At present, great importance is dedicated to the use of waste biomass for the sustainable provision and fractionation of natural resources. This is particularly true for the production of biopolymers to promote the development of novel material products based on sustainability. This growing interest is driven by socioeconomic and environmental factors. Feathers from chickens are regarded as waste from the poultry meat production sector. These organic wastes serve as natural keratin sources for synthesizing nanoparticles to develop a new generation of multifunctional biocomposites for drug delivery purposes. Thus, in this research keratin was isolated from feathers by extraction in subcritical water (SubCW) at 180 °C, 20 bar for 1 h. This recycled keratin was used to develop advanced keratin-based particles. The aim of this study was to explore the potential of subcritically extracted keratin to form electrostatically stabilized particles with different types of interaction agents—namely natural polyelectrolytes and a multivalent ionic crosslinker (TPP)—and to evaluate their performance as a multifunctional keratin-based delivery platform. To investigate the complexation ability of keratin, three polyelectrolytes with different functional groups were used for particle synthesis at specific pH values, namely alginate with carboxyl groups, chitosan with amino groups, and penta-ionic sodium tripolyphosphate (TPP) with phosphate groups. Dynamic Light Scattering (DLS) analysis showed that complex formation between keratin-alginate and keratin-chitosan resulted in microparticles, and colloidal particles were formed only in the case of keratin-TPP. The ATR-FTIR spectra of the particles indicate that electrostatic interactions were the driving force for the complex formation between keratin and oppositely charged polyelectrolytes. The antioxidant activity of keratin diminishes upon the incorporation of alginate, chitosan, and TPP. The keratin-TPP particles, identified as optimal, underwent additional assessment as a keratin-based delivery platform for the model drug amoxicillin. UV/VIS spectroscopy indicated the successful encapsulation of amoxicillin (encapsulation efficiency of 69%), with a gradual release reaching up to 96% over a 6-hours period. Antimicrobial examination showed that the increased inhibition against both E. coli and S. aureus in the keratin-based delivery platform compared to pure amoxicillin can be attributed to the successful and controlled release of the drug from the particles. Consequently, these particles exhibit promising potential as a delivery system, offering simultaneous antioxidant and potentially antimicrobial properties. The potential resistance of amoxicillin is acknowledged, but amoxicillin remains a relevant model drug for initial exploration of keratin-based delivery platforms. Further studies may explore the combination with other antibiotics for enhanced efficacy. The safety and purity of SubCW-extracted keratin are assured as it undergoes rigorous analysis, including SDS-PAGE and FTIR spectroscopy.

The increasing accumulation of plastic-based electronic waste, such as compact discs (CDs), poses a major challenge to the environment due to their longevity and limited recyclability. This study investigates the hydrothermal degradation of end-of-life CDs – which are mainly composed of polycarbonate – under subcritical and supercritical water conditions as a sustainable approach for waste recycling. The hydrothermal treatments were carried out at temperatures ranging from 250 °C to 450 °C for reaction times of 5 to 60 min. The resulting product phases, i.e. water-soluble, diethyl ether (DEE)-soluble and solid gaseous, were quantified. The composition of the DEE-soluble phase was characterised by gas chromatography. The results showed a strong dependence of the product distribution on temperature and residence time. The yield of the DEE-soluble phase peaked at 450 °C after 5 min (96.9 ± 1.0 %) and decreased at longer reaction times due to secondary decomposition into gas phase products. The major organic compounds in the DEE phase included bisphenol A, phenol and 4-isopropylphenol, while the concentration of other phenol derivatives such as 4-ethylphenol, 4-methylphenol (p-cresol) and 4-isopropenylphenol was generally low and below 5 %. These results show that hydrothermal treatment effectively converts waste CDs into valuable liquid and gaseous products, thereby reducing the amount of solid waste. The process offers a promising strategy for the recovery of resources from waste CDs.

Bio-based polymers are an important step towards solving environmental problems, but there is a need to consider and develop procedures for dealing with these materials at the end of their life and to ensure that effective disposal methods are available. Recently, polylactic acid (PLA) has replaced many plastics based on non-renewable resources. In this work, subcritical water was used for the chemical decomposition of virgin and waste PLA under different atmospheres. The main degradation product was lactic acid with very high yields. The highest yield of lactic acid was obtained under N2 atmosphere, where the optimum conditions were 200 degrees C and 60 min and the yield was 88.96 f 1.5 % for virgin PLA and 54.58 f 1.3 % for waste PLA. In an air atmosphere, the maximum yields of lactic acid were obtained at 250 degrees C and 30 min and were slightly lower than in the N2 atmosphere, i.e. 87.20 f 0.9 % for virgin PLA and 49.29 f 0.6 % for waste PLA. The lower yield of lactic acid from waste PLA is due to the impurities and additives in waste PLA. Other carboxylic acids were also formed in the aqueous phase, while the gas phase mainly contained CO2, N2/CO and C1-C5 hydrocarbons. The hydrothermal degradation pathway was presented and the electricity costs for lab-scale PLA recycling were estimated. With this sustainable technology, PLA could be successfully recycled down to its monomer, providing a secondary raw material for the re-synthesis of the polymer, closing the loop and reducing the impact on the environment.

Corncobs are a widespread and renewable by-product of corn cultivation that are typically considered waste or low-value material. Corncobs contain hemicellulose, cellulose, and lignin, which can be converted into valuable products using suitable techniques. Subcritical water is increasingly used as a green medium for the extraction of valuable components from biomass, as it has many advantageous properties (high yield, pure extracts, shorter times) compared to other organic solvents. For this reason, subcritical water was used in this study to extract valuable components from corncobs at different temperatures (150–250 °C) and reaction times (10–60 min). During the decomposition of corncobs, numerous valuable products are formed in the aqueous phase depending on the temperature and reaction time. In addition to sugars and their derivatives, phenolic compounds were also formed, which are of great importance in numerous applications. It was found that at low temperatures (150–170 °C) the hemicellulose in the corncobs begins to decompose and, in particular, the sugars (glucose, xylose, arabinose, and galactose) are initially formed in the aqueous phase. Higher temperatures (200 and 250 °C) are more favorable for the decomposition of corncobs into valuable components. The yield of sugars increases with temperature due to the degradation of the cellulose content of the lignocellulosic biomass. At the same time, several new valuable products (furfural, 5-hydroxymethylfurfural (5-HMF), 1,3-dihydroxyacetone, levulinic acid, and formic acid as well as phenolic components) are formed through the degradation of lignin and the further degradation of sugars. The most important products are certainly the furfurals, which are central platform compounds. The highest furfural content was reached at 200 °C and 60 min and accounted for almost half of all components in the aqueous phase (472.01 ± 5.64 mg/g dry extract). These biomass-derived sugars and derivatives can be used in the production of fuels, pharmaceuticals, biodegradable polymers, and surfactants.

The degradation of bisphenol A (BPA), the main monomer of polycarbonate, was investigated under subcritical water conditions to better understand its decomposition as a function of process conditions and to provide useful data for designing a recycling process to convert polycarbonate into valuable products. Hydrothermal experiments were conducted in a batch reactor at temperatures ranging from 250 to 350 degrees C, with reaction times from 5 to 30 min and water-to-material ratios of 5, 10, and 15 (mL/g), following a Box-Behnken design with response surface methodology (RSM). The influence of process parameters on phase distribution, total carbon content, and product composition was evaluated. The results showed that temperature and reaction time were the most significant factors affecting BPA decomposition, while the water-to-material ratio had a minor effect. The recovery of the DEE (diethyl ether)-soluble phase decreased with increasing temperature and time, accompanied by a corresponding increase in the water-soluble phase yield and total carbon content. Analysis of the DEE-soluble fraction revealed the sequential transformation of BPA into 4-isopropenylphenol, 4-isopropylphenol, and phenol, with phenol becoming the dominant degradation product at higher temperatures. These findings provide new insights into the hydrothermal decomposition mechanism of BPA and form a basis for understanding polycarbonate degradation and developing sustainable subcritical water recycling processes for polymeric materials.

Hydrothermal degradation processes are a particularly promising eco-friendly approach to keratin isolation from biomass. They, however, result in products with a broad molecular weight distribution, which can be particularly unfavorable for fiber production. In this study, we aimed to determine whether hydrothermally degraded feather and wool waste is suitable to produce nanofibers that retain the key functional properties of keratin, such as antioxidant activity and biocompatibility. Keratin/PEO blends were used for needleless electrospinning of nanofibers cross-linked with two different cross-linkers, ethylene glycol diglycidyl ether (EGDE) and pentaerythritol triacrylate (PETA), to improve their stability to water. The surface tension, pH, turbidity, zeta potential, and protein concentration of the keratin extract solutions were analyzed. The morphology of the produced nanofibers was analyzed using a scanning electron microscope, the surface chemical structure by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR analysis), and the cross-linking success by water contact angle measurements. The antioxidant capacity and the biocompatibility of the nanofiber mats with skin cells were investigated using a 2,2 '-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assay and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) vitality test, respectively. The results showed that despite the unfavorable starting materials with a wide molecular mass range from 3 to 15 kDa and low average molecular weights keratin products obtained by a green hydrothermal extraction process can be used to produce nanofibers with excellent antioxidant properties and skin cell biocompatibility. The cross-linking of the nanofibers resulted in hydrophobic nanofiber surfaces; however, it impaired their biocompatibility with skin cells compared to noncross-linked nanofibers.

At present, great importance is attached to the use of waste biomass for the sustainable provision and fractionation of natural resources. This is particularly true for the production of biopolymers to promote the development of novel material products based on sustainability. This increased focus is driven by socio-economic and environmental considerations. Feathers from chickens are regarded as a waste from the poultry meat production sector. These organic wastes can be used as natural keratin sources for applications in the formation of nanoparticles to develop a new generation of multifunctional biocomposites. Thus, in this research keratin was isolated from feathers by extraction in subcritical water (SubCW) at 180°C, 20 bar for 1 h. This recycled keratin was used to develop advanced keratin-based particles. To investigate the complexation ability of keratin, three polyelectrolytes with different functional groups were used for particle synthesis at specific pH values, namely alginate with carboxyl groups, chitosan with amino groups, and penta-ionic sodium tripolyphosphate (TPP) with phosphate groups. Dynamic Light Scattering (DLS) analysis showed that complex formation between keratin-alginate and keratin-chitosan resulted in microparticles, and colloidal particles were formed only in the case of keratin-TPP. The ATR-FTIR spectra of the particles indicate that electrostatic interactions were the driving force for the complex formation between keratin and oppositely charged polyelectrolytes. The antioxidant activity of keratin diminishes upon the incorporation of alginate, chitosan, and TPP. The keratin-TPP particles, identified as optimal, underwent additional assessment as a drug delivery system for the model drug amoxicillin. UV/VIS spectroscopy indicated the successful encapsulation of amoxicillin (encapsulation efficiency of 69.24%), with a gradual release reaching up to 96% over a 6-hour period. Antimicrobial examination showed that the increased inhibition against both E. coli and S. aureus in the drug delivery system compared to pure amoxicillin can be attributed to the successful and controlled release of the drug from the particles. Consequently, these particles exhibit promising potential as a delivery system, offering simultaneous antioxidant and potentially antimicrobial properties.

The hydrothermal degradation of different polyolefins (virgin and recycled HDPE, recycled LLDPE, metallocene LLDPE, LDPE waste, virgin and recycled PP, PP waste) and their blends in different forms (granulate, foil) was investigated with supercritical water at 450 °C. The degradation of HDPE was investigated in a time range from 15 min to 240 min. The maximum yield of the oil phase was obtained at a degradation time of 60 min and was over 90 %, therefore all further experiments were carried out at a reaction time of 60 min. It was found that the composition of the oil obtained, and its calorific value depend on the type of material degraded. The oils obtained from PE materials contained between 65.3 % and 69.5 % saturated hydrocarbons, 11.4 % to 17 % olefins and 8.9 % to 20 % aromatics, while the oils from PP materials contained 40.8 % to 45.9 % aromatics, 28.4 % to 33.4 % saturated hydrocarbons and 10.6 % to 19.2% olefins. The main compounds in the oils from PP materials were the C9 compounds and from PE materials the C16 compounds. An exception were the oils from rLLDPE-1-g and LDPE-b, in which C8 compounds were most abundant and which contained the highest proportion of C17 – C31 hydrocarbons (approx. 17 %) compared to oils from other PE and PP materials (1.3 % – 7.1 %). The HHV of the oils was between 29.4 and 45.7 MJ/kg and was highest for the oils where the gasoline/heavy oil ratio was less than 1, while the HHV of the gas phase was between 48.4 MJ/kg and 50.7 MJ/kg.

Plastics play a crucial role in our daily lives. The challenge, however, is that they become waste and contribute to a global environmental problem, increasing concerns about pollution and the urgent need to protect the environment. The accumulation and fragmentation of plastic waste, especially micro- and nanoplastics in aquatic systems, poses a significant threat to ecosystems and human health. In this study, the decomposition and fragmentation processes of conventional and biobased plastic waste in simulated water bodies (waters with different pH values) and in real water systems (tap water and seawater) are investigated over a period of one and six months. Three types of plastic were examined: thermoplastic polyethylene terephthalate and thermoset melamine etherified resin in the form of nonwovens and biobased polylactic acid (PLA) in the form of foils. Such a comprehensive study involving these three types of plastics and the methodology for tracking degradation in water bodies has not been conducted before, which underlines the novelty of the present work. After aging of the plastics, both the solid fraction and the leachate in the liquid phase were carefully examined. The parameters studied include mass loss, structural changes and alterations in functional groups observed in the aged plastics. Post-exposure assessment of the fragmented pieces includes quantification of the microplastic, microscopic observations and confirmation of composition by in situ Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy. The leachate analysis includes pH, conductivity, turbidity, total carbon and microplastic size distribution. The results highlight the importance of plastic waste morphology and the minor degradation of biobased PLA and show that microfibers contribute to increased fragmentation in all aquatic systems and leave a significant ecological footprint. This study underlines the crucial importance of post-consumer plastic waste management and provides valuable insights into strategies for environmental protection. It also addresses the pressing issue of plastic pollution and provides evidence-based measures to mitigate its environmental impact.

This research showcases the use of hydrothermally extracted solutions from poultry feathers and wool as eco-friendly and versatile textile finishes. These solutions, derived from waste biomass containing the keratin biopolymer, were obtained through environmentally conscious hydrothermal degradation processes. Initially, the study focused on analysing the chemical parameters and properties of both dialysed and non-dialysed solutions extracted from feathers and wool. The investigation tracked primarily the presence of keratin within these solutions. Upon application to polyester textiles as the reference material, the presence of these solutions on the fabric surface was confirmed successfully. A thorough physicochemical analysis of the treated textiles involved various analytical techniques. These encompassed surface composition analysis via X-ray Photoelectron Spectroscopy (XPS) and Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), assessment of wettability through Contact Angle measurements, determination of surface charge using surface zeta potential, and examination of the thermal and flame-retardant properties via Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and calorimetric tests. In addition, the colour, UV radiation transmission and antioxidant activity were evaluated using standard tests. The remarkable effects of the treatment have been observed in the exceptional antioxidative action, fire resistance, UV protection and enhanced hydrophilicity of these innovative multifunctional textiles. This approach holds significant implications across research, economics and society, enriching Material Science by deepening the understanding of materials and their multifaceted properties. Moreover, it promotes resource efficiency, opens new sustainable textile market prospects, and contributes to social impact by supporting environmental sustainability, engaging communities and ensuring health and safety benefits.

Pistachio and walnut shells accumulate in large quantities as waste during food processing and represent a promising lignocellulosic biomass for the extraction of valuable components. Subcritical water technology was used as an environmentally friendly technique to study the extraction of active ingredients and other valuable degradation products from walnut and pistachio waste. Subcritical water extraction (SWE) was carried out under different process conditions (temperature (150–300 °C) and short reaction times (15–60 min)) and compared with conventional extraction using different organic solvents (acetone, 50% acetone and ethanol). The extracts obtained from pistachio and walnut shell waste are rich in various bioactive and valuable components. The highest contents of total phenols (127.08 mg GA/g extract at 300 °C for 15 min, from walnut shells), total flavonoids (10.18 mg QU/g extract at 200 °C for 60 min, from pistachio shells), total carbohydrates (602.14 mg TCH/g extract at 200 °C for 60 min, from walnut shells) and antioxidant activity (91% at 300 °C, for 60 min, from pistachio shells) were determined when the extracts were obtained via subcritical water. High contents of total phenols (up to 86.17 mg GA/g extract) were also determined in the conventional extracts obtained with ethanol. Using the HPLC method, sugars and their valuable derivatives were determined in the extracts, with glucose, fructose, furfurals (5-hydroxymethylfurfural (5-HMF) and furfural) and levulinic acid being the most abundant in the extracts obtained by subcritical water. The results show that subcritical water technology enables better exploitation of biowaste materials than conventional extraction methods with organic solvents, as it provides a higher yields of bioactive components such as phenolic compounds and thus extracts with high antioxidant activity, while at the same time producing degradation products that are valuable secondary raw materials.

Tetra pak packaging is one of the most frequently used types of packaging in the food industry. The recycling of the tetra pak packaging waste presents a difficult task because of its multi-layered, multi-component structure. In this study, the degradation of tetra pak packaging in subcritical (SubCW) and supercritical (SCW) water was investigated. The experiments were carried out in one (SCW) or two stages (SubCW and SCW), whereby the influence of the reaction temperature and time on the yield and composition of the products obtained was investigated. The maximum oil phase yield achieved in a one-stage and a two-stage degradation process was 60.7% and 65.5%, respectively. The oil and gas phases were composed of different types of hydrocarbons. Higher temperature and longer time led to higher amounts of saturated aliphatic hydrocarbons in both the oil and gas phases. The aqueous phase contained sugars (glucose, fructose) and sugar derivatives (levulinic acid, glyceraldehyde, furfurals). Based on these results, the degradation pathway of waste tetra pak packaging in SubCW and SCW was proposed. The results of the study show that the degradation of waste tetra pak packaging with SubCW and SCW is a promising recycling process.

This research showcases the use of hydrothermally extracted solutions from poultry feathers and wool as eco-friendly and versatile textile finishes. These solutions, derived from waste biomass containing the keratin biopolymer, were obtained through environmentally conscious hydrothermal degradation processes. Initially, the study focused on analysing the chemical parameters and properties of both dialysed and non-dialysed solutions extracted from feathers and wool. The investigation tracked primarily the presence of keratin within these solutions. Upon application to polyester textiles as the reference material, the presence of these solutions on the fabric surface was confirmed successfully. A thorough physicochemical analysis of the treated textiles involved various analytical techniques. These encompassed surface composition analysis via X-ray Photoelectron Spectroscopy (XPS) and Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), assessment of wettability through Contact Angle measurements, determination of surface charge using surface zeta potential, and examination of the thermal and flame-retardant properties via Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and calorimetric tests. In addition, the colour, UV radiation transmission and antioxidant activity were evaluated using standard tests.The remarkable effects of the treatment have been observed in the exceptional antioxidative action, fire resistance, UV protection and enhanced hydrophilicity of these innovative multifunctional textiles. This approach holds significant implications across research, economics and society, enriching Material Science by deepening the understanding of materials and their multifaceted properties. Moreover, it promotes resource efficiency, opens new sustainable textile market prospects, and contributes to social impact by supporting environmental sustainability, engaging communities and ensuring health and safety benefits.

The (bio)degradation of plastics in soil is a complex process that depends on several factors, such as the type of plastic, environmental conditions, microbial activity, and the presence of other organic matter in the soil. Ageing in soil thus also influences the physicochemical properties of plastic materials to understand the mechanisms and investigate the changes in plastic properties in soil due to decomposition and followed by fragmentation, the gravimetric, morphological, surface, and thermal properties of plastics were studied some of them for the first time. The study was performed for three different plastics materials, polyethylene terephthalate (PET-fib) and melamine etherified resin (MER-fib) in the form of nonwoven fabrics and polylactic acid (PLA) in the form of foils. The materials were exposed to soil for one, three and six months, only in the case of PLA foil for final four months. The results show that remarkable changes were observed especially for MER-fib and PLA after exposure to soil, which is related to the bio and chemical degradation proceses. The biodegradation process was indicated with the soil microorganisms used in the study (lactic acid bacteria, photosynthetic organisms, yeasts, actinomycetes, and enzymatically active fungi), while chemical degradation showed that it may occur at the surface of the material with changes in elemental composition and chemical functionality. The microbial end products of biodegradation of MER-fib are presumably NH3 and CO2, while for PET-fib it is CO2 and for PLA it is CO2 and H2O, including several proposed conversion products in partial pathways. The study represent an important contribution to understanding the behaviour of the analysed (bio)plastics and the changes in their properties after exposure to natural systems for pollution countermeasures and cleaner production.

Plastics are widely used due to their versatile properties and numerous applications. However, the proper management of plastic waste is a major challenge, even though it is recyclable. The process of repeated recycling can cause the quality of the material to decrease as unwanted contaminants and pollutants increase. This can affect the chemical recycling of plastics at the end of their life and the recovery of secondary products that can be used in other applications. In this study, the chemical degradation of virgin polypropylene (vPP) and recycled polypropylene (rPP) was investigated in supercritical water at a temperature of 450 °C and a reaction time of 15 to 240 min. The oil phase was the primary decomposition product and was obtained in high yield, which reached a maximum after 30 min of reaction time and was 96.9 % for vPP and 94.5 % for rPP. The results of our study show that there are some differences in the product composition depending on which material (vPP or rPP) is chemically recycled.

The isolation of keratin from poultry feathers using subcritical water was studied in a batch reactor at temperatures (120–250 °C) and reaction times (5–75 min). The hydrolyzed product was characterized by FTIR and elemental analysis, while the molecular weight of the isolated product was determined by SDS-PAGE electrophoresis. To determine whether disulfide bond cleavage was followed by depolymerization of protein molecules to amino acids, the concentration of 27 amino acids in the hydrolysate was analyzed by GC/MS. The optimal operating parameters for obtaining a high molecular weight protein hydrolysate from poultry feathers were 180 °C and 60 min. The molecular weight of the protein hydrolysate obtained under optimal conditions ranged from 4.5 to 12 kDa, and the content of amino acids in the dried product was low (2.53% w/w). Elemental and FTIR analyses of unprocessed feathers and dried hydrolysate obtained under optimal conditions showed no significant differences in protein content and structure. Obtained hydrolysate is a colloidal solution with a tendency for particle agglomeration. Finally, a positive influence on skin fibroblast viability was observed for the hydrolysate obtained under optimal processing conditions for concentrations below 6.25 mg/mL, which makes the product interesting for various biomedical applications.

The particles from the gas-saturated solutions (PGSS) process was employed to micronize brown algae pigments separated by different extraction techniques. The particle formation of pigments with a coating material, polyethylene glycol (PEG), was carried out by the PGSS process using supercritical CO2. Environmental scanning electron microscopy (ESEM) and Fourier-transform infrared spectroscopy (FTIR) were performed to characterize the produced particles, while encapsulation efficiency was determined using spectrophotometric methods. The physical properties of obtained microparticles were also determined. The PGSS process enabled a high encapsulation yield in the range from 61.60 to 73.73%, and high encapsulation efficiency in terms of chlorophyll a, chlorophyll b, and carotenoid content. The release of CO2 during the PGSS process gave the microparticles their characteristic open and porous form, and enhanced the solubility and flow properties at the same time.

Plastics are among the most-used materials globally, with thousands of different grades and a wide range of applications. However, its end-of-life management is a common issue, despite most plastics produced today containing highly recyclable thermoplastics. The quality of recycled plastic material should be enhanced as it depends on several factors, such as cross-contamination, presence of additives, impurities and degradation rate. In this study, a comparative analysis of thermochemical characteristics of virgin and recycled commonly-used thermoplastic polymer, high-density polyethylene (HDPE), was performed to study the impact of recycling on the material properties. The proximate and ultimate analysis, identification of functional groups and thermal behaviour were performed to study the chemical changes in the recycled and virgin material. The results showed that recycled HDPE started to degrade at a lower temperature than virgin HDPE, with a lower degradation rate (92.7 wt.%) compared to virgin HDPE (99.6 wt.%) due to the presence of impurities and other factors. Calorific values of both samples were comparable, while the degree of crystallinity was 79.8 % for virgin HDPE and around 19 % lower for recycled HDPE samples. Significant differences between recycled and virgin material were also obtained in terms of melting and crystallisation enthalpies.

Among the most pressing environmental issues is the rapidly increasing accumulation and fragmentation of plastic waste materials, particularly in freshwater and marine environments. In this study, polyethylene terephthalate (PET) plastic waste, as one of the major environmental concerns, was exposed to various aquatic environments in the form of plastic bottles and non-woven fibres to investigate the end-of-life behaviour and the formation of micro-, and nanoplastics during the degradation process. The research focuses on tracking plastic waste in model waters (with pH values of 4, 7 and 10) and real waters (seawater and tap water). Both the solid and liquid phases were analysed for fragmentation and leaching of plastics after one month of observation. In the solid phase, gravimetric analysis, presence of functional groups by Fourier Transform Infrared Spectroscopy (ATR-FTIR), morphology and size by optical microscope were measured. In the liquid phase, ecological parameters (pH, conductivity, turbidity, chemical oxygen demand (COD) and total organic carbon (TOC)) and micro/nanoplastic formation (particle size and FTIR analysis under the microscope) were characterised. The results show that PET debris litter to the aquatic environment, in the form of non-woven fibres, has greater negative environmental impacts on turbidity, COD and micro/nano fragment formation. The outcomes of this study indicate a potentially hazardous risk of improperly treated plastic material in various aquatic environments, especially with the type of material structure, such as fibre structure, due to the increased release of micro/nanoplastic into the aquatic environment, which may have serious eco-toxicological effects on wildlife. This study underlies that due to the rapid fragmentation of fibrous PET plastic material, the latter should be properly collected and processed.

The chemical degradation of PVC waste in SCW between 400 and 425 °C and reaction times from 30 to 60 min was studied. The PVC waste in SCW decomposed into the gas, oil, water soluble, and solid phases. The highest yield of the gas and oil phases was achieved at the temperature of 425 °C after 60 min. By increasing the reaction time at 400 °C, the yield of chloride ions in the aqueous phase increased and reached the maximum at 60 min. The gas and oil phases contained many valuable compounds similar to crude oil. Alkanes and chloroalkanes; alkenes, alicyclic, and aromatic hydrocarbons; as well as alcohols were the main groups of hydrocarbons in the oil phase, while the gas phase contained only light hydrocarbons (C1–C6), CO2, and small amounts of H2. This confirmed that the largest chlorine content remains in the aqueous phase and does not pass into the gas phase. It can be concluded that SCW presents effective decomposition media for plastic waste.