Solid Wood Products 27 1 1 



Siau et al. (1978) vacuum-impregnated with methyl methacrylate specimens 

 cut from 6-inch-diameter trees of 22 hardwood species grown on southern pine 

 sites (listed in table 3-1). They found that fractional volumetric retentions of 

 monomer, and cured polymer, were related to longitudinal air permeabilities and 

 the anatomical structure of the species. Siau et al. concluded that the five diffuse 

 porous woods (red maple, yellow-poplar, black tupelo, sweetgum, and sweet- 

 bay) are very suitable for the production of wood-polymer composites. Difficult- 

 to-treat, and unsuitable for wood-polymer composites were hackberry, white 

 oak, post oak, blackjack oak, black oak, and low-permeability cherrybark oak. 

 Permeable cherrybark oak, the remaining red oaks, and the ashes, elms, and true 

 hickory were moderately permeable and appeared moderately suitable for manu- 

 facture of wood-polymer composites. 



PRODUCTS STABILIZED WITH POLYETHYLENE GLYCOL 



The polymers of dihydric alcohols are polyethers with an oxygen atom sepa- 

 rating the hydrocarbon groups and with reactive hydroxyl groups only on the 

 ends; up to molecular weights of 6,000, they are highly soluble in water. 

 Because of the low vapor pressure of polyethylene glycol (PEG), it remains in 

 the cell walls when wood impregnated with it is dried; this bulking action 

 prevents the wood from shrinking. PEG-bulked wood feels moist when relative 

 humidity is above 70 percent because of its hygroscopicity, but certain polyure- 

 thane finishes tend to reduce this. The treated wood is highly stable to changes in 

 humidity, but in water the PEG is leached out with time. Treatment causes a 

 slight loss in abrasion resistance and bending strength, but toughness is essen- 

 tially unaffected when the wood contains about 45 percent PEG. With many 

 woods, the anti-shrink efficiency is about 80 percent. PEG treatment is used 

 where wood must have dimensional stability to prevent cracking and checking. 

 Art carvings can be preserved in this manner. 



Merz and Cooper (1968) provided data specific to black oak. They treated 

 freshly sawn, green heartwood blocks measuring 1.5 inches long the grain, 3 

 inches in the tangential direction, and 1.5 inches in the radial direction. Treat- 

 ment consisted of soaking the blocks in a 50-percent water solution of PEG 1000 

 held at 140°F. Observations of wood stability were made at intervals up to 384 

 hours of treatment. They found that a 96-hour treatment reduced tangential and 

 volumetric shrinkage by about 65 percent and radial shrinkage by 68 percent. 

 Longer treatments reduced shrinkage even more, but not sufficiently to be of 

 practical significance. Warping of the blocks was inconsequential after 96 hours; 

 some hairline checks were observed, but their occurrence was not related to 

 treatment time. The blocks absorbed PEG in amounts equivalent to 44 percent of 

 their dry weight after 96 hours, and only an additional 14 percent in 228 more 

 hours. 



Englerth and Mitchell (1967) suggest that stabilized low-cost bowls can be 

 made from permeable 8-inch-diameter green log sections that are free of splits. 

 By their procedure, one end of the log is sawn smooth and a turning-lathe 

 faceplate securely screwed to it. The exterior of the green wood is shaped to 



