https://uvadoc.uva.es/handle/10324/56019 Fri, 10 Apr 2026 20:27:16 GMT 2026-04-10T20:27:16Z https://uvadoc.uva.es/handle/10324/80731 This study investigates the manufacture and environmental assessment of acoustic insulation foams made from recycled polyethylene (RM) from packaging film waste. Blends of RM with virgin polyethylene (PE) and ethylene-vinyl acetate (EVA) were used to produce cellular structures through chemical (Ch) and physical (Ph) foaming processes. The aim was to develop materials with properties comparable to commercial acoustic insulation products in construction sector, assessing structural integrity and acoustic performance via dynamic stiffness. Products with performance like the commercial were achieved with recycled content ranging from 40 to 80 wt%. These successful cases were also evaluated for environmental impact. The life cycle assessment considered two approaches: one analysing the production of 1 kg of foam (standardized density values), where physical foaming showed a lower environmental footprint, and the other evaluating the mass needed to achieve the dynamic stiffness of the commercial reference (empirical density values), which favoured chemical foaming for producing foams with comparable properties but lower densities. Although physical foaming has environ- mental advantages, the higher densities achieved with RM limit its viability. Consequently, chemical foaming is more environmentally favourable due to lower material consumption. Therefore, Ch_RM:EVA,80:20 is optimal for technical requirements, while Ch_RM:PE,40:60 is more environmentally advantageous. The compromise solution that addresses both technical and environmental aspects is Ch_RM:EVA,40:60. This foam showed acoustic performance equivalent to the commercial, achieved through a manufacturing process and recycled content minimizing environmental impacts. Furthermore, transforming packaging waste into a long-lasting product also reduces waste accumulation and delays non-sustainable but necessary processes like energy generation. Wed, 01 Jan 2025 00:00:00 GMT https://uvadoc.uva.es/handle/10324/80731 2025-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/76995 Micronized nanocellular polymers show great potential to be used as core materials for vacuum insulation panels due to their reduced thermal conductivity under vacuum. However, as a result of their nanocellular structure, these materials are characterized by thermal radiation contributions higher than 4 mW/(m·K). This work studies how to further enhance their thermal insulation behavior by adding infrared blockers to reduce thermal radiation. Three different opacifiers (titanium(IV) oxide, graphene nanoplatelets, and silicon carbide) are used in different contents (2.5, 5, 10, 15, and 20 wt%). The obtained powders are characterized to determine the apparent density, the particle size distribution, and the thermal conductivity. The addition of infrared blockers leads to an increase in apparent density which is also related to the opacifier’s particle size. For each infrared blocker, there is an optimum concentration to achieve the minimum thermal conductivity. Finally, compacted panels are produced to analyze their behavior as VIP cores by measuring thermal conductivity under vacuum conditions. A minimum thermal conductivity of 9.6 mW/(m·K) is obtained for the compacted panel containing 10 wt% of silicon carbide, a reduction of 2 mW/(m·K) regarding the sample without opacifier. Wed, 01 Jan 2025 00:00:00 GMT https://uvadoc.uva.es/handle/10324/76995 2025-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/76986 Compacted panels based on micronized nanocellular polymers show reduced thermal conductivity in comparison with bulk nanocellular polymers, especially under vacuum, so they are promising materials to be used as vacuum insulation panels (VIP). The discontinuous structure formed by micrometric particles allows for decreasing the conduction through the solid phase since the contact points between the particles act as additional thermal resistances to the heat transmission. However, the discontinuous structure also leads to the appearance of the coupling effect, which cannot be modeled using the typical equations for cellular polymers. In this work, a semi-empirical model able to predict the thermal conductivity of compacted panels based on nanocellular poly(methyl-methacrylate) (PMMA) is developed. The model allows quantifying each heat transfer mechanism contribution (conduction through the solid phase, conduction through the gas phase, radiation, and coupling effect). The model shows that the contribution of the coupling effect in the compacted panels is higher than 50 % of the total thermal conductivity for pressures higher than 5 mbar, supporting the need for the model to correctly predict the insulation performance of these materials. The model predicts minimum thermal conductivities of 32.5 mW/(m·K) at ambient pressure and of 10 mW/(m·K) at maximum vacuum. Wed, 01 Jan 2025 00:00:00 GMT https://uvadoc.uva.es/handle/10324/76986 2025-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/76085 The hierarchical structure and high molecular weight of bovine collagen fibres, along with their widespread availability, make this animal protein a promising candidate for biofilm production. However, unlike conven- tional thermoplastics, collagen processing is challenging due to its complex intra- and intermolecular in- teractions. This study investigated the use of supercritical carbon dioxide (sCO2) as a plasticising agent to modify these interactions during a pretreatment phase prior to film formation via extrusion-compression moulding. Different supercritical conditions were tested, and the combined effect of sCO2 and glycerol (Gly), a common plasticiser, was evaluated. Microstructural analyses of the pretreated powders and resulting biofilms revealed an unconventional plasticisation mechanism, characterised by the loss of the triple-helix structure and the formation of a randomly cross-linked network. This effect was particularly pronounced under supercritical conditions at higher temperatures (80 ◦C and 80–300 bar), where the loss of surface water from the collagen fibres and in- teractions between functional groups in denatured fibres led to enhanced plasticity. As a result, the extruded films exhibited a reduction in stiffness of up to 20 % and an increase in elongation at break by more than 50 %. In contrast, pretreatments at lower temperatures and pressures (35 ◦C and 80 bar) caused only minor chain scission, preserving the triple-helix structure and yielding rigid films with limited deformability. These findings demon- strated that controlling supercritical conditions in the presence of glycerol during collagen pretreatment is an effective strategy to enhance the processability and mechanical performance of collagen-based biofilms. Wed, 01 Jan 2025 00:00:00 GMT https://uvadoc.uva.es/handle/10324/76085 2025-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/62854 In the present study, a promising flame retardant consisting of 80 wt% silane-modified nanosepiolites functionalized with 20 wt% graphite (SFG) is used to obtain a synergistic effect principally focussed on the thermal stability of water-blown rigid polyurethane (RPU) foams. Density, microcellular structure, thermal stability and thermal conductivity are examined for RPU foams reinforced with different contents of SFG (0, as reference material, 2, 4 and 6 wt%). The sample with 6 wt% SFG presents a slightly thermal stability improvement, although its cellular structure is deteriorated in comparison with the reference material. Furthermore, the influence of SFG particles on chemical reactions during the foaming process is studied by FTIR spectroscopy. The information obtained from the chemical reactions and from isocyanate consumption is used to optimize the formulation of the foam with 6 wt% SFG. Additionally, in order to determine the effects of functionalization on SFG, foams containing only silane-modified nanosepiolites, only graphite, or silane-modified nanosepiolites and graphite added separately are studied here as well. In conclusion, the inclusion of SFG in RPU foams allows the best performance to be achieved. Sat, 01 Jan 2022 00:00:00 GMT https://uvadoc.uva.es/handle/10324/62854 2022-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/62666 Highly transparent polyisocyanurate–polyurethane (PUR–PIR) aerogels were synthesized, and their optical properties were studied in detail. After determining the density and structural parameters of the manufactured materials, we analyzed their optical transmittance. It was demonstrated that the catalyst content used to produce the aerogels can be employed to tune the internal structure and optical properties. The results show that the employment of lower catalyst amounts leads to smaller particles forming the aerogel and concomitantly to higher transmittances, which reach values of 85% (650 nm) due to aerogel particles acting as scattering centers. Thus, it was found that the lower this size, the higher the transmittance. The effect of the sample thickness on the transmittance was studied through the Beer–Lambert law. Finally, the scattering mechanisms involved in the light attenuation were systematically evaluated by measuring a wide range of light wavelengths and determining the transition between Rayleigh and Mie scattering when the particles were larger. Therefore, the optical properties of polyurethane aerogels were studied for the first time, opening a wide range of applications in building and energy sectors such as glazing windows. Sat, 01 Jan 2022 00:00:00 GMT https://uvadoc.uva.es/handle/10324/62666 2022-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/62638 Polyurethane foams with a hybrid structure between closed cell and open cell were fabricated and fully characterized. Sound absorption measurements were carried out in order to assess their acoustic performance at different frequency ranges. The cellular structure of these systems was studied in detail by defining some novel structural parameters that characterize the cell wall openings such as the average surface of holes (Sh), the number of holes (h), and the area percentage thereof (%HCW). Therefore, these parameters allow to analyze quantitatively the effect of different structural factors on the acoustic absorption performance. It has been found that the parameters under study have a remarkable influence on the normalized acoustic absorption coefficient at different frequency ranges. In particular, it has been demonstrated that increasing the surface of the holes and the percentage of holes in the cell walls allows increasing the acoustic absorption of these types of foams, a promising statement for developing highly efficient acoustic insulators. Additionally, we could determine that a suitable minimum value of hole surface to reach the highest sound dissipation for these samples exists. Sat, 01 Jan 2022 00:00:00 GMT https://uvadoc.uva.es/handle/10324/62638 2022-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/61558 Polyisocyanurate (PIR) foam is a thermal insulating material widely used in many industries such as construction, refrigeration, piping/tubing among others. In this research the production, characterization and modeling of the thermal conductivity of PIR foams synthesized with a hydrofluorolefin (HFO 1233zd (E)) as physical foaming agent have been studied. The results have shown that increasing the amount of HFO reduces the density, but the cellular structure is not modified. The relative mechanical properties are the same for the concentrations of HFO considered. In addition, the aging of thermal conductivity as a function of time has been studied in detail. The experimental results have been deeply analyzed using a theoretical model to predict the thermal conductivity The results show that the thermal conductivity and the rate of aging at early stages are reduced for the higher concentrations of HFO. This result has been related to the lower temperature reached during the foaming reaction for higher contents of the physical blowing agent. Sun, 01 Jan 2023 00:00:00 GMT https://uvadoc.uva.es/handle/10324/61558 2023-01-01T00:00:00Z