Softwood fibers

The cells that make up the stmctural elements of wood are of various si2es and shapes and are firmly bonded together. Dry wood cells may be empty or pardy filled with deposits such as gums, resias, or other extraneous substances. Long and poiated cells, known as fibers or tracheids, vary gready ia length within a tree and from species to species. Hardwood fibers are - 1 mm long, and softwood fibers are - 3 to 8 mm. 

In hardwoods, morphological structural elements in longitudinal series comprise the segmented structure termed vessel . Vessels, which are exposed in transverse section, constitute about 10-46% of the stem volume in deciduous hardwoods and are cells of relatively large diameters (50-300 p.m). Vessels have in short the appearance of open vertical tubes within the wood structure because their end walls have partially dissolved. By comparison, the hardwood vessel diameter can be as much a 10 times the diameter of a softwood fiber. 

Hardwood fibers, because of the presence of vessels, occupy a proportionally smaller volume of wood tissue than softwood fibers... 

In the standing, living tree the bordered-pit membranes between softwood fibers act as valves to prevent the spread of air or bubbles into sap-filled cells in the event of tree injury and potential rupture to vertical water columns. Unfortunately, they perform a similar function in the processing of wood into commercial products. For example, during wood drying, substantial capillary and surface tension forces are developed upon water retreat from the fiber lumens through the pits, and the membranes move effectively (particularly in earlywood) to seal the apertures in the direction of water... 

Pits with some form of border also occur at irregular intervals along softwood fibers where the fibers contact ray cells (Figure 22). Such pits are very rare in hardwood fibers, but in softwoods they are abundant and conspicuous, especially in earlywood. These pits are known technically as ray cross-field pits (see Figure 11), and they... 

Figure 10. Photomicrograph of delignified cell-wall softwood fibers...

In Fig. 15, it is seen that the sheet made of cotton linters is more conductive than the other sheets. The sheet made with "Seagull W" hardwood pulp is the least conductive while the three other pulps have intermediate conductivity values. This behaviour seems to be related to the size of the different types of fibers used to make the sheets. As mentioned previously, hardwood fibers are shorter than softwood fibers, and consequently, there are more interfiber contacts in the sheets made of hardwood fiber. The surface area of a contact is very important to the conductivity. There may be a constrictive effect due to smaller surface at these contacts which results in a restricted flow of ions through the paper, and therefore a lower conductivity. Cotton linters are chemically different and longer than wood fibers and the sheet made of these fibers is more conductive. The difference between the three softwood pulps is probably related to a different chemical composition of its fibers. 

U.S. Pat. No. 6,942,829 [72] discloses a method of forming a polymer-wood composite material comprising 20-80% by weight of cellulose filler such as hardwood fiber, softwood fiber, hemp, jute, rice hulls, and wheat straw, 20-80% of a thermoplastic polymer such as polypropylene, polyethylene, polyamides, polyesters, and other polymers, 0.1-10% of a blend of a nonionic compatibilizer and a lubricant. 

Snow load, 272- 274 Snow on a deck, 272 Softwood fiber, 86, 100 Soil Block test, 431 Soil-block cultures, 434 Solar radiant exposure, 615 Solar radiation (UV light), 531 Solid board, 2, 16, 36, 267, 280, 281, 288, 311 Soundwall, 252, 269, 281-286 Bending moment, 282... 

Hardwood fiber, 100 Kaolin, 128 Mineral fillers, 100 Precipitated silica, 128 Silica, 128 Softwood fiber, 100 Talc, 128... 

Optical microscopy of the paper in the mold liner, as well as a gummed label on the Pb, was used to identify and quantitate the hardwood and softwood fibers composing the papers. The species of trees represented included Scotch pine, spruce, aspen, alder, and birch. The fibers were determined to be definitely not North American, inconsistent with those found in Western Europe or Scandinavia, but consistent with an Eastern European origin. 

Table 3. Partition of medium size bleached softwood fibers. AKD-sized to various degrees. Distribution in percent...

One question that naturally arises is Do the fibers in our samples have the same surface properties and partition between the phases just like a well defined chemical species partition between two phases Or do the fibers that are found in the top phase have different properties from those in the bottom phase To investigate this question we have distributed medium size bleached softwood fibers in the usual way in the basal system. We have then collected fibers from the bottom phase and partitioned them again. The results are given in table 2. 

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