Antishrink efficiency, wood

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. 

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. 

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.)... 

The results from fluorescence microscopy of stained freeze-dried sections indicated the presence of PEG 400 within the cell wall capillary matrix. This result contrasts with the demonstrated lack of penetration of heavier-molecular-weight PEG 3350. In terms of dimensional stabilization tests on the antishrink efficiency of various PEG solutions, the greatest stability was achieved when the amount taken up by wood was at the lower limit of the fiber saturation point, around 30%. Fiber saturation point is a dynamic concept related to water and holocellulose, and as such it has reduced value in degraded wood. In view of this, and when the treatment process for freeze-drying wood with residual nonevaporating PEG is involved, the notion of specific surface is better. 

Recent experiments to determine the dimension stabilizing efficiency of water soluble fire retardent chemicals (41) showed ammonium sulfamate to be superior to phosphate salts, giving anti shrink efficiencies of 51 to 66% compared to polyethylene glycol-1000 values of 63 to 77%, Sodium silicate, because of its alkalinity, caused collapse of the wood that resulted in negative antishrink efficiencies. Strongly alkaline systems should hence be avoided. 

---