L. Delmotte

Parameters influencing wood-dowel welding by high-speed rotation

Oven-dry dowels, insertion of hot dowels, cross-cut dowels, substrate holes of step-decreasing diameter as a function of depth, use of ethylene glycol or other compounds able to decrease the glass transition temperature of wood components have all been shown to contribute to improving weld joint strengths in a variety of less drastic conditions than the 10 mm/8 mm dowel/substrate hole diameter difference. The results show that once the depth of the dowel is much greater than 15 mm, then almost all the conditions used improve the weld strength. This means that the proportion of area welded in relation to the tensile strength of the dowel itself is a determining factor. The greater this area the higher the strength, irrespective of the application conditions used. Thus, over a certain welded area the dowel breaks when tested in tensile, i.e., the joint is stronger than the dowel. Temperatures > 180°C are reached during the quick welding step with the temperature decreasing in less than 1 min to 60–70°C. The same chemical reactions as occurring in vibrational welding have been shown by solid-state 13C-NMR analysis to also occur in dowel rotation welding. In dowel rotation welding the production of carbohydrate-derived furanic aldehydes is higher (a) from the wood material of the substrate in which the hole is pre-drilled rather than from the material of the wood dowel itself, (b) when the weld joint strength is good, and (c) when the rate of dowel insertion is higher.

Wheat straw particleboard bonding improvements by enzyme pretreatment

Three kinds of enzyme were used to treat wheat straw. Particleboards bonded with a UF resin were made with the treated wheat straw as a raw material. The results obtained show that the enzyme action is not affected under certain conditions when separated from the living cell producing it. The free-radical content of wheat straw was observed by electron spin resonance (ESR) to clearly increase after it is treated with cellulases from Trichoderma sp. and Aspergillus niger. The wheat straw benzene-ethanol or ether extracts content decreases after wheat straw treatment with lipases from Candida rugosa. This indirectly indicates that the surface wax of wheat straw is reduced if wheat straw is treated with lipases. The pH-values of wheat straw are somewhat changed by the enzyme treatment indicating that its buffering capacity is decreased. Wheat straws surface wax is one of the main adhesion inhibitors in its use as a raw material for particleboard. The better properties of UF-bonded particleboard made using enzyme treated wheat straw can be explained on this basis. In this regard the effect of cellulases from Aspergillus niger yields the best result.

Synthesis and characterization of montmorillonite-type phyllosilicates in a fluoride medium

Abstract The fluorine route is thoroughly investigated for the hydrothermal synthesis of montmorillonite in the Na2O-MgO-Al2O3-SiO2-H2O system. Using the optimal conditions suggested by Reinholdt et al. (2001) for the crystallization of pure montmorillonites with the formula Na2x(Al2(1−x)Mg2x □)Si4O10(OH)2, several parameters (x, Mg content, duration of crystallization, F/Si atomic ratio, pH, nature of counterbalance cation) are varied independently from their ideal values. The products are analysed by various techniques (X-ray diffraction, thermogravimetric analysis-differential thermal analysis, 29Si, 27Al and 19F magic angle spinning-nuclear magnetic resonance). It appears that a pure montmorillonite can only be obtained within a narrow x range (0.10 ≤x ≤ 0.20). The presence of F in the starting hydrogel and the crystallization time also have significant effects on the purity of the final products. It is shown that a small amount of fluorine is needed for the crystallization of pure montmorillonite phyllosilicates.

Catalyst-free soft-template synthesis of ordered mesoporous carbon tailored using phloroglucinol/glyoxylic acid environmentally friendly precursors

Carbon porous materials with a periodically ordered pore structure, controlled pore size and geometry and high thermal stability are synthesized using self-assembly of environmentally friendly phloroglucinol/glyoxylic acid precursors with an amphiphilic triblock copolymer template. Glyoxylic acid, a plant-derived compound, is used for the first time as a substituent of carcinogen formaldehyde usually employed in such a synthesis. Thanks to the double functionality, i.e., aldehyde and carboxylic acid, glyoxylic acid plays not only the role of a cross-linker for the formation of the resin but also the role of a catalyst by creation of H-bonding or specific reactions between the precursors. Hence, no extra catalyst such as strong acids (HCl) or bases (NaOH) is any longer required. Carbon films and powders were successfully prepared with high surface areas (up to 800 m2 g−1), high porous volume (up to 1 cm3 g−1), tunable pore size (0.6 nm to 7 nm) and various pore architectures (hexagonal, cubic, and ink-bottle) by tuning the precursor ratio and by applying different manufacturing engineering strategies. Insights on the synthesis mechanism of the phenolic resin and carbon mesostructures were obtained using several analysis techniques, i.e., nuclear magnetic resonance (13C NMR) and FTIR spectroscopy, temperature programmed desorption coupled with mass spectrometry (TPD-MS) and thermo-gravimetric analysis (TGA).

New range of Al–Mg organoclays with tailored hydrophobicity: incorporation of fluoride as a local probe to study the octahedral character

Abstract A series of inorganic–organic hybrids with a phyllosilicate-like structure were prepared using a single-step templating sol–gel procedure. The synthesis involves reaction of magnesium nitrate and aluminum acetylacetonate with octyltriethoxysilane, to give products where saponite is the inorganic parent. These hybrids were characterized by X-ray diffraction, solid-state 29 Si, 13 C and 27 Al nuclear magnetic resonance, infrared spectroscopy and thermogravimetry. The results showed that the hybrid materials exhibit lamellar structures, similar to those found in natural inorganic silicate saponite. The influence of the substitution of magnesium and silicon by aluminum was evident from 29 Si and 13 C NMR studies. A high degree of condensation was obtained. The hydrophobic character was evaluated by wettability measurements. These materials hold promise as sorbents for solid-phase extraction of organic pollutant molecules, due to their highly hydrophobic character.

Solid wood joints by in situ welding of structural wood constituents

Abstract Mechanically-induced wood flow welding, without any adhesive, is here shown to rapidly yield wood joints satisfying the relevant requirements for structural application. The mechanism of mechanically-induced vibrational wood flow welding is shown to be due mostly to the melting and flowing of the amorphous polymer materials interconnecting wood cells, mainly lignin, but also some hemicelluloses. This causes the partial detachment of long wood cells and wood fibres and the formation of an entanglement network in a matrix of melted material which then solidifies. Thus, it forms a wood cell/fibre entanglement network composite having a molten lignin polymer matrix. During the welding period, some of the detached wood fibres no longer held by the interconnecting material are pushed out of the joint as excess fibre. Cross-linking chemical reactions of lignin and of carbohydrate-derived furfural also occur. Their presence has been identified by CP-MAS 13C NMR. These reactions are, however, relatively minor contributors during the very short welding period. Their contribution increases after welding has finished, explaining why relatively longer holding times under pressure after the end of welding contribute strongly to obtaining a good bond.

Selective Capture of Water Using Microporous Adsorbents To Increase the Lifetime of Lubricants

Long live lubricants: The selective capture of water from lubricants using nanosized microporous aluminophosphate (AEI) and aluminosilicate materials was studied. Nearly 98 % of the moisture was removed from the lubricating oil under ambient conditions, resulting in a significant improvement in the lubricating service lifetime. Moreover, both the lubricant and the microporous sorbents can be recovered and reused.The selective capture of water from lubricants using nanosized microporous aluminophosphate and aluminosilicate materials was studied with an aim to increase the lifetime of the lubricating mineral oil. The amount of water present in oxidized lubricating oil before and after treatment with microporous materials was studied by FTIR spectroscopy and determined quantitatively using the Karl Fischer titration method. Nanosized aluminophosphate revealed a high selectivity for water without adsorbing other additives, in contrast to nanosized aluminosilicates which also adsorb polar oxidation products and ionic additives. About 98 % of the initial moisture could be removed from the lubricating oil under ambient conditions, resulting in a significant improvement in the lubricating service lifetime. Moreover, no by-products are formed during the process and both the lubricant and the sorbents can be recovered and reused, thus the method is environmentally friendly.

Environmentally benign synthesis of nanosized aluminophosphate enhanced by microwave heating

The problem addressed with our paper is on the efficient utilization of reacting materials for enhanced syntheses of nanosized aluminophosphate molecular sieve by microwave heating, and decreasing or almost eliminating the related waste. The synthesis procedure deals with the environmental issues concerning the future manufacture re-use and disposal of non-reacted chemicals associated with the production of nanosized aluminophosphate. Nanosized AlPO-18 has been prepared by a multicycle synthesis approach via re-using non-reacted compounds from precursor suspensions with minimal requirement of chemical compensation after recovering of crystalline nanoparticles from each step. This approach is implied as environmentally benign and results in almost complete consumption of the organic templates and phosphorous acid without disposing these harmful reagents to the environments. Thus the use of highly expensive and non-desirable chemicals can be reduced and result in reasonable yield while production cost is attained. Also, the use of microwave irradiation leads to the preparation of nanocrystalline material within 5 min, instead of 3 days by using conventional heating, which makes the process economically viable and environmentally benign.

Influence of Wood Welding Frequency on Wood Constituents Chemical Modifications

Interesting chemical differences betwen weldlines obtained at 100 Hz and 150 Hz frequencies in linear vibration wood welding were observed by FT-IR and 13C NMR. An increase in the proportion of unoxidized phenolic groups in the lignin is observed by FT-IR and the increased joint strength observed is ascribed to the improved adhesion derived from this. The much decreased level of oxidation due to the much shorter welding time possible at 150 Hz was clearly observed by 13C NMR by a marked decrease, even disappearance, of the presence of dark coloured quinones in the weldline at 150 Hz. This yielded colourless weldlines.

Lactic acid/wood-based composite material. Part 1: Synthesis and characterization

As biomass feedstock, wood and lactic acid biopolymers have been used as constituents of an innovative biocomposite material possessing remarkable properties. Three different systems were made by soaking lactic acid oligomers into solid wood and then oven heating to induce in situ polymerisation, confirmed by Fourier transformed infrared spectroscopy (FTIR) and gel permeation chromatography (GPC) analysis. Combinations of treatment systems and heating durations, implying structural wood modification, led to different physical behaviours of the composites. The first obtained material was in the form of softened and easily bendable wood. Subjected to an extended heating period, this softened material could then regain its initial hardness. Another treatment parameter combination directly led to densified wood with improved properties. These two main composite materials are expected to be useable for bending, stamping or flooring industrial uses, depending on their physical condition.