The growing demand for sustainable flame-retardant biocomposites highlights a significant research gap: understanding how the thermal compression process affects fire performance in terms of the strength of flame retardant (FR) and substrate interactions. This is particularly important for polylactic acid (PLA) and flax systems, where excessive interactions between the FR and the matrix can compromise mechanical properties. In contrast, weak interactions may lead to the loss of the FR during processing. To address this challenge, we present the first systematic comparison of two bio-based flame-retardant approaches: weak interaction through an impregnation process (using phytic acid and triethanolamine) and strong covalent grafting (using phytic acid and urea). We evaluate their resilience to vacuum-assisted thermal compression. The study reveals that both methods initially provide similar levels of flame retardancy, with a 28% reduction in the peak heat release rate (pHRR). However, after thermocompression, the impregnated composites lose their flame-retardant performance due to partial volatilisation of TEA and a significant reduction in PLA molecular weight. In contrast, the thermocompressed CG samples retain their flame-retardant properties, demonstrating the effectiveness of the CG process under thermal compression. Regarding mechanical properties, a significant decrease in maximum tensile strength is observed after flame-retardant treatment. This study highlights the importance of flame-retardant/material interactions in developing processable, bio-based flame-retardant composites, representing a significant step toward sustainable, fire-safe materials suitable for large-scale production.

Monomer impregnation is a great strategy to modify various wood properties. By choosing the right impregnant, it may lead to a higher flame retardancy of treated wood, contributing to its use in specific sectors such as building interior finishes. Yellow birch (Betula alleghaniensis Britt.) and sugar maple (Acer saccharum Marsh.) were surface-impregnated with an acrylate and a phosphorus acrylate monomer under vacuum and exposed to an electron beam for polymerisation. A surface chemical retention of 100 g.m− 2 was obtained for sugar maple, while the impregnation of yellow birch samples reached one around 200 g.m− 2. X-ray densitometry confirmed an asymmetric density profile due to the monomer penetration concentrated in the first millimetres of the samples. Microtomography and Raman spectroscopy highlighted the penetration path of the monomers in the wood, mainly through the vessels. The lumens of the cells close to the surface were also filled with polymers. The phosphorus monomer surface impregnation positively impacted the thermal and fire properties of the modified wood. A 25

In this study, we propose an innovative approach to improve the sustainability of polyvinylidene fluoride (PVDF) coatings by incorporating an epoxy vitrimer primer. The dynamic nature of the vitrimer allows for controlled coating removal under specific conditions, facilitating end-of-life management and recyclability. The self-stratifying coating, developed through a one-step application and curing process, consists of an epoxy vitrimer bottom layer and a PVDF top layer. This system was designed to spontaneously form two distinct layers during curing. Two vitrimer resins containing disulfide dynamic bonds were evaluated as base layers: polysulfide epoxy (EPS35) and diglycidyl ether of vanillyl alcohol (DGEVA). The epoxy/fluorinated systems were applied on different substrates (carbon coated aluminum or copper foils) and at different thicknesses (from 25 mu m to 230 mu m) and then characterized. All systems present two distinct coating layers with the epoxy on the substrate and the PVDF on top. Cross hatch cutter test results confirmed the perfect adhesion of the coating at room temperature. The epoxy layers self-healing was proved, highlighting the achievement of a dynamic network. Finally, the coating films were removed easily from the substrate under thermal stimuli of at least 100 degrees C. Finally, the influence of key parameters on stratification, applied wet thickness, substrate and epoxy formulation was evaluated. In all cases, a well-defined stratification (type I), perfect adhesion at room temperature (type "0") and a total removal at 100 degrees C was consistently observed.

Environmental sustainability and multifunctionality are now key drivers for smart coatings design and applications. In a circular economy that promotes durable materials, the challenge is to develop multi-functional onepot coating materials. The eco-efficient self-stratification process allows the spontaneous formation of complex polymer multilayers in only one step of formulation, application, and curing. This leads to the simultaneous production of both an undercoat and a finishing coating with all the properties needed to protect a material. In addition, film formation in a single application step drastically reduces adhesion failures and contamination between layers. The original idea in this study was to conceive a self-stratifying and self-healing coating formulation using a bio-based epoxy resin and a PDMS-based vitrimer, by taking advantage of the self-healing properties of the vitrimers. This newly discovered class of polymers possess dynamic covalent bonds. This epoxy resin - dynamic PDMS blend was successfully applied on polycarbonate substrates by spraying and exhibited a type I stratification associated with room temperature self-healing properties. Furthermore, the coating showed great adhesion to the substrate, on the contrary to the dynamic-PDMS when applied directly onto polycarbonate. The stratification was observed with SEM-EDS imaging. The self-healing property was proven by optical microscopy imaging of scratches under different thermal treatments. FT-IR and wet contact angle were used to further characterize the synthetized dyn-PDMS.

Wood is a natural composite widely employed as a residential building interior finishing. Although wood is readily available and offers benefits to the occupants, such as enhanced well-being, it is rarely employed in commercial construction due, amongst others, to the potential hazard of fire propagation. The application of flame retardant (FR) treatments leads to a reduction of wood flammability and supports wood as interior finishing. Polyelectrolyte complexes (PECs) deposition is an innovative surface treatment that has already proven its efficiency for fabrics. For wood, recent studies have highlighted that the weight gain impacted the fire-retardancy, and a minimum of 2 wt.-% was set to obtain fire protection. This study explored the potential of surface delignification to activate the wood surface and facilitate the PEC impregnation. Yellow birch (Betula alleghaniensis, Britt.) was surface delignified (0.3 mm) using sodium chlorite. The treatment impact on wood was evaluated by spectroscopy analysis (FTIR, Raman), and the increase in wood wettability was demonstrated (contact angle decreases from 50(degrees) to 35(degrees) after the surface delignification). Then, PECs consisting of polyethyleneimine and sodium phytate were surface impregnated in wood and delignified wood. The flame retardancy was evaluated using a cone calorimeter. Despite the increase in weight gain (1.5 wt.-%+/- 0.3 wt.-% to 4.3 wt.-% +/- 2.5 wt.-%), fire performance was not improved. This study demonstrates that lignin strongly affects char formation, even in the presence of PECs.

Environmental sustainability and multifunctionality are now key drivers for smart coatings design and applications. In a circular economy that promotes durable materials, the challenge is to develop multi-functional one-pot coating materials. The eco-efficient self-stratification process allows the spontaneous formation of complex polymer multilayers in only one step of formulation, application, and curing. This leads to the simultaneous production of both an undercoat and a finishing coating with all the properties needed to protect a material. In addition, film formation in a single application step drastically reduces adhesion failures and contamination between layers. The original idea in this study was to conceive a self-stratifying and self-healing coating formulation using a bio-based epoxy and a PDMS-based vitrimer, by taking advantage of the self-healing properties of the vitrimers, this newly discovered class of polymer with dynamic bonds. This epoxy – dynamic PDMS blend was successfully applied on polycarbonate substrates by spraying and exhibited a type I stratification associated with room temperature self-healing properties. Furthermore, the coating showed great adhesion to the substrate, on the contrary to the dynamic-PDMS when applied directly onto polycarbonate. The stratification was observed with SEM-EDS imaging. The self-healing property was proven by optical microscopy imaging of scratches under different thermal treatments. FT-IR and wet contact angle were used to further characterize the synthesized dyn-PDMS.

This work investigates the effect of flame-retardant additives on the thermo-mechanical and dynamic properties of poly(butylene terephthalate) (PBT) vitrimers. The vitrimers were synthesized and compounded in a single step by reactive extrusion from commercially available PBT, an epoxy resin, a zinc-based transesterification catalyst, and aluminum phosphinate (AlPi) as a conventional flame retardant additive. We demonstrated that the presence of AlPi in relatively large amount (20 wt.-%) is compatible with the formation of the vitrimer network and does even play the role of a transesterification (co)catalyst accelerating the exchange reactions and improving the processability of the vitrimer. UL-94 flammability tests also confirm the effective role of AlPi as flame retardant in vitrimer.

In a high-rise building, due to the risk of flame spread and strict regulations associated, wood use is limited for interior finishes. This study aimed to evaluate the effect of a thin organosilicon layer (similar to 500 nm) prepared by atmospheric pressure plasma on the fire behavior of a wood substrate. The coating was deposited from hexamethyldisiloxane in argon on both untreated wood and wood with a preparatory coating of primer. The primer reduces the presence of cracks in the plasma layer and ensures more homogenous coverage of the substrates. Finally, the flame retardancy analysis highlights an improvement in fire behavior only when the primer is used. Our study suggests that plasma thin deposition has a synergic effect with primer to fireproof wood.

This study describes an experimental investigation on the fire performance of intumescent coatings using two different bench-scale experimental methodologies. Steel plates with and without a commercially available thin-intumescent coating were tested using a 26 dm3 propane-fired furnace or an array of natural-gas-fired radiant panels in accordance with the Heat-Transfer Rate Inducing System (H-TRIS) test method. Research outcomes demonstrate how the two bench-scale experimental methodologies can be adopted to effectively research and develop intumescent coatings for a range of equivalent thermal exposures. A comprehensive comparative analysis between the two methods was performed based on the transient swelling behaviour of the intumescent coating and the temperature of the steel substrate. The H-TRIS test method imposes well-defined and stable thermal conditions at the exposed surface of the swelling intumescent coating, while the mixed convective-radiative thermal conditions inside the bench-scale furnace occur over the whole coating surface, and their distribution and homogeneity are difficult to quantify in practice. Also, at high temperatures, the turbulent flow fields inside the furnace affected the coating degradation, showing detachment (partial or total, gradual, or sudden) of the swelled char and generating increased uncertainty of the thermal and physical conditions, but reproducing scenarios more realistic and similar to real compartment fires. Lastly, the H-TRIS test method allows for the measurement of the transient coating swelling during heating, but also exposed the tested samples to higher oxygen concentrations than those tested inside the furnace.

The application of a flame retardant coating is an effective solution to enhance the fire retardancy of wood flooring. However, finding the right balance between reducing the flame propagation and good overall coating properties while conserving wood appearance is complex. In order to answer this complex problem, transparent ultraviolet (UV)-curable flame retardant wood coatings were prepared from an acrylate oligomer, an acrylate monomer, and the addition of the tri(acryloyloxyethyl) phosphate (TAEP), a phosphorus-based monomer, at different concentrations in the formulation. The coatings’ photopolymerisation, optical transparency, hardness, water sorption and thermal stability were assessed. The fire behaviour and the adhesion of the coatings applied on the yellow birch panels were evaluated, respectively, using the cone calorimeter and pull-off tests. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) analyses were performed on the collected burnt residues to obtain a better understanding of the flame retardancy mechanism. Our study reveals that phosphorus monomer addition improved the coating adhesion and the fire performance of the coated wood without impacting the photopolymerisation. The conversion percentage remained close to 70% with the TAEP addition. The pull-off strength reached 1.12 MPa for the coating with the highest P-monomer content, a value significantly different from the non-flame retarded coating. For the same coating formulation, the peak of heat release rate decreased by 13% and the mass percentage of the residues increased by 37% compared to the reference. However, the flame-retarded coatings displayed a higher hygroscopy. The action in the condensed phase of the phosphorus flame retardant is highlighted in this study.

Different types of passive fireproofing materials exist such as intumescent paints. Our approach was to modify the design the material instead of changing the formulations. By combining two concepts namely intumescence and delamination, and adjustable design, new effective fire barrier was developed to protect composites. It was evaluated using a burn-through fire scenario (heat flux of 116 kW/m2 and temperature of flame of 1100 °C). The fire barrier revealed to provide fire protection to the composite and stabilized the temperature at the backside of the composite plate under 200 °C. Characterisations (cross-section observations, expansion measurements, etc.) were carried out on the samples and a mechanism of action was proposed.