Density extractive-free

In studies of wood ehemistry it is important to remove extraetives with a multipurpose solvent sueh as methanol before wood density determination so that the correct extractive-free density data are gathered. Wood density anomalies led to extractive studies on larch species in the 1960s (Uprichard, 1963), with both polyphenols and arabinogalactan making large contributions to the apparent (unextracted) basic wood density. 

However, the extractive-free basic density of this wood is actually 500 kg m"", so if it were not bulked by extractives it should only shrink by 15% on oven-drying and by 7.5% on drying to 15% moisture content. 

This wood has 30 kg of extractives in a cubic metre of green wood and, assuming a density of 1400 kg m for these extractives (Tarkow and Krueger, 1961), they will occupy 0.021 m of the swollen cell wall per m of swollen wood. If the extractives were not present, the extractive-free basic density would be 500 kg m and the wood would shrink by 15%, i.e. the cell wall would shrink by 0.15 m per m of swollen wood. However the water soluble extractives occupy 0.021 m of the cell wall for every m of swollen wood, so the wood and the cell wall can only shrink by 0.150-0.021 m, i.e. 0.129 m per m of swollen wood rather than by 0.150 m per m which would be expected of an extractive-free wood having a basic density of 500 kg m. The oven-dry volumetric shrinkage will be only 12.9% rather than 15.0%. 

If extractives were located in the lumens rather than in the cell walls this timber would shrink by 15% on oven-drying. However, the expected shrinkage for extractive-free wood of this density (530 kg m ) would be 15.9%. The estimated shrinkage on drying to 15% moisture content is 94% (7.5/7.95) of that predicted (7.95%) and the estimated fibre saturation point would be 28%. 

Clearly shrinkage is dependent on the extractive-free basic density, the amount of extractives in the wood, and the distribution of the extractives between the cell wall and the lumen. The bulking of the cell wall with extractives explains part of the shrinkage variation observed in Figure 4.3. 

Further basic density is eomplicated by the presence of extractives, which vary from less than 1% of the oven-dry mass in sapwood to well over 10% in the heartwood of some species. Extractives increase the weight of a wooden member without contributing to its strength, and consume chemical without contributing to the pulp yield. In rigorous studies the extracted (extractive-free) basic density may be needed in order to compare pulp yields or mechanical properties between samples or species. 

Figure 5.6. Within-tree variations in extractive-free basic density of radiata pine from various regions in New Zealand (Cown, 1992). Temperature and rainfall are major influences on wood density, outerwood being more sensitive than corewood outerwood density decreases by 7 kg m per degree increase in latitude and for each 100 m rise in altitude.

According to the European Disposables and Nonwoven Association, the tests for polyacrylate S APs include pH, residual monomers, particle size distribution, moisture content, free swelling capacity, centrifuge retention capacity, absorption under pressure, flowrate, density, extractables, respirable particles, and dust. 

Presumes a metabolizable energy density of 16.74 kJ/g of dry matter based on the modified Atwater values of 14.64, 35.56, and 14.64 kJ/g for protein, fat, and carbohydrate (nitrogen-free extract, NEE), respectively. Rations greater than 18.83 kJ/g should be corrected for energy density rations less than 16.74 kJ/g should not be corrected for energy. To convert kj to kcal, divide by 4.184. 

Extracted from U.S. Standard Atmosphere, 1976, National Oceanic and Atmospheric Administration, National Aeronautics and Space Administration and tte U.S. Air Force, Washington, 1976. Z = geometric altitude, T = temperature, P = pressure, g = acceleration of gravity, M = molecular weight, a = velocity of sound, i = viscosity, k = thermal conductivity, X = mean free path, p = density, and H = geopotential altitude. The notation 1.79.—5 signifies 1.79 X 10 . ... 

The value of AE is obtained by the extraction of the potential of the two curves at one and the same current density, so it is free from the 1R drop between the air electrode and the reference electrode. 

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