APRÈN. Portal de la producció docent del professorat de la UPC

Crystallization kinetics in polymers is a very important topic in the field of plastics technology since crystallization is correlated with the properties of polymers. Crystallization deals with the orientation and arrangement of polymer crystals in their microstructure and this in turn dictates the degree of crystallinity of polymer affecting their thermal properties, optical properties, mechanical properties and the general application of polymers. In terms of applications, polypropylene (PP) is one of the most utilized polymers in the plastic industry hence it is imperative to recycle them and maintain them in the circular economy loop. Blending of Polypropylene is a sustainable and material efficient way of polymer recycling and to successfully engineer blended recycled PP, it is important to understand the crystallization kinetics of individual types of polypropylene and their blends. In this work, crystallization growth kinetics of the different types of polypropylenes and their blends were investigated via two distinct routes using isothermal analysis. Both Differential Scanning Calorimetry and Polarized Light Optical Microscopy using a Heating stage at various isothermal crystallization temperatures were employed to investigate the nucleation rate, growth rate and overall crystallization kinetics of polypropylene and its blends. In analysis the results gained from the experiments, the Avrami´s Law which is the basis for understanding crystallization kinetics of polymers was used in evaluating the growth rate of Polypropylene Homo, Polypropylene Block, and Polypropylene Random polymers, as well as blends consisting of Polypropylene Random and Block, Polypropylene Homo and Random and Polypropylene Homo and Block types. This was done to investigate and understand the effects the samples had on each other in terms of crystallization kinetics.

This master's thesis endeavours to redesign the shower drain for Podcomp, a Swedish company specialized in the manufacturing of prefabricated bathrooms with fibreglass composite materials, as well as other parts of these bathrooms. The present work aims to align with emerging aesthetic trends while adding value and versatility to their product line. Formerly constrained to a singular bathroom model, the company seeks to diversify its offerings by integrating aesthetically pleasing and functionally shower solutions. The primary challenge lies in devising a design that not only meets the demands of contemporary bathroom aesthetics but also remains economically viable. Moreover, the redesign must enhance the materials used, ensuring durability and longevity while adhering to manufacturing constraints within the company's facilities. Concurrently, strict adherence to prevailing Swedish regulations governing bathroom fixtures is imperative to ensure market compliance and customer satisfaction. This research encompasses a multidisciplinary approach, integrating principles from materials engineering, industrial design, and regulatory compliance. By leveraging innovative materials and design methodologies, the project aims to develop a shower solution that meets customer expectations. Key objectives include: 1. Redefining the aesthetics of the shower siphon to harmonize with modern bathroom design paradigms. 2. Enhancing functionality and performance while maintaining cost-effectiveness. 3. Optimizing materials selection to ensure durability, sustainability, and ease of fabrication. 4. Adhering to Swedish regulatory standards to guarantee product safety and market acceptance. Through a comprehensive analysis of existing drains in the market, coupled with iterative prototyping and rigorous testing, this study seeks to deliver a redesigned shower drain that epitomizes both form and function. By integrating seamlessly into the company's prefabricated bathroom units, the redesigned siphon aims to elevate the overall user experience while consolidating the company's position as an industry leader in innovative bathroom solutions.

This thesis focuses on the development and characterization of nanocellulose-based hydrogels generated from wood particles and seaweed for use as inks in 3D printing for biomedical applications. Wood-derived nanocellulose gel was prepared via TEMPO oxidation followed by high-shear fibrillation, whereas seaweed-based nanocellulose gels were created using direct and bleached fibrillation. The resultant hydrogels, which display good shear-thinning properties, were then used for extrusion-based printing. A thorough assessment of printing parameters revealed that 0.75% (w/w) TEMPO-oxidized nanocellulose gel achieved optimal printability at 5 kPa, while raw and bleached seaweed gels demonstrated higher extrusion and better ink fidelity at 10 kPa and 9 kPa, respectively. Among the two crosslinkers used, calcium chloride and acetic acid, calcium chloride was the most efficient crosslinker for stabilizing seaweed-based constructs, generating mechanically durable and handleable structures. However, TEMPO-derived hydrogels displayed uneven crosslinking outcomes with both crosslinkers, requiring additional modifications. Water uptake analysis highlighted the gels' capacity for controlled swelling, a critical attribute for biomedical applications such as tissue scaffolds and drug delivery systems. This work underscores the versatility and promise of nanocellulose-based bioinks, contributing valuable insights toward their advancement in regenerative medicine and bioprinting technologies.

This thesis explores the characterization of pure Niobium (Nb) fabricated via Laser Powder Bed Fusion (LPBF), with a focus on its thermal and electrical properties, which are critical for high-temperature applications. In the context of the INFN_ LNL SPES project, where materials must withstand extreme conditions, Nb is evaluated as a potential alternative to traditional refractory metals like tungsten and tantalum. The study first examines the electrical resistivity and thermal conductivity of the LPBF-manufactured Nb samples, comparing the results against established literature values for standard Nb. The findings indicate that the thermal conductivity and electrical resistivity of the AM Nb samples are slightly lower than those of the standard Nb. This discrepancy is attributed oxidation phenomenon and to inherent microstructural defects, such as grain boundary irregularities and anisotropy, typical of additive manufacturing processes. Despite these minor differences, the results suggest that AM Nb exhibits properties sufficiently close to those of standard Nb, supporting its viability for certain applications where cost and material efficiency are critical. Additionally, Scanning Electron Microscope (SEM) imaging was conducted to further understand the microstructural characteristics of the samples, which revealed common additive manufacturing defects like surface roughness and micro-cracks. These observations help explain the minor deviations in the thermal and electrical properties of the AM Nb samples from the standard ones. In the context of the SPES project, the application potential of LPBF-produced Nb extends beyond traditional uses, especially in components requiring high thermal conductivity and structural integrity.

This work explores alloys in the Al–Mg–Si system for application in space. To be considered suitable for space applications, an alloy must meet requirements that include, not exhaustively, high strength-to-weight ratio, high thermal performance, optimal radiation shielding and resistance. Due to its lightweight and high-strength, aluminium and its alloys are considered suitable options. The ability to achieve increased strength via age-hardening, sets aluminium alloys as strategic materials for future space programs. Age-hardening promote precipitation that prevents dislocation motion, thus increasing strength. However, when subjected to space, energetic particle irradiation from the Sun can cause degradation of aluminium alloys as it induces both dissolution of precipitates and formation of extensive networks of dislocation loops. To mitigate the deleterious impact of energetic particle irradiation, one solution has been the development of new ultrafine-grained (UFG) aluminium alloys, where the large amount of grain-boundaries promote the fast-annihilation of radiation damage. Nevertheless, developing an UFG aluminium alloy with high thermal stability against recrystallisation has been a major challenge. For these reasons, this work addresses on the synthesis of an UFG AA6061 alloy using a severe plastic deformation (SPD) technique known as high-pressure torsion (HPT). After demonstrating the feasibility of synthesis, the research investigates the precipitation behaviour in the UFG AA6061 alloy compared with its coarse-grained (CG) counterpart through a combination techniques such as differential scanning calorimetry (DSC) and scanning transmission electron microscopy (S/TEM). Thermal stability of the UFG AA6061 alloy was also investigated via in situ TEM experiments. The findings indicate that the phenomenon of precipitation hardening is highly dependent on the average grain size of the two CG and UFG AA6061 alloys. The phenomenon of precipitation was also demonstrated to be accelerated in the UFG alloy and this was reflected by the fact that intermediate metastable phases such as the β ′′ were not observed in the UFG AA6061 alloy, and that the equilibrium phase (β), rapidly formed at lower temperatures. It was found via analytical S/TEM mapping techniques that the UFG AA6061 alloy presents limited precipitation ability taking place mainly at intra-granular positions and with low volumetric densities when compared with the CG AA6061 alloy. These characteristics were responsible for recrystallization of UFG microstructure at around of 180°C when tested via in situ heating. This thesis highlights the potential of UFG aluminium alloys for application in sapce, but also underlines the difference between the UFG AA6061 alloy and the UFG crossover aluminium alloys, the AlMgZnCuAg, which due to its high volume density of T-phase precipitates and low (highly negative) enthalpy of formation for precipitation (compared to β precipitates in AA6061 alloys) restricts grain boundary movement and delays recrystallisation via intra-granular precipitation and growth.

The homogenization heat treatment of as-cast billets is a significant process in aluminium extrusions. This process is characterized by a large evolution in the microstructure when going through the different stages of the morphological process. This change involves several key steps: the disruption of eutectic morphology by processing inter dendritic phases into round shapes, reduction of in grain segregation though diffusion, re-melting of low melting phases to achieve enhanced extrusion surface finish, and precipitation of nano sized dispersions (for alloys containing Cr, Zr, Mn, and Sc) to arrest grain boundary movement and avoid recrystallization. Post homogenization cooling may also cause reprecipitation of some phase that can change the flow stress required for the next extrusion. However, all these precipitates have an adverse effect on the mechanical characteristics of the alloy and inhibit age hardening ability requiring their dissolution during solution heat treatment. The processes of development of microstructure take place during homogenization and subsequent cooling. Therefore, the main aim of the present study is to systematically investigate the microstructural change during homogenization heat treatment and the chemical composition of the samples before and after the treatment. Investigation carried out on as-cast 6xxx aluminium billets shows that both ßAl5FeSi intermetallic phase and coarse Mg2Si particles are detrimental to the subsequent operations like extrusion. For proper surface quality of the extruded products, the billets are heat treated thorough homogenization before the extrusion is carried out. Typically, during the heat treatment, there are unwanted intermetallic particles, ß-AlFeSi platelets, are converted to rounded α-Al(FeMn)Si intermetallic particles. The reactions, which take place during homogenization process, were investigated up to the present time by experiments, providing some information about the process and alloys properties. In the present study the transformations of 6060 and 6063 have also been studied using Light Optical Microscope, hardness tester and Optical Emission Spectroscopy.

In the last decades, there has been exponential growth in the photovoltaic (PV) industry, bringing the total cumulative installed PV capacity to over 1.5 TWp by the end of 2023. Nevertheless, a total of 78 million tonnes of PV panels is estimated globally by 2050. Recycling is essential to manage this incoming quantity of end-of-life (EoL) PV panels, preventing inappropriate disposal, which can be dangerous for the environment due to some hazardous substances contained in the panels. This thesis aims to present a complete analysis of the current situation regarding EoL solar panels, describing the existing recycling technologies to recover valuable materials. Moreover, the current recycling process implemented by EcoWeTech S.r.l was described. Further, characterization tests were performed to determine the composition of the recycled fractions achieved during the process, to identify if there were impurities that would impact their quality. Finally, potential applications of the obtained materials in different industries were explored, to reintegrate them into the circular economy.

With the European Union's (EU) goal to modernize manufacturing processes and economic activities towards Industry 5.0, the Italian eyewear industry, renowned globally for its excellence and innovation, faces the challenge of adapting to the principles of a regenerative, circular economy. This approach emphasizes minimizing waste, maximizing resource circulation, and increasing the use of renewable energy and sustainable materials. This thesis studies the current manufacturing processes, materials, and energy efficiency within the industry, and explores the potential of electric heating methods (induction, radiofrequency, and microwave) to enhance energy efficiency, product quality and traceability. Particular attention is given to the application of more efficient heating technologies and the recent development of sustainable materials. By referencing the EU Reference Documents on Best Available Techniques (BREFs) and relevant research, this study aims to provide a framework for the Italian eyewear industry to improve productivity and achieve sustainable manufacturing practices. ​

Periodic surfaces have been shown to promote stent cell migration and proliferation and avoid platelet adhesion. Surfaces patterned with direct laser interference patterning (DLIP) have been investigated for many metallic materials, with promising results and new possibilities. To bring surface structuring benefits to new technologies like bioresorbable stents, cost-effective large-scale manufacturing is essential for increased affordability and accessibility. Bioresorbable stents, such as PLLA stents, can be made with additive manufacturing on a rotating steel rod. This is a cost-effective, reliable, and quick manufacturing technique, in which drugs can be embedded in its matrix. Printing PLLA on a modified surface can be sufficient for the material to shape its inner surface to the desired pattern. The feasibility of such a process was addressed, as well as problems like oxide transfer from the steel onto the PLLA, PLLA formability and final resulting surface. To do so, steel samples were modified via DLIP, an existing technique for PLLA stamping was adapted, and results were characterized via laser confocal microscopy, scanning electron microscopy, contact angle and raman spectroscopy. Results have shown that pattern transfer is possible, but oxide transfer occurs and modifications on methodology are needed to avoid it. Different patterns were characterized and had different transferability behaviors, but the overall analysis also revealed consistent patterns in terms of height, which could promote uniform endothelialization on the stent and, consequently, an improvement in overall bioresorbable stents efficacy and safety.