Search Results (432)

The rapid growth in the use of carbon fiber-reinforced polymers (CFRPs) and fused-deposition-modeled (FDM) polylactic acid (PLA) has generated substantial non-biodegradable and thermoplastic waste streams, creating urgent needs for scalable recycling and valorization strategies. This study develops and evaluates an integrated route that chemically recovers carbon fibers (CFs) from CFRP waste and converts them into high-performance reinforcements for recycled PLA matrices. CFRP fragments were pre-swollen in acetic acid (120 °C, 1 h), then depolymerized by means of oxidation with 1 M KMnO₄ (100 °C, 2 h), washed, dried (100 °C, 24 h), and size-reduced by means of cryogenic milling. Recycled CFs (treated) and untreated CFRP fragments were blended with 3D-printing PLA waste at 10, 20 and 30 wt.% via melt mixing (175 °C, 5 min, 70 rpm) and molded into ASTM D638 dog-bone specimens. Materials were characterized via XRD, FTIR, Raman, SEM and mechanical testing. XRD and Raman confirmed retention of the graphitic backbone after treatment; FTIR and Raman revealed oxygen-containing surface functionalization consistent with oxidation, while SEM showed effective removal of epoxy and improved fiber surface cleanliness. Compared with neat PLA (tensile strength 45.4 MPa; modulus 2.6 GPa; elongation 6.3%), composites reinforced with chemically recycled CFs exhibited marked mechanical enhancement: at 30 wt.% treated CF, the tensile strength increased to 102.6 MPa (+126%), elastic modulus to 11.7 GPa (+350%), and toughness to 250.3 MPa, while ductility decreased to 2.9%. Equivalent composites with untreated CFRP exhibited smaller gains (30 wt.%: tensile 87.3 MPa; modulus 10.3 GPa), highlighting the benefit of epoxy removal and surface activation for fiber–matrix adhesion. The proposed chemical recycling pathway is operationally simple and cost-effective, produces reusable CFs with preserved graphitic structure and enhanced surface chemistry, and enables the fabrication of high-performance, waste-derived PLA composites suitable for structural and engineering applications. This work demonstrates a viable waste-to-value approach that advances circularity for both CFRP and 3D-printing polymer waste streams. Full article

This study investigates asymmetric consumer responses to recycled thermoplastics, with a focus on the roles of eco-consciousness, sustainability knowledge, perceived concerns, trust, and value congruence. Using survey data from Hungarian consumers, the study applies linear and binary logistic regression analyses to examine how these factors influence brand perception, willingness to pay, and communication preferences. The results show that economic concerns act as a dominant barrier, significantly reducing both brand evaluations and willingness to pay, while functional concerns play a more limited role. Trust in sustainability communication and positive brand perception emerge as strong predictors of willingness to pay, with brand perception showing a stronger effect. Eco-consciousness consistently influences consumer responses, whereas sustainability knowledge demonstrates more selective and context-dependent effects. In addition, consumers show a clear preference for credible, evidence-based communication, while informal and promotional signals are less effective. Overall, the findings highlight the importance of reducing perceived risk, strengthening brand perception, and aligning sustainability communication with consumer expectations to support the adoption of recycled thermoplastics in the automotive industry. Full article

Additive manufacturing offers transformative opportunities but faces barriers due to costly, imported filaments. This study at Caraga State University, Cabadbaran Campus, developed a prototype automated filament extrusion system using recycled thermoplastics, specifically polypropylene (PP) and PET, to address material scarcity and plastic waste. Employing a developmental–descriptive design, the system integrated heating, extrusion, spooling, and microcontroller-based controls. Results confirmed functional capability, producing filaments with acceptable dimensional consistency, though challenges in accuracy and flexibility remain. The project advances sustainable, affordable 3D printing, supports circular economy principles, enhances technical education, and empowers local innovators toward inclusive, environmentally responsible manufacturing. Full article

Polymer-based composites with magnetic properties are promising materials that are able to combine the usual polymer features (low density, high electrical resistance, enhanced flexibility, and processability, etc.) with magnetic properties typically associated with ferro- or ferrimagnetic metals, alloys or metal oxide. The combination of recycled NdFeB powders with additive manufacturing techniques based on material extrusion enables the production of magnetic composites. The novelty of this approach lies in the use of 3D printing supported by an external magnetic field, which is used to align the particles during the printing process and thus improve the final magnetic properties. This approach represents a sustainable strategy for the recovery of electronic waste, converting it into high-value-added magnetic materials intended for additive manufacturing applications. Micrometric particles made of a Neodymium–Iron–Boron (NdFeB) alloy are compounded with a flexible thermoplastic matrix made of polybutylene adipate-co-terephthalate (PBAT). The NdFeB alloy is recovered from permanent magnets of obsolete hard drives and is demagnetized, ground to powder under an inert atmosphere, and finally sieved to a particle size below 50 µm. The obtained powder is mixed with the polymer using a twin-screw extruder. The composite material containing the NdFeB particles is then processed to obtain a calibrated filament, used for the fused deposition modeling (FDM) three-dimensional (3D) printing of magnetic composites. To improve the composite’s ferromagnetic behavior, the particles were aligned along the stacking direction of the layers during the 3D FDM process by printing directly onto a permanent magnet placed on the build plate. Composites containing up to 50% by weight of recycled NdFeB powder were successfully processed using FDM technology, exhibiting increased stiffness, with the storage modulus rising from 123 to 178 MPa at 20 °C, while magnetic field-assisted printing increased the remanence from 11 to 28 emu/g and improved the reduced remanence from 0.21 to 0.49, corresponding to an estimated fourfold improvement in the magnetic energy product. Full article

This study evaluates the industrial-scale feasibility of injection moulding of a recycled polypropylene composite reinforced with recycled fibers derived from an industrial waste stream. Although previous laboratory-scale research has demonstrated the potential of natural fiber-reinforced thermoplastics, their large-scale industrial implementation remains limited due to uncertainties related to processability, reproducibility, and manufacturing robustness. In this work, the composite material is validated through injection moulding trials carried out in four independent industrial companies located in Andalusia (Spain) and three industrial case studies across different industrial sectors in Slovenia, operating under real production conditions. The extrusion process was characterized in terms of process stability, confirming continuous operation with automated dosing and stable material flow without interruptions under industrial conditions. Injection processing parameters, cycle stability, part quality, and defect formations are also considered important when assessing the manufacturing feasibility. The multi-site validation approach enables the evaluation of reproducibility across different injection moulding systems and mould geometries, providing critical insights into the scalability and technological readiness level of recycled natural fiber-reinforced polypropylene composites. Although direct energy consumption measurements were not systematically recorded, the observed processing stability and cycle repeatability indicate a consistent and energy-efficient operation under industrial processing conditions. The results contribute to bridging the gap between laboratory-scale material development and real industrial implementation. Full article

Development of sustainability systems for assessment of environmental impacts remains a paramount challenge for green and circular manufacturing of polymers. In this study, a comprehensive life cycle assessment (LCA) framework is developed for European polymeric waste by integrating OpenLCA, Ecoinvent v3.11, and Python-based machine learning (ML) algorithms. Cradle-to-gate, service-life, and cradle-to-grave assessments are performed for representative thermoplastic composite systems, including PP–PET–cotton, HDPE–glass fiber, and PEEK–carbon fiber composites, covering domestic, engineering, and high-performance polymer categories. The results demonstrate that raw material extraction and manufacturing stages dominate environmental impacts, contributing the highest shares to climate change, ecotoxicity, and non-renewable energy consumption. PP-based composite systems exhibit the lowest overall environmental burdens due to lower processing energy and simpler molecular structures, while HDPE-based systems show moderate impacts. PEEK-based composites present the highest impacts per unit mass, driven by energy-intensive synthesis and high processing temperature. Environmental impacts are evaluated using EF v3.1 and ReCiPe methodologies, supported by Monte Carlo simulations and ML-assisted uncertainty quantification. Monte Carlo simulations and ML-assisted LCA provide probabilistic ranges, uncertainty quantification, and predictive insights into impact indicators, enabling the development of a quantitative sustainability system based on probability–impact relationships. A Europe-wide assessment of 57 Mt of polymeric waste highlights that environmental burdens are concentrated in countries with high polymer production and consumption, emphasizing the importance of energy mix, recycling efficiency, and waste management strategies. Overall, this work demonstrates that digitalized LCA coupled with ML offers a powerful decision-support framework for sustainable polymer design, recycling optimization, and circular economy policy development, supporting the transition toward low-carbon and resource-efficient polymer systems in Europe. Full article

The railway sector is crucial for transportation, but infrastructure maintenance generates significant waste and requires large amounts of materials, increasing environmental impact. Circular economy integration mitigates this impact through material recovery. This study focused on the recycling of bushes embedded in railways sleepers, currently disposed of in landfills, obtaining high-density polyethylene (HDPE). The developed scalable process converted contaminated bushes into pellets, whose environmental sustainability was assessed through life cycle analysis. Challenges of the recycled material, such as high viscosity and heterogeneity, were partially addressed with a slipping agent and a compatibilizer, increasing the material melt index from 0.71 to 1.62 g/10 min. Carbon fiber waste addition improved thermal stability, mechanical stiffness, and electrical conductivity. Compatibilized blends offered the best balance of mechanical properties but lower electrical conductivity. The Young modulus was increased from 1.20 GPa for the neat matrix to 4.40 GPa for the system containing 30% carbon fibers in weight, with no significant decreases in the yield stress, while showing the lowest electrical conductivity. To reduce environmental impact and produce a tougher material without compromising conductivity, the compatibilizer was replaced with HDPE from PET bottle caps, resulting in comparable mechanical properties and higher electrical conductivity but reduced fiber/matrix interface. Full article

Adhesives and sealants are critical yet still underrepresented components in packaging science. Existing reviews mainly address specific chemistries, sealing technologies, or application niches, whereas integrated analyses of adhesive and sealant families within a unified packaging-system framework remain limited. This review addresses this gap by proposing a three-dimensional classification framework—functional role, material chemistry and activation mechanism, and performance constraints—that connects functional roles, processing routes, regulatory constraints, and circularity requirements. The framework is applied across natural, synthetic, hot-melt, pressure-sensitive, and tie-layer adhesives, as well as conventional thermoplastic, barrier-oriented, and biodegradable sealant systems. Special attention is given to hybrid systems operating at the boundary between bonding and sealing, and to the performance–recyclability trade-offs that arise in multilayer architectures. Structure–property–function relationships are analysed qualitatively with respect to bond and seal strength, seal initiation temperature, hot-tack behaviour, and end-of-life compatibility. Part I establishes the classification and functional groundwork for the two-part review; Part II will extend the analysis to quantitative performance data, advanced materials, and emerging technologies. Full article

The increasing demand for sustainable and lightweight structural systems has motivated the development of alternative materials for wind turbine tower applications, where conventional steel structures are associated with high material consumption and environmental impact. In this study, a novel steel-reinforced recycled thermoplastic composite system is proposed as an alternative structural solution. To enable the design and practical application of such composite systems, the mechanical properties of the recycled thermoplastic matrix were experimentally characterized. Compression and tensile tests revealed average yield strengths of approximately 32 MPa in compression and 7.8 MPa in tension. To account for the environmental conditions encountered in field applications, the temperature-dependent mechanical behavior of the material was investigated. Since the critical mechanical response of the thermoplastic matrix in the composite system is governed by compression rather than tension, the study was limited to compression tests under elevated temperatures. The results show that the compressive yield strength decreases to approximately 31 MPa at 55 °C. An analytical model based on the transformed-section approach was also developed to predict the flexural behavior of the composite section and was validated through three-point bending tests, with an analytically predicted yield load of approximately 31.5 kN showing good agreement with experimental results. To assess structural applicability at a larger scale, a full-scale composite wind turbine tower was designed and manufactured, and its dynamic performance was evaluated through field measurements under natural wind loading conditions. The results indicate that the composite tower exhibits comparable dynamic behavior to a conventional steel tower, with a first natural frequency of approximately 3.08 Hz compared to 2.89 Hz for the steel tower, along with enhanced damping characteristics. These findings demonstrate that steel-reinforced recycled thermoplastic composites offer a promising and sustainable alternative for wind turbine tower applications, with potential for broader use in structural systems. Full article

Presently, there is little to no literature that investigates the effect of electron beams on para-aramid (Kevlar^®) fiber polymer (KFRP) composites. Therefore, we assessed the effect of homogeneous low-potential electron beam irradiation (HLEBI) on Kevlar-reinforced recyclable thermoplastic (TP) polypropylene (PP) (KFRPP). Samples were assembled in an interlayered configuration of four-sized KF plies between five PP sheets [PP1-KF1-PP2-KF2-PP3-KF2-PP2-KF1-PP1] designated [PP]₅[KF]₄, which were hot-pressed at 493 K at 4 MPa for 7 min. Experimental results show when an HLEBI setting of 250 kV cathode potential (V_c) at an 86 kGy dose is applied to finished sample surfaces, the Charpy impact strength (a_uc) at median fracture probability (P_f of 0.50) is increased 59% from 72.5 kJ/m² when untreated to 115.6 kJ/m² thereafter, while a 170 kV–129 kGy setting increased a_uc about 15%, to 83.3 kJ/m², when compared to the untreated sample. Scanning electron microscopy (SEM) showed the 250 kV–86 kGy HLEBI increases KF/PP adhesion with increased consolidation and KF bundling, while the electron spin resonance (ESR) showed HLEBI generates dangling bonds (DBs) in KF and PP, which is evidence of the strengthening KF/PP interface. X-ray photoelectron spectroscopy (XPS) of the N1s spectrum of Kevlar fiber from the fracture region of the untreated sample showed a dominant peak at 399.5 eV with 82.7% area, which is characteristic of the Kevlar backbone N–(C=O)–, indicating poor adhesion with fiber pullout. However, the dominant peak was shifted in the 250 kV–86 kGy sample to that of strongly bonded imines, –C=N–, at 398.6 eV and 36.8%, indicating strong bonds generated at the KF/PP interface. Together, the N1s, C1s and O1s spectra indicate increased polar groups, reduced weak Van der Waals forces, and the generation of a strong active nitrogen-containing interphase, acting to reduce fiber pullout to increase the impact strength of the [PP]₅[KF]₄ composite system. Full article

Sustainable production in dental and orthodontic 3D printing has gained increasing attention due to environmental concerns and the need for cost-effective and resource-saving solutions. This study presents a proof of concept for using recycled polymers and fused granular fabrication (FGF) in a closed-loop 3D printing approach, omitting intermediate filament manufacturing. A desktop 3D printer served as the kinematic platform and was modified with a pellet-based extruder to directly process recycled polyethylene terephthalate glycol (PETG) flakes, obtained by shredding previously printed PETG parts, into dental models. Dimensional accuracy was evaluated using optical 3D scanning analysis. The results indicate that models produced from recycled PETG are, in principle, suitable for dental and orthodontic applications within the investigated scope. This technical note provides initial evidence supporting the integration of recycled thermoplastics into dental and orthodontic model fabrication as part of sustainable additive manufacturing workflows. Potential pathways for workflow integration in clinical and laboratory environments, as well as directions for future research, are outlined, including the optimization of printing parameters and process stability. The main technical challenges were unreliable feedstock flow, causing bridging and jamming, while thermal creep from insufficient inlet cooling promoted premature softening of the flakes, causing torque spikes and unstable feeding. Full article

Lightweight thermoplastic sandwich structures have a potential in terms of high specific strength, recyclability, repairability, and reduced manufacturing costs and cycle times, thereby widening their applicability in the aviation industry. However, joining thermoplastic skins to the core is considered a critical process in determining the structural integrity of fully recyclable sandwich systems. Despite rapid technological progress, a comprehensive assessment of manufacturing routes capable of achieving reliable skin/core fusion bonding remains lacking. Therefore, this review critically examines manufacturing techniques for thermoplastic-based sandwich panels, with particular emphasis on advanced processes that achieve effective skin/core fusion bonding. Within conventional manufacturing routes, compression moulding and double-belt lamination have the potential for high-volume production and process automation. Skin/core fusion bonding via in situ core formation enhances manufacturing flexibility, particularly for achieving complex designs. Emerging approaches, including additive manufacturing, automated fibre placement, and welding-based methods, are identified as promising fusion-bonding strategies. This offers enhanced manufacturing simplicity and efficiency by minimising interlinked processing stages and eliminating the need for intricate mould patterns. Future advancements are expected to focus on highly integrated and scalable manufacturing routes capable of simultaneously achieving skin consolidation, in situ core formation, and skin/core fusion bonding within a single process. In particular, continuous welding-assisted manufacturing and additive manufacturing-based approaches are highlighted as promising pathways for improving structural integration, recyclability, and production efficiency in next-generation thermoplastic sandwich structures. Overall, this review provides a structured foundation to guide future research directions and support the development of more efficient, scalable, and structurally reliable thermoplastic sandwich manufacturing technologies. Full article

This paper presents the results of research conducted on the influence of thermoplastic extrusion parameters (layer height per pass—L_h and the percentage fill density—I_d) and heat treatment (annealing) on the compressive strength of specimens manufactured by thermoplastic extrusion of virgin and recycled polyethylene terephthalate glycol (PETG and rPETG) filaments. To support the study, using the parameters L_h = (0.10–0.20) mm and I_d = (50–100)%, 90 compression test specimens were manufactured from PETG and rPETG (45 specimens for each material), which were subsequently subjected to heat treatment by annealing at a temperature of 75 °C for a period of 180 min. The results obtained highlight a significant correlation between the variable manufacturing parameters (L_h and I_d) and the compressive strengths (C_s). The average compressive strengths of the 45 specimens made from PETG are 44.15% lower than the average compressive strengths of the specimens made from rPETG. The annealing heat treatment resulted in a 31.40% decrease in the average compressive strengths of the specimens made from PETG and a 0.63% increase in the average compressive strengths of the specimens made from rPETG. The specimens made from PETG exhibited increased thermal sensitivity, which led to molecular relaxation, while rPETG exhibited superior thermal stability acquired through recycling. Full article

The article focuses on the potential of recycled materials for the production of 3D printing filaments.. The individual parts are focused on defines the relationship between circular economy/3D printing technology, and the key motivations for the use of recyclates in the context of sustainability. Core of the article describes different types of recycled polymers, with emphasis on the number of recycling cycles and the associated changes in material properties. It also includes a discussion of degradation processes resulting from repeated thermal loading, i.e., mechanical recycling. Simultaneously, individual recyclates are comparatively evaluated in terms of mechanical properties, rheological characteristics (particularly the melt flow index), and their processability in 3D printing. Furthermore, key challenges are identified, and perspective directions for future research in this field are outlined. Full article

The widespread adoption of additive manufacturing, particularly selective laser sintering (SLS), has raised concerns about the disposal of unused thermoplastic powder residues, such as polyamide 12 (PA12). The high cost of PA12 and its degradation during the SLS process highlight the need for sustainable reuse strategies. This study evaluates the feasibility of reprocessing non-sintered PA12 powder without the addition of virgin material through fused deposition modeling (FDM) and injection molding (IM). Thermal analysis showed that the material retains processing temperatures comparable to virgin PA12. However, a significant reduction in melt flow index (≈61%) was observed, reflecting reduced processability and suggesting molecular-level changes affecting chain mobility. Injection molding demonstrated consistent mechanical behavior and good ductility, confirming its suitability for processing recycled PA12. In contrast, FDM processing resulted in higher variability and reduced ductility, mainly due to limitations in interlayer bonding associated with the increased viscosity of the material. Overall, the results highlight injection molding as a robust route for the valorization of non-sintered PA12, while FDM remains a feasible but less reliable alternative requiring further optimization. Full article