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At least 37 records · Page 2

Discovery and adaptation of microbes that degrade oxidized low-density polyethylene films

There is a growing interest in developing a methodology for effectively cleaving carbon–carbon (C–C) bonds in polymer backbones through bioconversion processes that utilize microorganisms and their enzymes. This upsurge of interest is driven by the goal of achieving a circular economy. Polyolefin post-consumer plastics are a substantial source of carbon, but the recycling potential is severely limited. Upcycling routes are needed for converting polyolefin post-consumer plastics into value-added products while concurrently mitigating adverse environmental effects. These materials contain carbon-based chemicals that can, in principle, serve as the feedstock for microbial metabolism. Some microbes have been reported to grow on polyolefin plastics, but the rate of biodegradation is insufficient for industrial processes. In this study, low-density polyethylene (LDPE) films were subjected to two mild ozone-based oxidation treatments, which facilitated biodegradation. The degree of oxidation was determined by Fourier transform infrared spectroscopy via analysis of the carbonyl index (1,710/1,460 cm −1 ), which ranged from 0.3 to 2.0, and also via analysis of the carboxylic acid content. Following oxidation of the films, studies were conducted to investigate the ability of a panel of polyvinyl alcohol-degrading microbes to degrade the oxidized films. A defined minimal medium was used to cultivate and assess microbial growth on the oxidized films. Following 45 days of cultivation, the most effective strains were further cultivated up to three additional generations on the oxidized film substrates to improve their ability to degrade the oxidized LDPE films. After these enrichments, we identified a strain from the third generation of Pseudomonas sp. Rh926 that exhibited significant cell growth and reduced the oxidized LDPE film mass by 25% in 30 days, demonstrating an enhanced capacity for degrading the oxidized LDPE films.

Adaptation↗

Polylactic acid (PLA)-based multifunctional and biodegradable nanocomposites and their applications

Polylactic acid (PLA)-based nanocomposites are emerging as multifunctional, biodegradable materials, offering sustainable alternatives to petroleum-based plastics. This review examines recent advancements in PLA nanocomposites, focusing on enhanced mechanical strength, thermal stability, and biodegradability achieved through nanofillers like metallic particles, carbon-based materials, and ceramics. Techniques such as in situ polymerization, melt mixing, and electrospinning enable application-specific improvements. PLA's limitations, including brittleness and low barrier properties, are addressed to support diverse applications: in packaging (e.g., extended shelf life), biomedicine (e.g., degradable implants), and electronics (e.g., flexible devices). Despite challenges with filler dispersion and thermal resistance, continued innovations expand PLA's potential across multiple industries, contributing to a sustainable, circular economy.

Biodegradable polymers↗

Toward a Circular Bioeconomy: Designing Microbes and Polymers for Biodegradation

Polymer production is rapidly increasing, but there are no large-scale technologies available to effectively mitigate the massive accumulation of these recalcitrant materials. One potential solution is the development of a carbon-neutral polymer life cycle, where microorganisms convert plant biomass to chemicals, which are used to synthesize biodegradable materials that ultimately contribute to the growth of new plants. Realizing a circular carbon life cycle requires the integration of knowledge across microbiology, bioengineering, materials science, and organic chemistry, which itself has hindered large-scale industrial advances. This review addresses the biodegradation status of common synthetic polymers, identifying novel microbes and enzymes capable of metabolizing these recalcitrant materials and engineering approaches to enhance their biodegradation pathways. Design considerations for the next generation of biodegradable polymers are also reviewed, and finally, opportunities to apply findings from lignocellulosic biodegradation to the design and biodegradation of similarly recalcitrant synthetic polymers are discussed.

59 BASIC BIOLOGICAL SCIENCES↗

Multiscale Modeling and Experimental Insights into High-Temperature Soil Biodegradation Dynamics of Semi-Crystalline Poly(Lactic Acid) Nonwoven Fabrics

This study investigates the biodegradation of semi-crystalline poly(lactic acid) (PLA) nonwovens (NWs) in soil at 58 °C using both experimental and mathematical modeling approaches. The model utilizes a system of parabolic diffusion-reaction partial differential equations (PDEs) to elucidate chemical transformations over time and in space. It accounts for phenomena such as the diffusion of water and lactic acid monomers through the polymer matrix and into the surrounding soil, along with their microbial breakdown. It also accounts for the initial PLA crystallinity and predicts its evolution in time. The model is solved numerically for a single filament, and the results were used to shed light on PLA NW transformations observed in soil over a 180-day incubation period. Various characterization techniques, including scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and Raman spectroscopy, were employed to assess morphological changes, crystallinity, and molecular changes in the NWs throughout the experiment. By comparing the experimental data with the model predictions, the hydrolysis rate coefficient was found to be 3.37 × 10 -7 s -1 , while the rate of microbial degradation of lactic acid monomers was faster, of the order of 9.63 × 10 -7 s -1 . The findings highlight the significant role of crystallinity in the biodegradation process. The PLA degradation ceases when no amorphous material remains, and the crystallinity reaches 0.8, as observed in the experiments by day 120. Furthermore, this research contributes to a deeper understanding of PLA biodegradation dynamics and offers insights for effectively managing biodegradable materials in environmental settings.

Diffusion−reaction modeling↗

Blending Compostable Plastics for Packaging Applications

Non-sustainable packaging materials (polymers) are a large portion of the increasing amount of plastic waste that become environmental pollutants. While many biodegradable or compostable polymers have been developed in recent years, most fail to compete with the non-sustainable polymers dominating the market, due to lack of certain desired properties, such as thermal (high melt temperature) and mechanical (high ductility) performance. For example, the popular compostable polymer polylactic acid (PLLA) has a high melt temperature but is very brittle. Another polymer, poly(d-valerolactone) (PVL) demonstrates great ductility but has a very low melt temperature. By blending PLLA and PVL, there is an opportunity to create a new biodegradable material with synergistic desired properties for packaging applications. In this study, we produce several (9) physical blends of PVL and PLLA with varying compositions of the two polymers while applying three different materials to make them more compatible (compatibilizers). We test the success of compatibilization by scanning electron microscopy (SEM), mechanic testing (strain at break) and differential scanning calorimetry (melting temperature). Overall, we highlight several promising materials with high compatibility and desired thermomechanical properties for sustainable packaging. Ideally, these materials could help mitigate future plastic pollution in Colorado and beyond.

blending↗

Sustainable Polymer for Polyolefin Replacement (CRADA Final Report)

Sustainable Chemicals, LLC (Participant, Sust-Chem) develops renewable, biodegradable bioplastics for the replacement of large-volume petrochemical plastics such as polyethylene (PE) and polypropylene (PP). Participant’s patented bioplastics will find use in everyday items such as plastic bags, flexible containers, packaging, and toys and will address customers' ask for goods that are sustainable but don't cost a premium. Participants’ plastic comes from plant biomass and at the end of its lifecycle, is compostable or chemically recyclable. During the CRADA, Participant and Contractor will jointly refine the polymerization process used to make our bioplastic. Participant and Contractor will focus on technologies that are economically and industrially feasible, complete with full polymer characterization.

36 MATERIALS SCIENCE↗

Soil Sensors in Agriculture: From Unsustainable to Biodegradable

Commercially available bi-metallic temperature sensors have long exploited differential thermal expansions between materials to produce an actuation-induced readout from a bi-metal helix. When dispersed in agricultural land, electronic components are used to transmit information at the cost of an increased environmental footprint. This paper briefly recaps the proposed sensor, which employs a biodegradable bi-material helix composed of a polymer and metal. Proposed polymer sheetings of cellulose acetate and polylactic acid are characterized via TGA, DMA, and DSC to evaluate plasticizer content, shrinkage, and an appropriate sensor work-use range. Finally, the deflection of non-biodegradable bi-polymer strips is quantified for various combinations to determine if bi-polymer deflection is possible.

47 OTHER INSTRUMENTATION↗

Mechanisms of Polyethylene Terephthalate Pellet Fragmentation into Nanoplastics and Assimilable Carbons by Wastewater Comamonas

Comamonadaceae bacteria are enriched on poly(ethylene terephthalate) (PET) microplastics in wastewaters and urban rivers, but the PET-degrading mechanisms remain unclear. Here, we investigated these mechanisms with Comamonas testosteroniKF-1, a wastewater isolate, by combining microscopy, spectroscopy, proteomics, protein modeling, and genetic engineering. Compared to minor dents on PET films, scanning electron microscopy revealed significant fragmentation of PET pellets, resulting in a 3.5-fold increase in the abundance of small nanoparticles (<100 nm) during 30-day cultivation. Infrared spectroscopy captured primarily hydrolytic cleavage in the fragmented pellet particles. Solution analysis further demonstrated double hydrolysis of a PET oligomer, bis(2-hydroxyethyl) terephthalate, to the bioavailable monomer terephthalate. Supplementation with acetate, a common wastewater co-substrate, promoted cell growth and PET fragmentation. Of the multiple hydrolases encoded in the genome, intracellular proteomics detected only one, which was found in both acetate-only and PET-only conditions. Homology modeling of this hydrolase structure illustrated substrate binding analogous to reported PET hydrolases, despite dissimilar sequences. Mutants lacking this hydrolase gene were incapable of PET oligomer hydrolysis and had a 21% decrease in PET fragmentation; re-insertion of the gene restored both functions. Thus, we have identified constitutive production of a key PET-degrading hydrolase in wastewater Comamonas, which could be exploited for plastic bioconversion.

54 ENVIRONMENTAL SCIENCES↗

Bioconversion of self-neutralized chemically depolymerized lignin streams into polyhydroxyalkanoates

Lignin is a chemically complex, diverse, and abundant plant polymer mainly composed of aromatic monomers. These aromatic monomers make lignin a potential source of aromatics and a viable substitute for petrochemically-derived aromatics. However, the structural recalcitrance of lignin requires harsh reagents from the chemical process and expensive catalysts for effective depolymerization. This chemical process often results in poor yields of chemical intermediate mixtures of varying bioavailability and/or toxicity. Furthermore, the cost of additional reagents required to separate or detoxify these intermediates makes processing lignin impractical. We report progress towards the use of such chemically depolymerized lignin streams by employing bacterial strains to produce polyhydroxyalkanoates (PHA). PHAs are a group of biodegradable microbial polyesters that have potential as a replacement for petroleum-based plastics. In this study we utilized two distinct lignin streams obtained after chemical depolymerization of lignin under alkaline and acidic pH in the presence of catalysts. We mixed the alkali-treated depolymerized stream with the acid-treated depolymerized stream to create a solution of neutral-pH chemically depolymerized lignin (CDL). We found moderate to substantial growth of both native and non-native PHA producers on the mixture of CDL as well as its aliphatic and aromatic components. PHA was detected by Sudan Black B staining in C. necator H16, P. putida KT2440, and E. coli LSBJ STQKAB grown on mixed CDL as the sole carbon source. For C. necator H16 and E. coli LSBJ STQKAB we found that PHA content was greater when grown on mixed CDL when compared to their preferred carbon source by GC-FID quantification. Our study provided progress towards a cost-competitive, sustainable, and industrially relevant use for lignin.

Winkler, Gordon L. W. [Univ. of Wisconsin, Madison↗

Elucidating biodegradation of dimethyl terephthalate by two Rhodococcus strains for its valorization applications

Dimethyl terephthalate (DMT) serves as the precursor in the production of polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate. The widespread use of DMT in the polymer industry and its ubiquitous existence in end products raise alarms about its potential harm to humans and animals. DMT can enter the environment through the degradation of polymers and their end products, and cause endocrine disruption, oxidative stress, and an elevated risk of cancer. In recent years, DMT has also gained renewed interest in its potential for plastic recycling and upcycling. In this study, we identified two strains of Rhodococcus that possess DMT-degrading capabilities and utilized transcriptomic analysis and gene knockout to elucidate the mechanisms of DMT degradation. R. opacus PD630 and R. jostii RPET were found to convert up to 1 g/L DMT into mono-methyl terephthalate (MMT). A putative DMTase (RS34275) was identified for this conversion. R. jostii RPET also demonstrates the ability to convert DMT into MMT and to utilize MMT for its cellular growth via the terephthalate pathway. A putative MMTase (RS21885) as the sole enzyme was identified for the conversion of MMT into terephthalate in the RPET strain. In addition, we successfully produced lycopene and lipids from an engineered RPET strain using DMT as a substrate. Our findings will facilitate future DMT bioremediation and bio-upcycling of DMT-associated plastics, enabling the production of value-added products.

Biodegradation↗

The phototrophic purple non‐sulfur bacteria Rhodomicrobium spp. are novel chassis for bioplastic production

Abstract Petroleum‐based plastics levy significant environmental and economic costs that can be alleviated with sustainably sourced, biodegradable, and bio‐based polymers such as polyhydroxyalkanoates (PHAs). However, industrial‐scale production of PHAs faces barriers stemming from insufficient product yields and high costs. To address these challenges, we must look beyond the current suite of microbes for PHA production and investigate non‐model organisms with versatile metabolisms. In that vein, we assessed PHA production by the photosynthetic purple non‐sulfur bacteria (PNSB) Rhodomicrobium vannielii and Rhodomicrobium udaipurense. We show that both species accumulate PHA across photo‐heterotrophic, photo‐hydrogenotrophic, photo‐ferrotrophic, and photo‐electrotrophic growth conditions, with either ammonium chloride (NH 4 Cl) or dinitrogen gas (N 2 ) as nitrogen sources. Our data indicate that nitrogen source plays a significant role in dictating PHA synthesis, with N 2 fixation promoting PHA production during photoheterotrophy and photoelectrotrophy but inhibiting production during photohydrogenotrophy and photoferrotrophy. We observed the highest PHA titres (up to 44.08 mg/L, or 43.61% cell dry weight) when cells were grown photoheterotrophically on sodium butyrate with N 2 , while production was at its lowest during photoelectrotrophy (as low as 0.04 mg/L, or 0.16% cell dry weight). We also find that photohydrogenotrophically grown cells supplemented with NH 4 Cl exhibit the highest electron yields – up to 58.89% – while photoheterotrophy demonstrated the lowest (0.27%–1.39%). Finally, we highlight superior electron conversion and PHA production compared to a related PNSB, Rhodopseudomonas palustris TIE‐1. This study illustrates the value of studying non‐model organisms like Rhodomicrobium for sustainable PHA production and indicates future directions for exploring PNSB metabolisms.

59 BASIC BIOLOGICAL SCIENCES↗

In-Silico Design of Next Generation Cellulose-Derived Packaging Materials (CRADA Final Report)

Developing sustainable solutions for single-use packaging is an important objective to combat the environmental crisis of plastics pollution. Most embodiments of cellulose-based packaging materials, including CellophaneTM, are completely biodegradable in both terrestrial and marine environments. However, petroleum-derived alternatives offer some performance advantages for metrics such as moisture barriers and mechanical properties. This project leverages molecular dynamics simulation to investigate how molecular modifications to cellulose-based polymer assemblies impact their material properties. An important performance criterion for the modified materials was to retain biodegradability; thus, modifications by naturally occurring, biodegradable additives were the focus of this study. Specifically, we developed models with xylan and lignin of varying monomeric compositions into the cellulose matrix. The mechanical properties were investigated by performing stress-strain simulations, and the water barrier and hydrophobicity were investigated by simulating the water contact angle. Our findings indicate that the incorporation of xylan into the cellulose matrix tends to increase the mechanical properties with an optimal loading of ~27 wt%. We also predict that orienting the nanoscale directionality of the xylan chains such that they are perpendicular to the cellulose fibrils will dramatically increase mechanical strength. In contrast, the incorporation of lignin tends to weaken the composite at all loadings investigated. Simulations of water contact angle predicted that coating polymers on the surface of the cellulose assembly creates a more hydrophobic surface than incorporating them throughout the matrix. Of the coatings investigated, lignin resulted in the most hydrophobic surface, followed by pectin and keratin, which both imparted modest increases in hydrophobicity. Future experimental work done by Futamura will focus on designing material prototypes to capitalize on the predictions of performance enhancement obtained from molecular modeling. While substantial progress was made by the simulations performed in this project, there still exists a vast parameter space that we were unable to investigate, including branching, functional group decoration, and degree of polymerization of polymer additives. However, the methods developed in this initial investigation will facilitate more rapid evaluation of the impact of molecular characteristics on the performance of biopolymer composite materials and thereby accelerate future materials discovery efforts in this area.

36 MATERIALS SCIENCE↗

Tailoring High Hardness and Rigidity in Biodegradable Thermoplastic Polyurethanes

In response to escalating environmental concerns, there is a pressing demand for materials capable of delivering both sustainability and robust mechanical properties, thereby substituting nonrenewable counterparts in various applications. This study presents a comprehensive investigation into the synthesis and characterization of biobased aliphatic thermoplastic polyurethanes (TPUs) that exhibit impressive mechanical properties, including tensile strength in the range of 48–41 MPa and flexural modulus up to 2.2 GPa. These biodegradable TPUs displayed high shore A and D hardness between 95 and 98 and 51–42, respectively, and thus can be categorized as “extra hard” plastics according to the durometer scale for PUs. Herein, we have prepared a series of four 100% biobased polyester polyols from biobased diacid and chain-extender as precursors with molecular weights varying from 500 to 1400 g/mol. The corresponding TPUs that were prepared by using an aliphatic diisocyanate were evaluated for their thermal stability, microphase separation, mechanical properties, and biodegradation. By leveraging renewable feedstocks, these TPUs offer a sustainable alternative to petroleum-derived materials, with their mechanical performance meeting conventional benchmarks. Furthermore, postcomposting analysis revealed significant surface degradation, affirming their biodegradability and environmental compatibility.

36 MATERIALS SCIENCE↗

Production of high-performance biodegradable polyurethane products made from algae precursors

We successfully developed and scaled the production of high-performance, fully biodegradable thermoplastic polyurethanes (TPUs) derived from algae-based precursors. By employing innovative flow chemistry and chemo-enzymatic methodologies, the research team produced materials with up to 100% bio-based content that match or exceed the mechanical properties of traditional petroleum-based plastics. These algae-derived TPUs were proven to be fully home-compostable, achieving over 90% decomposition within 110 to 120 days while demonstrating practical advantages such as reduced solvent requirements in fabric coating applications.

36 MATERIALS SCIENCE↗

Sandwich-structured paper composite with water and oil resistance for food packaging and tableware applications

The growing environmental challenges posed by plastic waste from disposable tableware highlight the urgent need for sustainable alternatives. Traditional plastics decompose over centuries, generating microplastics that threaten ecosystems and human health. While lignin has emerged as a promising material for plastic replacement, its inherent dark brown color and processing challenges in paper-based products have limited its application, particularly in food-contact materials. Here, to address these limitations, we have developed biodegradable sandwich-structured paper composites comprising parchment paper as surface layers and a lignin-polymer core with polyvinyl alcohol (PVA) and polylactic acid (PLA). This innovative structure eliminates the need for binders, minimizing potential food contamination, and enables direct application as packaging or molded tableware. Lignin micro- and nano-particles (LMNP) enhances durability and provides natural water and oil resistance without harmful additives, such as per- and polyfluoroalkyl substances (PFAS), while PVA and PLA improve the composite's tenacity. The resulting material, composed of 65 wt% lignin, demonstrates excellent water and oil resistance, with no penetration exceeding 1 h, and exhibits enhanced tensile strength (45 MPa), making it a viable and eco-friendly alternative for disposable tableware.

36 MATERIALS SCIENCE↗

Making an s1G Self-Preserving Environmental DNA (eDNA) Filter from Sustainable Materials

Environmental DNA (eDNA) sampling of aquatic environments is a powerful new tool for resource managers to use in detecting the presence of rare and endangered species. The use of eDNA for species detection is quickly becoming an industry-standard methodology in environmental science, and the technology sector is moving quickly to create purpose-built tools for eDNA sampling. Smith-Root, Inc. pioneered the new technology of self-preserving eDNA filters that automatically preserve the DNA captured on filters by desiccating the internal filter membrane. This capability saves the sampling technician significant time in the field and drastically reduces the potential for sample contamination. One main constraint of this new technology, however, is the necessity of single-use plastics for eDNA sampling. Single-use designs are employed because sampling equipment must be devoid of potential contaminating DNA, and the time required to sterilize equipment is often not cost-effective for practitioners. Thus, this technology is creating a significant new source of plastic waste—something that eDNA practitioners, and society, would like to avoid. This project explores the use of alternative bio based polymers and composites as replacements for incumbent industrial standards for eDNA filtration systems, with an emphasis on ease of processing and biodegradable options. 8 candidate materials, 3 for the top filter housing and 5 for the bottom filter housing, were investigated to replace incumbent housing materials. Of the 8 candidates, 2 materials were identified for future investigation which met performance requirements, were bio-based and could potentially offer better disposal options like soil degradation or composting, features sought by the customers of these products. The top housing candidate, material 1, has comparable performance to the incumbent material and equally manufacturable. The bottom housing candidate, material 6, improved desiccation performance by 81% after 1 hour in comparison to the incumbent material, is 100% bio-based, compostable and can be sourced domestically throughout the U.S.A.

36 MATERIALS SCIENCE↗

Oxidative Funneling of PVDC (CRADA Final Report)

Poly(vinylidene chloride) (PVDC) is a major polymer product from the Participant. PVDC-containing plastics are not commonly recycled. To overcome the challenges associated with recycling PVDC and multi-layer materials, we propose a tandem catalytic-biological process to convert PVDC containing waste to upcycled, tunable products such as polyhydroxyalkanoates (PHAs). PHAs are commercially relevant, biodegradable polymers that are useful in packaging, biomedical, and personal care applications. This technology, which the Contractor has named oxidative funneling (OxFun), uses a metal-promoted autoxidation step to depolymerize co-mingled polymers to a mixture of oxygenated compounds, which an engineered bacterium can funnel to a single bioproduct: here, medium chain length polyhydroxyalkanoates (mcl-PHAs). The proposed oxidation chemistry is amenable to inclusion of additional polymers, and the biocatalyst can be engineered to convert the deconstruction products to a variety of valuable chemicals, thus presenting a tunable system for both feedstock variability and target product. Pseudomonas putida KT2440 – a metabolically robust microbe that has been engineered and proven viable for upcycling deconstructed polystyrene (PS), high density polyethlene (HDPE), and polyethylene terephthalate (PET) – can be engineered with enzymes capable of de-chlorinating PVDC deconstruction products (e.g., 2,2-dichloroacetate) in addition to PE-derived substrates into mcl-PHAs.

36 MATERIALS SCIENCE↗

All 2D Material Printed Diodes and Circuits on Paper for Sustainable Electronics

Sustainable electronics aim to reduce environmental impact by using ecofriendly materials, energy-efficient manufacturing, and recyclable components. However, existing approaches rely on complex, resource-intensive methods, rare metals, or nanomaterials with limited stability as well as plastic substrates, raising sustainability issues. Solution-processed two-dimensional (2D) materials offer a promising alternative: water-based and biocompatible conductive, semiconductive, and insulating 2D material inks can be produced with scalable techniques and are suitable for the fabrication of fully printed devices on low-cost and biodegradable paper substrates. However, 2D material only and fully printed diodes on paper have not yet been reported. Here, we demonstrate fully inkjet-printed 2D material-based diodes on paper using metal-insulator-semiconductor and metal-insulator-metal-semiconductor architectures. Water-based graphene and MoS2 inks, prepared by liquid-phase exfoliation, are used for the metallic and insulating films, while electrochemical exfoliation is used to produce the semiconducting MoS2 ink. The highest forward-to-reverse current ratio obtained is 330 (at ±2 V), while the forward current density is 1 mA/cm2 (at 1 V), making the diode performance comparable to the best solution-processed diodes reported so far. However, in contrast to previous works, fabrication occurs entirely at room temperature and ambient pressure, without using high-pressure sputtering, thermal evaporation, and any precious metal ink. The devices maintain stable performance under bending up to strain of 4% over 10,000 cycles. Finally, the diodes are successfully integrated with other 2D-material based electrical components to realize fully printed RC circuits, differentiators, integrators, and AC-to-DC converters onto paper, hence demonstrating the suitability of our approach for sustainable and disposable integrated circuits.

2D materials↗