Evaluation of environmental degradability based on the number of methylene units in poly(butylene n-alkylenedionate)

Can poly(butylene succinate) degrade in seawater?

Poly(butylene succinate) (PBSu) is a promising biodegradable polymer in natural environments. However, its biodegradability in marine environments is debatable. It is well known that the biodegradability of biodegradable polymers depends on their molecular weight. In this study, we explored the effect of the molecular weight of PBSu on its biodegradability through biochemical oxygen demand (BOD) testing in seawater. PBSu samples with different molecular weights were prepared by size-exclusion chromatography (SEC). After biodegradation testing, we extracted the residual organic matter from seawater to evaluate changes in the molecular weight by SEC, revealing that PBSu was enzymatically hydrolysed in seawater. Low-molecular-weight (LMW)-PBSu exhibited higher biodegradability in seawater while high-molecular-weight PBSu underwent hydrolysis over an extended period. Moreover, we evaluated the changes in microbial flora during biodegradation testing using amplicon sequencing of the culture media, which revealed that the microbial flora changed in response to the presence of PBSu. These findings suggest that PBSu is a potential biodegradable polymer at a sufficiently low molecular weight or when the degradation period is sufficiently long.

Synthesis of Biomass-Based Linear Aliphatic Polyesters Based on Sebacic Acid and 1,18-Octadecanedioic Acid and Their Thermal Properties and Odd-Even Effect

A series of biomass-based linear aliphatic polyesters are synthesized by combining sebacic acid (SA) (C10 diacid) and 1,18-octadecanedioic acid (OA) (C18 diacid) with a series of diols with varied alkyl chain lengths (C2 to C10 diols). SA and OA are obtainable from castor oil and palm oil, respectively. The reaction extent (polymerization extent) is high (≥96%) in all cases, and the number-average molecular weight (Mn) is 10 000-43 000 g mol-1 after purification. A possible limitation of currently available biomass-derived polyesters is their relatively low melting temperatures (Tm). The polyesters synthesized using OA with a long alkyl chain (C18 chain) in the present work exhibit relatively high Tm values of 78-93 °C, which are rather close to that (105-118 °C) of low-density polyethylene (LDPE), and may serve as biomass-based alternatives to LDPE with respect to thermal properties. Scientifically notably, an odd-even effect is observed in the Tm values. Polyesters with an even total-number of carbon atoms in the repeating unit have higher Tm values than their odd total-number counterparts likely due to their different orientations of dipoles of the polar ester groups along the backbone chain.

Polymer Biodegradation in Aquatic Environments: A Machine Learning Model Informed by Meta-Analysis of Structure-Biodegradation Relationships

Polymers are widely produced and contribute significantly to environmental pollution due to their low recycling rates and persistence in natural environments. Biodegradable polymers, while promising for reducing environmental impact, account for less than 2% of total polymer production. To expand the availability of biodegradable polymers, research has explored structure-biodegradability relationships, yet most studies focus on specific polymers, necessitating further exploration across diverse polymers. This study addresses this gap by curating an extensive aerobic biodegradation data set of 74 polymers and 1779 data points drawn from both published literature and 28 sets of original experiments. We then conducted a meta-analysis to evaluate the effects of experimental conditions, polymer structure, and the combined impact of polymer structure and properties on biodegradation. Next, we developed a machine learning model to predict polymer biodegradation in aquatic environments. The model achieved an Rtest2 score of 0.66 using Morgan fingerprints, detailed experimental conditions, and thermal decomposition temperature (Td) as the input descriptors. The model's robustness was supported by a feature importance analysis, revealing that substructure R-O-R in polyethers and polysaccharides positively influenced biodegradation, while molecular weight, Td, substructure -OC(═O)- in polyesters and polyalkylene carbonates, side chains, and aromatic rings negatively impacted it. Additionally, validation against the meta-analysis findings confirmed that predictions for unseen test sets aligned with established empirical biodegradation knowledge. This study not only expands our understanding across diverse polymers but also offers a valuable tool for designing environmentally friendly polymers.

A predictive model to assess the accumulation of microplastics in the natural environment

The use of plastics inevitably leads to (micro-)plastics entering and accumulating in the natural environment, affecting biodiversity, food security and human health. Currently, a comprehensive and universally applicable methodology to quantify microplastic accumulation in the natural environment is lacking. This study proposes an integrated biodegradation model that provides the possibility to examine and compare the microplastic formation and accumulation of different polymer types in diverse natural environments. The proposed model derives carbon mass flow streams from experimental mineralisation curves (CO2 evolution) of polymers and predicts the concentrations and residence times of the different plastic states during their biodegradation processes. The model allows for the description of the accumulation potential of polymers, as the time-integrated concentration of microplastics present in the natural environment during a timeframe of 100 years after a polymer enters the natural environment. The model is applied to estimate the accumulation potential of three polymers with different biodegradation profiles in soil: polybutylene succinate (PBS), polylactic acid (PLA) and polyethylene (PE). It is demonstrated that the dimensionless accumulation potential of PBS in soil is near zero (between 3.0·10-4 and 0.002) which corresponds to a potentially very low level of accumulation. On the other hand PE shows a near maximum value of 1 which corresponds to the almost completely non-biodegradable character of this polymer in soil. PLA exhibits a wide range of values in between that of PBS and PE which reflects its reported relatively slow biodegradation in soil. The proposed model can be used to guide material selection in product design by quantifying the microplastic accumulation of these different polymer types. To demonstrate its use, plastic candy wrappers and agricultural mulch films were selected as case studies. Both case studies show that high biodegradation rates can limit or prevent microplastic accumulation in soil.

Polyester biodegradability: importance and potential for optimisation

To reduce global CO2 emissions in line with EU targets, it is essential that we replace fossil-derived plastics with renewable alternatives. This provides an opportunity to develop novel plastics with improved design features, such as better reusability, recyclability, and environmental biodegradability. Although recycling and reuse of plastics is favoured, this relies heavily on the infrastructure of waste management, which is not consistently advanced on a worldwide scale. Furthermore, today's bulk polyolefin plastics are inherently unsuitable for closed-loop recycling, but the introduction of plastics with enhanced biodegradability could help to combat issues with plastic accumulation, especially for packaging applications. It is also important to recognise that plastics enter the environment through littering, even where the best waste-collection infrastructure is in place. This causes endless environmental accumulation when the plastics are non-(bio)degradable. Biodegradability depends heavily on circumstances; some biodegradable polymers degrade rapidly under tropical conditions in soil, but they may not also degrade at the bottom of the sea. Biodegradable polyesters are theoretically recyclable, and even if mechanical recycling is difficult, they can be broken down to their monomers by hydrolysis for subsequent purification and re-polymerisation. Additionally, both the physical properties and the biodegradability of polyesters are tuneable by varying their building blocks. The relationship between the (chemical) structures/compositions (aromatic, branched, linear, polar/apolar monomers; monomer chain length) and biodegradation/hydrolysis of polyesters is discussed here in the context of the design of biodegradable polyesters.

Environmental biodegradability of recombinant structural protein

Next generation polymers needs to be produced from renewable sources and to be converted into inorganic compounds in the natural environment at the end of life. Recombinant structural protein is a promising alternative to conventional engineering plastics due to its good thermal and mechanical properties, its production from biomass, and its potential for biodegradability. Herein, we measured the thermal and mechanical properties of the recombinant structural protein BP1 and evaluated its biodegradability. Because the thermal degradation occurs above 250 °C and the glass transition temperature is 185 °C, BP1 can be molded into sheets by a manual hot press at 150 °C and 83 MPa. The flexural strength and modulus of BP1 were 115 ± 6 MPa and 7.38 ± 0.03 GPa. These properties are superior to those of commercially available biodegradable polymers. The biodegradability of BP1 was carefully evaluated. BP1 was shown to be efficiently hydrolyzed by some isolated bacterial strains in a dispersed state. Furthermore, it was readily hydrolyzed from the solid state by three isolated proteases. The mineralization was evaluated by the biochemical oxygen demand (BOD)-biodegradation testing with soil inocula. The BOD biodegradability of BP1 was 70.2 ± 6.0 after 33 days.

Ranking environmental degradation trends of plastic marine debris based on physical properties and molecular structure

As plastic marine debris continues to accumulate in the oceans, many important questions surround this global dilemma. In particular, how many descriptors would be necessary to model the degradation behavior of ocean plastics or understand if degradation is possible? Here, we report a data-driven approach to elucidate degradation trends of plastic debris by linking abiotic and biotic degradation behavior in seawater with physical properties and molecular structures. The results reveal a hierarchy of predictors to quantify surface erosion as well as combinations of features, like glass transition temperature and hydrophobicity, to classify ocean plastics into fast, medium, and slow degradation categories. Furthermore, to account for weathering and environmental factors, two equations model the influence of seawater temperature and mechanical forces.

Accumulation of micro and nano-plastic in the oceans has emerged as a global challenge. Here, the authors predict a hierarchy of features that regulate their degradation and surface erosion by a thorough analysis of polymer structure, composition, physical properties and degradation data.

Biodegradation of Polymeric Mulch Films in Agricultural Soils: Concepts, Knowledge Gaps, and Future Research Directions

The agricultural use of conventional, polyethylene-based mulch films leads to the accumulation of remnant film pieces in agricultural soils with negative impacts for soil productivity and ecology. A viable strategy to overcome this accumulation is to replace conventional with biodegradable mulch films composed of polymers designed to be degraded by soil microorganisms. However, understanding polymer biodegradation in soils remains a significant challenge due to its dependence on polymer properties, soil characteristics, and prevailing environmental conditions. This perspective aims to advance our understanding of the three fundamental steps underlying biodegradation of mulch films in agricultural soils: colonization of the polymer film surfaces by soil microorganisms, depolymerization of the polymer films by extracellular microbial hydrolases, and subsequent microbial assimilation and utilization of the hydrolysis products for energy production and biomass formation. The perspective synthesizes the current conceptual understanding of these steps and highlights existing knowledge gaps. The discussion addresses future research and analytical advancements required to overcome the knowledge gaps and to identify the key polymer properties and soil characteristics governing mulch film biodegradation in agricultural soils.