In this work, PM_2.5 was sampled at Dunkerque, a medium-sized city located in northern France. The mean concentration of PM_2.5 during the sampling period was 12.6 ± 9.5 μg·m⁻³. Samples were analyzed for elemental and organic carbon (EC/OC), water-soluble organic carbon (WSOC), humic-like substances (HULIS-C), water-soluble inorganic ions, and major and trace elements. The origin and the variations of species concentrations were examined using elemental enrichment factors, bivariate polar plot representations, and diagnostic concentration ratios. Secondary inorganic ions were the most abundant species (36% of PM_2.5), followed by OC (12.5% of PM_2.5). Secondary organic carbon (SOC) concentrations were estimated to account for 52% of OC. A good correlation between SOC and WSOC indicated that secondary formation processes significantly contribute to the WSOC concentrations. HULIS-C also represents almost 50% of WSOC. The determination of diagnostic ratios revealed the influence of anthropogenic emission sources such as integrated steelworks and fuel oil combustion. The clustering of 72 h air masses backward trajectories data evidenced that higher concentrations of PM_2.5, OC, and secondary inorganic aerosols were recorded when air masses came from north-eastern Europe and the French continental sector, showing the considerable impact of long-range transport on the air quality in northern France.

In the present work, an innovative range of foams based on flax gum-filled epoxy resin was developed, reinforced or not by flax fibers. Foams and composites with different gum and epoxy resin contents were produced and their mechanical and thermal performances were characterized. To enhance the organic flax gum filler’s cross-linking, we exploited the oxidized components’ reactivity with the amine hardener (isophorone diamine). We compared the materials obtained with those derived from the native components. The flax gum and fibers were primarily characterized by chemical analysis, NMR, and FTIR to evaluate the mild oxidation of the native materials. The formation of chemical bonds between the oxidized polymer chains, epoxy resin, and hardener was evidenced by FTIR, and the materials were then studied by SEM and X-ray computed micro-tomography (CT) and submitted to mechanical and thermal tests. The relevance of the oxidation treatment was highlighted through a significant increase in density and mechanical performance (+36% and +81%, respectively, for the 100% flax gum material). The positive effect of the flax fibers on homogeneity evidenced through micro-CT analysis was also clearly addressed. This set of promising results paves the way for the future development of fully flax-based insulation composite materials.

In the present work, an innovative range of foams, based on flax gum-filled epoxy resin was developed, reinforced or not by flax fibers. Foams and composites with different gum and epoxy resin contents were produced and characterized for mechanical and thermal performances. To enhance the organic flax gum filler's cross-linking, we exploited the oxidized components' reactivity with the amine hardener (isophorone diamine). We compared the materials obtained with those derived from the native components. Flax gum and fibers were primarily characterized by chemical analysis, NMR, and FTIR to evaluate the mild oxidation of native materials. The formation of chemical bonds between oxidized polymer chains, epoxy resin, and hardener has been evidenced by FTIR, and the materials were then studied by SEM, X-ray computed micro-tomography (CT), and submitted to mechanical and thermal tests. The relevance of oxidation treatment was highlighted, through a significant increase in density and mechanical performances (+36% and +81%, respectively for the 100% flax gum material). The positive effect of flax fibers on homogeneity evidenced through micro-CT analysis was also clearly addressed. This set of promising results paves the way for future development of fully flax-based insulation composite materials.