Recycled Plastic Research Articles

Combined effect of silica fume and various fibers on fresh and hardened properties of concrete incorporating HDPE aggregates

Recycling of waste plastics has become essential to mitigate their detrimental impact on the environment. However, it can be used in the construction sector to fulfill construction needs and conserve natural resources. Previous research has demonstrated that incorporating plastic aggregate reduces the strength properties of concrete; hence, there is a need to improve its strength properties. In this study, high-density polyethylene (HDPE) plastic is incorporated in aggregate form, as a partial substitute for natural coarse aggregates (NCA) at volumetric ratios of 10 %, 30 %, and 50 %. Various strength enhancement techniques, including the addition of macro synthetic fibers (MSF), steel fibers (SF), and substituting 20 % of cement with silica fume, were employed. The results indicated that workability of concrete is improved with an increase in the content of HDPE coarse aggregates (HCA). Furthermore, concrete containing 30 % HCA performed better in terms of strength compared to concrete with 10 % and 50 % HCA. The findings demonstrate that concrete containing fibers performs better than concrete without fibers. The utilization of 0.75 % MSF and 1 % SF dosage leads to a 93 % improvement in splitting tensile strength, a 72 % improvement in flexural strength, and a 48 % improvement in compressive strength for concrete containing 30 % HCA. Using scanning electron microscopy, it was found that incorporating HCA weakens the internal matrix. However, the addition of a precise amount of fibers and pozzolanic materials resulted in improvements in microstructure. The significance of this research lies in the utilization of HDPE waste materials in concrete by simultaneous usage of different fibers.

Alkali pretreatment-assisted catalytic pyrolysis of waste cellulose acetate for selective preparation of levoglucosenone

With the increasing demand for cellulose acetate (CA) in industrial and daily applications, the disposal of its waste has emerged as an environmental concern. In this study, a novel and sustainable method for value-added utilization of waste CA was proposed, which involved NaOH pretreatment and subsequent catalytic pyrolysis using phosphoric acid-activated carbon (PAC) to prepare levoglucosone (LGO). The effects of pretreatment temperatures and NaOH concentrations on the physicochemical characteristics of CA were thoroughly investigated. Furthermore, the pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) experiments were conducted to methodically assess the impacts of both pretreatment and pyrolysis conditions on the production of LGO. The results indicated that NaOH pretreatment could effectively hydrolyze the ester bonds in CA, leading to the removal of acetyl groups and a decrease in thermal stability. At a pretreatment temperature of 40 °C, a NaOH concentration of 0.5 mol/L, a catalyst/sample ratio of 1/3, and a pyrolysis temperature of 400 °C, the LGO yield could reach 11.52 wt%, much higher than that obtained from catalytic pyrolysis of CA (2.70 wt%). This study provides an efficient method for treating waste CA and demonstrates its potential for conversion into high-value chemicals, laying a solid foundation for the green recycling of waste plastics.

Development of a sustainable polymer composite: enhancing properties of waste plastic with ground tire rubber reinforcement

The growing interest in utilizing waste for composite development has prompted investigations across social, economic, and environmental domains. This study focuses on utilizing recyclable waste plastic materials and micro-sized ground tire rubber (GTR) of varying sizes (600 μm, 300 μm, and 150 μm) to create a polymer matrix composite (PMC). Employing a thermal blending technique, the manufacturing process adjusts the composition ratios of polymer and GTR from 90:10 to 50:50. Subsequently, Energy Dispersive Spectroscopy (EDS) is utilized to analyze the PMC composition, while Fourier-transform infrared spectroscopy confirms functional group and chemical structure. The study demonstrates significant improvements in various properties upon adding GTR to High-Density Polyethylene (HDPE) and Low-Density Polyethylene (LDPE) composite materials. For HDPE-GTR composites, the melting temperature (Tm) ranged from 120.29 °C to 138.53 °C, crystallization temperature (Tc) from 102.84 °C to 127.14 °C, and enthalpy of melting (ΔHm) from 70.96 to 139.67 J g−1. Crystallinity (Xc) varied from 48.43% to 52.96%. In LDPE-GTR composites, Tm ranged from 106.08 °C to 129.57 °C, Tc from 90.27 °C to 112.20 °C, ΔHm from 75.59 to 142.53 J g−1, and Xc from 51.59% to 54.05%. Moreover, mechanical properties such as tensile strength, flexural modulus, and impact strength exhibited enhancements with GTR addition to the polymer matrix. These findings underscore the potential of sustainable waste utilization, advancing environmentally friendly and resource-efficient composite materials.

Catalytic Synergy between Lewis Acidic Alumina and Pt in Hydrodechlorination for Plastic Chemical Recycling.

Pyrolysis-based plastic chemical recycling has gained significant industrial attention due to its advantage of eliminating complex plastic sorting processes. However, plastic pyrolysis oil contains various components that require stringent removal before subsequent processes. In particular, Cl compounds originating from the decomposition of poly(vinyl chloride) can cause serious corrosion of reactors and catalyst deactivation in downstream processes. While extensive research has been conducted on the removal of other heteroatoms (S, N, and O) from organic compounds via hydrotreating, studies on the removal of Cl have been scarce. In this study, hydrodechlorination over Pt catalysts on various supports is comprehensively investigated using 1,2-dichloroethane as a model reactant. Our results demonstrate that Pt on γ-Al2O3 can exhibit exceptionally high catalytic activity compared to those on other supports due to a distinct bifunctional mechanism. Rigorous studies reveal that the Lewis acidic pentacoordinated Al sites of γ-Al2O3 activate C-Cl bonds, whereas Pt activates H2 and provides spillover H to remove Cl as HCl. The bifunctional mechanism enables the minimized use of precious Pt (<0.1 wt %) to achieve high activity. Pt/γ-Al2O3 also allows for efficient Cl removal (96.8%) with high stability in treating waste plastic pyrolysis oil containing 7500 ppm of Cl.

Isoconversional Analysis of the Catalytic Pyrolysis of ABS, HIPS, PC and Their Blends with PP and PVC.

Thermochemical recycling of plastics in the presence of catalysts is often employed to facilitate the degradation of polymers. The choice of the catalyst is polymer-oriented, while its selection becomes more difficult in the case of polymeric blends. The present investigation studies the catalytic pyrolysis of polymers abundant in waste electric and electronic equipment (WEEE), including poly(acrylonitrile-butadiene-styrene) (ABS), high-impact polystyrene (HIPS) and poly(bisphenol-A carbonate) (PC), along with their blends with polypropylene (PP) and poly(vinyl chloride) (PVC). The aim is to study the kinetic mechanism and estimate the catalysts' effect on the activation energy of the degradation. The chosen catalysts were Fe2O3 for ABS, Al-MCM-41 for HIPS, Al2O3 for PC, CaO for Blend A (comprising ABS, HIPS, PC and PP) and silicalite for Blend B (comprising ABS, HIPS, PC, PP and PVC). Thermogravimetric experiments were performed in a N2 atmosphere at several heating rates. Information on the degradation mechanism (degradation steps, initial and final degradation temperature, etc.) was attained. It was found that for pure (co)polymers, the catalytic degradation occurred in one-step, whereas in the case of the blends, two steps were required. For the estimation of the activation energy of those degradations, isoconversional kinetic models (integral and differential) were employed. In all cases, the catalysts used were efficient in reducing the estimated Eα, compared to the values of Eα obtained from conventional pyrolysis.

Catalytic pyrolysis of plastic waste using activated carbon from cotton waste

This study introduces a novel approach to plastic waste management and energy recovery by synthesizing highly porous activated carbon from an often-overlooked resource, waste cotton fabric (WCF), using H3PO4 as an activating agent. The synthesized waste cotton fabric activated carbon samples (WCF-AC) were utilized as a solid acid catalyst in the catalytic pyrolysis of low-density polyethylene (LDPE), with the aim of converting LDPE into fuel-range hydrocarbons. This research highlights the potential of bio-based waste materials in the synthesis of eco-friendly and cost-effective catalysts for feedstock recycling. The impact of the H3PO4 impregnation ratio and the carbonization/activation temperature on the physicochemical properties of the resulting WCF-AC samples was investigated, providing valuable insights into the optimization of activated carbon production. The catalytic activity of the synthesized WCF-AC samples was evaluated, demonstrating a reduction of 12°C in the LDPE degradation temperature. Furthermore, this work revealed a substantial increase in the formation of carbocyclic compounds, with light aromatics such as benzene, toluene, and xylene constituting up to 43 % of the pyrolysis output. In certain instances, a decrease in heavier hydrocarbons beyond C11 was observed, indicating the selective yield of specific range hydrocarbons. This study underscores the potential of bio-based acid catalysts, such as the synthesized activated carbon presented here, in plastic recycling. The approach adopted in this research aligns with the principles of the circular economy, promoting resource efficiency and sustainability.

(Invited) The Activation of Alkanes at Electrochemical Interfaces Using Real-Time Control of Potentials: Novel Avenues for Energy Storage and Sustainable Chemical Manufacturing

Producing fuels and chemicals using renewable electricity holds the promise to enable a truly sustainable circular economy based on sustainably produced carriers of electrical energy and sustainably produced chemicals. The science which allows us to link electricity to chemical transformations, electrocatalysis, remains chiefly focused on the electricity-driven transformation of small inorganic molecules such as CO2, H2O, N2, as well as the oxidation and reduction of alcohols. However, comprehensive electrification of society will require electrocatalytic reactions that can promote the central processes that sustain today’s society: alkane transformations. In this presentation, I will show how fundamental understanding of the interfacial processes occurring in electrocatalytic reactions, combined with monolayer-sensitive differential electrochemical mass spectrometry, allows us to independently control the elementary steps (adsorption, transformation, desorption) of complex alkane transformation reactions, allowing for the room-temperature fragmentation of ethane into methane, as well as for enabling the extraction of the chemical energy stored in alkanes in the form of electricity. I will show how we can apply these technologies to expand the reaction scope of electrocatalysis, allowing for novel avenues in energy storage, chemical synthesis and plastics recycling.

Screening of polyurethane-degrading microbes using a quenching fluorescence probe by microfluidic droplet sorting

Excessive use of polyurethane (PU) polymers has led contributed to serious environmental pollution. The plastic recycling technology using microorganisms and enzymes as catalysts offers a promising green and low-carbon approach for managing plastic waste. However, current methods for screening PU-degrading strains suffer from drawbacks such as being time-consuming and inefficient. Herein, we present a novel approach for screening PU-degrading microorganisms using a quenching fluorescent probe along with the fluorescence-activated droplet sorting (FADS). The FPAP could specifically recognize the 4,4′-methylenedianiline (MDA) derivates released from PU degradation, with fluorescence quenching as a response. Based on the approach, we successfully screen two PU-degrading strains (Burkholderia sp. W38 and Bacillus sp. C1). After 20 d of cultivation, strain W38 and C1 could degrade 41.58% and 31.45% of polyester-PU film, respectively. Additionally, three metabolites were identified during the degradation of PU monomer (2,4-toluene diamine, 2,4-TDA) and a proposed degradation pathway was established. Consequently, the fluorescence probe integrated with microfluidic droplet systems, demonstrates potential for the development of innovative PU-biocatalysts. Furthermore, the identification of the 2,4-TDA degradation pathway provides valuable insights that can propel advancements in the field of PU biodegradation.

Environmental benefit of recycling plastics from waste electrical & electronic equipment

Plastic recycling from waste electrical and electronic equipment (WEEE) can effectively deal with both the resource crisis and environmental pollution. However, the life cycle environmental impacts of recycling plastics derived from WEEE are still unclear. Therefore, this study adopts life cycle assessment and machine learning methods to estimate the environmental impacts and mitigation potentials of WEEE plastics recycling. We find the environmental degradation of WEEE waste plastics recycling are mainly from electricity consumption and transportation during the disassembly and granulation stages. Significant variation in the reduction effect of WEEE plastics recycling technologies is observed, ranging from 13 % to 77 %. The WEEE generation is projected to exhibit an S-shaped trend from 103 tonnes in 1980 to 15.42 million tonnes (Mt) in 2050, contributing to 10.33 Mt of carbon reduction. Improving the efficiency of WEEE plastics recycling technologies and enhancing legal recycling of waste air conditioner can efficiently reduce environmental emissions.

Investigation of the Impact of Single and Double Filtration Systems on Post-Consumer PE Film Waste.

Due to the diversity of plastic film waste streams available on the market and the associated variety of contaminants' size and number, the use of melt filtration is necessary. Currently, single and double filtration systems are state of the art in the plastic recycling industry, depending on the application of the produced post-consumer recyclate (PCR). Using PCR for thin films demands small contamination sizes, which are easier to reach using a second filtration step. In the case of relatively clean post-consumer input materials, it must be investigated whether the additional load from the second filter has a counterproductive effect on the material and whether single filtration would be sufficient. For this paper, polyethylene (PE) film waste stemming from a separate post-consumer collection in Austria was processed using an industrial-sized recycling machine with different combinations of filter sizes and systems. Melt flow rate (MFR), ash content, oxidation onset temperature (OOT), and optical contaminant detection were measured to investigate the influence of single and double filtration systems. The investigation showed that, even though the contamination amount and size were reduced, the second filter had a distinct effect on specific properties.

Industrial and Laboratory Technologies for the Chemical Recycling of Plastic Waste.

Synthetic polymers play an indispensable role in modern society, finding applications across various sectors ranging from packaging, textiles, and consumer products to construction, electronics, and industrial machinery. Commodity plastics are cheap to produce, widely available, and versatile to meet diverse application needs. As a result, millions of metric tons of plastics are manufactured annually. However, current approaches for the chemical recycling of postconsumer plastic waste, primarily based on pyrolysis, lag in efficiency compared to their production methods. In recent years, significant research has focused on developing milder, economically viable methods for the chemical recycling of commodity plastics, which involves converting plastic waste back into monomers or transforming it into other valuable chemicals. This Perspective examines both industrial and cutting-edge laboratory-scale methods contributing to recent advancements in the field of chemical recycling.

Plastic waste management in urban areas: Key takeaways from the “Send Plastic Home” project in Bangkok, Thailand

This study evaluates the plastic waste recycling program, named “Send Plastic Home,” tailored for urban areas in Thailand. Thirteen strategically located plastic drop-off points were implemented, and their effectiveness was assessed using the Productivity Index (PI). In-depth interviews and group discussions were conducted to identify key stakeholders and estimate the Social Return on Investment (SROI) associated with the project. Moreover, the environmental impacts of various plastic waste management scenarios were investigated and compared. To improve the PI of drop-off points, pass-through points for smaller amounts of plastic and drive-through points for bulk returns are recommended. Increasing drop-off points in highly populated areas, coupled with effective multi-channel public relations, would be beneficial. The current plastic waste management approach, combining recycling and waste-to-energy methods, yields commendable environmental benefits, particularly in mitigating marine aquatic ecotoxicity. With a collected plastic waste volume of 22,135 kg, greenhouse gas emissions and waste management costs are minimized by 27 tonCO2eq and 1803 USD, respectively. The program operates effectively, as evidenced by an impressive SROI ratio of 8.45. These findings provide a data-driven foundation and actionable insights for the design and implementation of more efficient plastic waste collection infrastructures in urban environments, aligning with the circular economy concept.

Material Recycling of Plastics—A Challenge for Sustainability

The complexity of plastic polymers and even more so of additives has increased enormously in recent years. This makes the material recycling of plastic waste considerably more difficult, especially in the case of mixed plastic waste. Some additives have now been strictly regulated or even completely banned for good reasons (‘legacy additives’). Material or mechanical recycling generally uses old plastics that still contain these substances. Consequently, products that are manufactured using such recyclates are contaminated with these harmful substances. This poses a major challenge for sustainability, as there is a conflict of objectives between protecting the health of consumers, especially vulnerable groups, conserving resources and recycling, keeping material cycles ‘clean’ and destroying pollutants, and transporting them to a safe final sink. With regard to the first objective, we recommend avoiding the use of contaminated recyclates for products with intensive contact with consumers (‘contact-sensitive products’) until further notice. We also show that the climate policy challenges for the plastics (and chemical) industry necessitate defossilization (‘feedstock change’). This turnaround can only succeed if solely closed-loop recycling takes place in the future; recyclates should primarily replace virgin plastics. For material or mechanical recycling, this means that this can only work if used plastics with a high degree of homogeneity and known formulation are collected separately, as is already the case today with PET bottles. The objective of this article is to illustrate the increasing complexity of plastic polymers and additives, especially legacy additives, which will force a legislative readjustment of todays’ material recycling.

Triboelectric Nanogenerators Using Recycled Disposable Medical Masks for Water Wave Energy Harvesting

AbstractIn the current daily life of people, the usage for disposable medical masks (DMMs) continues to be high. Discarded DMMs eventually become plastic pollution, threatening the marine environment seriously. At present, the common plastic recycling methods are extensive and not completely applicable for DMM recycling. In this work, according to the special structural and material characteristics of DMMs, a simple and effective recycling solution is proposed based on triboelectric nanogenerators (TENGs). First, a pulsed electric field system is designed and fabricated to treat the recycled films. The sterilizing rate reaches 91.8%, and the film surface potential is enhanced at the same time. Then, the feasibility of the treated films to be applied as the friction layers of TENGs is verified. Moreover, the recycled films are upgraded by chemical and physical methods, improving the output current of the basic TENG by 3.28 times. Finally, a complete TENG device is constructed to harvest water wave energy, 93.75% of which is made from recycled DMM materials. Under water waves, the power density of 18.22 W m−3 is achieved. Starting from TENG technology, this study combines circular economy and clean energy development, which is of significance for carbon neutralization.

Bacterial surface display of PETase mutants and MHETase for an efficient dual-enzyme cascade catalysis

Biological degradation of PET plastic holds great potential for plastic recycling. However, the high costs associated with preparing free enzymes for degrading PET make it unfeasible for industrial applications. Hence, we developed various cell catalysts by surface-displaying PETase mutants and MHETase using autotransporters in E. coli and P. putida. The efficiency of surface display was enhanced through modifying the host, co-expressing molecular chaperones, and evoluting the autotransporter. In strain EC9F, PET degradation rate was boosted to 3.85 mM/d, 51-fold and 23-fold increase compared to free enzyme and initial strain ED1, respectively. The reusability of cell catalyst EC9F was demonstrated with over 38 % and 30 % of its initial activity retained after 22 cycles of BHET degradation and 3 cycles of PET degradation. The highest reported PET degradation rate of 4.95 mM/d was achieved by the dual-enzyme cascade catalytic system EC9F+EM2+R, a mixture of cell catalyst EC9F and EM2 with surfactant rhamnolipid.

A comprehensive approach to physical recycling of hazardous waste HDPE industrial drums: Overcoming challenges in safety and foam interference

The regeneration of hazardous waste plastics are prerequisites for the sustainable development, and treatment of waste high density polyethylene (HDPE) industrial drums poses a significant challenge in the field of waste plastic recycling. In this study, a multi-step collaborative system was established for the decontamination and classification process of hazardous waste industrial drums. The yield of recycled HDPE particles exceeds 80 wt%. Through multiple experimental verifications, the optimal addition amount of antifoaming agent is 0.6 wt%, achieving the best balance between antifoaming effect and consumption. The motion process of antifoaming agent microdroplets in a static mixer was simulated. And also, through large-scale statistical analysis, the stability and reliability of physical properties and environmental safety of recycled HDPE particles were verified, supporting their reuse in various fields. In sum, this study proposes a feasible physical recycling strategy for hazardous waste HDPE industrial drums, and provides basic data from industrial practice and technical insights.

Lifecycle Management for Sustainable Plastics: Recent Progress from Synthesis, Processing to Upcycling.

Plastics, renowned for their outstanding properties and extensive applications, assume an indispensable and irreplaceable role in modern society. However, the ubiquitous consumption of plastic items has led to a growing accumulation of plastic waste. Unreasonable practices in the production, utilization, and recycling of plastics have led to substantial energy resource depletion and environmental pollution. Herein, the state-of-the-art advancements in the lifecycle management of plastics are timely reviewed. Unlike typical reviews focused on plastic recycling, this work presents an in-depth analysis of the entire lifecycle of plastics, covering the whole process from synthesis, processing, to ultimate disposal. The primary emphasis lies on selecting judicious strategies and methodologies at each lifecycle stage to mitigate the adverse environmental impact of waste plastics. Specifically, the article delineates the rationale, methods, and advancements realized in various lifecycle stages through both physical and chemical recycling pathways. The focal point is the attainment of optimal recycling rates for waste plastics, thereby alleviating the ecological burden of plastic pollution. By scrutinizing the entire lifecycle of plastics, the article aims to furnish comprehensive solutions for reducing plastic pollution and fostering sustainability across all facets of plastic production, utilization, and disposal.

Influence of Carboxylic Acid Structure on the Kinetics of Polyurethane Foam Acidolysis to Recycled Polyol.

Closed-loop recycling of plastics is needed to bridge the gap between the material demands imposed by a growing global population and the depletion of nonrenewable petroleum feedstocks. Here, we examine chemical recycling of polyurethane foams (PUFs), the sixth most produced polymer in the world, through PUF acidolysis via dicarboxylic acids (DCAs) to release recyclable polyols. Acidolysis enables recycling of the polyol component of PUFs to high-quality materials, and while the influence of DCA structure on recycled PUF quality has been reported, there are no reports that examine the influence of DCA structure on the kinetics of polyol release. Here, we develop quantitative relationships between DCA structure and PUF acidolysis function for ∼10 different DCA reagents. PUF acidolysis kinetics were quantified with ∼1 s time resolution using the rate of carbon dioxide (CO2) gas generation, which is shown to occur concomitantly with polyol release. Pseudo-zeroth-order rate constants were measured as a function of DCA composition, reaction temperature, and DCA concentration, and apparent activation barriers were extracted. Our findings demonstrate that DCA carboxyl group proximity and phase of transport are descriptors of PUF acidolysis rates, rather than expected descriptors like pK a. DCAs with closer proximity acid groups exhibited faster PUF acidolysis rate constants. Furthermore, a shrinking core mechanism effectively describes the kinetic functional form of the kinetics of PUF acidolysis by DCAs. Measurements of acidolysis kinetics for model PUF (M-PUF) and end-of-life PUF (EOL PUF) confirm the applicability of our analysis to postconsumer materials. This work provides insights into the physical and chemical mechanisms controlling acidolysis, which can facilitate the development of efficient closed-loop PUF chemical recycling schemes.

Towards sustainable and recyclable plastic materials: Vanilin-based epoxy bio-composites with spruce bark powder and hydrochar, pioneering green chemistry solutions for shape memory applications

The negative impacts of fossil-based plastic production and its excessive usage are significant and multifaceted, affecting both the planet and humanity in various ways. In this study, a novel approach to developing sustainable and recyclable materials sourced from lignocellulosic biomass is introduced. This methodology involves formulating an epoxy-based resin using diglycidyl ether of vanillin (DGEVA) for curing with dodecenylsuccinic anhydride (DDSA), in presence of significant proportions (5–20 wt%) of either spruce bark (SB) powder or its hydrochar (HTC). Through thermomechanical analyses conducted via Dynamic Mechanical Analysis (DMA), it was ascertained that while the inclusion of SB has minimal impact on material performance, the incorporation of HTC leads to significant improvements. Specifically, a substantial enhancement in storage modulus is observed, increasing from 1.5 GPa to 3.1 GPa, and a rise in the damping factor from 56°C to 61°C. These findings are further corroborated by Scanning Electron Microscopy (SEM) analysis, which demonstrates excellent compatibility between the bioresin matrix and the biofillers. Moreover, this investigation underscores the remarkable mechanical and chemical recycling capabilities of the systems, which are notably improved by the presence of spruce bark or HTC particles, in addition to their inherent shape-memory properties. This approach not only showcases the feasibility of sustainable material development but also highlights the potential for an effective waste utilization in enhancing material properties and reducing the environmental impact.

Processability Characteristics of Biocomposite from Recycled High‐Density Polyethylene and Brewers’ Spent Grain

AbstractThe current awareness of the environmental impact of the massive consumption of fossil fuel‐based resources has prompted the development of biocomposites based on plastic and agro‐industrial waste instead of virgin raw materials, promoting the new circular economy trend. This study uses a torque rheometer to analyze the effect of brewers’ spent grain (BSG) on processing a postconsumer high‐density polyethylene (rHDPE)‐based biocomposite. Processing parameters are measured to contrast the effect of BSG (20 and 40 wt%) and the addition of a coupling agent at low (10 rpm) and high speed (90 rpm). This work allows determining the viability of manufacturing recycled plastic biocomposite with agro‐industrial waste at an industrial scale.