Phenolic foams (PF) have a combination of properties that make them attractive for a number of engineering applications such as insulation, lightening, energy absorption and fire protection. Phenolic ...foams exhibit excellent fire-retardant behaviour but have insufficient mechanical properties (e.g. fatigue, flexural properties and friability) for different applications in comparison to other foam materials. Hence, numerous studies have tried to improve these mechanical properties without deteriorating its excellent fire-retardant behaviour. Different approaches have been investigated, such as the addition of fibres and particles or the chemical modification of the PF base resin. This work will first briefly present generalities from resin synthesis to foam production. The main part will review the existing papers dealing with the improvement of the compressive and flexural strength as well as the friability. Moreover, evolution of the cell size with these mechanical properties will be presented, although there is no well-defined link between them. Then, the influence of these modifications on the fire-retardant behaviour of PF will be discussed. Finally, the last part will present work to substitute phenol from petroleum sources to environmental friendly sources.
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•Density in relation with cell morphology is the key factor controlling the mechanical properties of phenolic foams.•Modification of phenolic foams by additive and/or reactive routes allows the improvement of their final properties.•Dicyandiamide is the most efficient additive for higher compressive strength and lower friability.•Aramide fiber addition induces the reduction of friability without impacting mechanical properties.•Phenolated lignins are very promising bio-based resins for production of sustainable phenolic foams.
• The genetic structure of bacterial and fungal communities was characterized in the rhizosphere of Medicago truncatula Gaertn. cv. Jemalong line J5 at five developmental stages (three vegetative and ...two reproductive stages), and in three compartments (bulk soil, rhizosphere soil and root tissues). • The genetic structure of microbial communities was determined by cultivation-independent methods using directly extracted DNA that was characterized by automated ribosomal intergenic spacer analysis (ARISA). • Principal component analyses (PCA) indicate that, for all developmental stages, the genetic structure of microbial communities differed significantly by compartment, with a major shift in the community in root tissues corresponding to the most intimate compartment with the plant. • Differences were also recorded during plant development, the most significant being observed during the transition between vegetative and reproductive stages. Throughout this period, plants were shown to establish the highest level of symbiotic association (mycorrhization, nodulation) with arbuscular mycorrhizal fungi and Rhizobia. During the reproductive stages, the dynamics of the genetic structure differed between bacterial and fungal communities. At the last reproductive stage, the genetic structure of bacterial communities became close to that recorded during the first vegetative stages, suggesting a resilience phenomenon, whereas the genetic structure of fungal communities remained different from the vegetative stages and also from the early reproductive stages, suggesting a persistence of the rhizosphere effect.
The genetic structures of bacterial communities associated with Medicago truncatula Gaertn. cv. Jemalong line J5 (Myc⁺ Nod⁺) and its symbiosis-defective mutants TRV48 (Myc⁺ Nod⁻) and TRV25 (Myc⁻ ...Nod⁻) were compared. Plants were cultivated in a fertile soil (Châteaurenard, France) and in soil from the Mediterranean basin showing a low fertility (Mas d'Imbert, France). Plant growth, root architecture, and the efficiency of root symbiosis of the three plant genotypes were characterized in the two soils. Structures of the bacterial communities were assessed by automated-ribosomal intergenic spacer analysis (A-RISA) fingerprinting from DNA extracted from the rhizosphere soil and root tissues. As expected, the TRV25 mutant did not develop endomycorrhizal symbiosis in any of the soils, whereas mycorrhization of line J5 and the TRV48 mutant occurred in both soils but at a higher intensity in the Mas d'Imbert (low fertility) than in the Châteaurenard soil. However, modifications of plant growth and root architecture, between mycorrhizal (J5 and TRV48) and nonmycorrhizal (TRV25) plants, were recorded only when cultivated in the Mas d'Imbert soil. Similarly, the genetic structures of bacterial communities associated with mycorrhizal and nonmycorrhizal plants differed significantly in the Mas d'Imbert soil but not in the Châteaurenard soil. Multivariate analysis of the patterns allowed the identification of molecular markers, explaining these differences, and markers were further sequenced. Molecular marker analysis allowed the delineation of 211 operational taxonomic units. Some of those belonging to the Comamonadaceae and Oxalobacteraceae (β-Proteobacteria) families were found to be significantly more represented within bacterial communities associated with the J5 line and the TRV48 mutant than within those associated with the TRV25 mutant, indicating that these bacterial genera were preferentially associated with mycorrhizal roots in the Mas d'Imbert soil.
The recently described staphylococcal enterotoxins (SE) G and I were originally identified in two separate strains of Staphylococcus aureus. We have previously shown that the corresponding genes seg ...and sei are present in S. aureus in tandem orientation, on a 3.2-kb DNA fragment (Jarraud, J. et al. 1999. J. Clin. Microbiol. 37:2446-2449). Sequence analysis of seg-sei intergenic DNA and flanking regions revealed three enterotoxin-like open reading frames related to seg and sei, designated sek, sel, and sem, and two pseudogenes, psi ent1 and psi ent2. RT-PCR analysis showed that all these genes, including seg and sei, belong to an operon, designated the enterotoxin gene cluster (egc). Recombinant SEG, SEI, SEK, SEL, and SEM showed superantigen activity, each with a specific V beta pattern. Distribution studies of genes encoding superantigens in clinical S. aureus isolates showed that most strains harbored such genes and in particular the enterotoxin gene cluster, whatever the disease they caused. Phylogenetic analysis of enterotoxin genes indicated that they all potentially derived from this cluster, identifying egc as a putative nursery of enterotoxin genes.
Background and aims To assess how plant genotype and rhizosphere bacterial communities may interact, the genetic structure and diversity of bacterial communities in the rhizosphere soil of different ...Medicago truncatula genotypes were studied in relation to the plant carbon and nitrogen nutrition at the whole plant level. Methods The genetic structure and diversity of plant-associated rhizosphere bacterial communities was analysed by Automated Ribosomal Intergenic Spacer Analysis and 454-pyrosequencing. In parallel, the carbon and nitrogen nutrition of the plants was estimated by a phenotypic description at both structural level (growth) and functional level (using carbon and nitrogen isotope labeling and an ecophysiological framework). Results An early effect of the plant genotype was observed on the rhizosphere bacterial communities, while few significant differences were detected at the plant structural phenotypic level. However, at a functional level, the different Medicago truncatula genotypes could be distinguished by their different nutritional strategies. Moreover, a comparison analysis showed that ecophysiological profiles of the different Medicago truncatula genotypes were correlated to the genetic structure and the diversity of the rhizosphere bacterial communities. Conclusions The exploration of the genetic structure and diversity of rhizosphere bacterial communities combined with an ecophysiological approach is an innovative way to progress in our knowledge of plant-microbe interactions in the rhizosphere.
Sequencing of the 5' end of the large ribosomal subunit (LSU rDNA) and quantitative polymerase chain reaction (qPCR) were combined to assess the impact of four annual Medicago species (Medicago ...laciniata, Medicago murex, Medicago polymorpha and Medicago truncatula) on the genetic diversity of arbuscular mycorrhizal (AM) fungi, and on the relative abundance of representative AM fungal genotypes, in a silty-thin clay soil (Mas d'Imbert, France). Two hundred and forty-six Glomeromycete LSU rDNA sequences from the four plant species and the bulk soil were analysed. The high bootstrap values of the phylogenetic tree obtained allowed the delineation of 12 operational taxonomic units (OTUs), all belonging to Glomus. Specific primers targeting Glomeromycetes and major OTUs were applied to quantify their abundance by qPCR. Glomeromycetes and targeted OTUs were significantly more abundant in the root tissues than in the bulk soil, and the frequencies of three of them differed significantly in the root tissues of the different plant species. These differences indicate that, despite the absence of strict host specificity in mycorrhizal symbiosis, there was a preferential association between some AM fungal and plant genotypes.
A soil microcosm experiment was conducted to evaluate the influence of copper contamination on the dynamics and diversity of bacterial communities actively involved in wheat residue decomposition. In ...the presence of copper, a higher level of CO₂ release was observed, which did not arise from greater wheat decomposition but from a higher level of stimulation of soil organic matter mineralization (known as the priming effect). Such functional modifications may be related to significant modifications in the diversity of active bacterial populations characterized using the DNA stable-isotope probing approach.
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