Papers by Keyword: Recycling

Abstract: The paper presents a selection method of the most used thermal insulation materials used in the thermal rehabilitation of a building. A good thermal insulation requires that the material chosen, meets the technical and safety characteristics, is easily recyclable and is reasonable in price. After establishing the characteristics that must be analysed, the calculation is make to establish the optimal thermal insulation for a certain type of building. The calculation method takes into account the characteristics established, as the most important for the completion of the paper for thermal insulation and at the end, the material that best meets the required conditions is indicate. This method can be used for any type of building, for any type of thermal insulation, walls, roof, ceilings, etc., provided we correctly impose the desired characteristics.

Abstract: The global accumulation of scrap tyres presents a growing environmental and public health challenge due to their resistance to degradation and limited recycling options. Addressing this issue through innovative reuse strategies is vital for advancing sustainable construction practices. This study explores the integration of shredded scrap tyres as a lightweight fill material in gabion wall construction, promoting circular economy principles by transforming waste into a valuable engineering resource. A novel method was developed using shredded tyres, cut into pieces measuring 100 mm × 50 mm, mixed with rockfill (75–100 mm in size), and placed within gabion units. The structural behavior of these modified gabions was analyzed with a focus on lateral and vertical displacement patterns, bulging behavior, and overall stability. Factor of safety calculations indicated that a gabion unit with a height and depth of 3 meters could achieve a significant unit weight reduction up to 8.2 kN/m³ compared to conventional rockfill gabions, which typically weigh between 15 and 19 kN/m³. The introduction of tyre pieces resulted in a void ratio of approximately 0.4, suggesting effective packing and compaction. The lightweight gabion units demonstrated the capacity to safely support the load of three stacked units without significant deformation, validating their structural integrity for practical applications. To maintain optimal performance, it is essential to keep the unit weight at or below 8.2 kN/m³ and ensure a void ratio between 0.3 and 0.4. Further testing is recommended to evaluate compatibility across varying rock and tyre densities. Overall, this research highlights a sustainable and cost-effective approach to scrap tyre reuse, contributing to resource efficiency, waste reduction, and the development of eco-friendly materials for retaining wall applications in civil engineering.

Abstract: Carbon fiber–reinforced polymer (CFRP) composites are extensively used in aerospace applications; however, their end-of-life management remains a critical challenge. This study investigates an unconventional recycling route based on the direct hot compression molding of CFRP waste powders, aiming to valorize industrial composite scraps without the addition of virgin polymers or binding agents. The material investigated corresponds to the finest fraction (~300 μm) obtained from a sieving process applied to industrial CFRP scrap powders derived from trimming residues and partially cured aeronautical prepregs. The use of this fine powder fraction promotes effective particle aggregation and consolidation during molding, preventing powder loss during demolding and enabling the fabrication of relatively thick panels despite the absence of additional bonding agents. Compression molding was carried out at 250 °C and 1.5 bar for 20 min. Two material configurations were analyzed: uncoated compression-molded panels and panels coated with a thin polyester layer. The recycled materials were characterized through morphological, thermomechanical, and mechanical analyses. The results indicate that the polyester-coated panels exhibit improved mechanical performance compared to the uncoated configuration. In comparison with previous studies focused on coarser powder fractions (≤1 mm), the present work highlights the potential of the finest powder fraction for effective consolidation, demonstrating the strong influence of particle size on the processability and properties of compression-molded recycled CFRP. These findings confirm the viability of direct compression molding as a sustainable and scalable recycling strategy for tailoring CFRP waste reuse as a function of powder size.

Abstract: The utilisation of friction-induced solid-state recycling, methodically adapted to the CoNform process, facilitates the continuous production of semi-finished products. The material intended for recycling is conveyed continuously via a rotating wheel. The volume flow is influenced by fixed surfaces, deflections, and constrictions, thereby creating an asymmetrical flow profile. In order to effect a change in the mechanical properties of the semi-finished product, the material fed into the process can be modified. This enables the amalgamation of two alloys or the direct transition between them. The inhomogeneous flow conditions present within the tool give rise to the mixing of materials, thereby creating a graded multi-material zone. The multi-material zone was divided into different areas and traced back to the process conditions. Within the transitions, the connections between the alloys were examined, as well as the influence on the boundary layer. Material properties were determined for the individual areas and located along the length of the profile.

Abstract: Polymer processing in modern industry is often not efficient from the point of view of energy and material consumption. This production system must be revised to pursue a circularity of products and materials. Recent developments in additive manufacturing technologies for polymers and polymer-based composites are enabling changes of production paradigm from “Design for Manufacturing” to “Manufacturing for Design”, providing new intriguing lightweight solutions. This paper summarizes the lesson learned from the RELIVE project “REcycling of pLastic wastes integrating extrusion and additIVE manufacturing techniques”, in terms of methodology and results.

Abstract: Recycling aluminum chips remains a major challenge in aluminum manufacturing because it is difficult to retain the original quality alloy properties while reducing the carbon footprint and ensuring a sustainable process. This work investigates the microstructural evolution and bonding quality of compacted AA6082 chips processed through friction extrusion/consolidation. The residual material left inside the extrusion container after processing at a high extrusion ratio was analyzed using SEM, EDS, and EBSD to understand bonding mechanisms and microstructure evolution in front of the die. The SEM results show that voids are still present between the chips in the initial compacted material which already shows bonding, while these voids are reducing towards the die interface, particularly related to the present severe plastic deformation. EDS analysis confirms the presence of Al (Fe,Mn)Si intermetallic particles, which break and disperse in the matrix because of shear deformation due to die rotation. EBSD analysis reveals that grains are coarser near the base material, and subdivisions of grains near the die interface are significant because of continuous dynamic recrystallization.

Abstract: Nowadays, the growing demand for sustainable solutions in manufacturing has shifted research attention toward innovative recycling strategies. Among these, the Solid-State Recycling (SSR) technique has emerged as a viable approach to transform metal swarf into new products. Within the SSR family, friction stir extrusion (FSE) has gained particular interest as a promising method for producing wires from metal scraps, but recently, it was also employed for tube manufacturing. In literature, tube production via chip recycling often involves multi-step approaches, first consolidating/homogenizing the recycled chips and then extruding. In other cases, the tubes are manufactured directly from a bulk material, losing the sustainable goal. For this reason, this study aims to propose a single-step process in which aluminium chips are directly turned into a consolidated tube without any intermediate step. In addition, specific attention was given to the study of tool geometry, aiming to investigate the effect of a tapered tool’s shape on the material flow and the overall process performance. Experimental tests were conducted to characterize the microstructure of extruded tubes and to calibrate numerical simulations employed for investigating process dynamics. Results revealed that the reduced contact diameter of the chamfered tool generated lower processing temperatures but higher strain levels, fundamentally shifting the bonding mechanism from thermal assistance to mechanical dominance in oxide film breakage. Microstructural analysis demonstrated that the flat tool, characterized by predominant frictional heating and lower deformation, produced larger grain diameters due to thermally induced coarsening. Conversely, the chamfered tool yielded significantly refined grain structures through severe plastic deformation and dynamic recrystallization under suppressed thermal conditions, indicating superior consolidation quality and enhanced particle bonding.

Abstract: Titanium is a Critical Raw Material for the European aerospace sector, yet its manufacturing is characterized by high buy-to-fly ratios and significant waste in form of chips. Solid-state recycling (SSR) presents a low-energy alternative to remelting for chip revalorisation. However, its viability is strictly limited by their oxidation. This study investigates the influence of milling parameters (cutting speed and radial depth of cut), and coolants (emulsion, LCO2 and dry), on cutting forces and chip quality (morphology and oxidation) to define a process window for generating low oxidation chips, enabling further SSR routes. By correlating cutting forces with chip analysis, the results reveal that emulsion cooling yields the chips with the least oxidation, despite potential oil contamination of the feedstock with oils. While LCO2 effectively reduces oxidation at lower material removal rates, high thermal loads overwhelm its cooling capacity, resulting in oxidation comparable to dry cutting. These findings establish the machining parameters necessary to produce high-quality, recyclable feedstock, bridging the gap between subtractive manufacturing and circular material flows.

Abstract: Environmental worries have increased due to the sharp rise in single-use plastics in healthcare institutions, especially with relation to medical plastic waste. This study explores the viability of using low-cost, small-scale technology to recycle such trash into goods with added value. Samples of medical plastic, such as vials, syringes, and bottles of intravenous solution, were gathered at Al-Shamiya General Hospital, sanitized, and mechanically destroyed. Two processing units were created: a 3D printing filament extruder and a manual injection molding machine. While the injection molding machine generated molded components based on the applied mold design, the extruder successfully produced filaments suitable with fused deposition modeling. The technical feasibility of converting sterilized medical plastics into useful products for everyday use and healthcare was validated by experimental results. The results highlight the potential of decentralized recycling strategies to lessen the environmental impact of medical waste, promote circular economy principles, and decrease plastic pollution, so long as stringent safety and sterilizing measures are followed.

Abstract: The current experimental study aims to confirm some critical conclusions of the preliminary research regarding the possibilities of valorizing the residue material generated the Abrasive Water Jet (AWJ) procedures for industrial material processing, namely the Spent Garnets (SG), by innovatively integrating them in cement-based materials (mortar and concrete) and further on, in construction-eco products (paving pre-cast units, road construction, concrete for structural or non-structural elements, etc.). The use of SG wastes is considered as partial substitution of fine aggregates (sand) in cementitious materials, simultaneously offering the possibility of reducing the use and exploitation of aggregate, as limited natural resource. The methodology consists in developing a regular mortar mix, the Reference (R), on which several substitution percentages were applied with respect to the natural sand quantity, by Spent Garnets (SGs) provided by local producers. The substitution percentages initially ranged from 10 to 50% with respect to the Reference mix, as specified by recent, international studies, and they were also used in the preliminary evaluation, as well. Further on, the relevant substitution percentages were established as 30% and 50% values, and the corresponding mortar mixes were realized. The specific comparative analysis was performed in terms of mechanical performance at early age (7-day mechanical strengths) and also at 28 days. The obtained results are validating the initial results, proving the consistency of the previous conclusions and encouraging the use of SG wastes in cement-based construction materials. Complementary studies are further on considered and prepared, focused on using SGs as aggregate partial replacement in pavement eco-blocks, due to their high demand on the construction market.