Biodegradation of renewable polyurethane foams in marine environments occurs through depolymerization by marine microorganisms

Microplastics in the marine environment: Challenges and the shift towards sustainable plastics and plasticizers

The United Nations (UN) estimate that around 75-199 million tons of plastic is floating in the world's oceans today. Continuous unintentional disposal of plastic waste in marine environments has and continues to cause significant biological impacts to various marine organisms ranging from mild difficulties in swimming or superficial damage to critical organ malfunctions and mortality. Over time, plastics in these environments degrade into microplastics which are now acknowledged as a pervasive harmful pollutant found in the cryosphere, atmosphere and hydrosphere. In response to this issue, the production of bespoke biodegradable bioplastics derived from renewable resources, such as vegetable oils, starch and plant fibres, is emerging to mitigate our reliance on environmentally persistent conventional fossil fuel-based plastics. While bioplastics degrade more readily than conventional plastics, they present new challenges, including leaching of toxic chemical additives and plasticizers into the environment. Consequently, various techniques have been explored in the search for sustainable plasticizers, from cheap, non-toxic compounds, such as vegetable oils and sugars to hyperbranched structures with limited migration. This article seeks to explain the intricate relationship between the problem of microplastics in marine environments and the strategies that have been investigated to address it thus far.

Marine fungi degrade plastic and can be conditioned to do it faster

Plastics are a prevalent and persistent pollutant in the environment. As plastic production increases, finding ways to degrade these recalcitrant polymers is paramount. Many terrestrial fungi, across the kingdom, degrade various types of plastic. Plastics are the fastest-growing habitat in the oceans, and we hypothesized that fungi isolated from the ocean would demonstrate high success rates in degrading polyurethane (PU). To test this, visual degradation assays were performed by inoculating 1% PU medium with 68 different fungal strains cultured from marine habitats. The area of clearance of the fungus was measured periodically, to determine a relative degradation rate. Of the 68 fungal strains, 42 demonstrated the ability to degrade PU. We conditioned the nine fastest PU degraders through serial inoculations into liquid media with increasing concentrations of PU, starting at 1% and going up to 12%. The growth rates of the original and conditioned fungi were then compared in new inoculation trials, and results show that three of the nine conditioned fungi demonstrate higher PU degradation rates than their unconditioned counterparts. Marine fungi, coupled with conditioning, show promise for developing novel mycoremediation technologies.

Aging of plastics and microplastics in the environment: a review on influencing factors, quantification methods, challenges, and future perspectives

The ubiquitous presence of fragmented plastic particles needs comprehensive understanding of its fate in the environment. The long-term persistence of microplastics (MPs) in the environment is a significant threat to the ecosystem. Even though various degradation mechanisms (physical, chemical, and biological) of commonly used plastics have been demonstrated, quantifying the degradation of MPs over time to predict the consequence of plastic littering and its persistence in the environment remains a challenge. Different advanced analytical techniques have been used to quantify the degradation of MPs by introducing various parameters such as bond indices, crystallinity, and carbon-oxygen ratio. However, a simple and widely accepted reliable methodology for comparing the environmental factors and their influence on the MP degradation has yet to be developed and validated. This paper reviews a section of relevant literature (n = 38) to synthesize an overview of methods implemented for the quantification of fragmentation and aging of MPs in natural and artificial environment. In addition, the inherent weakness and extrinsic factors affecting the degradation of MPs in the environment is discussed. Finally, it proposes challenges and future scope as guideline for research on MP degradation in the environment.

The threat of microplastics and microbial degradation potential; a current perspective

Microplastics in marine environments come from various sources, and over the years, their buildup in marine environments suggests an inevitable need for the safe mitigation of plastic pollution. Microplastics are one of the chief and hazardous components of marine pollution, as they are transferred through the food chain to different trophic levels, affecting living organisms. They are also a source of transfer for pathogenic organisms. Upon transfer to humans, several toxic effects can occur. This review aims to assess the accumulation of microplastics in marine environments globally, the threat posed to humans, and the biodegradation potential of bacteria and fungi for future mitigation strategies. The versatility of bacteria and fungi in the biodegradation of different types of plastics has been discussed, with a focus on the microbial majority that has been cultivated in labs from the marine environment. We also propose that the exploration of yet-to-be-cultivated microbial majority can be a way forward for employing future strategies to mitigate microplastics.

Recognizing microplastic deposits on sandy beaches by altimetric positioning, μ-Raman spectroscopy and multivariate statistical models

Understanding the extent and implications of microplastic (MP) pollution along the São Paulo State coastline in southeastern Brazil is crucial, considering the significant environmental burden imposed by industrial and port activities in this region. This research aims to understand the complex dynamics of MP deposition on sandy beaches, which poses severe environmental risks to coastal ecosystems, marine organisms, and humans. Using a comprehensive five-step methodology-geodetic surveys, sediment collection, μ-RAMAN spectrometry for polymer identification, and multivariate statistical models-we analyzed the distribution of MPs across six coastal compartments (C1 to C6). The results (128 samples from 34 profiles) revealed relatively high MP concentrations in C3 and C2, which were likely influenced by local human activities. Various shape types of MPs, such as pellets, fragments, and fibers, present distinct distribution patterns based on their physical properties and emission sources. Fragments and foam were the most prevalent, accounting for 42 % and 35 %, respectively, of the 1026 MP items identified in total. Statistical analyses revealed significant correlations between MP types and beach morphometric features, with higher elevations correlating with increased MP concentrations, particularly for pellets and foam. Beaches with intermediate slopes (0.05 < tanβ <0.12) and openings to the southern quadrant tended to accumulate more MPs. This research underscores the importance of tailored management strategies that consider the unique characteristics of each coastal region to mitigate the impacts of MP pollution. The findings contribute to the development of targeted monitoring and environmental remediation strategies, which are crucial for protecting marine life and maintaining the integrity of coastal environments.

Mechanically Robust and Biodegradable Electrospun Membranes Made from Bioderived Thermoplastic Polyurethane and Polylactic Acid

Petroleum-based plastic waste plagues the natural environment, but plastics solve many high-performance solutions across industries. For example, porous polymer membranes are used for air filtration, advanced textiles, energy, and biomedical applications. Sustainable and biodegradable Bioplastic membranes can compete with nonrenewable materials in strength, durability, and functionality but biodegrade under select conditions after disposal. Membranes electrospun using a blend of bioderived thermoplastic polyurethane (TPU) and polylactic acid (PLA) perform effectively under tensile and cyclic loading, act adequately as an air filter media, and biodegrade in a home-compost environment, with the aliphatic formulation of TPU showing greater biodegradability compared to the formulation containing aromatic moieties. Blending TPU with PLA dramatically increases the strain at break of the PLA membrane, while the addition of PLA in TPU stiffens the material considerably. Measurements of the pressure drop and filtration efficiency deem this electrospun membrane an effective air filter. This membrane provides a solution to the need for quality air filtration while decreasing the dependence on petroleum feedstocks and addressing the issue of plastic disposal through biodegradation.

Degradation of Polymer Materials in the Environment and Its Impact on the Health of Experimental Animals: A Review

The extensive use of polymeric materials has resulted in significant environmental pollution, prompting the need for a deeper understanding of their degradation processes and impacts. This review provides a comprehensive analysis of the degradation of polymeric materials in the environment and their impact on the health of experimental animals. It identifies common polymers, delineates their degradation pathways, and describes the resulting products under different environmental conditions. The review covers physical, chemical, and biological degradation mechanisms, highlighting the complex interplay of factors influencing these processes. Furthermore, it examines the health implications of degradation products, using experimental animals as proxies for assessing potential risks to human health. By synthesizing current research, the review focuses on studies related to small organisms (primarily rodents and invertebrates, supplemented by fish and mollusks) to explore the effects of polymer materials on living organisms and underscores the urgency of developing and implementing effective polymer waste management strategies. These strategies are crucial for mitigating the adverse environmental and health impacts of polymer degradation, thus promoting a more sustainable interaction between human activities and the natural environment.

Current Progress in Research into Environmentally Friendly Rigid Polyurethane Foams

Polyurethane foams are materials characterized by low density and thermal conductivity and can therefore be used as thermal insulation materials. They are synthesized from toxic and environmentally unfriendly petrochemicals called isocyanates and polyols, which react with each other to form a urethane group via the displacement of the movable hydrogen atom of the -OH group of the alcohol to the nitrogen atom of the isocyanate group. The following work describes the synthesis of polyurethane foams, focusing on using environmentally friendly materials, such as polyols derived from plant sources or modifiers, to strengthen the foam interface derived from plant precipitation containing cellulose derived from paper waste. The polyurethane foam industry is looking for new sources of materials to replace the currently used petrochemical products. The solutions described are proving to be an innovative and promising area capable of changing the face of current PU foam synthesis.

Optimization of Laminated Bio-Polymer Fabrication for Food Packaging Application: A Sustainable Plasma-Activated Approach

The current level of packaging consumption imposes a need to fabricate single-use food packaging with renewable and compostable materials, such as bio-polyesters (e.g., polylactic acid, PLA and polybutylene succinate, PBS) or cellulose, but their use is still problematic. Fabrication of bio-compostable composites can specifically address impeding challenges, and adhesive lamination, achieved with compostable glue, is becoming more and more popular with respect to the less versatile hot lamination. In this context, plasma activation, a chemical-free oxidation technique of a material's surface, is used to increase the affinity of three different biomaterials (cellulose, PLA and PBS) toward a compostable polyurethane adhesive to decrease its amount by gluing bio-polyesters to cellulose. Optical Microscopy reveals activation conditions that do not affect the integrity of the materials, while Water Contact Analyses confirm the activation of the surfaces, with contact angles decreased to roughly 50 deg in all cases. Unexpectedly, ζ-potential analyses and subtractive infrared spectroscopy highlight how the activation performed superficially etches cellulose, while for both PLA and PBS, a general decrease in surface potential and an increase in superficial hydroxyl group populations confirm the achievement of the desired oxidation. Thus, we rationalize continuous activation conditions to treat PLA and PBS and to glue them to neat cellulose. While no beneficial effect is observed with activated PLA, bi-laminate composites fabricated with activated PBS fulfill the benchmark for adhesion strength using less than before, while oxygen permeation analyses exclude plasma-induced etching even at a nanoscale.

Effects of polymerization types on plastics ingestion and biodegradation by Zophobas atratus larvae, and successions of both gut bacterial and fungal microbiomes

Recent studies demonstrated that plastic degradation in Zophobas atratus superworms is related to the gut microbiota. To determine whether the biodegradation and gut-microbiota were influenced by ingested plastic polymerization types, foams of polypropylene (PP), polyurethane (PU) and ethylene vinyl acetate (EVA) were selected as representatives of polyolefins, polyester and copolymers, and the sole feedstock for superworms for 45 d. Both growth and survival rates of superworms were influenced by the type of plastic diet. Although the total consumptions of EVA- and PP-fed groups were similar at 29.03 ± 0.93 and 28.89 ± 1.14 mg/g-larva, which were both significantly higher than that of PU-fed groups (21.63 ± 2.18 mg/g-larva), the final survival rates of the EVA-fed group of 36.67 ± 10.41% exhibited significantly lower than that of the PP- and PU-fed groups of 76.67 ± 2.89% and 75.00 ± 7.07%, respectively, and even the starvation group of 51.67 ± 10.93%. The Illumina MiSeq results revealed similarities in the dominant gut bacterial communities between PU- and EVA-fed groups, with an increase in relative abundance of Lactococcus, but significant differences from the PP-fed groups, which had two predominant genera of unclassified Enterobacteriaceae and Enterococcus. Compared to bran-fed groups, changes in gut fungal communities were similar across all plastics-fed groups, with an increase in the dominant abundance of Rhodotorula. The abundance of Rhodotorula increased in the order of polyolefin, polyester, and copolymer. In summary, plastic ingestion, larval growth, and changes in gut bacterial and fungal community of superworms were all influenced by foam diets of different polymerization types, and especially influences on the gut microbiomes were different from each other.

Biodegradation of Polyurethane by Fungi Isolated from Industrial Wastewater-A Sustainable Approach to Plastic Waste Management

Polyurethane (PU) is a type of polymer, which exists in various forms in the environment. Very few studies are available concerning the structure or enzymatic mechanism of the microbial community, which can degrade PU. Degradation of PU remains a difficult problem with respect to the environmental and biological disciplines. This study mainly focused on identifying the micro-organisms able to degrade polyurethane and confirming the degradation by performing a plate assay, Sturm test and scanning electron microscopy. Optimal culture conditions for maximum PU degradation were also analyzed through classical methods. A soil burial test was conducted by placing polyurethane films in the soil for one month, and the microbe growing on the surface of polyurethane films-with a maximum degradation of 55%-was isolated and identified as Aspergillus versicolor (ARF5). The culture medium was also optimized with different physical and chemical parameters for maximum PU degradation. The presence of CO2 as a by-product of PU biodegradation was confirmed through the Sturm test.

Rapid biodegradation of microplastics generated from bio-based thermoplastic polyurethane

The accumulation of microplastics in various ecosystems has now been well documented and recent evidence suggests detrimental effects on various biological processes due to this pollution. Accumulation of microplastics in the natural environment is ultimately due to the chemical nature of widely used petroleum-based plastic polymers, which typically are inaccessible to biological processing. One way to mitigate this crisis is adoption of plastics that biodegrade if released into natural environments. In this work, we generated microplastic particles from a bio-based, biodegradable thermoplastic polyurethane (TPU-FC1) and demonstrated their rapid biodegradation via direct visualization and respirometry. Furthermore, we isolated multiple bacterial strains capable of using TPU-FC1 as a sole carbon source and characterized their depolymerization products. To visualize biodegradation of TPU materials as real-world products, we generated TPU-coated cotton fabric and an injection molded phone case and documented biodegradation by direct visualization and scanning electron microscopy (SEM), both of which indicated clear structural degradation of these materials and significant biofilm formation.

Investigations into the characterization, degradation, and applications of biodegradable polymers by mass spectrometry

Biodegradable polymers have been getting more and more attention because of their contribution to the plastic pollution environmental issues and to move towards a circular economy. Nevertheless, biodegradable materials still exhibit various disadvantages restraining a widespread use in the market. Therefore, additional research efforts are required to improve their performance. Mass spectrometry (MS) affords a relevant contribution to optimize biodegradable polymer synthesis, to confirm macromolecular structures, to examine along the time the progress of degradation processes and highlight advantages and drawbacks in the extensive applications. This review aims to provide an overview of the MS investigations carried out to support the synthesis of biodegradable polymers, with helpful information on undesirable products or polymerization mechanism, to understand deterioration pathways by the structure of degradation products and to follow drug release and pharmacokinetic. Additionally, it summarizes MS studies addressed on environmental and health issues related to the extensive use of plastic materials, that is, potential migration of additives or microplastics identification and quantification. The paper is focused on the most significant studies relating to synthetic and microbial biodegradable polymers published in the last 15 years, not including agro-polymers such as proteins and polysaccharides.

Impact of Bark-Sourced Building Blocks as Substitutes for Fossil-Derived Polyols on the Structural, Thermal, and Mechanical Properties of Polyurethane Networks

The hydrophilic extractives isolated from black alder (Alnus glutinosa) bark through hot water extraction were characterized as novel renewable macromonomers capable of forming polyurethane (PU) networks based on a commercial polyisocyanate, with partial or complete replacement of petroleum-derived polyol polyether. The bark-sourced bio-polyol mainly consists of the xyloside form of the diarylheptanoid oregonin, along with oligomeric flavonoids and carbohydrates, resulting in a total OH group content of 15.1 mmol·g-1 and a molecular weight (Mn) of approximately 750 g∙mol-1. The 31P NMR data confirmed a similar proportion of aliphatic OH and phenolic groups. Three-component PU compositions were prepared using polyethylene glycol (Mn = 400 g∙mol-1), bio-polyol (up to 50%), and polymeric diphenylmethane diisocyanate, which were pre-polymerized in tetrahydrofuran (THF) solution with tin organic and tertiary amine catalysts. The resulting mixture was cast and subjected to thermal post-curing. Calculation and experimental data confirmed the crosslinking activity of the bark-sourced bio-polyol in PU, leading to an increase in glass transition temperature (Tg), a decrease in sol fraction yield upon leaching of cured PU networks in THF, a significant increase in Young's modulus and tensile strength. The macromonomers derived from bark promoted char formation under high temperature and oxidative stress conditions, limiting heat release during macromolecular network degradation compared to bio-polyol-free PU. It was observed that amine catalysts, which are active in urethane formation with phenolic groups, promoted the formation of PU with higher Tg and modulus at tensile but with less limitation of heat liberation during PU macromolecular structure degradation. The high functionality of the bark-derived bio-polyol, along with the equal proportion of phenolic and aliphatic OH groups, allows for further optimization of PU characteristics using three variables: increasing the substitution extent of commercial polyethers, decreasing the NCO/OH ratio, and selecting the type of catalyst used.

Fungal Biodegradation of Polyurethanes

Polyurethanes (PURs) are versatile polymers used in a wide variety of fields, such as the medical, automotive, textile, thermal insulation, and coating industries as well as many everyday objects. Many PURs have applications that require a long service life, sometimes with exposure to aggressive conditions. They can undergo different types of physicochemical and biological degradation, but they are not compostable, and many of them constitute persistent waste in the environment. Although both bacteria and fungi can be involved in the degradation of PURs, fungi are often the main biodegradation agents. The chemical structure of PURs determines their degree of biodegradation. Fungal biodegradation of PURs is linked to the production of enzymes, mainly esterases and proteases, alongside laccases, peroxidases, and tyrosinases, which can modify the structure of polyurethane compounds by forming carbonyl groups. The experimental analysis of the biodegradation of PUR can be carried out by bringing the polymer into contact with a mold in pure culture or with a microbial consortium. Then, global measurements can be taken, such as weight loss, tensile tests, or the ability of microorganisms to grow in the presence of PUR as the sole carbon source. The analysis of the chemical structure of the polymer and its degradation products after fungal growth can confirm biodegradation and specify the mechanism. The main avenues of future research are directed towards the development of fully biodegradable PURs and, on the contrary, towards the development of PURs that are more resistant to degradation phenomena, in particular biodegradation, for applications where the material is in contact with living organisms.

Effect of Polymer Properties on the Biodegradation of Polyurethane Microplastics

The release of fragments from plastic products, that is, secondary microplastics, is a major concern in the context of the global plastic pollution. Currently available (thermoplastic) polyurethanes [(T)PU] are not biodegradable and therefore should be recycled. However, the ester bond in (T)PUs might be sufficiently hydrolysable to enable at least partial biodegradation of polyurethane particles. Here, we investigated biodegradation in compost of different types of (T)PU to gain insights into their fragmentation and biodegradation mechanisms. The studied (T)PUs varied regarding the chemistry of their polymer backbone (aromatic/aliphatic), hard phase content, cross-linking degree, and presence of a hydrolysis-stabilizing additive. We developed and validated an efficient and non-destructive polymer particle extraction process for partially biodegraded (T)PUs based on ultrasonication and density separation. Our results showed that biodegradation rates and extents decreased with increasing cross-linking density and hard-segment content. We found that the presence of a hydrolysis stabilizer reduced (T)PU fragmentation while not affecting the conversion of (T)PU carbon into CO2. We propose a biodegradation mechanism for (T)PUs that includes both mother particle shrinkage by surface erosion and fragmentation. The presented results help to understand structure-degradation relationships of (T)PUs and support recycling strategies.