Wood as a substrate

As the science of adhesion has developed, various theories of adhesion have been advocated for one material or another. With wood as a substrate, mechanical interlocking, interdiffusion of polymers, intermolecular attractive forces, and covalent chemical bonding all have been proposed, either individually or collectively, to explain adhesion. In reality, no experiments reported to date have been able to disprove the existence of any one of these mechanisms, or to quantify their relative importance. A most exasperating feature of research on adhesion to wood is that factors presumed to be independent in experiments are never totally independent. 

It has repeatedly been established that the energy of aetivation of the reaction of polycondensation of PF resins, and also of urea formaldehyde (UF), melamine-formaldehyde (MF), and other resins, is markedly influenced by the presence of wood [24,33-39]. In the presence of wood as a substrate, the energy of activation of the polycondensation reaction, and hence of the hardening of PF and other resins is considerably lowered. This implies that resin polymerization and cross-linking proceeds at a much... 

As described in the previous section. Brown et al. obtained an aromatic yield of 1% in the catalytic fast pyrolysis of milled wood lignin with ZSM-5 at 600°C, which was considerable lower than the yields obtained from cellulose and hemicellulose [286]. Also, the coke yield from lignin (59%) was much higher. Huber et al. used the lignin residue obtained after H SO hydrolysis of maple wood as a substrate for pyrolysis in a fluidized-bed reactor with spray-dried ZSM-5 at 600°C [298]. Next to lignin, this substrate also contains humic residue, a compound also composed of phenolic entities. An aromatic and olefin yield of only 2% and 1% was obtained, compared to respective yields of 15% and 7% from pure maple wood. The coke yield from the solid residue (69%) was also much higher than the coke yield from maple wood (32%). 

Cantarella, M., CantareUa, L., GaUifiioco, A., Spera, A., Alfani, F., 2004. Comparison of different detoxification methods for steam-exploded poplar wood as a substrate for the bioproduction of ethanol in SHF and SSF. Process Biochemistry 39 (11), 1533—1542. 

In the acid hydrolysis process (79—81), wood is treated with concentrated or dilute acid solution to produce a lignin-rich residue and a Hquor containing sugars, organic acids, furfural, and other chemicals. The process is adaptable to all species and all forms of wood waste. The Hquor can be concentrated to a molasses for animal feed (82), used as a substrate for fermentation to ethanol or yeast (82), or dehydrated to furfural and levulinic acid (83—86). Attempts have been made to obtain marketable products from the lignin residue (87) rather than using it as a fuel, but currently only carbohydrate-derived products appear practical. 

Because the porous growth patterns of wood vary, the densities of various dry woods also vary (200-1200 kg/m- ). The porosity of wood, of course, greatly influences the wood s utility as a substrate. The wood porosity affects also the type and form of the adhesive as it affects the ability of the substrate to absorb water and other solvents from the adhesive, as well as allowing some of the adhesive to be absorbed over larger surface areas. 

Over the past two decades, considerable interest has been directed toward the conversion of cellulosic biomass (such materials as wood wastes, bagasse, and straw) into useful products, notably fuels. Several procedures, including fermentation, gasification, liquefaction, and pyrolysis, have been commercially applied to carbohydrates with various degrees of success. In order to use the polysaccharides present in lignocel-lulosic materials as a substrate in fermentation processes, pretreatments are necessary, such as with steam (under slightly acid conditions) or... 

These findings would indicate that it does not matter which type of lignocellulosic resource is used as a substrate for acetylation. Wood as well as agricultural residues and other sources of agromass can be incorporated into acetylated composites. 

The strategy of this method is to utilize the inherent porosity of bulky substrates in the construction of hierarchical stractures by incorporating additional pore systems. Diatoms are unicellular algae whose walls are composed of silica with an internal pore diameter at submicron to micron scales. Zeolitization of diatoms, in which zeolite nanoparticles are dispersed on the surface of diatoms followed by a hydrothermal conversation of a portion of the diatom silicas into zeolites, resulted in the formation of a micro/mesoporous composite material. Similarly, wood has also been used as a substrate to prepare meso/macroporous composites and meso/macroporous zeolites. After the synthesis, wood is removed by calcination. ... 

In the last test, a porous material, pine wood, was chosen as a substrate because it assures that air is to remain in intimate contact with the curing adhesive. The ability to lock the threads of an iron nut and bolt without use of an activator is a recognized test for determining whether a formulation is capable of anaerobic cure. 

Starch is not infrequently mentioned as an addition to paint, either as an adulterant or extender, or as a substrate for dyestuffs. It can be derived from various plant sources such as wheat (Triticum aestivum and T. durum), potato Solatium tuberosum) and rice (Oryza sativa). The so-called Paduan MS Ricetteper Far Ogni Sorte di Colore (late sixteenth or early seventeenth century/cf. and tr. Merrifield, 1849) describes the use of flour as a lake substrate 98. To make fine lake Take lime water in which brazil wood has been infused, and add it to the flour, so that it may become thick, and when the whole is well mixed, let the flour sink to the bottom, make it into a small loaf, dry it in an oven not too hot, then grind it up, and with lime water, make it into pellets, and let them dry in the shade. Carlyle (2001) found various mentions of starch used not directly as a pigment, but to gelatinise oil paint for example, she notes Field s comments that Indeed starch, as prepared by the laundress, has been lately recommended with high encomiums for this purpose (Field, 1841/cf. Carlyle, 2001). Bachhoffner, writing around that... 

Szczepkowski and Wood showed thiocystine can function as a substrate for rhodanese (thiosulfate cyanide sulfur transferase, EC 2.-8.1.1). (Table I)... 

Garcia, R., Triboulot, M.C., Merlin, A., et al. Variation of the viscoelastic properties of wood as a surface finishes substrate. Wood Sci. Technol. 34(2), 99-107 (2000) Lanzalunga, O., Bietti, M. Photo-and radiation chemical induced degradation of lignin model compounds. J. Photochem. Photobiol. B 56(2), 85-108 (2000)... 

Epoxy resins are also used in special appHcations, such as an overlaying procedure requiring a durable, heat-resistant bond of a difficult-to-bond overlay on a wood-base panel substrate. Metal sheets used as overlays, for example, often require an epoxy adhesive. 

Grain that is usable as food or feed is an expensive substrate for this fermentation process. A cheaper substrate might be some source of cellulose such as wood or agricultural waste. This, however, requires hydrolysis of cellulose to yield glucose. Such a process was used in Germany during World War II to produce yeast as a protein substitute. Another process for the hydrolysis of wood, developed by the U.S. Forest Products Laboratory, Madison, Wisconsin, uses mineral acid as a catalyst. This hydrolysis industry is very large in the former Soviet Union but it is not commercial elsewhere. 

Modern lacquers with a low organic solvent content are widely formulated as stable lattices. Such a modified latex is useful as a coating for substrates such as paper, wood, and metals, and as a binder in aqueous systems. 

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