Treesearch

Wood is a porous, permeable, hygroscopic, orthotropic, biological composite material of extreme chemical diversity and physical intricacy. Table 1.1 provides an overview of the may variables, including wood variables, that bear on the bonding and performance of wood in wood joints and wood-based materials. Of particular note is the fact that wood properties vary between species, between trees within a species, and even within a tree. Variability within a single species alone is enough to significantly challenge an adhesive to perform consistently and satisfactorily. In this chapter, we...

Literature dealing with the effect of excessive drying (overdrying) on wood surface inactivation to bonding is reviewed in two parts and critically evaluated, primarily for phenolic adhesives. Part 1 of the review, published earlier, covers physical mechanisms that could contribute to surface inactivation. The principal physical mechanism is the migration to the surface ofextractives that decrease wettability. Pan II of the review considers mechanisms involving chemical reactions: reduction of wood surface strength, oxidation and pyrolysis of wood bonding sites, and chemical interference...

Sweetgum (Liquidambar styraciflua L.) wood blocks were decayed by Postia (= Poria) placenta in soilblock cultures. Decay was terminated at various weight losses, and the pore volumes available to four low molecular weight molecules, (water, 4 Å,; glucose, 8 Å,; maltose, 10 Å; and raffinose, 128,) and three dextrans (Mr 6,000, 38 Å; 11,200, 51 Å; nd 17,500, 61 Å) were determined by the solute exclusion technique (Stone and Scallan 1968b). The volume in sound (undecayed) wood that was accessible to the seven probes varied from 1.0 ml g–1 for the three largest to 1.35 ml g–1 for water. Thus,...

Eleven types of aspen ultra-high-yield (90% and above) mechanical pubs were evaluated for their chemical compositions (including sulfur), handsheet strength, and optical properties, fiber length indices, and fiberizing energies. The pulping processes were stone groundwood, pressurized stone groundwood, refiner mechanical, thermomechanical, chemimechanical (alkaline sulfite), chemithermomechanical, bleached chemithermomechanical, peroxide chemimechanical, steam explosion, and biomechanical. Data were obtained from USDA Forest Service reports and other literature. Pulps made using chemical...

Chemical and morphological changes of incipient to advanced stages of palo podrido, an extensively delignified wood, and other types of white rot decay found in the temperate forests of southern Chile were investigated. Palo podrido is a general term for white rot decay that is either selective or nonselective for the removal of lignin, whereas palo blanco describes the white decayed wood that has advanced stages of delignification.

When a member is subjected to combined loading, such as combined bending and compression, the failure criterion contains more than one resistance variable. This paper addresses the practical effects of correlation among those resistance variables, both during the experimental inference of the failure criterion itself and during subsequent reliability analyses that employ it. There are two main findings. The first, of interest to experimental researchers. is that the mean failing load of a population is always less than the load that would be obtained from the exact (but as yet unknown)...

Flame retardants for wood alter the combustion properties of wood to reduce surface flame spread. Flame retardant chemicals cause acid catalyzed dehydration reactions in wood to facilitate the formation of char and reduce the effective heat of combustion, resulting in lower heat release and flame spread. Boron compounds can also form glassy fiis that may inhibit mass transfer of combustible vapors. This paper discusses the role of boron in providing flame retardancy to wood. Different loading levels of borax-boric acid, ranging from O to 20 percent add-on by weight, were applied to...

Fire endurance research activities and facilities at the FPL concern the ability of a wood member or assembly to withstand the effects of fire while acting as a fire barrier and supporting a load. Fire endurance is generally concerned with the post-flashover portion of the fire. The importance of fire endurance in fire safety is reflected in building code requirements for fire resistance ratings (1 hour, 2 hours, etc...) for building elements. The FPL fire endurance research program is oriented largely toward supporting: (1) the increased use of wood in commercial and multifamily buildings...

Currently, thermosetting adhesives are characterized by physical andchemical features such as viscosity, solids content, pH, and molecular distribution, and their reaction in simple gel tests. Synthesis of a new resin for a particular application is usually accompanied by a series of empirical laboratory and plant trials. The purpose of the research outlined in this paper was to develop techniques that could be used to characterize thermosetting resins by their time-dependent reaction to the environmental conditions--temperature and moisture--that influence both cure and bonding. Resin-impr...

This paper presents computer programs for adjusting the mechanical properties of 2-in. dimension lumber for changes in moisture content. Mechanical properties adjusted are modulus of rupture, ultimate tensile stress parallel to the grain, ultimate compressive stress parallel to the gain, and flexural modulus of elasticity. The models are valid for moisture contents from 8 to. 23 percent (assumed green value). Although test results can be adjusted for moisture content, such adjustments decrease in accuracy with increasing change in moisture content. For this reason, the specimens should be...