Biodegradation of polymers in managing plastic waste - A review

Biodegradation of Poly(Styrene-Alt-Maleic Anhydride) in Soil and Its Toxic Effects on the Environment

In recent years, synthetic polymers have become integral to modern society, but their improper disposal has led to significant environmental challenges. Therefore, it is of great significance to investigate the environmental impact of polymer waste. Herein, we conducted comprehensive research on the biodegradability of poly(styrene-alt-maleic anhydride) (PSM) when exposed to soil and microbes, as well as its toxic effects on soybean seedlings and Eisenia fetida. The biodegradation process of PSM was thoroughly evaluated using respirometry tests, Fourier transform infrared spectroscopy, gel permeation chromatography, weight loss analysis, and bacterial reproduction tests. After 90 days of incubation in soil, the mineralization ratio of PSM reached 15%, and the weight-average molecular weight gradually decreased from 28.0 to 14.5 kg/mol in the first 14 days. Additionally, PSM experienced a 50% degradation by Pseudomonas aeruginosa after 30 days. In terms of phytotoxicity, PSM showed slight effects on the morphology of soybean seedlings while inducing oxidative stress in roots. The toxic effects of PSM on Eisenia fetida were investigated using both filter paper and soil contact methods. The filter paper contact test showed that the LC50 value was above 1000.0 μg/cm2 at 48 h, while the soil contact test indicated an LC50 value of 93.34 g/kg at 7 days. In conclusion, PSM demonstrates excellent biodegradability and low biotoxicity, suggesting great potential for emerging environmental applications.

A comprehensive mechanism of polyester enzymatic depolymerization: A novel singular key parameter for streamlined eco-design

Plastic pollution persists due to polymers' resistance to depolymerization, making eco-design and enzymatic recycling essential for sustainability. However, understanding plastic depolymerization is complex, and studies often separate enzymatic from non-enzymatic degradation, despite their interconnectedness in practice. This study aims to simplify this process, unifying key factors into a single mechanism using polylactide (PLA) as a model. We demonstrate that the local glass transition temperature of the soaked material (Tgs) -a novel parameter-is the central factor enabling chain mobility for enzyme interaction, with chain mobility as the primary driver in degradation. Enzymatic hydrolysis initiates perforation, triggering non-enzymatic depolymerization when chain-end density is sufficient. This unified mechanism complements enzymologists' work, providing an innovative pathway to optimize enzymatic plastic recycling and accelerate polyester degradation under practical conditions.

Can the insects Galleria mellonella and Tenebrio molitor be the future of plastic biodegradation?

Plastics have been an integral part of human lives, enhancing the functionality and safety of many everyday products, contributing significantly to our overall well-being. However, petroleum-based plastics can take hundreds or even thousands of years to decompose, resulting in an unprecedented plastic waste accumulation in the environment. Widely used conventional plastic disposal methods as landfilling and incineration are also environmentally harmful, frequently leading to soil/water contamination and the release of microplastics. To overcome these limitations, researchers have been investigating novel sustainable alternatives for plastic waste management, such as the use of microorganisms, microbial-based enzymes, and, more recently, some insect larvae, being Galleria mellonella and Tenebrio molitor the most promising ones. In this review, we explore different methods of plastic waste disposal focusing on recent discoveries regarding biological plastic degradation using insects as alternative methods. We also discuss the plastic degradation mechanisms employed by G. mellonella and T. molitor larvae known so far, as salivary enzymes and the pool of microorganisms in their gut. Finally, this review highlights key challenges in plastic biodegradation, such as standardization and experimental comparability, while proposing innovative perspectives like using insects as bioreactors and exploring unexplored research directions.

Resolving the Kinetics of Single-Walled Carbon Nanotube-Polyester Polyurethane Nanoparticle Conjugate Fluorescence Sensors toward Polymer Degrading Enzymes

Single-walled carbon nanotubes (SWCNTs) are fluorescent materials that have been developed as sensors for measuring the activities of enzymes. However, most sensors to date rely on end-point measurement and empirical functions to correlate enzyme concentrations with fluorescence responses. Less emphasis is put on analyzing time-dependent fluorescence responses and their connections with enzymatic kinetics. Here, improved from our previous sensor design, we use trimethylchitosan-wrapped SWCNTs to measure the enzymatic degradation rate of Impranil nanoparticles, a polyester polyurethane model substrate. Through careful analysis of the characteristic time constant and saturation fluorescence, which are resolved from time-dependent brightening responses of the sensors, linear relations are found between fluorescence change rates and both enzyme concentrations and Impranil-to-SWCNT ratios, thus showing that the reaction is first-ordered toward both enzyme and substrate concentrations. The proposed sensor design and data analysis strategy can quantitively determine the relative enzymatic activity and provide insights into the kinetics of sensors and enzymatic reactions.

Promoting role of nitrogen-fixing bacteria and biochar on nitrogen retention and degradation of PBAT plastics during composting

Since the increasing number of polybutylene adipate terephthalate (PBAT)-based plastics entering the environment, the search for sustainable treatment methods has become a primary focus of contemporary research. Composting offers a novel approach for managing biodegradable plastics. However, a significant challenge in the composting process is how to control nitrogen loss and enhance plastic degradation. In this context, the effect of various additives on nitrogen retention, PBAT plastics degradation, and microbial community dynamics during composting was investigated. The findings revealed that the addition of nitrogen-fixing bacteria Azotobacter vinelandii and biochar (AzBC) significantly improved nitrogen retention and accelerated PBAT rupture within 40 days of composting. Specifically, the PBAT degradation rate in the AzBC group reached 29.6%, which increased by 12.14% (P < 0.05) compared to the control group. In addition, the total nitrogen (TN) content increased by 6.20% (P < 0.05), and the Nitrogen-fixing enzyme (NIT) content increased by 190 IU/L (P < 0.05). Further analysis of GC-MS confirmed the presence of low molecular weight fragmentation products, such as 6-(4-hydroxybutoxy)-6-oxohexanoic acid. The AzBC treatment promoted the proliferation of Klebsiella at the genus level that could enhance nitrogen retention and the bacteria that have the ability to degrade PBAT, such as Proteobacteria and Firmicutes at the phyla level, and Pseudoxanthomonas, Pseudomonas, and Flavobacterium genera at the genera level (P < 0.05). Correlation analysis indicated that the degradation of PBAT is positively correlated with Temperature (T), NIT, and TN, but negatively correlated with the organic matter (OM) content and germination index (GI). In conclusion, the co-application of biochar and Azotobacter vinelandii offers promising sustainable prospects for enhancing PBAT plastic degradation and reducing nitrogen loss during composting.

Thermal and structural changes of a starch flexible film and cellulosic semi-rigid tray during the biodegradation process under controlled composting conditions

Biopolymers used to mitigate the environmental impact needed establish biodegradation percentage. The thermal and structural changes of two plastic materials, a flexible film based on cassava starch - Poly(lactic acid) (PLA) and a semi-rigid cassava flour-stay cellulose fique fiber, were evaluated biodegradation under ISO 4855-1 standard. The tests were carried out for four weeks at constant temperature and flow of 58 °C ± 2 °C and 250 mL/h, using a mature compost as inoculum. The percentages of CO2, thermal, morphological, and structural changes, variation of degradation temperatures, glass transition temperatures (Tg), Melting temperatures (Tm) and enthalpies of fusion (Hm), were properly evaluated as indicators of the materials biodegradation of two materials. Scanning electron microscopy (SEM), showed the microorganisms colonization on the materials surface, evidencing the appearance of cracks and microbial population. The flexible film showed a biodegradation percentage of 98.24 %, the semi-rigid tray 89.06 %, and the microcrystalline cellulose, 81.37 %.

Investigating the inhibitory mechanism of methanogenesis during composting under the combined influence of amoxicillin and copper pollution

This study investigated the effects of different levels of combined amoxicillin and copper (Cu) pollution on the methanogenesis of microbial communities during aerobic composting of dairy manure. Three groups were established: the control group (CK), a low-level combined pollution group (L), and a high-level combined pollution group (H). As the level of pollution increased, carbohydrate metabolism decreased during the thermophilic phase of composting, while signal translation increased. Compared with the initial phase, functional genes related to the acetoclastic pathway decreased significantly in abundance during the thermophilic phase, and cdh had the lowest relative abundance among acetoclastic pathway with a decrease of 81.52%, 81.88%, and 84.73% in groups CK, L, and H, respectively. The cumulative methane emissions in group H decreased by 31.56% and 9.23%, respectively, compared with those from groups CK and L. These results contribute to understanding the effects of combined amoxicillin and Cu pollution on methane emissions during composting.

Genome-Centric Metagenomics Insights into the Plastisphere-Driven Natural Degradation Characteristics and Mechanism of Biodegradable Plastics in Aquatic Environments

Biodegradable plastics (BPs) are pervasively available as alternatives to traditional plastics, but their natural degradation characteristics and microbial-driven degradation mechanisms are poorly understood, especially in aquatic environments, the primary sink of plastic debris. Herein, the three-month dynamic degradation process of BPs (the copolymer of poly(butylene adipate-co-terephthalate) and polylactic acid (PLA) (PBAT/PLA) and single PLA) in a natural aquatic environment was investigated, with nonbiodegradable plastics polyvinyl chloride, polypropylene, and polystyrene as controls. PBAT/PLA showed the weight loss of 47.4% at 50 days and severe fragmentation within two months, but no significant decay for other plastics. The significant increase in the specific surface area and roughness and the weakening of hydrophobicity within the first month promoted microbial attachment to the PBAT/PLA surface. Then, a complete microbial succession occurred, including biofilm formation, maturation, and dispersion. Metagenomic analysis indicated that plastispheres selectively enriched degraders. Based on the functional genes involved in BPs degradation, a total of 16 high-quality metagenome-assembled genomes of degraders (mainly Burkholderiaceae) were recovered from the PBAT/PLA plastisphere. These microbes showed the greatest degrading potential at the biofilm maturation stage and executed the functions by PLA_depolymerase, polyesterase, hydrolase, and esterase. These findings will enhance understanding of BPs' environmental behavior and microbial roles on plastic degradation.

Isolation of marine polyethylene (PE)-degrading bacteria and its potential degradation mechanisms

Microbial degradation of polyethylene (PE) offers a promising solution to plastic pollution in the marine environment, but research in this field is limited. In this study, we isolated a novel marine strain of Pseudalkalibacillus sp. MQ-1 that can degrade PE. Scanning electron microscopy and water contact angle results showed that MQ-1 could adhere to PE films and render them hydrophilic. Analyses using X-ray diffraction, fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy showed a decrease in relative crystallinity, the appearance of new functional groups and an increase in the oxygen-to‑carbon ratio of the PE films, making them more susceptible to degradation. The results of gel permeation chromatography and liquid chromatography-mass spectrometry indicated the depolymerization of the long PE chains, with the detection of an intermediate, decanediol. Furthermore, genome sequencing was employed to investigate the underlying mechanisms of PE degradation. The results of genome sequencing analysis identified the genes associated with PE degradation, including cytochrome P450, alcohol dehydrogenase, and aldehyde dehydrogenase involved in the oxidative reaction, monooxygenase related to ester bond formation, and esterase associated with ester bond cleavage. In addition, enzymes involved in fatty acid metabolism and intracellular transport have been identified, collectively providing insights into the metabolic pathway of PE degradation.

Aging properties of polyethylene and polylactic acid microplastics and their adsorption behavior of Cd(II) and Cr(VI) in aquatic environments

In this study, we examined the aging characteristics of polyethylene (PE) and polylactic acid (PLA) microplastics (MPs), examining the adsorption behaviors and mechanisms concerning Cd(II) and Cr(VI) under both single and binary systems. The results revealed that aging treatment changed the physicochemical properties of MPs. The aging mechanisms of PLA and PE MPs were shown to be similar by the 2D-FTIR-COS study. These mechanisms involve the formation of oxygen-containing functional groups through the combination of carbon chain breakdown and oxygen. Aged MPs had a greater ability to adsorb metal ions than pristine MPs, with PLA MPs outperforming PE MPs. After 30 days of aging, Cd(II) adsorption increased by 40.61 % and 25.49 % for PE and PLA MPs, respectively, while Cr(VI) adsorption increased by 37.50 % and 69.29 %, respectively. The adsorption ability of PE and PLA MPs with Cd(II) or Cr(VI) under binary systems was less than that under single systems, with Cd(II) exhibiting more adsorption competitiveness than Cr(VI). Humic acid (HA), ionic species and strength, solution pH, and adsorption of Cd(II) and Cr(VI) were found to be significantly correlated. Further investigation into the adsorption mechanisms of Cd(II) and Cr(VI) on PE and PLA MPs revealed that pore-filling, electrostatic interactions, complexation, and hydrogen bonding play important roles in the adsorption process. The study's conclusions are crucial for assessing the risk associated with concurrent contamination by metal ions and microplastics.

Towards Sustainable Orthodontics: Environmental Implications and Strategies for Clear Aligner Therapy

The increasing concern over environmental sustainability has prompted various industries to reassess their practices and explore greener alternatives. Dentistry, as a significant contributor to waste generation, is actively seeking methods to minimize its environmental footprint. This paper examines the environmental implications of clear aligner therapy (CAT) in orthodontics and explores strategies to prioritize sustainability in aligner manufacturing and usage. CAT has gained popularity as a viable alternative to traditional fixed appliances due to advancements in biomaterials and computer-aided design (CAD) and manufacturing (CAM) technologies. The global market for clear aligners is expanding rapidly, with significant growth projected in the coming years. To address these challenges, this paper proposes adopting the principles of reduce, reuse, recycle, and rethink (4Rs) in orthodontic practices. Strategies such as minimizing resource consumption, incorporating recycled materials, and promoting proper aligner disposal and recycling can significantly reduce environmental harm. This paper explores emerging technologies and materials to mitigate the environmental impacts of CAT. Additionally, initiatives promoting aligner recycling and repurposing offer promising avenues for reducing plastic waste and fostering a circular economy. In conclusion, while CAT offers numerous benefits in orthodontic treatment, its environmental impact cannot be overlooked. By implementing sustainable practices and embracing innovative solutions, the orthodontic community can contribute to a more environmentally conscious future while continuing to provide quality care to patients.

Eco-friendly approaches for mitigating plastic pollution: advancements and implications for a greener future

Plastic pollution has become a global problem since the extensive use of plastic in industries such as packaging, electronics, manufacturing and construction, healthcare, transportation, and others. This has resulted in an environmental burden that is continually growing, which has inspired many scientists as well as environmentalists to come up with creative solutions to deal with this problem. Numerous studies have been reviewed to determine practical, affordable, and environmentally friendly solutions to regulate plastic waste by leveraging microbes' innate abilities to naturally decompose polymers. Enzymatic breakdown of plastics has been proposed to serve this goal since the discovery of enzymes from microbial sources that truly interact with plastic in its naturalistic environment and because it is a much faster and more effective method than others. The scope of diverse microbes and associated enzymes in polymer breakdown is highlighted in the current review. The use of co-cultures or microbial consortium-based techniques for the improved breakdown of plastic products and the generation of high-value end products that may be utilized as prototypes of bioenergy sources is highlighted. The review also offers a thorough overview of the developments in the microbiological and enzymatic biological degradation of plastics, as well as several elements that impact this process for the survival of our planet.

Biodegradation of low-density polyethylene film by two bacteria isolated from plastic debris in coastal beach

Low-density polyethylene (LDPE) conduces massive environmental accumulation due to its high production and recalcitrance to environment. In this study, We successfully enriched and isolated two strains, Nitratireductor sp. Z-1 and Gordonia sp. Z-2, from coastal plastic debris capable of degrading LDPE film. After a 30-day incubation at 30 ℃, strains Z-1 and Z-2 decreased the weight of branched-LDPE (BLDPE) film by 2.59 % and 10.27 % respectively. Furthermore, high temperature gel permeation chromatography (HT-GPC) analysis revealed molecular weight reductions of 7.69 % (Z-1) and 23.22 % (Z-2) in the BLDPE film. Scanning electron microscope (SEM) image showed the presence of microbial colonization and perforations on the film's surface. Fourier transform infrared spectroscopy (FTIR) analysis indicated novel functional groups, such as carbonyl and carbon-carbon double bonds in LDPE films. During LDPE degradation, both strains produced extracellular reactive oxygen species (ROS). GC-MS analysis revealed the degradation products included short-chain alkanes, alkanols, fatty acids, and esters. Genomic analysis identified numerous extracellular enzymes potentially involved in LDPE chain scission. A model was proposed suggesting a coordinated role between ROS and extracellular enzymes in the biodegradation of LDPE. This indicates strains Z-1 and Z-2 can degrade LDPE, providing a basis for deeper exploration of biodegradation mechanisms.

Soil Microplastic Pollution and Microbial Breeding Techniques for Green Degradation: A Review

Microplastics (MPs), found in many places around the world, are thought to be more detrimental than other forms of plastics. At present, physical, chemical, and biological methods are being used to break down MPs. Compared with physical and chemical methods, biodegradation methods have been extensively studied by scholars because of their advantages of greenness and sustainability. There have been numerous reports in recent years summarizing the microorganisms capable of degrading MPs. However, there is a noticeable absence of a systematic summary on the technology for breeding strains that can degrade MPs. This paper summarizes the strain-breeding technology of MP-degrading strains for the first time in a systematic way, which provides a new idea for the breeding of efficient MP-degrading strains. Meanwhile, potential techniques for breeding bacteria that can degrade MPs are proposed, providing a new direction for selecting and breeding MP-degrading bacteria in the future. In addition, this paper reviews the sources and pollution status of soil MPs, discusses the current challenges related to the biodegradation of MPs, and emphasizes the safety of MP biodegradation.

Mature compost promotes biodegradable plastic degradation and reduces greenhouse gas emission during food waste composting

Mature compost can promote the transformation of organic matter (OM) and reduce the emission of polluting gases during composting, which provides a viable approach to reduce the environmental impacts of biodegradable plastics (BPs). This study investigated the impact of mature compost on polybutylene adipate terephthalate (PBAT) degradation, greenhouse gas (GHG) emission, and microbial community structure during composting under two treatments with mature compost (MC) and without (CK). Under MC, visible plastic rupture was advanced from day 14 to day 10, and a more pronounced rupture was observed at the end of composting. Compared with CK, the degradation rate of PBAT in MC was increased by 4.44 % during 21 days of composting. Thermobifida, Ureibacillus, and Bacillus, as indicator species under MC treatment, played an important role in PBAT decomposition. Mature compost reduced the total global warming potential (GWP) by 25.91 % via inhibiting the activity of bacteria related to the production of CH4 and N2O. Functional Annotation of Prokaryotic Taxa (FAPROTAX) further revealed that mature compost addition increased relative abundance of bacteria related to multiple carbon (C) cycle functions such as methylotrophy, hydrocarbon degradation and cellulolysis, inhibited nitrite denitrification and denitrification, thus alleviating the emission of GHGs. Overall, mature compost, as an effective additive, exhibits great potential to simultaneously mitigate BP and GHG secondary pollution in co-composting of food waste and PBAT.

Fabrication of Vascular Grafts Using Poly(ε-Caprolactone) and Collagen-Encapsuled ADSCs for Interposition Implantation of Abdominal Aorta in Rhesus Monkeys

The production of small-diameter artificial vascular grafts continues to encounter numerous challenges, with concerns regarding the degradation rate and endothelialization being particularly critical. In this study, porous PCL scaffolds were prepared, and PCL vascular grafts were fabricated by 3D bioprinting of collagen materials containing adipose-derived mesenchymal stem cells (ADSCs) on the internal wall of the porous PCL scaffold. The PCL vascular grafts were then implanted in the abdominal aorta of Rhesus monkeys for up to 640 days to analyze the degradation of the scaffolds and regeneration of the aorta. Changes in surface morphology, mechanical properties, crystallization property, and molecular weight of porous PCL revealed a similar degradation process of PCL in PBS at pH 7.4 containing Thermomyces lanuginosus lipase and in situ in the abdominal aorta of rhesus monkeys. The contrast of in vitro and in vivo degradation provided valuable reference data for predicting in vivo degradation based on in vitro enzymatic degradation of PCL for further optimization of PCL vascular graft fabrication. Histological analysis through hematoxylin and eosin (HE) staining and fluorescence immunostaining demonstrated that the PCL vascular grafts successfully induced vascular regeneration in the abdominal aorta over the 640-day period. These findings provided valuable insights into the regeneration processes of the implanted vascular grafts. Overall, this study highlights the significant potential of PCL vascular grafts for the regeneration of small-diameter blood vessels.

Effects of polyethylene microplastics occurrence on estrogens degradation in soil

Growing focus has been drawn to the continuous detection of high estrogens levels in the soil environment. Additionally, microplastics (MPs) are also of growing concern worldwide, which may affect the environmental behavior of estrogens. However, little is known about effects of MPs occurrence on estrogens degradation in soil. In this study, polyethylene microplastics (PE-MPs) were chosen to examine the influence on six common estrogens (estrone (E1), 17α-estradiol (17α-E2), 17β-estradiol (17β-E2), estriol (E3), diethylstilbestrol (DES), and 17α-ethinylestradiol (17α-EE2)) degradation. The results indicated that PE-MPs had little effect on the degradation of E3 and DES, and slightly affected the degradation of 17α-E2, however, significantly inhibited the degradation of E1, 17α-EE2, and 17β-E2. It was explained that (i) obvious oxidation reaction occurred on the surface of PE-MPs, indicating that PE-MPs might compete with estrogens for oxidation sites, such as redox and biological oxidation; (ii) PE-MPs significantly changed the bacterial community in soil, resulting in a decline in the abundance of some bacterial communities that biodegraded estrogens. Moreover, the rough surface of PE-MPs facilitated the estrogen-degrading bacterial species (especially for E1, E2, and EE2) to adhere, which decreased their reaction to estrogens. These findings are expected to deepen the understanding of the environmental behavior of typical estrogens in the coexisting system of MPs.

Microplastics release from face masks: Characteristics, influential factors, and potential risks

Since the COVID-19 pandemic, face masks have been used popularly and disposed of improperly, leading to the generation of a large amount of microplastics. The objective of this review is to provide a comprehensive insight into the characteristics of mask-derived microplastics, the influential factors of microplastics release, and the potential risks of these microplastics to the environment and organisms. Mask-derived microplastics were predominantly transparent fibers, with a length of <1 mm. The release of microplastics from masks is mainly influenced by mask types, use habits, and weathering conditions. Under the same conditions, surgical masks release more microplastics than other types of masks. Long-term wearing of masks and the disinfection for reuse can promote the release of microplastics. Environmental media, UV irradiation, temperature, pH value, and mechanical shear can also influence the microplastics release. The risks of mask-derived microplastics to human health via inhalation cannot be neglected. Future studies should pay more attention to the release of microplastics from the masks with alternative materials and under more weathering conditions.

Exploring the substrate spectrum of phylogenetically distinct bacterial polyesterases

The rapid escalation of plastic waste accumulation presents a significant threat of the modern world, demanding an immediate solution. Over the last years, utilization of the enzymatic machinery of various microorganisms has emerged as an environmentally friendly asset in tackling this pressing global challenge. Thus, various hydrolases have been demonstrated to effectively degrade polyesters. Plastic waste streams often consist of a variety of different polyesters, as impurities, mainly due to wrong disposal practices, rendering recycling process challenging. The elucidation of the selective degradation of polyesters by hydrolases could offer a proper solution to this problem, enhancing the recyclability performance. Towards this, our study focused on the investigation of four bacterial polyesterases, including DaPUase, IsPETase, PfPHOase, and Se1JFR, a novel PETase-like lipase. The enzymes, which were biochemically characterized and structurally analyzed, demonstrated degradation ability of synthetic plastics. While a consistent pattern of polyesters' degradation was observed across all enzymes, Se1JFR stood out in the degradation of PBS, PLA, and polyether PU. Additionally, it exhibited comparable results to IsPETase, a benchmark mesophilic PETase, in the degradation of PCL and semi-crystalline PET. Our results point out the wide substrate spectrum of bacterial hydrolases and underscore the significant potential of PETase-like enzymes in polyesters degradation.

Commercialization potential of PET (polyethylene terephthalate) recycled nanomaterials: A review on validation parameters

Polyethylene Terephthalate (PET) is a polymer which is considered as one of the major contaminants to the environment. The PET waste materials can be recycled to produce value-added products. PET can be converted to nanoparticles, nanofibers, nanocomposites, and nano coatings. To extend the applications of PET nanomaterials, understanding its commercialization potential is important. In addition, knowledge about the factors affecting recycling of PET based nanomaterials is essential. The presented review is focused on understanding the PET commercialization aspects, keeping in mind market analysis, growth drivers, regulatory affairs, safety considerations, issues associated with scale-up, manufacturing challenges, economic viability, and cost-effectiveness. In addition, the paper elaborates the challenges associated with the use of PET based nanomaterials. These challenges include PET contamination to water, soil, sediments, and human exposure to PET nanomaterials. Moreover, the paper discusses in detail about the factors affecting PET recycling, commercialization, and circular economy with specific emphasis on life cycle assessment (LCA) of PET recycled nanomaterials.

Visualization of isothermal crystallization and phase separation in poly[(R)-3-hydroxybutyrate]/poly(L-lactic acid) by low-frequency Raman imaging

The visualization of the variation of the inter/intra molecular interaction (C = O⋯CH3) between poly[(R)-3-hydroxybutyrate] (PHB) and poly-L-lactic acid (PLLA) in the PHB/PLLA miscible blend during phase separation and crystallization process was successfully investigated using Raman imaging. Images of the blend were developed using high- and low-frequency Raman spectra acquired during the isothermal crystallization of the blend, and both of them were compared. The low-frequency region allowed to observe the changes in the hydrogen bonds between the molecular chains in the blend during phase separation and crystallization via a band at 75 cm-1 derived from PHB. The imaging results obtained using the band at 75 cm-1 due to hydrogen bonding (C = O⋯CH3) between molecular chains were in good agreement with the results obtained using the C = O stretching band at 1720 cm-1. Herein, we demonstrated that the low-frequency region of the Raman spectrum is more sensitive to detecting the start of the phase separation and crystallization of PHB than the corresponding high-frequency region.

A review of microalgae biofilm as an eco-friendly approach to bioplastics, promoting environmental sustainability

In this comprehensive review, we delve into the challenges hindering the large-scale production of microalgae-based bioplastics, primarily focusing on economic feasibility and bioplastic quality. To address these issues, we explore the potential of microalgae biofilm cultivation as a sustainable and highly viable approach for bioplastic production. We present a proposed method for producing bioplastics using microalgae biofilm and evaluate its environmental impact using various tools such as life cycle analysis (LCA), ecological footprint analysis, resource flow analysis, and resource accounting. While pilot-scale and large-scale LCA data are limited, we utilize alternative indicators such as energy efficiency, carbon footprint, materials management, and community acceptance to predict the environmental implications of commercializing microalgae biofilm-based bioplastics. The findings of this study indicate that utilizing microalgae biofilm for bioplastic production offers significant environmental sustainability benefits. The system exhibits low energy requirements and a minimal carbon footprint. Moreover, it has the potential to address the issue of wastewater by utilizing it as a carbon source, thereby mitigating associated problems. However, it is important to acknowledge certain limitations associated with the method proposed in this review. Further research is needed to explore and engineer precise techniques for manipulating microalgae biofilm structure to optimize the accumulation of desired metabolites. This could involve employing chemical triggers, metabolic engineering, and genetic engineering to achieve the intended goals. In conclusion, this review highlights the potential of microalgae biofilm as a viable and sustainable solution for bioplastic production. While acknowledging the advantages, it also emphasizes the need for continued synthetic studies to enhance the efficiency and reliability of this approach. By addressing the identified drawbacks and maximizing the utilization of advanced techniques, we can further harness the potential of microalgae biofilm in contributing to a more environmentally friendly and economically feasible bioplastic industry.

Recent developments in bio-based polyethylene: Degradation studies, waste management and recycling

Nowadays, the tendency to replace conventional fossil-based plastics is increasing considerably; there is a growing trend towards alternatives that involve the development of plastic materials derived from renewable sources, which are compostable and biodegradable. Indeed, only 1.5 % of whole plastic production is part of the small bioplastics market, even when these materials with a partial or full composition from biomass are rapidly expanding. A very interesting field of investigation is currently being developed in which the disposal and processing of the final products are evaluated in terms of reducing environmental harm. This review presents a compilation of polyethylene (PE) types, their uses, and current problems in the waste management of PE and recycling. Particularly, this review is based on the capabilities to synthesize bio-based PE from natural and renewable sources as a replacement for the raw material derived from petroleum. In addition to recent studies in degradation on different types of PE with weight loss ranges from 1 to 47 %, the techniques used and the main changes observed after degradation. Finally, perspectives are presented in the manuscript about renewable and non-renewable polymers, depending on the non-degradable, biodegradable, and compostable behavior, including composting recent studies in PE. In addition, it contributes to the 3R approaches to responsible waste management of PE and advancement towards an environmentally friendly PE.

A Review of Biodegradable Plastics: Chemistry, Applications, Properties, and Future Research Needs

Environmental concerns over waste plastics' effect on the environment are leading to the creation of biodegradable plastics. Biodegradable plastics may serve as a promising approach to manage the issue of environmental accumulation of plastic waste in the ocean and soil. Biodegradable plastics are the type of polymers that can be degraded by microorganisms into small molecules (e.g., H2O, CO2, and CH4). However, there are misconceptions surrounding biodegradable plastics. For example, the term "biodegradable" on product labeling can be misconstrued by the public to imply that the product will degrade under any environmental conditions. Such misleading information leads to consumer encouragement of excessive consumption of certain goods and increased littering of products labeled as "biodegradable". This review not only provides a comprehensive overview of the state-of-the-art biodegradable plastics but also clarifies the definitions and various terms associated with biodegradable plastics, including oxo-degradable plastics, enzyme-mediated plastics, and biodegradation agents. Analytical techniques and standard test methods to evaluate the biodegradability of polymeric materials in alignment with international standards are summarized. The review summarizes the properties and industrial applications of previously developed biodegradable plastics and then discusses how biomass-derived monomers can create new types of biodegradable polymers by utilizing their unique chemical properties from oxygen-containing functional groups. The terminology and methodologies covered in the paper provide a perspective on directions for the design of new biodegradable polymers that possess not only advanced performance for practical applications but also environmental benefits.

Discovery of a polyesterase from Deinococcus maricopensis and comparison to the benchmark LCCICCG suggests high potential for semi-crystalline post-consumer PET degradation

Plastic pollution remains a significant environmental challenge, with conventional waste management strategies proving insufficient in addressing the problem. Enzymatic degradation has emerged as a promising alternative, with LCCICCG, an engineered metagenome-derived cutinase, being the most effective in degrading polyethylene terephthalate (PET), the most commonly produced and discarded polyester. However, more efficient PET-hydrolases are needed for the upscaling of a PET-waste biorefinery. In this regard, the study reports the characterization of a novel, phylogenetically distinct, thermophilic polyesterase from Deinococcus maricopensis (DmPETase) and its comparison to LCCICCG. DmPETase is capable of degrading various synthetic polymers, including PET, polyurethane, as well as four semi-crystalline aliphatic polyesters. DmPETase was found to be comparable to LCCICCG at 50 °C in degrading semi-crystalline sections of post-consumer PET bottles, but it appeared to be less sensitive to crystallinity degree increase. This property makes DmPETase a new template for protein engineering endeavors to create an efficient biocatalyst to be integrated into the bio-recycling process of PET waste, without the need for amorphization of the materials.

A critical review and future perspective of plastic waste recycling

Plastic waste is increasing rapidly due to urbanisation and globalization. In recent decades, plastic usage increased, and the upward trend is expected to continue. Only 9% of the 7 billion tonnes of plastic produced were recycled in India until 2022. India generates 1.5 million tonnes of plastic waste (PW) every year and ranks among top ten plastic producer countries. Large amount of waste plastics could harm environment and human health. The current manuscript provides a comprehensive approach for mechanical and chemical recycling methods. The technical facets of mechanical recycling relating to collection, sorting, grading, and general management to create plastic products with additional value have been elaborated in this study. Another sustainable methods aligned with the chemical recycling using pyrolysis, gasification, hydrocracking, IH2 (Integrated Hydropyrolysis 2), and KDV (Katalytische Drucklose Verolung) techniques have also been highlighted with the critical process parameters for the sustainable conversion of plastic waste to valuable products. The review also adheres to less carbon-intensive plastic degrading strategies that take a biomimetic approach using the microorganism based biodegradation. The informative aspects covering the limitations and effectiveness of all PW technologies and its applications towards plastic waste management (PWM) are also emphasized. The existing practices in PW policy guidelines along with its economic and ecological aspects have also been discussed.

Effect of the Presence of Lignin from Woodflour on the Compostability of PHA-Based Biocomposites: Disintegration, Biodegradation and Microbial Dynamics

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) has gained attention as a possible substitute for conventional polymers that could be integrated into the organic recycling system. Biocomposites with 15% of pure cellulose (TC) and woodflour (WF) were prepared to analyze the role of lignin on their compostability (58 °C) by tracking the mass loss, CO₂ evolution, and the microbial population. Realistic dimensions for typical plastic products (400 µm films), as well as their service performance (thermal stability, rheology), were taken into account in this hybrid study. WF showed lower adhesion with the polymer than TC and favored PHBV thermal degradation during processing, also affecting its rheological behavior. Although all materials disintegrated in 45 days and mineralized in less than 60 days, lignin from woodflour was found to slow down the bioassimilation of PHBV/WF by limiting the access of enzymes and water to easier degradable cellulose and polymer matrix. According to the highest and the lowest weight loss rates, TC incorporation allowed for higher mesophilic bacterial and fungal counts, while WF seemed to hinder fungal growth. At the initial steps, fungi and yeasts seem to be key factors in facilitating the later metabolization of the materials by bacteria.

Structural Rearrangements of Polylactide/Natural Rubber Composites during Hydro- and Biotic Degradation

In the work, the impact of the biological medium and water on structural rearrangements in pure polylactide and polylactide/natural rubber film composites was studied. Polylactide/natural rubber films with a rubber content of 5, 10, and 15 wt.% were obtained by the solution method. Biotic degradation was carried out according to the Sturm method at a temperature of 22 ± 2 °C. Hydrolytic degradation was studied at the same temperature in distilled water. The structural characteristics were controlled by thermophysical, optical, spectral, and diffraction methods. Optical microscopy revealed the surface erosion of all samples after exposure to microbiota and water. Differential scanning calorimetry showed a decrease in the degree of crystallinity of polylactide by 2-4% after the Sturm test, and a tendency to an increase in the degree of crystallinity after the action of water was noted. Changes in the chemical structure were shown in the spectra recorded by infrared spectroscopy. Due to degradation, significant changes in the intensities of the bands in the regions of 3500-2900 and 1700-1500 cm^-1 were shown. The X-ray diffraction method established differences in diffraction patterns in very defective and less damaged regions of polylactide composites. It was determined that pure polylactide hydrolyzed more readily under the action of distilled water than polylactide/natural rubber composites. Film composites were more rapidly subjected to biotic degradation. The degree of biodegradation of polylactide/natural rubber composites increased with the rise in the content of natural rubber in the compositions.

Influence of Pomelo (Citrus maxima) Pericarp Essential Oil on the Physicochemical Properties of HomChaiya Rice (Oryza sativa L. cv. HomChaiya) Flour-Derived Edible Films

The food industry is increasingly interested in using active edible packaging to address environmental problems caused by conventional synthetic polymers, such as pollution and degradation. The present study took advantage of this opportunity to develop active edible packaging using Hom-Chaiya rice flour (RF), incorporating pomelo pericarp essential oil (PEO) at varying concentrations (1-3%). Films without PEO were used as controls. Various physicochemical parameters, structural and morphological observations were examined in the tested films. Overall, the results showed that the addition of PEO at varying concentrations significantly improved the qualities of the RF edible films, particularly the film's yellowness (b*) and total color. Furthermore, RF-PEO films with increased concentrations significantly reduced the film's roughness and relative crystallinity, while increasing opacity. The total moisture content in the films did not differ, but water activity was significantly reduced in the RF-PEO films. Water vapor barrier properties also improved in the RF-PEO films. In addition, textural properties, including tensile strength and elongation at break, were better in the RF-PEO films compared with the control. Fourier-transform infrared spectroscopy (FTIR) revealed strong bonding between the PEO and RF in the film. Morphological studies showed that the addition of PEO smoothed the film's surface, and this effect increased with concentration. Overall, the biodegradability of the tested films was effective, despite variations; however, a slight advancement in degradation was found in the control film. Lastly, the antimicrobial properties of the RF-PEO films exhibited excellent inhibitory effects against various pathogens, including Staphylococcus aureus (S. aureus), Listeria monocytogenes (L. monocytogenes), Escherichia coli (E. coli), and Salmonella typhimurium (S. typhimurium). This study demonstrated that RF and PEO could be an effective combination for developing active edible packaging that delivers desirable functional properties and excellent biodegradability.

Water evaporation induced in-situ interfacial compatibilization for all-natural and high-strength straw-fiber/starch composites

In this paper, we proposed a novel and green strategy based on water evaporation induced in-situ interfacial compatibilization (WEIC) mechanism for fabricating high-strength and all-natural lignocellulose/starch composites. This mechanism exploits the natural compatibility of the lignocellulose and starch and was tested through an internal mixing process with regulated water evaporation. Specifically, we revealed that a restrained layer was in-situ formed at the interface of the lignocellulose and starch during the internal mixing process; a faster water evaporation rate thickens this restrained layer, restricts the starch's molecular movement and significantly increases the composite's mechanical properties. The highest tensile strength and Young's modulus of the composites achieved are 21.7 ± 0.8 MPa and 2.2 ± 0.1 GPa, respectively, superior to many existing starch/lignocellulose composites. Thus, this work provides new insight into the compatibilization of various hydrophilic polysaccharides and paves new avenues for developing greener and more facile methods to fabricate all-polysaccharide composites.

Anaerobic Biodegradability of Commercial Bioplastic Products: Systematic Bibliographic Analysis and Critical Assessment of the Latest Advances

Bioplastics have entered everyday life as a potential sustainable substitute for commodity plastics. However, still further progress should be made to clarify their degradation behavior under controlled and uncontrolled conditions. The wide array of biopolymers and commercial blends available make predicting the biodegradation degree and kinetics quite a complex issue that requires specific knowledge of the multiple factors affecting the degradation process. This paper summarizes the main scientific literature on anaerobic digestion of biodegradable plastics through a general bibliographic analysis and a more detailed discussion of specific results from relevant experimental studies. The critical analysis of literature data initially included 275 scientific references, which were then screened for duplication/pertinence/relevance. The screened references were analyzed to derive some general features of the research profile, trends, and evolution in the field of anaerobic biodegradation of bioplastics. The second stage of the analysis involved extracting detailed results about bioplastic degradability under anaerobic conditions by screening analytical and performance data on biodegradation performance for different types of bioplastic products and different anaerobic biodegradation conditions, with a particular emphasis on the most recent data. A critical overview of existing biopolymers is presented, along with their properties and degradation mechanisms and the operating parameters influencing/enhancing the degradation process under anaerobic conditions.

Effect of porosity on mechanical and biological properties of bioprinted scaffolds

Treatment of tissue defects commonly represents a major problem in clinics due to difficulties involving a shortage of donors, inappropriate sizes, abnormal shapes, and immunological rejection. While many scaffold parameters such as pore shape, porosity percentage, and pore connectivity could be adjusted to achieve desired mechanical and biological properties. These parameters are crucial scaffold parameters that can be accurately produced by 3D bioprinting technology based on the damaged tissue. In the present research, the effect of porosity percentage (40%, 50%, and 60%) and different pore shapes (square, star, and gyroid) on the mechanical (e.g., stiffness, compressive and tensile behavior) and biological (e.g., biodegradation, and cell viability) properties of porous polycaprolactone (PCL) scaffolds coated with gelatin have been investigated. Moreover, human foreskin fibroblast cells were cultured on the scaffolds in the in-vitro procedures. MTT assay (4, 7, and 14 days) was utilized to determine the cytotoxicity of the porous scaffolds. It is revealed that the porous scaffolds produced by the bioprinter did not produce a cytotoxic effect. Among all the porous scaffolds, scaffolds with a pore size of about 500 μm and porosity of 50% showed the best cell proliferation compared to the controls after 14 days. The results demonstrated that the pore shape, porosity percentage, and pore connectivity have an important role in improving the mechanical and biological properties of porous scaffolds. These 3D bioprinted biodegradable scaffolds exhibit potential for future application as polymeric scaffolds in hard tissue engineering applications.

Microplastics in sewage sludge: Distribution, toxicity, identification methods, and engineered technologies

Microplastic pollution is becoming a global challenge due to its long-term accumulation in the environment, causing adverse effects on human health and the ecosystem. Sludge discharged from wastewater treatment plants (WWTPs) plays a critical role as a carrier and primary source of environmental microplastic contamination. A significantly average microplastic variation between 1000 and 301,400 particles kg^-1 has been reported in the sludge samples. In recent years, advanced technologies have been successfully applied to address this issue, including adsorption, advanced oxidation processes (AOPs), and membrane bioreactors (MBRs). Adsorption technologies are essential to utilizing novel adsorbents (e.g., biochar, graphene, zeolites) for effectively removing MPs. Especially, the removal efficiency of polymer microspheres from an aqueous solution by Mg/Zn modified magnetic biochars (Mg/Zn-MBC) was obtained at more than 95%. Also, advanced oxidation processes (AOPs) are widely applied to degrade microplastic contaminants, in which photocatalytic by semiconductors (e.g., TiO₂ and ZnO) is a highly suitable approach to promote the degradation reactions owing to strongly hydroxyl radicals (OH*). Biological degradation-aided microorganisms (e.g., bacterial and fungal strains) have been reported to be suitable for removing microplastics. Yet, it was affected by biotic and abiotic factors of the environmental conditions (e.g., pH, light, temperature, moisture, bio-surfactants, microorganisms, enzymes) as well as their polymer characteristics, i.e., molecular weight, functional groups, and crystallinity. Notably, membrane bioreactors (MBRs) showed the highest efficiency in removing up to 99% microplastic particles and minimizing their contamination in sewage sludge. Further, MBRs illustrate the suitability for treating high-strength compounds, e.g., polymer debris and microplastic fibers from complex industrial wastewater. Finally, this study provided a comprehensive understanding of potential adverse risks, transportation pathways, and removal mechanisms of microplastic, which full-filled the knowledge gaps in this field.

End-of-life biodegradation? how to assess the composting of polyesters in the lab and the field

The aerobic composting of biodegradable plastics can be a promising solution to the growing issue of waste accumulation. Therefore, this article offers a review of papers investigating the biodegradability of polyesters (PLA, PHB, PBS and PCL) in home- and industrial composting. Not only the thermal and biodegradation properties are discussed, but also a comparison is made between the different polyesters under the same composting conditions. From this review, it becomes clear that composting shows promise for polyester waste management. However, although several methods for assessing the composting properties of polyester have been developed, the fact that they rarely follow the same standards does not allow for a comparative analysis that would clearly define composting as the most viable solution.

Insight into the microplastics release from disposable face mask: Simulated environment and removal strategy

The fight against the COVID-19 epidemic significantly raises the global demand for personal protective equipment, especially disposable face masks (DFMs). The discarded DFMs may become a potential source of microplastics (MPs), which has attracted much attention. In this work, we identified the detailed source of MPs released from DFMs with laser direct infrared spectroscopy. Polypropylene (PP) and polyurethane (PU) accounted for 24.5% and 57.1% of released MPs, respectively. The melt-blown fabric was a dominant MPs source, however, previous studies underestimated the contribution of mask rope. The captured polyethylene terephthalate (PET), polyamide (PA), polyethylene (PE), and polystyrene (PS) in airborne only shared 18.4% of released MPs. To deepen the understanding of MPs release from medical mask into the aquatic environment, we investigated the effects of environmental factors on MPs release. Based on regression analysis, the effects of temperature, incubation time, and wearing time significantly affect the release of MPs. Besides, acidity, alkalinity, sodium chloride, and humic acid also contributed to the MPs release through corroding, swelling, or repulsion of fibers. Based on the exposure of medical mask to simulated environments, the number of released MPs followed the order: seawater > simulated gut-fluid > freshwater > pure water. Considering the risk of MPs released from DFMs to the environment, we innovatively established a novel flotation removal system combined with cocoamidopropyl betaine, achieving 86% removal efficiency of MPs in water. This work shed the light on the MPs release from DFMs and proposed a removal strategy for the control of MPs pollution.

Synthesis, Characterization, and Soil Burial Degradation of Biobased Polyurethanes

There is an urgent need for developing degradable polymeric systems based on bio-derived and sustainable materials. In recent years, polyurethanes derived from castor oil have emerged due to the large availability and sustainable characteristics of castor oil. However, these polymers are normally prepared through tedious and/or energy-intensive procedures or using high volatile and/or toxic reagents such as volatile isocyanates or epoxides. Furthermore, poor investigation has been carried out to design castor oil derived polyurethanes with degradable characteristics or thorough specifically sustainable synthetic procedures. Herein, castor oil-derived polyurethane with more than 90% biomass-derived carbon content and enhanced degradable features was prepared through a simple, eco-friendly (E-factor: 0.2), and scalable procedure, employing a recently developed commercially available biomass-derived (61% bio-based carbon content) low-volatile polymeric isocyanate. The novel material was compared with a castor oil derived-polyurethane prepared with a commercially available fossil-based isocyanate counterpart. The different castor oil-derived polyurethanes were investigated by means of water uptake, soil burial degradation, and disintegration tests in compost. Characterization analyses, including thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and scanning electron microscopy (SEM), were carried out both prior to and after degradation tests. The results suggest potential applications of the degradable castor oil-derived polyurethane in different fields, such as mulch films for agricultural purposes.

Polystyrene microplastics induce apoptosis and necroptosis in swine testis cells via ROS/MAPK/HIF1α pathway

Microplastics (MPs) generally refer to the plastic fragments or particles smaller than 5 mm in diameter, which are closely concerned due to their widespread presence in the environment. Recent studies have shown that MPs have a serious threat on the reproductive health of organisms. Pigs are often selected as the model animals because of their high similarity to human tissues and organs. However, there are no reports on the effects and mechanisms of MPs exposure on swine germ cells. In the present study, we established swine testis (ST) cell models exposed to 250, 500, and 1000 μg/ml polystyrene microplastics (PS-MPs, 1-10 μm), respectively. The findings revealed that PS-MPs reduced cell viability dose-dependently. Acridine orange/ethidium bromide staining and flow cytometry results indicated the occurrence of apoptosis and necrosis in ST cells under PS-MPs exposure, and the expression changes of relevant marker genes (B-cell lymphoma-2, Bcl-2 Associated X, Caspase-3, Caspase-9, Receptor-interacting protein kinase 1, Receptor-interacting protein kinase 3, Mixed lineage kinase domain-like, and Caspase-8) were clarified via quantitative real-time PCR and western blot. Further mechanistic studies found that PS-MPs treatment induced excessive intracellular reactive oxygen species (ROS) production, which promoted the phosphorylation of mitogen-activated protein kinase (MAPK) pathway-related genes (P38, c-Jun N-terminal kinase, extracellular regulated protein kinases) and activated the downstream gene hypoxia-inducible factor (HIF1α). In conclusion, our study suggests that PS-MPs treatment causes apoptosis and necroptosis in ST cells via ROS/MAPK/HIF1α signaling pathway.

Polyhydroxybutyrate Rice Hull and Torrefied Rice Hull Biocomposites

Raw and torrefied rice hulls (RRH and TRH) were incorporated into polyhydroxybutyrate (PHB) as fillers using extrusion and injection molding to produce biomass-polymer composites. Filler and composite materials were characterized by particle size analysis, thermomechanical analysis, thermogravimetric analysis, differential scanning calorimetry, FTIR analysis, CHNSO analysis, and mechanical testing. Heat distortion temperature of the RRH composites were 16–22 °C higher than TRH composites. The RRH composite samples showed a 50–60% increase in flexural modulus and 5% increase in stress at yield compared to PHB, while TRH composite samples showed nearly equal flexural modulus and a 24% decrease in stress at yield. The improved mechanical properties of the RRH composites in comparison to TRH composites were due to better particle-matrix adhesion. FTIR analysis showed RRH particles contained more surface functional groups containing oxygen than TRH particles, indicating that RRHs should be more compatible with the polar PHB plastic. SEM images showed space between filler and plastic in TRH composites and better wetted filler particles in the RRH composites.

Screening confinement of entanglements: Role of a self-propelling end inducing ballistic chain reptation

Synthetic and natural nanomaterials with self-propelling mechanisms continue to be explored to boost chain mobility beyond normal reptation in the crowded environments of entangled chains. Here we employ scaling theory and numerical simulations to demonstrate that activating one chain end of a singular or isolated chain boosts entanglement-constrained chain reptation from the one-dimensional diffusive mobility as described by the de Gennes-Edwards-Doi model to ballistic motion along the entanglement tube contour. The active chain is effectively screened from the constraint of entanglements on length scales exceeding the tube size.