Effects of ultraviolet light (315 nm), temperature and relative humidity on the degradation of polylactic acid plastic films

Coastal plastic pollution: A global perspective

Coastal ecosystems have ecological importance worldwide and require control and prevention measures to mitigate human pollution. The objective of this study was to perform a systematic review to provide a comprehensive overview of the global issue of coastal plastic pollution. 689 articles were eligible for qualitative synthesis and 31 were considered for quantitative analysis. There was an exponential increase in articles addressing coastal plastic pollution over the past 50 years. Studies were mainly carried out on beaches, and plastic bottles were the most found item, followed by cigarette butts. Polyethylene was the predominant plastic polymer, and white microplastic fragments stood out. China published most articles on the topic and Brazil had the highest number of sites sampled. Meta-analysis had significant effect sizes based on the reported data. These findings carry significant implications for environmental policies, waste management practices, and targeted awareness campaigns aimed at mitigating plastic pollution.

Effect of Aging on Tensile and Chemical Properties of Polylactic Acid and Polylactic Acid-Like Polymer Materials for Additive Manufacturing

Additive manufacturing, with its fast development and application of polymeric materials, led to the wide utilization of polylactic acid (PLA) materials. As a biodegradable and biocompatible aliphatic polyester, produced from renewable sources, PLA is widely used in different sectors, from industry to medicine and science. The aim of this research is to determine the differences between two forms of the PLA material, i.e., fused deposition modeling (FDM) printed filament and digital light processing (DLP) printed resin, followed by aging due to environmental and hygiene maintenance conditions for a period of two months. Specimens underwent 3D scanning, tensile testing, and Fourier transform infrared (FTIR) spectrometry to obtain insights into the material changes that occurred. Two-way Analysis of Variance (ANOVA) statistical analysis was subsequently carried out to determine the statistical significance of the determined changes. Significant impairment can be observed in the dimensional accuracies between both materials, whether they are non-aged or aged. The mechanical properties fluctuated for aged FDM specimens: 15% for ultimate tensile stress, 15% for elongation at yield, and 12% for elastic modulus. Regarding the DLP aged specimens, the UTS decreased by 61%, elongation at yield by around 61%, and elastic modulus by 62%. According to the FTIR spectral analysis, the PLA materials degraded, especially in the case of resin specimens. Aging also showed a significant influence on the elastic modulus, ultimate tensile stress, elongation at yield, elongation at break, and toughness of both materials, which was statistically shown by means of a two-way ANOVA test. The data collected in this research give a better understanding of the underlying aging mechanism of PLA materials.

The aging behavior of degradable plastic polylactic acid under the interaction of environmental factors

Microplastics leaching from aging biodegradable plastics pose potential environmental threats. This study used response surface methodology (RSM) to investigate the impact of temperature, light, and humidity on the aging characteristics of polylactic acid (PLA). Key evaluation metrics included the C/O ratio, functional groups, crystallinity, surface topography, and mechanical properties. Humidity was discovered to have the greatest effect on the ageing of PLA, followed by light and temperature. The interactions between temperature and light, as well as humidity and sunlight, significantly impact the aging of PLA. XPS analysis revealed PLA underwent aging due to the cleavage of the ester bond (O-C=O), resulting in the addition of C=O and C-O. The aging process of PLA was characterized by alterations in surface morphology and augmentation in crystallinity, resulting in a decline in both tensile strength and elongation. These findings might offer insights into the aging behavior of degradable plastics under diverse environmental conditions.

Evaluation and Modeling of Polylactide Photodegradation under Ultraviolet Irradiation: Bio-Based Polyester Photolysis Mechanism

In our study, we investigated the accelerated aging process of PLA under 253.7 nm UV-C irradiation with the use of the GPC, NMR, FTIR, and DSC methods and formal kinetic analysis. The results of GPC and DSC indicated a significant degree of destructive changes in the PLA macromolecules, while spectroscopic methods NMR and FTIR showed maintenance of the PLA main structural elements even after a long time of UV exposure. In addition to that, the GPC method displayed the formation of a high molecular weight fraction starting from 24 h of irradiation, and an increase in its content after 144 h of irradiation. It has been shown for the first time that a distinctive feature of prolonged UV exposure is the occurrence of intra- and intermolecular radical recombination reactions, leading to the formation of a high molecular weight fraction of PLA decomposition products. This causes the observed slowdown of the photolysis process. It was concluded that photolysis of PLA is a complex physicochemical process, the mechanism of which depends on morphological changes in the solid phase of the polymer under UV radiation.

Effect of Degradation on the Physicochemical and Mechanical Properties of Extruded Films of Poly(lactic acid) and Chitosan

This study addresses the fabrication of extruded films using poly(lactic acid) (PLA) and chitosan, with and without maleic anhydride as a compatibilizing agent, for potential applications in disposable food packaging. These films underwent controlled conditions of UV irradiation, water condensation, and temperature variations in an accelerated weathering chamber. The investigation analyzed the effect of different exposure periods on the structural, morphological, mechanical, and thermal properties of the films. It was observed that PLA films exhibited a lower susceptibility to degradation compared to those containing chitosan. Specifically, the pure PLA film showed an increase in elastic modulus and strength during the initial 144 h of exposure, associated with cross-linking induced by UV radiation. On the other hand, film Q2 composed of PLA, chitosan, and maleic anhydride and Q1 without maleic anhydride experienced a tensile strength loss of over 50% after 244 h of exposure. The Q2 film exhibited greater homogeneity, leading to increased resistance to degradation compared to that of Q1. As the degradation time increased, both the Q1 and Q2 films demonstrated a decline in thermal stability. These films also exhibited alterations in crystallinity attributed to the chemo-crystallization process, along with fluctuations in the glass transition temperature and crystallization, particularly at 288 h.

Vegetal Polyphenol Extracts as Antioxidants for the Stabilization of PLA: Toward Fully Biobased Polymer Formulation

The use of natural antioxidants as substitutes for traditional synthetic stabilizers has been investigated for the stabilization of biobased and biodegradable polymers, with the aim of designing fully biobased plastic formulations. This study focused on the thermo- and photostabilization of poly(lactic acid) (PLA) using vegetal polyphenol extracts as biosourced antioxidants. The polyphenols were extracted by microwave-assisted extraction from the valorization of vegetal waste, and their potential as antioxidant additives was evaluated (e.g., polyphenol content, composition, and antioxidant activity). PLA was then formulated with 2 wt % of the extracts exhibiting the highest antioxidant activities: green tea residues, pomegranate peels, grape marc, bramble leaves, and yellow onion peel extracts. The efficiency of the natural additives as thermal stabilizers was evaluated and compared with a synthetic antioxidant using rheological and thermal analyses. The results demonstrated the capacity of grape marc extract and pomegranate peel extract to significantly improve PLA thermal stability during processing and thermo-oxidation. Finally, photorheology was conducted to evaluate the influence of the bioadditives on the biopolyester photodegradation. The different polyphenol extracts seemed to significantly hinder the photo-oxidation of PLA and constitute very promising natural UV stabilizers, combining UV absorbers and antioxidant functions.

Photodegradation of biodegradable plastics in aquatic environments: Current understanding and challenges

Direct and indirect photolysis are important abiotic processes in aquatic environments through which plastics can be transformed physically and chemically. Transport of biodegradable plastics in water is influenced by vertical mixing and turbulent flow, which make biodegradable plastics remain susceptible to sunlight and photolysis despite their high density. In general, biodegradable plastics are composed of ester containing polymers (e.g., poly(butylene succinate), polyhydroxyalkanoate, and polylactic acid), whereas non-biodegradable plastics are composed of long chains of saturated aliphatic hydrocarbons in their backbones (e.g., polyethylene, polypropylene, and polystyrene). Based on the reviewed knowledge and discussion, we may hypothesize that 1) direct photolysis is more pronounced for non-biodegradation than for biodegradable plastics, 2) smaller plastics such as micro/nano-plastics are more prone to photodegradation and photo-transformation by direct and indirect photolysis, 3) the production rate of reactive oxygen species (ROS) on the surface of biodegradable plastics is higher than that of non-biodegradable plastics, 4) the photodegradation of biodegradable plastics may be promoted by ROS produced from biodegradable plastics themselves, and 5) the subsequent reactions of ROS are more active on biodegradable plastics than non-biodegradable plastics. Moreover, micro/nanoplastics derived from biodegradable plastics serve as more effective carriers of organic pollutants than those from non-biodegradable plastics and thus biodegradable plastics may not necessarily be more ecofriendly than non-biodegradable plastics. However, biodegradable plastics have been largely unexplored from the viewpoint of direct or indirect photolysis. Roles of reactive oxygen species originating from biodegradable plastics should be further explored for comprehensively understanding the photodegradation of biodegradable plastics.

Preparation of a nanocellulose/nanochitin coating on a poly(lactic acid) film for improved hydrolysis resistance

Growing concerns regarding plastic waste have prompted various attempts to replace plastic packaging films with biodegradable alternatives such as poly(lactic acid) (PLA). However, their low hydrolysis resistance owing to the presence of aliphatic polyesters limits the shelf life of biodegradable polymers. Hydrolysis leads to the deterioration of mechanical performance, which is a key disadvantage of biodegradable plastics. In this study, a layer-by-layer (LBL) assembly method was used for the dip-coating of biorenewable, biodegradable nanocellulose/nanochitin on the PLA surface. Additional crosslinking and compression of the coated nanofibers, each containing carboxylic acid and amine groups, respectively, were induced through electromagnetic microwave irradiation to protect the PLA film by improving hydrolysis resistance. The coatings were examined by morphological observations and water contact angle measurements. The LBL coatings of differently charged nanofibers of 10.6 μm were reduced to 40 % after microwave treatment, and the thickness does not vary after the hydrolysis experiment. Microwave irradiation increased the water contact angle owing to amide linkage formation, thereby preventing the peeling off of coating layers. Improved hydrolysis resistance inhibited the reduction in molecular weight and tensile strength. These findings could be used to develop sustainable and biodegradable plastic packaging films with a prolonged shelf life.

Dermal and oral exposure risks to heavy metals from 3D printing metal-fill thermoplastics

Manufacturing advancements in polymer printing now allow for the addition of metal additives to thermoplastic feedstock up to 80-90 % by weight and subsequent printing on low-cost desktop 3D printers. Particles associated with metal additives are not chemically bound to the plastic polymer, meaning these particles can potentially migrate and become bioavailable. This study investigated the degree to which two human exposure pathways, oral (ingestion) and dermal (skin contact), are important exposure pathways for metals (copper, chromium, and tin) from metal-fill thermoplastics used in consumer fused filament fabrication (FFF). We found that dermal exposure to copper and bronze filaments presents the highest exposure risk due to chloride (Cl-) in synthetic sweat driving copper (Cu2+) release and dissolution. Chromium and tin were released as micron-sized particles < 24 μm in diameter with low bioaccessibility during simulated oral and dermal exposure scenarios, with potential to undergo dissolution in the gastrointestinal tract based on testing using synthetic stomach fluids. The rate of metal particle release increased by one to two orders of magnitude when thermoplastics were degraded under 1 year of simulated UV weathering. This calls into question the long-term suitability of biodegradable polymers such as PLA for use in metal-fill thermoplastics if they are designed not to be sintered. The greatest exposure risk appears to be from the raw filaments rather than the printed forms, with the former having higher metal release rates in water and synthetic body fluids for all but one filament type. For brittle feedstock that requires greater handling, as metal-fill thermoplastics can be, practices common in metal powder 3D printing such as wearing gloves and washing hands may adequately reduce metal exposure risks.

Accelerating the Biodegradation of Poly(lactic acid) through the Inclusion of Plant Fibers: A Review of Recent Advances

As the global demand for plastics continues to grow, plastic waste is accumulating at an alarming rate with negative effects on the natural environment. The industrially compostable biopolymer poly(lactic acid) (PLA) is therefore being adopted for use in many applications, but the degradation of this material is slow under many end-of-life conditions. This Perspective explores the feasibility of accelerating the degradation of PLA through the formation of PLA-plant fiber composites. Topics include: (a) key properties of PLA, plant-based fibers, and biocomposites; (b) mechanisms of both hydrolytic degradation and biodegradation of PLA-fiber composites; (c) end-of-life degradation of PLA and PLA-plant fiber composites in aerobic and anaerobic conditions, relevant to compost, soil and seawater (aerobic), and landfills (anaerobic); and (d) sustainability and environmental impact of PLA and PLA-plant fiber composites, as evaluated using life cycle assessment. Additional degradation modes, including thermal and photodegradation, which are relevant during processing and use, have been omitted for clarity, as have other types of PLA biocomposites. Multiple studies have shown that the addition of some types of plant fibers to PLA (to form PLA biocomposites) accelerates both water transport in the material and hydrolysis, presenting a possible avenue for improving the end-of-life degradation of these materials. To facilitate the continued development of materials with enhanced biodegradability, we identify a need to implement testing protocols that can distinguish between different degradation mechanisms.

Effect of Olive Pit Reinforcement in Polylactic Acid Biocomposites on Environmental Degradation

Polylactic acid (PLA) is a biomaterial widely used as an alternative to petroleum-based polymeric matrices in plastic components. PLA-based biocomposites reinforced with lignocellulosic waste are currently receiving special attention owing to their mechanical properties, low toxicity, recyclability, and biodegradability. The influence of the percentage of waste on their properties and resistance to degradation are some of the points of great relevance. Therefore, a series of PLA-based biocomposites containing different percentages of olive pits (5, 15, 25 and 40% wt.) were manufactured and characterized both (a) immediately after manufacture and (b) after one year of storage under environmental conditions. The results obtained were analyzed to evaluate the influence of the incorporation of olive pits on the resistance to degradation (measured through Carbonyl Indices, CI), mechanical properties (tensile, flexural and impact strength), structure (Fourier Transform Infrared Spectroscopy, FT-IR; and, X-ray Diffraction, XRD), morphology (Scanning Electron Microscopy, SEM) and water absorption capacity of the manufactured materials. PLA degradation, corroborated by Differential Scanning Calorimetry (DSC), FT-IR, and XRD, resulted in a decrease in tensile and flexural strengths and an increase in the tensile and flexural moduli. This trend was maintained for the biocomposites, confirming that reinforcement promoted the PLA degradation.

Fate and environmental behaviors of microplastics through the lens of free radical

Microplastics (MPs), as plastics with a size of less than 5 mm, are ubiquitously present in the environment and become an increasing environmental concern. The fate and environmental behavior of MPs are significantly influenced by the presence of free radicals. Free radicals can cause surface breakage, chemical release, change in crystallinity and hydrophilicity, and aggregation of MPs. On the other hand, the generation of free radicals with a high concentration and oxidation potential can effectively degrade MPs. There is a limited review article to bridge the fate and environmental behaviors of MP with free radicals and their reactions. This paper reviews the sources, types, detection methods, generation mechanisms, and influencing factors of free radicals affecting the environmental processes of MPs, the environmental effects of MPs controlled by free radicals, and the degradation strategies of MPs based on free radical-associated technologies. Moreover, this review elaborates on the limitations of the current research and provides ideas for future research on the interactions between MPs and free radicals to better explain their environmental impacts and control their risks. This article aims to keep the reader abreast of the latest development in the fate and environmental behaviors of MP with free radicals and their reactions and to bridge free radical chemistry with MP control methodology.

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.

A review on biodegradable polylactic acid (PLA) production from fermentative food waste - Its applications and degradation

Due to its low carbon footprint and environmental friendliness, polylactic acid (PLA) is one of the most widely produced bioplastics in the world. Manufacturing attempts to partially replace petrochemical plastics with PLA are growing year over year. Although this polymer is typically used in high-end applications, its use will increase only if it can be produced at the lowest cost. As a result, food wastes rich in carbohydrates can be used as the primary raw material for the production of PLA. Lactic acid (LA) is typically produced through biological fermentation, but a suitable downstream separation process with low production costs and high product purity is also essential. The global PLA market has been steadily expanding with the increased demand, and PLA has now become the most widely used biopolymer across a range of industries, including packaging, agriculture, and transportation. Therefore, the necessity for an efficient manufacturing method with reduced production costs and a vital separation method is paramount. The primary goal of this study is to examine the various methods of lactic acid synthesis, together with their characteristics and the metabolic processes involved in producing lactic acid from food waste. In addition, the synthesis of PLA, possible difficulties in its biodegradation, and its application in diverse industries have also been discussed.

Polystyrene nanoplastics differentially influence the outcome of infection by two microparasites of the host Daphnia magna

The accumulation of micro- and nanoplastic particles in freshwater bodies has given rise to much concern regarding their potential adverse effects on aquatic biota. Beyond their known effects on single species, recent experimental evidence suggests that host-parasite interactions can also be affected by environmental concentrations of micro- and nanoplastics. However, investigating the effects of contaminants in simplified infection settings (i.e. one host, one parasite) may understate their ecological relevance, considering that co-infections are common in nature. We exposed the cladoceran Daphnia magna to a fungal parasite of the haemolymph (Metschnikowia bicuspidata) and a gut microsporidium (Ordospora colligata), either in single or co-infection. In addition, Daphnia were raised individually in culture media containing 0, 5 or 50 mg l^-1 of polystyrene nanoplastic beads (100 nm). Only few infections were successful at the higher nanoplastic concentration, due to increased mortality of the host. While no significant effect of the low concentration was detected on the microsporidium, the proportion of hosts infected by the fungal parasite increased dramatically, leading to more frequent co-infections under nanoplastic exposure. These results indicate that nanoplastics can affect the performance of distinct pathogens in diverging ways, with the potential to favour parasite coexistence in a common zooplanktonic host. This article is part of the theme issue 'Infectious disease ecology and evolution in a changing world'.

Inhibition of aged microplastics and leachates on methane production from anaerobic digestion of sludge and identification of key components

Large amounts of microplastics (MPs) accumulate in the sludge anaerobic digestion system after being treated by the wastewater treatment plants, inevitably leading to aging and chemicals leaching. However, no information is available about the effects of aged MPs and leachates on the anaerobic digestion of sludge. In this study, the effects of different aged MPs ((polyethylene (PE), polyethylene terephthalate (PET), polyvinyl chloride (PVC), and polylactic acid (PLA)) and leachates on anaerobic methanogenesis of sludge were investigated. PLA-related treatments caused no adverse effects on anaerobic digestion. While PE-, PET-, and PVC-related treatments significantly inhibited methane production with an order of leachates (26.4-42.4 %) > MPs (16.1-22.9 %) > aged MPs (2.4-11.8 %). For different leachates, PET leachate caused the strongest inhibitory effects. The same order was found for the methane potential and hydrolysis coefficient. These results suggest that the inhibition of MPs on methanogenesis is mainly caused by the leachates. Based on biochemical and microbial community analysis, the primary mechanism is that the leachates induce oxidative stress, damaging microbial cells and reducing microbial activity, consequently inhibiting methanogenesis. Furthermore, via effect-directed analysis, methyl benzoate (MB), dimethyl phthalate (DMP), and 2,4-Di-tert-butylphenol (DTBP) were identified as key components in the PET-leachate inhibiting anaerobic methanogenesis.

Enzymes' Power for Plastics Degradation

Plastics are everywhere in our modern way of living, and their production keeps increasing every year, causing major environmental concerns. Nowadays, the end-of-life management involves accumulation in landfills, incineration, and recycling to a lower extent. This ecological threat to the environment is inspiring alternative bio-based solutions for plastic waste treatment and recycling toward a circular economy. Over the past decade, considerable efforts have been made to degrade commodity plastics using biocatalytic approaches. Here, we provide a comprehensive review on the recent advances in enzyme-based biocatalysis and in the design of related biocatalytic processes to recycle or upcycle commodity plastics, including polyesters, polyamides, polyurethanes, and polyolefins. We also discuss scope and limitations, challenges, and opportunities of this field of research. An important message from this review is that polymer-assimilating enzymes are very likely part of the solution to reaching a circular plastic economy.

Explication of mechanism governing atmospheric degradation of 3D-printed poly(lactic acid) (PLA) with different in-fill pattern and varying in-fill density

With the popularity of 3D-printing technology, poly(lactic acid) (PLA) has become a very good option for layer by layer printing as it is easy to handle, environment friendly, has low costs and most importantly, it is highly adaptable to different materials including carbon, nylon and some other fibres. PLA is an aliphatic poly-ester that is 100% bio-based and is bio-degradable as well. It is one of the rare bio-polymers to compete with traditional polymers in terms of performance and environmental impact. However, PLA is sensitive to water and susceptible to degradation under natural conditions of ultra-violet rays (UV), humidity, fumes, etc. There are many reports on the bio-degradation and photo-degradation of PLA which deal with the accelerated weathering test. However, the accelerated weathering test instruments lack the ability to correlate the stabilities maintained by the test with the actual occurrences during natural exposure. Thus, an attempt has been made in the present work to expose the 3D-printed PLA samples to actual atmospheric conditions of Aurangabad city (M.S.) in India. The degradation of PLA after the exposure is studied and a mechanism is elucidated. Additionally, the tensile properties of the PLA samples are evaluated to correlate the extent of degradation and the material performance. It was found that though the performance of PLA deteriorates with the exposure time, the combination of in-fill pattern and volume plays an important role on the tensile properties and the extent of degradation. It is concluded herein that with natural exposure, the degradation of PLA occurs in two stages, supported by a side reaction. Thus, this study offers a new perspective towards the life of components in actual application by exposing PLA to the natural atmosphere and evaluating its strength and structure.

Physicochemical Properties of UV-Irradiated, Biaxially Oriented PLA Tubular Scaffolds

PLA and its blends are the most extensively used materials for various biomedical applications such as scaffolds, implants, and other medical devices. The most extensively used method for tubular scaffold fabrication is by using the extrusion process. However, PLA scaffolds show limitations such as low mechanical strength as compared to metallic scaffolds and inferior bioactivities, limiting their clinical application. Thus, in order to improve the mechanical properties of tubular scaffolds, they were biaxially expanded, wherein the bioactivity can be improved by surface modifications using UV treatment. However, detailed studies are needed to study the effect of UV irradiation on the surface properties of biaxially expanded scaffolds. In this work, tubular scaffolds were fabricated using a novel single-step biaxial expansion process, and the surface properties of the tubular scaffolds after different durations of UV irradiation were evaluated. The results show that changes in the surface wettability of scaffolds were observed after 2 min of UV exposure, and wettability increased with the increased duration of UV exposure. FTIR and XPS results were in conjunction and showed the formation of oxygen-rich functional groups with the increased UV irradiation of the surface. AFM showed increased surface roughness with the increase in UV duration. However, it was observed that scaffold crystallinity first increased and then decreased with the UV exposure. This study provides a new and detailed insight into the surface modification of the PLA scaffolds using UV exposure.

Screening of Polyethylene-Degrading Bacteria from Rhyzopertha Dominica and Evaluation of Its Key Enzymes Degrading Polyethylene

Polyethylene (PE) is widely used, and it has caused serious environmental problems due to its difficult degradation. At present, the mechanism of PE degradation by microorganisms is not clear, and the related enzymes of PE degradation need to be further explored. In this study, Acinetobacter baumannii Rd-H2 was obtained from Rhizopertha dominica, which had certain degradation effect on PE plastic. The degradation performance of the strains was evaluated by weight loss rate, SEM, ATR/FTIR, WCA, and GPC. The multi-copper oxidase gene abMco, which may be one of the key genes for PE degradation, was analyzed and successfully expressed in E. coli. The laccase activity of the gene was determined, and the enzyme activity was up to 159.82 U/L. The optimum temperature and pH of the enzyme are 45 °C and 4.5 respectively. It shows good stability at 30-45 °C. Cu²⁺ can activate the enzyme. The abMCO was used to degrade polyethylene film, showing a good degradation effect, proving that the enzyme could be the key to degrading PE.

Biodegradation of Biodegradable Polymers in Mesophilic Aerobic Environments

Finding alternatives to diminish plastic pollution has become one of the main challenges of modern life. A few alternatives have gained potential for a shift toward a more circular and sustainable relationship with plastics. Biodegradable polymers derived from bio- and fossil-based sources have emerged as one feasible alternative to overcome inconveniences associated with the use and disposal of non-biodegradable polymers. The biodegradation process depends on the environment's factors, microorganisms and associated enzymes, and the polymer properties, resulting in a plethora of parameters that create a complex process whereby biodegradation times and rates can vary immensely. This review aims to provide a background and a comprehensive, systematic, and critical overview of this complex process with a special focus on the mesophilic range. Activity toward depolymerization by extracellular enzymes, biofilm effect on the dynamic of the degradation process, CO2 evolution evaluating the extent of biodegradation, and metabolic pathways are discussed. Remarks and perspectives for potential future research are provided with a focus on the current knowledge gaps if the goal is to minimize the persistence of plastics across environments. Innovative approaches such as the addition of specific compounds to trigger depolymerization under particular conditions, biostimulation, bioaugmentation, and the addition of natural and/or modified enzymes are state-of-the-art methods that need faster development. Furthermore, methods must be connected to standards and techniques that fully track the biodegradation process. More transdisciplinary research within areas of polymer chemistry/processing and microbiology/biochemistry is needed.

Investigating the sustainability of agricultural plastic products, combined influence of polymer characteristics and environmental conditions on microplastics aging

The accelerated use of plastic products for agricultural practices has raised global concern regarding their negative impacts on soil health. This study aims to better understand the combined influence of polymer characteristics and environmental conditions on microplastic photodegradation within the agricultural soil system. For this purpose, the photodegradation behavior of low density polyethylene (LDPE) microplastics was studied through accelerated UVA radiation experiments under two different relative humidity (RH₁₀ and RH₇₀) and soil deposition conditions. The variations of plastics' surface physiochemistry due to the accelerated photodegradation were studied using Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy (ATR-FTIR), X-ray Photoelectron Spectroscopy (XPS), and Field Emission Scanning Electron Microscopy (FE-SEM). The carbonyl and vinyl indices were calculated using the ATR-FTIR information to compare the degree of microplastics' photodegradation. The plastics' bulk characteristics, including the percentage of crystallinity and molecular weight distributions, were examined using the Differential Scanning Calorimetry (DSC) and Gel Permeation Chromatography (GPC). Furthermore, the extent of UVA light interaction with the microplastics was studied by determining spectral quantum yield. The results demonstrated that new LDPE microplastics with a lower molecular weight (Mw = 233 kD) were subjected to a greater extent of photodegradation than those with greater molecular weight (Mw = 515 kD). Elevated relative humidity (RH₇₀) limited the photooxidation process of microplastics and consequently reduced the surface chemistry alterations. Deposition of soil particles with respect to the plastic particles impacted the photodegradation behavior. The microplastics covered by soil particles were not degraded, unlike those deposited next to the soil particles. The knowledge developed through this study could encourage the farmers and agricultural stakeholders to apply more efficient practices to remove plastic residuals after harvesting and conduct proper plastic disposal practices to protect soil health.

Interactions of microplastics with organic, inorganic and bio-pollutants and the ecotoxicological effects on terrestrial and aquatic organisms

As emerging contaminants, microplastics (MPs) have attracted global attention. They are a potential risk to organisms, ecosystems and human health. MPs are characterized by small particle sizes, weak photodegradability, and are good environmental carriers. They can physically adsorb or chemically react with organic, inorganic and bio-pollutants to generate complex binary pollutants or change the environmental behaviors of these pollutants. We systematically reviewed the following aspects of MPs: (i) Adsorption of heavy metals and organic pollutants by MPs and the key environmental factors affecting adsorption behaviors; (ii) Enrichment and release of antibiotic resistance genes (ARGs) on MPs and the effects of MPs on ARG migration in the environment; (iii) Formation of "plastisphere" and interactions between MPs and microorganisms; (iv) Ecotoxicological effects of MPs and their co-exposures with other pollutants. Finally, scientific knowledge gaps and future research areas on MPs are summarized, including standardization of study methodologies, ecological effects and human health risks of MPs and their combination with other pollutants.

Natural Ageing of PLA Filaments, Can It Be Frozen?

The physical ageing of polylactic acid (PLA) is a phenomenon that changes the material’s properties over time. This ageing process is highly dependent on ambient variables, such as temperature and humidity. For PLA, the ageing is noticeable even at room temperatures, a process commonly referred to as natural ageing. Stopping the ageing by freezing the material can be helpful to preserve the properties of the PLA and stabilise it at any time during its storage until it is required for testing. However, it is essential to demonstrate that the PLA’s mechanical properties are not degraded after defrosting the samples. Four different methods for stopping the ageing (anti-ageing processes) are analysed in this paper—all based on freezing and defrosting the PLA samples. We determine the temperature and ambient water vapor influence during the freezing and defrosting process using desiccant and zip bags. The material form selected is PLA filaments (no bulk material or scaffold structures) printed at 190 °C with diameters between 400 and 550 µm and frozen at −24 °C in the presence or absence of a desiccant. The impact of the anti-ageing processes on PLA’s ageing and mechanical integrity is studied regarding the thermal, mechanical and fractographical properties. In conclusion, an anti-ageing process is defined to successfully stop the natural ageing of the PLA for an indefinite length of time. This process does not affect the mechanical properties or the structural integrity of the PLA. As a result, large quantities of this material can be produced in a single batch and be safely stored to be later characterised under the same manufacturing and ageing conditions, which is currently a limiting factor from an experimental point of view as polymeric filament properties can show significant variety from batch to batch.

Upcycling to Sustainably Reuse Plastics

Plastics are now indispensable in daily lives. However, the pollution from plastics is also increasingly becoming a serious environmental issue. Recent years have seen more sustainable approaches and technologies, commonly known as upcycling, to transform plastics into value-added materials and chemical feedstocks. In this review, the latest research on upcycling is presented, with a greater focus on the use of renewable energy as well as the more selective methods to repurpose synthetic polymers. First, thermal upcycling approaches are briefly introduced, including the redeployment of plastics for construction uses, 3D printing precursors, and lightweight materials. Then, some of the latest novel strategies to deconstruct condensation polymers to monomers for repolymerization or introduce vulnerable linkers to make the plastics more degradable are discussed. Subsequently, the review will explore the breakthroughs in plastics upcycling by heterogeneous and homogeneous photocatalysis, as well as electrocatalysis, which transform plastics into more versatile fine chemicals and materials while simultaneously mitigating global climate change. In addition, some of the biotechnological advances in the discovery and engineering of microbes that can decompose plastics are also presented. Finally, the current challenges and outlook for future plastics upcycling are discussed to stimulate global cooperation in this field.

The role of (bio)degradability on the management of petrochemical and bio-based plastic waste

In order to mitigate the social and ecological impacts of post-consumer plastic made of conventional petrochemical polymers, the market of (bio)degradable plastics have recently become more widespread. Although (bio)degradable plastics could be an environmentally friendly substitute of petrochemical ones, the consequences of their presence in the waste management system and in the environment (if not correctly disposed) are not always positive and plastic pollution is not automatically solved. Consequently, this work aims to review how plastic (bio)degradability affects the municipal solid waste management cycle. To this end, the state-of-the-art of the intrinsic (bio)degradability of conventional and unconventional petrochemical and bio-based polymers has been discussed, focusing on the environment related to the waste management system. Then, the focus was on strategies to improve polymer (bio)degradability: different types of eco-design and pre-treatment approach for plastics has been investigated, differently from other works that focused only on specific topics. The information gathered was used to discuss three typical disposal/treatment routes for plastic waste. Despite many of the proposed materials in eco-design have increased the plastics (bio)degradability and pre-treatments have showed interesting results, these achievements are not always positive in the current MSW management system. The effect on mechanical recycling is negative in several cases but the enhanced (bio)degradability can help the treatment with organic waste. On the other hand, the current waste treatment facility is not capable to manage this waste, leading to the incineration the most promising options. In this way, the consumption of raw materials will persist even by using (bio)degradable plastics, which strength the doubt if the solution of plastic pollution leads really on these materials. The review also highlighted the need for further research on this topic that is currently limited by the still scarce amount of (bio)degradable plastics in input to full-scale waste treatment plants.

Thermal Properties and Dynamic Characteristics of Electrospun Polylactide/Natural Rubber Fibers during Disintegration in Soil

In this work, PLA/NR electrospun fibers were used as substrates for growing basil. Thermal characteristics of initial samples and after 60 and 220 days of degradation were determined using differential scanning calorimetry. In the process of disintegration, the melting and glass transition temperatures in PLA/NR composites decreased, and in PLA fibers these values increased slightly. TGA analysis in an argon environment confirmed the effect of NR on the thermal degradation of PLA/NR fibers. After exposure to the soil for 220 days, the beginning of degradation shifted to the low-temperature region. The dynamic characteristics of the fibers were determined by the EPR method. A decrease in the correlation time of the probe-radical in comparison with the initial samples was shown. FTIR spectroscopy was used to analyze the chemical structure before and after degradation in soil. In PLA/NR fibrous substrates, there was a decrease in the intensity of the bands corresponding to the PLA matrix and the appearance of N-H C-N groups due to biodegradation by soil microorganisms.

Environmental behaviors of microplastics in aquatic systems: A systematic review on degradation, adsorption, toxicity and biofilm under aging conditions

Microplastics (MPs, < 5 mm) in the environment have attracted worldwide attention due to their wide distribution and difficulty in handling. Aging processes such as UV irradiation, biodegradation, physical abrasion and chemical oxidation can affect the environmental behavior of MPs. This review article summarizes different aging processes of MPs and subsequent effects on the adsorption of pollutants, the leaching of additives, and the toxicity of MPs. In addition, the formation process of biofilm on the surface of MPs and the interactions between biofilm and aged MPs are revealed. MPs can accumulate different environmental pollutants (organic pollutants, heavy metals, microorganisms, etc.) through surface adsorption, pore filling and distribution. Moreover, the aging of MPs affects their adsorption performance toward these pollutants due to a series of changes in their specific surface area and oxygen-containing functional groups. The release of some toxic additives such as phthalates after aging can enhance the toxic effects of MPs. Aging also changes the shape and size of MPs, which can affect the eating habits of the organisms and further increase the potential toxicity of MPs. This article conducts a systematical analysis and summary of the environmental behavior and physicochemical properties of MPs as well as the changes due to MPs aging, which helps to better understand the impact of aging on MPs in the environment. Future research on MPs aging should reduce the knowledge gap between laboratory simulation and actual conditions and increase the environmental relevance.

Anti-Gnawing, Thermo-Mechanical and Rheological Properties of Polyvinyl Chloride: Effect of Capsicum Oleoresin and Denatonium Benzoate

Anti-rodent polymer composites were prepared using non-toxic substances denatonium benzoate (DB) and capsicum oleroresin (CO) mixed with polyvinyl chloride (PVC) matrix. DB is mixed in zinc stearate (ZnSt) called DB/ZnSt, and CO, providing burning sensation, is impregnated in mesoporous silica named SiCO. There are three sets of sample: Blank, composites Set I and Set II. Set I consists of DB/ZnSt at concentration of 1.96 wt% and SiCO at concentration of 12.16 wt%, 14.47 wt%, 18.75 wt% and 23.53 wt%. Set II comprises SiCO at the same amount of Set I. The anti-rodent composites studied are anti-gnawing, surface morphology, thermo-mechanical and rheological properties. Anti-rodent testing is analyzed by one-way blocked analysis of variance (ANOVA) and compared with Tukey test with a 95% level of significance, presenting good anti-gnawing efficiency. The best rat-proof sample is II.4, consisting of SiCO 23.53 wt%, which presents percentage of weight loss from gnawing at 1.68% compared to weight loss of neat PVC at 59.74%. The addition of SiCO at concentration ranging from 12.16 to 23.53 wt% reduces tensile strength around 25–50%, elongation at break strength around 2–23%, shear storage modulus (G′) around 30%, shear loss modulus (G″) shear viscosity (η) and glass transition (Tg) around 43% compared to Blank. The increase in SiCO concentration slightly improves the thermal stability of PVC composites around 3%, but the addition of DB/ZnSt at 1.96 wt% slightly reduces those properties.

Aging of 3D Printed Polymers under Sterilizing UV-C Radiation

In the context of the COVID-19 pandemic, shortwave ultraviolet radiation with wavelengths between 200 nm and 280 nm (UV-C) is seeing increased usage in the sterilization of medical equipment, appliances, and spaces due to its antimicrobial effect. During the first weeks of the pandemic, healthcare facilities experienced a shortage of personal protective equipment. This led to hospital technicians, private companies, and even members of the public to resort to 3D printing in order to produce fast, on-demand resources. This paper analyzes the effect of accelerated aging through prolonged exposure to UV-C on mechanical properties of parts 3D printed by material extrusion (MEX) from common polymers, such as polylactic acid (PLA) and polyethylene terephthalate-glycol (PETG). Samples 3D printed from these materials went through a 24-h UV-C exposure aging cycle and were then tested versus a control group for changes in mechanical properties. Both tensile and compressive strength were determined, as well as changes in material creep properties. Prolonged UV-C exposure reduced the mechanical properties of PLA by 6-8% and of PETG by over 30%. These findings are of practical importance for those interested in producing functional MEX parts intended to be sterilized using UV-C. Scanning electron microscopy (SEM) was performed in order to assess any changes in material structure.

Surface-initiated atom-transfer radical polymerization (SI-ATRP) of bactericidal polymer brushes on poly(lactic acid) surfaces

We have modified the surface of poly(lactic acid) (PLA) by bromination in the presence of N-bromosuccinimide (NBS) under UV irradiation. This new approach to impart functionality to the surface does not effect the bulk of the material. Brominated PLA surfaces served as initiators for atom-transfer radical polymerization (SI-ATRP) of 2-(methacryloyloxy)ethyl]trimethylammonium chloride, a quaternary ammonium methacrylate (QMA). Grafting of poly(QMA) brushes rendered PLA films hydrophilic and these films displayed a three-order of magnitude increase in antimicrobial efficacy against Gram-negative bacteria such as Escherichia coli as compared to unmodified PLA. The two-step strategy described here to modify PLA surface represents a useful route to modified PLA materials for biomedical and antimicrobial packaging applications.

Characteristics, fate, and impact of marine plastic debris exposed to sunlight: A review

The increase of plastic production from the middle of the twentieth century was inevitably followed by an increase in the amount of plastic dumped in the natural environment. There, the plastic debris are exposed to sunlight, temperature, humidity, and physical stress. This can induce photo-oxidative and thermal degradation. This review discusses the mechanism of plastics UV weathering and its characteristics. Comparison of the photodegradation rate and physico-chemical properties are made according to the weathering mode (natural/accelerated) and medium (air/water). Since the photodegradation can lead to plastics fragmentation, this phenomenon is described along with the methodologies used in literature to evaluate the fragmentation. The impact of the photodegraded plastic debris on the marine environment is also presented in term of (i) photodegradation products and stabilizers leakage, (ii) organic pollutants accumulation, transfer, and leakage, and (iii) toxicity on marine organisms.

Characterisation and Modelling of PLA Filaments and Evolution with Time

The properties of polylactic acid (PLA) filaments have not yet been analysed in detail, and they are strongly affected by the extrusion process used in some additive manufacturing systems. Here we present the mechanical, thermal, physical, and fractographical properties of an extruded filament (not the bulk material or scaffolds), the basic building block of any PLA structure printed via material extrusion. This research aims to create a reference point for the modelisation of additively manufactured structures via extrusion processes, as the main building block is characterised in detail for a deep understanding. Furthermore, we investigated the natural ageing (up to one year), the effect of the printing (extruding) temperature (180 and 190 °C), and the effect of the crosshead speed during the tensile tests (10⁻¹ to 10² mm/min) to provide a deeper analysis of the material. The results showed that the material extruded at 190 °C performed better than the material extruded at 180 °C. However, after one hundred days of natural ageing, both materials behaved similarly. This was related to the flow-induced molecular orientation during the extrusion. The crosshead rate produced a logarithmic increase of the mechanical properties, consistent with the Eyring model. Additionally, the ageing produced significant changes in both the elastic modulus and the yield strength: from 2.4 GPa and 40 MPa, in one-day-aged samples, up to 4 GPa and 62 MPa once entirely aged. Finally, it was observed that the glass transition and the enthalpic relaxation increased with ageing, agreeing with the Kohlraushch–William–Watts model.

Fate of plastic film residues in agro-ecosystem and its effects on aggregate-associated soil carbon and nitrogen stocks

Biodegradable (Bio) plastic films are widely viewed as promising alternative products of low-density polyethylene (LDPE) films to minimize plastic debris accumulation and pollution in agroecosystems. Yet, this speculation indeed lacks of sufficient evidences. We conducted a landfill investigation on the aging characteristics of Bio and LDPE plastic films in maize field, and the effects on soil aggregate composition and carbon & nitrogen stocks. The degradation rate of Bio film was up to 41.1% while that of LDPE film was zero. Scanning electron microscope (SEM) showed that the crack formation of Bio film had a pronounced domino effect, and FTIR showed that old Bio film displayed an extra wide peak threshold ranging from 3000 to 3500 cm^-1. Particularly, the abundance of microplastics was elevated with the increased plastic residues, and the increment mostly resulted from Bio residues. Critically, plastic residues significantly lowered the soil macro-aggregates (>0.25 mm) proportion, while increasing that of micro-aggregates (0.1-0.25 mm) in LDPE, and silt/clay fraction (<0.1 mm) in Bio respectively. They significantly promoted total nitrogen content of the aggregates with the same size, but decreased the organic carbon content, dramatically lowering the C/N. Therefore, we first identified the fate of plastic film residues in agroecosystems and revealed the serious deficiencies of Bio plastic film.

Engineered Polystyrene-Based Microplastics of High Environmental Relevance

Microplastic (MP) pollution-an emerging environmental challenge of the 21st century-refers to accumulation of environmentally weathered polymer-based particles with potential environmental and health risks. Because of technical and practical challenges when using environmental MPs for risk assessment, most available data are generated using plastic models of limited environmental relevancy (i.e., with physicochemical characteristics inherently different from those of environmental MPs). In this study, we assess the effect of dominant weathering conditions-including thermal, photo-, and mechanical degradation-on surface and bulk characteristics of polystyrene (PS)-based single-use products. Further, we augment the environmental relevance of model-enabled risk assessment through the design of engineered MPs. A set of optimized laboratory-based weathering conditions demonstrated a synergetic effect on the PS-based plastic, which was fragmented into millions of 1-3 μm MP particles in under 16 h. The physicochemical properties of these engineered MPs were compared to those of their environmental counterpart and PS microbeads often used as MP models. The engineered MPs exhibit high environmental relevance with rough and oxidized surfaces and a heterogeneous fragmented morphology. Our results suggest that this top-down synthesis protocol combining major weathering mechanisms can fabricate improved, realistic, and reproducible PS-based plastic models with high levels of control over the particles' properties. Through increased environmental relevancy, our plastic model bolsters the field of risk assessment, enabling more reliable estimations of risk associated with an emerging pollutant of global concern.

Electrospun Polylactide/Natural Rubber Fibers: Effect Natural Rubber Content on Fiber Morphology and Properties

Non-woven polylactide-natural rubber fiber materials with a rubber content of 5, 10 and 15 wt.% were obtained by electrospinning. The thermal, dynamic, and mechanical properties of the fibers were determined. It was shown that the average fiber diameter increased with adding of the NR content, while the linear and surface densities changed slightly. Using the differential scanning calorimetry, the thermal characteristics were obtained. It was found that the glass transition temperature of polylactide increased by 2–5 °C, and the melting temperature increased by 2–4 °C in the presence of natural rubber in the samples. By the method of electronic paramagnetic resonance at T = 50 and 70 °C it was determined that the mobility of the amorphous phase in PLA/NR fibers increased with the addition of NR. The adding of NR at a content of 15 wt.% increased the value of elongation at break by 3.5 times compared to pure PLA.

An inexpensive anaerobic chamber for the genetic manipulation of strictly anaerobic bacteria

Strictly anaerobic bacteria are important to both human health and industrial usage. These bacteria are sensitive to oxygen, therefore, it is preferable to manipulate these microbes in an anaerobic chamber. However, commercial anaerobic chambers (CACs) are expensive, making them less accessible to scientists with a limited budget, especially to those in developing countries. The high price of commercial chambers has hindered, at least partially, the progress of research on anaerobes in developing countries. In the research presented here, we developed an inexpensive and reliable anaerobic chamber and successfully achieved routine maintenance of eleven strictly anaerobic bacterial strains. Furthermore, genetic manipulation examples have been set for both Clostridioidesdifficile 630 and Clostridiumbeijerinckii NCIMB 8052 strains to validate that the chamber could applied to advanced genetic engineering of strictly anaerobes. C. difficile and C. beijerinckii were both genetically manipulated in this chamber, showing it's utility for the genetic engineering of anaerobes. Most importantly, the anaerobic chamber was 76% - 88% less expensive than a CACs and has similar functionality with regards to the cultivation and manipulation of strictly anaerobic bacteria. The anaerobic chamber described in this study will promote the research of anaerobes in developing counties and scientists who have limited research budgets.

Marine bacterial biodegradation of low-density polyethylene (LDPE) plastic

Polyethylene has considered as non-degradable for decades, and their degradation through marine bacteria has rarely studied. However, LDPE found a significant source of pollution in the marine environment. In the present study, four bacterial strains capable of biodegradation of LDPE were isolated from the marine environment. These bacterial isolates H-237, H-255, H-256 and H-265 were revealed close similarity with Cobetia sp., Halomonas sp., Exigobacterium sp. and Alcanivorax sp., respectively based on 16S rRNA gene sequencing method. These bacterial isolates were individually incubated for 90 days supplied with LDPE films as a carbon source using the Bushnell-Haas medium. During the biodegradation assay, bacterial isolates were formed the viable biofilm on the LDPE surface, which decreased the thermal stability of the films. At the end of the incubation study, a maximum weight loss of 1.72% of LDPE film was observed by the bacterial isolate H-255. The bacterial attachment on the film changed the physical structure (surface erosion, roughness and degradation) which were confirmed by field emission scanning electron microscopy and atomic force microscopy. The changes in the chemical structure of the LDPE film were analyzed by Attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR). This ATR-FTIR showed the shifting of peaks of C-H stretch and C=C bond stretching and the new peaks formation of C-O and -C=C- bonds in comparison to control LDPE film. Further, biodegradation of LDPE film was also confirmed by remineralization of carbon and enzymatic activities. This study revealed that the active biodegradation of LDPE film by marine bacteria and these bacteria could reduce plastic pollution in the marine environment.

Laboratory simulation of microplastics weathering and its adsorption behaviors in an aqueous environment: A systematic review

Microplastics (MPs) pollution has become a global environmental concern. MPs alone and in combination with pollutants can potentially cause significant harm to organisms and human beings. Weathering of MPs under various environmental stresses increases the uncertainty of their environmental fates. Compared with field surveys, laboratory simulation experiments are appropriate to simplify the research procedures and investigate the mechanisms. In this review, the effects of abrasion, solar radiation, chemical and thermal oxidation, microbial adhesion and colonization, and other environmental factors on the MPs and the relative laboratory simulation methods were summarized and discussed. Photo-oxidation and abrasion are the most appliable methods due to easy operation and adjustable weathering degree. Furthermore, the structural and components changes in weathering process and the applied characterization methods were generalized. In addition, one of important environmental behaviors, adsorption of the weathered MPs towards two typical pollutants was analyzed. Finally, three priorities for research were proposed. This paper conducts systematic summarized of the MPs weathering process and provides a reference for future studies to accurately determine the environmental risks of weathering MPs.

Effects of Rutile-TiO2 Nanoparticles on Accelerated Weathering Degradation of Poly(Lactic Acid)

The effect of accelerated weathering on poly(lactic acid) (PLA) and a PLA nanocomposite with rutile titanium (IV) dioxide (rutile–TiO₂) was investigated. The accelerated weathering test applied consecutive steps of ultraviolet (UV) (at 340 nm and 0.76 W m⁻² irradiance) and moisture at 50 °C for 2000 h, following the ASTM D4329 standard. The morphology, chemical structure, molecular weight, crystallization, as well as mechanical and thermal properties were thoroughly studied. Samples were characterized after 500 h, 1000 h and 2000 h exposure. Different degradation mechanisms were proposed to happen during the weathering exposure and confirmed based on the experimental data. The PLA and PLA/TiO₂ surfaces presented holes and increasing roughness over the exposure time. The molecular weight of the weathered samples decreased due to chain scission during the degradation processes. Thermal stability decreased in the presence of TiO₂ and a double melting peak was observed for the PLA/TiO₂ nanocomposite. A general improvement in the mechanical properties of the PLA/TiO₂ nanocomposite was observed over time during the accelerated weathering analysis up to 1000 h of exposure time. After 2000 h of weathering exposure, the PLA and PLA/TiO₂ became extremely brittle and lost their ductile properties. This was ascribed to a significant increase in the degree of crystallinity upon weathering, which was accelerated in the presence of TiO₂. Atomic force microscopy (AFM) using amplitude modulation–frequency modulation (AM–FM) tool confirmed the mechanical changes in the surface area of the PLA samples after accelerated weathering exposure. The stiffness and Young’s modulus achieved higher values than the unweathered ones up to 1000 h of exposure time. The changes in the physical and chemical properties of PLA/TiO₂ over the ageing time confirm the photocatalytic activity of rutile–TiO₂.

Monitoring polymer degradation under different conditions in the marine environment

The perdurability of plastics in the environment is one of the major concerns of plastic pollution and, as a consequence, oceans are accumulating large amounts of plastic. The degradation of conventional and biobased materials was evaluated through a laboratory experiment for a year simulating four different conditions in the marine environment. The water column environmental compartment was simulated under euphotic and aphotic (with and without light availability) conditions. The seafloor environmental compartment was simulated with sediment under non-polluted and polluted conditions. By combining weight loss (%), spectroscopic and thermal analyses, the degradation patterns regarding the polymer structure were assessed. The studied biobased materials were polylactic acid (PLA) based materials and showed higher degradability than conventional ones. The weight loss of conventional materials was not influenced by the water column or sediment, while in PLA-based materials, the degradation rates were ca. 5 times greater in the sediment than in the water column. The absorbance (Abs) value at 3400 cm^-1 for polyethylene terephthalate (PET), and carbonyl (CO) index for PET and PLA could be useful to detect early signs of degradation. The crystallization index could be a useful parameter to discriminate degradation stages. The obtained results highlight the different degradability rates of materials depending on the specific environmental marine conditions.