Wood binder

Foundry binders Wood binders Rigid, 2-K structural adhesives... 

Phenolic resins are adaptable to many applieations. The list is very long, however, the major uses are wood binders, glass insulation binders, molding compounds, laminates, foundry binders, coatings, friction linings, abrasives, and oil well propants [59-66]. They have found their way into a number of new, high technology uses such as rocket motor wear parts, military armor, sports equipment. 

Though the discussion above was aimed primarily at wood binders, many of the ideas carry over into foundry and glass binding applications. For example, potassium hydroxide is used extensively in foundry binders as are esters and... 

Table II gives a number of derived parameters used to assess the lignin s suitability as a binder. For a full binder, lignins required a minimum of three sites per average molecule for formaldehyde grafting. None of the lignins studied approach this level. At least twice the number of sites found is required for steam exploded lignins and more for the kraft lignin. PF resins have an average of eight sites per molecule, a much higher density than projected, so PF resins are excellent wood binders.

The cyclic alkylene carbonates have also been applied as the cure-accelerators of phenol-formaldehyde (PF) [262-266] and sodium silicate [267] resin systems, which are widely used in foundry sand and wood binder applications. 

J. T. White reported at the Washington State University Symposium on Particleboard in 1973 that 18.7 percent of the formaldehyde manufactured in the U. S. A. went into wood binders likewise, 8.9 percent of the urea chemical produced in the U. S. A. went into wood binders. 

There have been many attempts to replace these resins with lignin derivatives for wood composite adhesives suitable for plywood, particleboard and waferboard. Most of these studies have been empirical in nature, and few have achieved further consideration for industrial application. As wood binders, technical lignins are variable in quality and poorly reactive in comparison to conventional resin systems such as phenol-formaldehyde (PF) resins. Consequently, they are not utilized on their own. Indeed, if they were, this would adversely affect production quality and times, and necessitate equipment changes. In the wood composite industry, resins having such deleterious effects are not likely to be used even if savings could be made in terms of material costs. 

With adjustments in composition to compensate for the chemical features of each aromatic hydroxyl source, a wood binder formulated with any of the materials discussed above [28] will be deemed highly effective if it can be (1) formulated at lower cost, (2) applied with conventional equipment, (3) reacted under the same process conditions, and (4) so strong an adhesive that... 

There are two major disadvantages often cited in the use of isocyanate wood binders. The first is a higher raw material cost as compared to conventional binders and the second is a tendency to adhere to metal transfer plates or press platens. The latter problem has been solved on a commercial scale by producing a multilayer product with solid veneers or phenolic-bound particles as face layers. All isocyanate-bound non-veneered board can be made by treating the metal surfaces with a release material or, more recently, using a self-releasable isocyanate. 

II. CHEMISTRY OF ISOCYANATE WOOD BINDERS A. Synthesis and Characterization... 

The debate over urethane formation in the wood/pMDI bondline may soon yield to studies of the peculiar morphology of this interphase. Recall that pMDI is a low viscosity, low molecular weight, low surface tension organic liquid. Consequently, pMDI wood binders readily wet and deeply penetrate into wood, as demonstrated by Shi and Gardner [27]. In fact the deep penetration of pMDI into wood contradicts traditional views on wood adhesion. The truly polymeric wood binders sueh as phenol formaldehyde (PF) and urea-formaldehyde (UF) are formulated for only moderate levels of wood penetration overpenetration is undesirable with these resins. By traditional standards, pMDI wood binders overpenetrate and yet they perform as well or better than other wood binding thermosets. One then wonders what becomes of the resin that does not span the gap between bonded wood particles Does it polymerize into a bulk phase within wood cell lumens, providing no benefit Or does the deep penetration provide some performance gain How deep is the penetration ... 

While pMDI wood binders are derived from formaldehyde, they are distinguished from other wood binders by a total laek of formaldehyde emission. This performance advantage has not displaced the less expensive UF and melamine-urea-formaldehyde... 

The moisture tolerance of pMDI is utilized in steam injection pressing (SIP), where steam is injected into the flake or strand mat (through the press platens) immediately prior to, and during compaction. SIP accelerates heat transfer and hotpress production, especially for very thick products such as laminated strand lumber. Besides accelerated production, steam processing increases the dimensional stability of the resulting composite [45,46]. Isocyanate resins appear to be the only exterior grade wood binders which can withstand the moisture extremes found in SIP [33,34,47]. 

Uses Base for wood adhesives, wood binders, and functional coatings, suitable for wood, uncoated paper, and cotton cloth substrates Features Good cold set, wet tack, and heat resist. suitable for RF cure applies. freeze-thaw stable... 

Uses Chemical intermediate intermediate yielding esters useful as lubricants, defoamers in rubber, pharmaceuticals antifoam in fermentation and paints antiblooming agent for pentachlorophenol-treated wood binder and lubricant for ceramics plasticizer of resin-treated papers mold release applies. emollient, solvent in cosmetics, pharmaceuticals boiler water additive (food contact) in food-pkg. adhesives... 

Uses Chemical intermediate antifoam in fermentation and paints antiblooming agent for pentachlorophenol-treated wood binder, lubri-... 

The recovered resin mixture was very tacky and has potential for recycling as a board resin. It was, however, very dark-colored and evolved a slight odor of levulinate ester. It may be used as a fine coal binder for making briquettes or as a waterproof granular fuel. Additional work is being conducted to determine the potential for wood binder recycling, but considerable interest has been shown in the low-cost coal binder applications, and the market could easily consume all the resins that can possibly be produced. 

C. E. Frazier, Isocyanate wood binders, in Handbook of Adhesive Technology, 2nd edn, A. Pizzi and K. L. Mittal, Eds., Dekker, New York, 2003, Chap 33. 

A considerable amount of effort has gone into overcoming the sticking problems. One approach has been to manufacture a three-ply board in which the two outside layers utilize a conventional wood binder, such as a phenol-formaldehyde resin, and the internal layer is bound with an isocyanate adhesive.Deutsch Novopan GmbH of West Germany has commercialized such a process to manufacture exterior structural grade particleboard. A board prepared in this manner does not completely circumvent the potential problem of formaldehyde emissions, although they may be reduced relative to a board made solely with a formaldehyde adhesive. 

MDI is mostly used in polyurethane chemistry. About 80% of MDI is used to make polyurethane foams, both flexible and rigid. Half of all the foam produced with MDI is rigid foam. This rigid foam is used in the insulation, construction, refrigeration, and packaging industries. Also, MDI is used in the production of spandex fibers. MDI is used as a wood binder and in foundry cores. The binding of wood flakes into oriented strandboard is replacing plywood in construction. 

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