature, NaOH concentration, and retention time. This study aims to evaluate the performance of commonly used printing inks with different compositions under various washing scenarios for plastic recycling in conjunction with different de-inking detergents containing surfactants or mixtures of surfactants. The results indicate that the pigments applied to the ink have no significant effect on the de-inking process, except for carbon black (PBk 7). Nitrocellulose (NC) binder systems exhibit high de-inkability (over 95%) under the condition of 55 °C and 1 wt.% NaOH. However, crosslinked binder systems can impede the de-inking effect, whether used as a binder system or as an overprint varnish (OPV). The de-inking process requires heating to 55 °C with 1 wt.% NaOH to achieve a substantial effect. Based on the findings in this work, breaking the Van der Waals forces, hydrogen bonds, and covalent bonds between the printing ink and plastic film is an essential step to achieve the de-inking effect. Further research is needed to understand the interaction between surfactants and printing inks, enabling the development of de-inkable printing inks and high-performance surfactants that allow for de-inking with less energy consumption. The surfactant and NaOH have a synergistic effect in cleaning the printing ink. NaOH provides a negative surface charge for the adsorption of the cationic head of the surfactant and can hydrolyze the covalent bonds at higher concentrations (>2 wt.%). Full article

(This article belongs to the Special Issue Advances in Recycling of Polymers)

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Open AccessArticle

Design and Construction of an Azo-Functionalized POP for Reversibly Stimuli-Responsive CO₂ Adsorption

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Rongrong Yuan

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Meiyu Zhang

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Hao Sun

Polymers 2023, 15(7), 1709; https://doi.org/10.3390/polym15071709 - 29 Mar 2023

Cited by 1 | Viewed by 987

Abstract

A porous azo-functionalized organic polymer (JJU-2) was designed and prepared via oxidative coupling polymerization promoted by FeCl₃. JJU-2 exhibited reversibly stimuli-responsive CO₂ adsorption properties as a result of the trans/cis isomerization of the polymer’s azo-functionalized skeleton. Under UV irradiation and [...] Read more.

A porous azo-functionalized organic polymer (JJU-2) was designed and prepared via oxidative coupling polymerization promoted by FeCl₃. JJU-2 exhibited reversibly stimuli-responsive CO₂ adsorption properties as a result of the trans/cis isomerization of the polymer’s azo-functionalized skeleton. Under UV irradiation and heat treatment, this porous material displayed various porous structures and CO₂ adsorption properties. The initial Brunauer-Emmett-Teller (BET) surface area of JJU-1 is 888 m² g⁻¹. After UV irradiation, the BET surface area decreases to 864 m² g⁻¹, along with the decrease of micropores around 0.50 nm and 1.27 nm during the trans-to-cis isomerization process. In addition, CO₂ sorption isotherms demonstrate an 8%t decrease, and the calculated Qst of CO₂ has decreased from 29.0 kJ mol⁻¹ to 26.5 kJ mol⁻¹ due to the trans to cis conversion of the azobenzene side group. It is noteworthy that JJU-2′s CO₂ uptakes are nearly constant over three cycles of alternating external stimuli. Therefore, this azo-functionalized porous material was a potential carbon capture material that was responsive to stimuli. Full article

(This article belongs to the Special Issue Advances in Recycling of Polymers)

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Open AccessArticle

Recycling of Epoxy/Fiberglass Composite Using Supercritical Ethanol with (2,3,5-Triphenyltetrazolium)₂[CuCl₄] Complex

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Alexander E. Protsenko

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Alexandra N. Protsenko

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Olga G. Shakirova

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Victor V. Petrov

Polymers 2023, 15(6), 1559; https://doi.org/10.3390/polym15061559 - 21 Mar 2023

Viewed by 645

Abstract

The widespread use of polymer composite materials (PCM) leads to an increase in non-recyclable waste. This paper discusses the feasibility of recycling fiberglass with an epoxy matrix by solvolysis in ethanol under supercritical conditions. The solvolysis process completes successfully within four hours in [...] Read more.

The widespread use of polymer composite materials (PCM) leads to an increase in non-recyclable waste. This paper discusses the feasibility of recycling fiberglass with an epoxy matrix by solvolysis in ethanol under supercritical conditions. The solvolysis process completes successfully within four hours in an environment of a pure solvent containing 10% water at a temperature of 280 °C when the solvent passes into the supercritical state. The treatment time increases up to 10 h at a process temperature of 250 °C. When using a coordination compound of copper(II) chloride with organic chloride salt having 2,3,5-triphenyltetrazolium as the counterion, having the composition of (2,3,5-triphenyltetrazolium)₂[CuCl₄], the treatment time is reduced. The addition of the complex of 5% by weight makes it possible to completely remove the epoxy matrix at a temperature of 250 °C for two hours. The products separated from the solvolysis liquid were studied by infrared spectroscopy. The resulting fibers were examined by thermogravimetric analysis and scanning electron microscopy. The residual strength of the recovered fibers is 98%. Thus, the resulting fibers can be reused in the composite industry. Including both for the production of decorative products and for the production of structural products made of polymer composite materials. Full article

(This article belongs to the Special Issue Advances in Recycling of Polymers)

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Open AccessArticle

Preparation and Properties of Waste Corrugated Paper Fiber/Polylactic Acid Co-Extruded Composite

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Polymers 2022, 14(21), 4569; https://doi.org/10.3390/polym14214569 - 28 Oct 2022

Cited by 1 | Viewed by 1016

Abstract

In order to explore the methods of recycling waste paper, reduce environment pollution, and develop a circular economy, the application of waste corrugated paper to the strengthening of polylactic acid (PLA) was studied. Plant fiber from waste corrugated paper (WCPF) was used to [...] Read more.

In order to explore the methods of recycling waste paper, reduce environment pollution, and develop a circular economy, the application of waste corrugated paper to the strengthening of polylactic acid (PLA) was studied. Plant fiber from waste corrugated paper (WCPF) was used to prepare WCPF/PLA composite via co-extrusion. The WCPF was extracted from the waste corrugated paper by beating in a Valli beating machine and grinding in a disc grinder. KH-550 coupling agent was used to modify the surface of WCPF to improve the interface adhesive strength between the WCPF and PLA matrix. The effects of the contents of WCPF and KH-550 coupling agent on the mechanical properties, microstructure, crystallization properties, and thermostability of the WCPF/PLA composite were studied. The results show that the WCPF can be well separated from each other. The WCPF can be uniformly dispersed in the PLA matrix through a co-extrusion process. WCPF can increase the mechanical strength and deformation resistance ability of WCPF/PLA composite, and KH-550 coupling agent can further improve that of the WCPF/PLA composite. This study is of obvious significance to the recycling of waste paper and the development of a circular economy. Full article

(This article belongs to the Special Issue Advances in Recycling of Polymers)

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Open AccessArticle

Preparation and Adsorption Properties of Graphene-Modified, Pitch-Based Carbon Foam Composites

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Polymers 2022, 14(20), 4455; https://doi.org/10.3390/polym14204455 - 21 Oct 2022

Cited by 2 | Viewed by 892

Abstract

In view of the good adsorption properties of graphene and carbon foam, they were combined to achieve the optimal matching of microstructures. Taking mesophase pitch as a raw material, pitch-based carbon foam was prepared by the self-foaming method. Graphene gel was prepared as [...] Read more.

In view of the good adsorption properties of graphene and carbon foam, they were combined to achieve the optimal matching of microstructures. Taking mesophase pitch as a raw material, pitch-based carbon foam was prepared by the self-foaming method. Graphene gel was prepared as the second phase to composite with the carbon foam matrix; graphene-modified, pitch-based carbon foam composites were finally obtained. Graphene gel was dispersed in the rich pore structure of carbon foam to improve its agglomeration and the porosity, and the active sites of the composite were further increased; the adsorption properties and mechanical properties of the composites were also significantly improved. The microstructure and morphology of the composites were studied by SEM, XRD and Raman spectroscopy; the compressive property and porosity were also tested. Methylene blue (MB) solution was used to simulate a dye solution for the adsorption test, and the influence of the composite properties and MB solution on the adsorption property was studied. Results showed that the compressive strength of the composite was 13.5 MPa, increased by 53.41%, and the porosity was 58.14%, increased by 24.15%, when compared to raw carbon foam. When the mass of the adsorbent was 150 mg, the initial concentration of the MB solution was 5 mg/L, and the pH value of the MB solution was 11; the graphene-modified carbon foam composites showed the best adsorption effect, with an adsorption rate of 96.3% and an adsorption capacity of 144.45 mg/g. Compared with the raw carbon foam, the adsorption rate and adsorption capacity of the composites were increased by 158.18% and 93.50%, respectively. Full article

(This article belongs to the Special Issue Advances in Recycling of Polymers)

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Open AccessArticle

Evaluation of Fatigue Life of Recycled Opaque PET from Household Milk Bottle Wastes

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Polymers 2022, 14(17), 3466; https://doi.org/10.3390/polym14173466 - 25 Aug 2022

Cited by 1 | Viewed by 1069

Abstract

Polyethylene terephthalate (PET) is among the most used thermoplastic polymers in large scale manufacturing. Opaque PET is increasingly used in milk bottles to save weight and to bring a glossy white aspect due to TiO₂ nanoparticles. The recyclability of opaque PET is [...] Read more.

Polyethylene terephthalate (PET) is among the most used thermoplastic polymers in large scale manufacturing. Opaque PET is increasingly used in milk bottles to save weight and to bring a glossy white aspect due to TiO₂ nanoparticles. The recyclability of opaque PET is an issue: whereas the recycling channels are well established for transparent PET, the presence of opaque PET in household wastes weakens those channels: opaque bottles cannot be mixed with transparent ones because the resulting blend is not transparent anymore. Many research efforts focus on the possibility to turn opaque PET into resources, as one key to a more circular economy. A recent study has demonstrated the improvement of the mechanical properties of recycled PET through reactive extrusion. In the present work, the lifespan of recycled opaque PET has been evaluated throughout tensile–tensile fatigue loading cycles at various steps of the recycling process: The specimens are obtained from flakes after grinding PET wastes (F-r-OPET), from a subsequent homogenization step (r-OPET-hom) and after reactive extrusion (Rex-r-OPET). Virgin PET is also considered as a comparison. First, tensile tests monitored by digital image correlation have been carried out to obtain the elastic modulus and ultimate tensile stress of each type of PET. The fatigue properties of reactive REx-r-OPET increase, probably associated with the rise of cross-linking and branching rates. The fatigue lifespan increases with the macromolecular weight. The fracture surface analysis of specimens brings new insight regarding the factors governing the fatigue behavior and the damaging mode of recycled PET. TiO₂ nanoparticles act as stress concentrators, contributing to void formation at multiple sites and thus promoting the fracture process. Finally, the fatigue life of REx-r-OPET is comparable to those of virgin PET. Upcycling opaque PET by reactive extrusion may be a relevant new route to absorb some of the growing amounts of PET worldwide. Full article

(This article belongs to the Special Issue Advances in Recycling of Polymers)

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Open AccessArticle

The Reinforcing Effect of Waste Polyester Fiber on Recycled Polyethylene

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Polymers 2022, 14(15), 3109; https://doi.org/10.3390/polym14153109 - 30 Jul 2022

Cited by 2 | Viewed by 1221

Abstract

To improve the performance and application value of recycled plastics, filling modification has been widely used in waste plastic reinforcement. In this study, recycled polyethylene (RPE) was reinforced via extrusion blending using waste polyester fiber (WPF) from a waste silk wadding quilt as [...] Read more.

To improve the performance and application value of recycled plastics, filling modification has been widely used in waste plastic reinforcement. In this study, recycled polyethylene (RPE) was reinforced via extrusion blending using waste polyester fiber (WPF) from a waste silk wadding quilt as a reinforcer. The effects of the amount of WPF on the mechanical properties, the thermal stability of RPE and the microstructure of the RPE/WPF composite were studied. The result shows that extrusion blending can evenly disperse WPF in RPE matrix and that WPF can clearly improve the tensile strength, flexural modulus, storage modulus and thermal stability of RPE. The tensile strength and flexural modulus almost achieved the maximum when the addition of WPF was 20 wt%. The storage modulus under this condition is also higher than that of other samples. This study provides a cheap and effective reinforcement method for waste plastics as well as a new idea for the reuse of WPF, which is of great significance to the reuse of waste and environmental protection. However, how to enhance the interface adhesion between WPF and RPE to further improve the enhancement effect needs further research. Full article

(This article belongs to the Special Issue Advances in Recycling of Polymers)

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Open AccessReview

The Key to Solving Plastic Packaging Wastes: Design for Recycling and Recycling Technology

by

Qian Ding

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Heping Zhu

Polymers 2023, 15(6), 1485; https://doi.org/10.3390/polym15061485 - 16 Mar 2023

Viewed by 2066

Abstract

Confronted with serious environmental problems caused by the growing mountains of plastic packaging waste, the prevention and control of plastic waste has become a major concern for most countries. In addition to the recycling of plastic wastes, design for recycling can effectively prevent [...] Read more.

Confronted with serious environmental problems caused by the growing mountains of plastic packaging waste, the prevention and control of plastic waste has become a major concern for most countries. In addition to the recycling of plastic wastes, design for recycling can effectively prevent plastic packaging from turning into solid waste at the source. The reasons are that the design for recycling can extend the life cycle of plastic packaging and increase the recycling values of plastic waste; moreover, recycling technologies are helpful for improving the properties of recycled plastics and expanding the application market for recycled materials. This review systematically discussed the present theory, practice, strategies, and methods of design for recycling plastic packaging and extracted valuable advanced design ideas and successful cases. Furthermore, the development status of automatic sorting methods, mechanical recycling of individual and mixed plastic waste, as well as chemical recycling of thermoplastic and thermosetting plastic waste, were comprehensively summarized. The combination of the front-end design for recycling and the back-end recycling technologies can accelerate the transformation of the plastic packaging industry from an unsustainable model to an economic cycle model and then achieve the unity of economic, ecological, and social benefits. Full article

(This article belongs to the Special Issue Advances in Recycling of Polymers)

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Open AccessReview

Sampling Scheme Conception for Pretreated Polyolefin Waste Based on a Review of the Available Standard Procedures

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Mohamad Hassan Akhras

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Joerg Fischer

Polymers 2022, 14(17), 3450; https://doi.org/10.3390/polym14173450 - 24 Aug 2022

Cited by 2 | Viewed by 1411

Abstract

Given the rapid development of plastics recycling in recent years, the need for guidelines for sampling and material characterization is steadily emerging. However, there still exists a considerable scarcity of methods that enable proper material data acquisition. This paper consists of two parts. [...] Read more.

Given the rapid development of plastics recycling in recent years, the need for guidelines for sampling and material characterization is steadily emerging. However, there still exists a considerable scarcity of methods that enable proper material data acquisition. This paper consists of two parts. The first part provides a critical review of the available sampling techniques that can be utilized in the field of plastics recycling. Several sampling studies were covered in the review alongside the prominent standardization institutions. It was found that neither the literature nor the standards provide a comprehensive practice that considers the distinctive characteristics of plastic waste and applies it to different situations along the value chain. In the second part, a proposal of a sampling plan for pretreated rigid plastic waste is conceptualized based on selected information from the reviewed methods. Two variants of the proposed plan were evaluated based on the flake size distribution and the apparent density of four different pretreated polyolefin (PO) waste materials. The results of the study showed that combining stratified random sampling with composite sampling yields a good sampling technique for rigid PO waste. Moreover, the analysis of a composite sample adequately conveys the true material properties of a sublot or lot. Full article

(This article belongs to the Special Issue Advances in Recycling of Polymers)

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