Antishrink efficiency

To improve dimensional stabUity, low molecular weight chemicals are used that penetrate the cell waUs and either bond to the ceU waU polymers or polymerize in the ceU waU. Improvements in dimensional stabUity are measured by antishrink efficiency (ASE) ... 

Table II Critical strength, losses caused by formaldehyde cross-linking of softwoods to various permanent weight gains and antishrink efficiencies, A.S.E.

Figure 1. Logarithm of heating time vs. temperature required to give three different reductions in swelling and shrinking when the heating was done beneath the surface of a molten metal to exclude oxygen (15). 0,1/16-in. thick Sitka spruce veneer , 1/2-in. thick cross sections of western white pine O, 3/8-in. flat sawn western white pine O, 15/16-in. thick eastern pine boards. Numbers on plot indicate antishrink efficiency (A.S.E.) in percent.

The specimens are then immersed in a molten wax or natural resin and the Cellosolve slowly distilled off. This step invariably involves some shrinkage. Antishrink efficiencies of 80% are, however, obtainable in this way with mixtures of beeswax and rosin. This treatment appears suitable for the preservation of wood artifacts. Christensen (43) has treated wood artifacts by replacing the water with tertiary butanol and this with polyethylene glycol-4000. 

The dimensional stability of Impreg made in the aforegoing way increases with an increase in the resin content of the veneer up to about 70% antishrink efficiency at a resin content of 30 to 35%. This ASE value is less than that obtainable with polyethylene glycol because of loss of water and subsequent contraction of the resin forming chemicals within the cell walls as polymerization occurs. 

Antishrink efficiencies (ASE) for the treated specimens were calculated from the changes in cross sections between the original untreated water swollen and oven dry conditions and the treated water swollen and second oven dry condition. Figure 1 is a plot of the ASE for the three species of cross sections and the yellow poplar sticks versus the resin content. The ASE values increase approximately linearly with an increase in resin content as resin... 

Table II. Efficiency of Furfuryl Alcohol Resin Treatment of Douglas fir and Engelmann Spruce cross Sections Cured at 120°C in Aluminum Foil, the Antishrink Efficiency CASE) and the Relative Abrasion Resistance.

Figure 1. Antishrink efficiency (ASE) vs. furfuryl resin content. O, yellow poplar sticks A, Douglas fir cross sections , Engelmann spruce cross sections X, loblolly pine cross sections...

Some research has been done on the addition of polar solvents to the nonpolar monomer in an attempt to swell the cell wall structure and anchor it in a swollen state (9). This can be done and the antishrink efficiency (ASE) does increase, but after the solvent evaporates, the wood is only partially loaded which in turn decreases the physical properties. Wood-polymer composites normally have about 10-15% ASE, which means that there is some penetration of the cell wall structure to reduce the swelling over that of untreated wood. 

Figure 4. Relationship between acetyl content and antishrink efficiency. Key O, spruce (31) > chir (41) and X> mango.

The early work on allylation was done by Kenaga and Sproull [13] using allyl chloride in pyridine. In the allyl chloride-pyridine case, antishrink efficiency (ASE) [2,14] is due not to the formation of allyl ethers in cellulose or lignin but rather to the bulking caused by the formation of water-soluble allyl pyridinium chloride polymers 115]. 

Figure 1. Relationship between antishrink efficiency (ASE) and chemical add-on caused by epoxide modification. Key , butylene oxide and O,...

Volumetric swelling coefficient determined from initial oven-dry volume and first water-swollen volume. Antishrink efficiency based on Sj. 

Dimensional Stability. As expected, the antishrink efficiency (ASE) is increased, and the amount of water absorbed is decreased because of polymer impregnation. Table II summarizes the results of... 

Table II. Antishrink Efficiency of Wood Treated with Various Polymers...

Antishrink efficiency = (1 - % swelling of treated wood/% swelling of control) X 100. (Reproduced, with permission from Ref. 3. Copyright 1981, Springer-Verlag.)... 

ASE = antishrink efficiency (reduction in swelling resulting from treatment)... 

Figure 4. Antishrink efficiency of methyl isocyanate-modified southern pine as a function of WPG. Key O, ASE, , ASE2 A, ASE3 , ASEt.

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