Sara Villanueva

As a building material, plywood products must fulfil several requirements such as aesthetic value, durability and good fire performance. To provide these attributes, high pressure laminates (HPL) are often used as top sheets, however, they are difficult to recycle due to their thermoset nature, require adhesives for bonding on wood substrates and are relatively expensive. In this study, thermoplastic sheets based on polylactic acid, polybutylene succinate, wood particles and ammonium polyphosphate were developed and their reaction-to-fire performance evaluated following adhesive-free bonding on poplar plywood. For comparison, plywood impregnated with flame retardants and plywood with flame-retarded HPL were investigated. It was found that the presence of an external top layer, either HPL or thermoplastic top sheets, worsens the fire performance of plywood, increasing heat release and total smoke production. However, plywood with thermoplastic top sheets showed lower peak heat release rate, maximum average rate of heat emission and total heat release than plywood with HPL. Time to ignition was significantly longer for plywood with HPL, and total smoke production was reduced. The results showed that reaction-to-fire performance of plywood with a flame-retarded top sheet is improved compared to HPL, reaching a predicted Euroclass C (EN 13501-1). Overall, the best result (Euroclass B) was obtained for impregnated plywood without any top layer.

Flame-retardant poly (ethylene terephthalate) composites (FR PET) have been developed with the potential to be used as substrates in applications where flexibility and transparency are required. Several phosphorous-based flame retardants of a different nature were selected here for compounding by melt blending with a low-molecular-weight PET polymer. The fire reaction, transparency, and mechanical properties were analyzed. TGA and cone calorimetry were used to elucidate the gas-phase and condensed-phase actions of flame retardants and their effectivity. Cone calorimeters showed an improved performance with the addition of flame retardants, particularly a reduction in generated heat, improving the FGI (fire growth index) value. However, a V0 classification (following the UL94 standard) was achieved only with the addition of an organic phosphonate, Aflammit PCO900, to the PET matrix. This behavior was linked to the early reaction of this flame retardant in the gas phase, in addition to a plastification effect that causes the removal of the polymer from the incident flame. The presence of flame retardants reduced the transparency of composites over the neat PET, but, nevertheless, a good optical performance remained. No special effect was observed on the crystallization parameters. Therefore, the increase in opacity can be attributed to the poor miscibility of flame retardants and/or differences in the diffraction index of the polymer and FR additives.

Polymeric materials, renowned for their lightweight attributes and design adaptability, play a pivotal role in augmenting fuel efficiency and cost-effectiveness in railway vehicle development. The tailored formulation of compounds, specifically designed for additive manufacturing, holds significant promise in expanding the use of these materials. This study centers on poly(lactic acid) (PLA), a natural-based biodegradable polymeric material incorporating diverse halogen-free flame retardants (FRs). Our investigation scrutinizes the printability and fire performance of these formulations, aligning with the European railway standard EN 45545-2. The findings underscore that FR in the condensed phase, including ammonium polyphosphate (APP), expandable graphite (EG), and intumescent systems, exhibit superior fire performance. Notably, FR-inducing hydrolytic degradation, such as aluminum hydroxide (ATH) or EG, reduces polymer molecular weight, significantly impacting PLA’s mechanical performance. Achieving a delicate balance between fire resistance and mechanical properties, formulations with APP as the flame retardant emerge as optimal. This research contributes to understanding the fire performance and printability of 3D-printed PLA compounds, offering vital insights for the rail industry’s adoption of polymeric materials.

Summary: In this study, the toxicity of combustion gases of polycarbonate/acrylonitrile butadiene styrene (ABS) blends that include aryl phosphates as flame‐retardants (FRs) was analyzed according to the European railway standard EN 45545‐2 (NBS chamber + FTIR). FRs have a significant influence on the evolution of the toxicity of gases generated during the combustion process. In the experiment, the asphyxiant hydrogen cyanide (HCN) was detected at the beginning of combustion (4 min of testing) as a product of ABS degradation. CO was generated throughout the test (8 min) because of the incomplete combustion of both the ABS and PC fractions. The presence of aryl phosphates promoted the inhibition of the flame. The reaction of PO·radicals in the gas phase resulted in OH·scavenging and a higher release of HCN and CO. The results suggest that aryl phosphates act in the first 4 min and do not have an effect later. FRs with lower thermal stability exhibited lower heat release and flame propagation but generated more toxic gases. This effect is attributed to the higher activity of the flame‐retardant in the gas phase. Further, additional fire performance parameters, including thermal stability (thermogravimetric analysis), flammability (UL94), and heat and smoke generation (cone calorimeter), were studied. It was found that aryl phosphates reduced the fire hazard, prevented the spread of the flame, reduced heat generation, increased the time to ignition, and, at the same time, promoted the emission of toxic gases that differ in function of the selected flame‐retardant.

Additive manufacturing (AM) of scaffolds enables the fabrication of customized patient-specific implants for tissue regeneration. Scaffold customization does not involve only the macroscale shape of the final implant, but also their microscopic pore geometry and material properties, which are dependent on optimizable topology. A good match between the experimental data of AM scaffolds and the models is obtained when there is just a few millimetres at least in one direction. Here, we describe a methodology to perform finite element modelling on AM scaffolds for bone tissue regeneration with clinically relevant dimensions (i.e., volume > 1 cm³). The simulation used an equivalent cubic eight node finite elements mesh, and the materials properties were derived both empirically and numerically, from bulk material direct testing and simulated tests on scaffolds. The experimental validation was performed using poly(ethylene oxide terephthalate)-poly(butylene terephthalate) (PEOT/PBT) copolymers and 45 wt% nano hydroxyapatite fillers composites. By applying this methodology on three separate scaffold architectures with volumes larger than 1 cm³, the simulations overestimated the scaffold performance, resulting in 150–290% stiffer than average values obtained in the validation tests. The results mismatch highlighted the relevance of the lack of printing accuracy that is characteristic of the additive manufacturing process. Accordingly, a sensitivity analysis was performed on nine detected uncertainty sources, studying their influence. After the definition of acceptable execution tolerances and reliability levels, a design factor was defined to calibrate the methodology under expectable and conservative scenarios.

Commercially mass-polymerized acrylonitrile–butadiene–styrene (ABS) polymers, pristine or modified by stabilization systems, have been injection molded and repeatedly exposed to ultravilolet A (UVA) radiation, mechanical recycling, and extra injection molding steps to study the impact of such treatments on the physicochemical, mechanical, colorimetric, and thermal-oxidative characteristics. The work focus on mimicking the effect of solar radiation behind a window glass as relevant during the lifetime of ABS polymers incorporated in electrical and electronic equipment, and interior automotive parts by using UVA technique. The accelerated aging promotes degradation and embrittlement of the surface exposed to radiation and causes physical aging, deteriorating mechanical properties, with an expressive reduction of impact strength (unnotched: up to 900%; notched: up to 250%) and strain at break (>1000%), as well as an increase in the yellowing index (e.g., 600%). UV-exposition promotes a slight increase in the tensile modulus (e.g., 10%). The addition of antioxidants (AOs) leads to a limited stabilization during the first UVA aging, although the proper AO formulation increases the thermal-oxidative resistance during all the cycles. Mechanical recycling promotes an increase in strain at break and unnotched impact strength alongside a slight decrease in tensile modulus, due to disruption of the brittle surface and elimination of the physical aging.