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International audience; Ramie plants (Boehmeria nivea) have been cultivated on ion-adsorption rare earth elements (REEs) mine tailings and showed a low ability to accumulate REEs, especially in the stems (REE= 24±17 mg kg-1) with higher concentration in leaves and roots (REE= 57 to 66 mg kg-1). Ramie individual fibers were isolated using three degumming processes: a traditional alkali treatment (AT), a steam explosion (SE) treatment after a neutral (SEN) or after a basic (SEB) impregnation. Cellulose-rich (> 80%) fine fibers with very low amounts of non-cellulosic sugars (

The tension on the supply of surgical and FFP2 masks during the first wave of the COVID-19 pandemic leads to study the potential reuse of these masks. As washing is easily adaptable at home, this treatment solution was retained. In this work, thirty-six references of surgical masks and four FFP2 masks were tested without being worn or washed and after several washing cycles. The results highlighted a great heterogeneity of performances depending on the mask trademarks, both for surgical masks and FFP2. The quality of the meltblown and spunbond layers and the presence/absence of electrostatic charges at the fiber surface are put forward to explain the variability of results, both on differential pressures and filtration efficiencies. The differential pressure and the particle filtration efficiency of the washed masks were maintained up to 10 washing cycles and met the standard requirements. However, an immersion in water with a detergent induces an efficiency decrease for submicronic particles. This lower performance, constant after the first washing cycle, can be explained by the loss of electrostatic charges during the washing cycle. The modifications of surface properties after washing also lead to a loss of the hydrophobic behavior of type IIR surgical masks, which can therefore no more be considered as resistant to blood projections.

The project consists in the implementation of a biocomposite based on tannin resin and natural rubber matrices with the bast fibres of Triumfetta cordifolia A.Rich.“Okong” from the equatorial region of Cameroon as reinforcement. A study of this still little known fibre is necessary. This paper evaluates the physico-chemical and mechanical characteristics of the fibers. The fibers are extracted by us. A series of experiments is conducted for this purpose: morphological observation with a scanning electron microscope (SEM); density evaluation with a helium pycnometer; absorption rate evaluation according to the protocol available in the literature, Fourier Transform Infrared Spectrometry (FT-IR), chemical composition evaluation according to ASTM 1972 and ASTM 1977 standards, thermogravimetric analysis (TGA) and tensile tests on fiber bundles according to NF T25-501-3. The results show that the fiber is made up of several elementary fibers with oval cross-sections. A density of 1.477g/cm3 close to that of hemp. These fibers have a water absorption rate of 342.5%, which correlates with the presence of free hydroxyl functional groups obtained from the spectrometry study (FT-IR). Chemical analysis reveals that the fiber is made up of celluloses (44.4%), hemicelluloses (30.8%), lignins (18.9%), pectins (3.3%), waxes (0.5%) and minerals (2.1%). In addition, we learn that the fibers studied dehydrate at 11.49%, showinga notable thermal stability around 235°C with a peak thermal decomposition of cellulose located at 420°C. In terms of mechanical behaviour, the results reveal that the fibers offer a Young’s modulus in traction of 12.4 ± 6.9 GPa, a tensile strength of 526 ± 128 MPa and an elongation at break of 2.25%. The information thus obtained makes it possible to place these fibers in the same fiber group as flax and jute. They could therefore be used for the same types of applications. They also inform us that these fibers can withstand the temperatures of composite shaping by thermocompression.

Également publié le 15/10/2021 sous la référence FR3109113; The present invention relates to a flame retardant treatment of a lignocellulosic material, characterized in that it comprises the following steps: - optionally steam explosion of the lignocellulosic material, - impregnation of the optionally steam-exploded lignocellulosic material, in or with an aqueous solution comprising from 0.5% to 10% of phytic acid and from 1% to 30% of urea, and preferably from 3% to 7% of phytic acid and from 15% to 22% of urea, said percentages being expressed by weight relative to the total weight of the aqueous solution, - optionally drying of the impregnated lignocellulosic material, until it has a moisture content ranging from 5% to 20%, said percentages being expressed by weight relative to the total weight of the impregnated lignocellulosic material, - cooking of the impregnated and optionally dried lignocellulosic material, the resulting flame-retarded lignocellulosic material comprising a content of phosphorus originating from the phytic acid ranging from 0.1% to 10%, preferably ranging from 0.3% to 3%, said percentages being expressed by weight relative to the total weight of the flame-retarded lignocellulosic material. The invention also relates to the resulting flame-retarded lignocellulosic material and the use thereof for manufacturing: - flame-retarded composite materials based on plant fibres, - woven or nonwoven flame-retarded flexible materials based on plant fibres, and particularly textiles, - flame-retarded materials based on wood fibres and/or on wood particles, and particularly flame-retarded wood panels.; La présente invention a pour objet un procédé d’ignifugation d’une matière lignocellulosique caractérisé en ce qu’il comprend les étapes suivantes :- éventuellement explosion à la vapeur de la matière lignocellulosique,- imprégnation de la matière lignocellulosique, éventuellement explosée à la vapeur, dans ou avec une solution aqueuse comprenant de 0,5% à 10% d’acide phytique et de 1% à 30% d’urée, et de préférence de 3% à 7% d’acide phytique et de 15% à 22% d’urée, lesdits pourcentages étant exprimés en masse par rapport à la masse totale de la solution aqueuse,- séchage de la matière lignocellulosique imprégnée, jusqu’à ce qu’elle présente une humidité allant de 5% à 20%, lesdits pourcentages étant exprimés en masse par rapport à la masse totale de la matière lignocellulosique imprégnée,- cuisson de la matière lignocellulosique imprégnée et séchée,la matière lignocellulosique ignifugée ainsi obtenue comprenant une teneur en phosphore provenant de l’acide phytique allant de 0,1% à 10%, de préférence allant de 0,3 % à 3%, lesdits pourcentages étant exprimés en masse par rapport à la masse totale de la matière lignocellulosique ignifugée. L’invention concerne encore la matière lignocellulosique ignifugée ainsi obtenue et son utilisation pour la fabrication :- de matériaux composites ignifugés à base de fibres végétales,- de matériaux souples ignifugés tissés ou non tissés à base de fibres végétales, et notamment de textiles,- de matériaux ignifugés à base de fibres de bois et/ou de particules de bois, et notamment de panneaux de bois ignifugés.

International audience; The Piptadeniastrum Africanum bark tannin extract was characterized using MALDI TOF, ATR-FT MIR. It was used in the development of a resin with Vachellia nilotica extract as a biohardener. This tannin is consisting of Catechin, Quercetin, Chalcone, Gallocatechin, Epigallocatechin gallate, Epicatechin gallate. The gel time of the resin at natural pH (pH = 5.4) is 660 s and its MOE obtained by thermomechanical analysis is 3909 MPa. The tenacity of Urena lobata fibers were tested, woven into unidirectional mats (UD), and used as reinforcement in the development of biocomposite. The fibers tenacity at 20, 30 and 50 mm lengths are respectively 65.41, 41.04 and 33.86 cN·Tex−1 . The UD biocomposite obtained had very interesting mechanical properties. Its density, tensile MOE, ultimate strength, bending MOE and MOR are respectively 926 kg·m−3 , 6 GPa, 55 MPa, 9.3 GPa and 68.3 MPa. This biocomposite can be used in a building exterior structure.

This study aims to investigate the causes of the differential behavior of extractives on the water resistance of the welded joints of three tropical woods. The welded joints of these chemically cha...

Fine hemp fibers (cottonized hemp) were processed using steam explosion. The quantification of the defibration rate was performed by image processing. Based on this method, the hemp defibration was optimized using a response surface methodology based on three-variable central composite design for the production of elementary fibers with low variability. Optimal parameters for the steam processes were as follows: time = 4.1 min; temperature = 191℃. Biomass was impregnated with a solution of NaOH (8%) before treatment, leading to a defibration rate of 91.2%, which is producing ≈50% fibers with length

International audience; Flax fiber is an industrially available, renewable product with attractive technical properties for the composite industry such as density, mechanical strength and sound/heat insulation. Applications are developing quickly for biocomposites based on these fibers. However, unlike plastics, there is no standard used to assess its degree of contamination by microorganisms. Thus, the aims of this work were to detect and quantify molds in samples of nonwoven fibrous materials from industry and high resin content natural matrix-natural fiber biocomposites. In a first attempt, we tried to evaluate the fungal development on the nonwoven materials as defined in the ISO 846 standard. Despite the materials having been inoculated with molds, no fungal mycelium could be detected by this way. To validate this observation, we developed a qualitative approach based on the specific aniline blue method to stain the mycelium present in the material. This allowed us to detect the mold occurrence in the material and to evaluate the colonization extent on the nonwoven fibrous materials incubated under different conditions. The biocide efficiency of a boric acid pretreatment of flax fibers used in the manufacturing process of nonwoven fibrous materials and high resin content natural matrix-natural fiber biocomposites was determined by grading the mold development using the microscope-based method that we developed. The results showed clearly that in optimal mold growth conditions, (Aw > 0.6, 26 degrees C) the colonization of the material was hampered by the boric acid pretreatment of the flax fibers. To get semi-quantitative data of the colonization extent, we used a molecular method. DNA was extracted from the different materials and the ribosomal region of the fungal DNA was amplified by PCR allowing the detection and the quantification of fungal colonization in the biosourced material. Results confirmed the microscopy-based method. Work is currently in progress to determine risk classes of mold colonization in wood-derived and fibrous-based composite materials.

Chestnut hydrolysable tannins are phenolic materials that have been considered too unreactive to compete in the phenolic resin adhesives market for exterior boards for the building industry. However, an article in 1973 describing 3 years industrial application of chestnut hydrolysable tannins during the first oil crisis indicated that this was not the case. We have extended this old work by using superior phenolic resins formulations and producing phenol-formaldehyde-chestnut tannin adhesives where a substitution of up to 80% of the phenol is possible with remarkably good results. The reactions involved were clarified by 13C NMR and MALDI-TOF mass spectrometry.

Chestnut hydrolysable tannins are phenolic materials that have been considered too unreactive to compete in the phenolic resin adhesives market for exterior boards for the building industry. However, an article in 1973 describing 3 years of industrial application of chestnut hydrolysable tannins during the first oil crisis indicated that this was not the case. This previous work has been extended by using superior phenolic resins formulations and producing phenol–formaldehyde–chestnut tannin adhesives where a substitution of up to 80% of the phenol is possible with remarkably good results. The reactions involved were clarified by 13C NMR and MALDI–TOF mass spectrometry.

Holding wood pieces together by rotationally welded dowels can be used to make blockboard panels with the dowels inserted in the side of the wood substrate slats. Pre-oiling the dowels with sunflower oil: (i) eases their insertion in the pre-drilled substrate, (ii) allows the insertion of dowels to a much greater depth by its lubricating action for welding, thus allowing more layers of wood to be joined and (iii) provides an improved water resistance to the welded joint. The strength of the joints prepared with this system is comparable to those already obtained with other welded dowel systems but with improved water resistance.

Low molecular mass acetylated organosolv lignin from wheat straw and from depolymerised low sulphur organosolv wood lignin have been shown to markedly improve both the water resistance and the mechanical performance of welded dowel wood joints. The acetylated oligomers distribution and extent of acetylation of the two lignins were determined by Matrix assisted laser desorption ionization-time-of-flight mass spectrometry. Extensive acetylation was confirmed by CP-MAS 13C NMR spectrometry. Force–displacement measurements on welded dowel joints to which acetylated wood lignins were added showed a ductile behaviour. This is due to the interpenetration of the elastic acetylated lignin network into the more rigid composite network of the welded interphase.

Albumin-based rigid and elastic foams were prepared by mechanically beating water solutions of the protein mixed with formaldehyde and camphor. The resulting foams were cross-linked in a traditional or in a microwave oven. Formaldehyde was used as hardener of the protein and camphor as a plasticizer. Thermal conductivity was tested and found to be acceptable for thermal insulation but did not appear to be influenced by variations in foam density. Scanning electron microscopy of the different formulations showed some differences in cells structure. Formulations of different water content, formaldehyde hardener content, camphor content and oven curing time were tested. Within certain limits (a) increases in water proportion rendered the foam more elastic, (b) higher formaldehyde content increased foam rigidity and strength up to a value beyond which no further increase occurred, (c) the amount of camphor influences markedly the compression strength and foam elasticity/plasticity, (d) curing time improving foam strength up to 5 min in microwave curing, without any further effect for longer heating times. Only addition of glycerol, yielded truly soft elastic foams.

Holding wood pieces together by rotationally welded dowels can be used to make blockboard panels with the dowels inserted in the side of the wood substrate slats. The average results for both tensile and three-point bending tests indicate that a 20° dowel insertion angle yields strength results better than 10° and 0° insertion angles. Applied load vs deformation in the two types of tests showed that blockboard panel stiffness was greater for the panels with 20° dowel insertion angle.

Dowel insertion rates whether accelerating or constant are determining parameters for the tensile strength of welded dowel joints. Dowel insertion at acceleration up to 4–7 m/s2 appears to yield the best results at the lower dowel insertion speed, characteristic of welding by manual drills. Strength results for dowel welded joints of 24 mm depths of up to 2700 N/mm2 have been obtained. Constant dowel insertion rates appear instead to yield best results when the insertion rate is much higher and can be better controlled, as it is the case for a computer controlled dowel insertion equipment. Strength results for dowel welded joints of 24 mm depths of up to 4700 N/mm2 have been obtained for insertion rates of 18–20 mm/s and welding time as short as 1.2 s. The results indicate that at low to medium insertion rates, the greater is the acceleration the better are the results. At fast insertion rates the acceleration has only little effect. The predominant effect is that a short welding time yields a high streng...

Numerical models using a 3-D finite element analysis method and the behaviour of dowel-welded wood joints are presented. Simulation results for step butt wood joints with two welded wood dowels under shear are analyzed and a good agreement with the experimental results is shown. Anisotropic elasto-plastic constitutive law with hardening associated with material densification, without distinction between radial and tangential properties, was used for the compressive behaviour of wood. The good coherence of the results obtained demonstrates clearly the capability of the model developed to simulate accurately the non-linear behaviour of dowel-welded wood joints to failure.

Comparison of three types of furniture joints such as scarf joints, step butt joints and dovetail joints held together either by one or two welded dowels, glued dowels and steel nails showed that the dowels always gave better shear strength and greater stiffness than the steel nails. The results of welded dowels and glued dowel joints were found to be comparable. The application of the welded joint technique to joints where the number of dowels is limited by the narrow space in which they can be applied, such as in furniture, can give results comparable to those obtained by gluing the same dowels.

9 pages; International audience; Shrink-fitting, a common bonding technique in metal assemblies, was used for mortise and tenon wood joints. The joints had considerable strength. Shrink-fitting yielded joint strengths comparable to those obtained by using several welded dowels. Increasing the number of welded dowels, however, produced joints of higher strength than those bonded just by shrink-fitting. Combining in the same joint both dowel welding and shrink-fitting yielded joint strengths higher than those obtained by the individual techniques alone, and at the same time allowing decreasing the number of welded dowels needed.