Densified wood

Pellets are a cylindrical form of densified wood particles that have several advantages compared to the raw material (mostly sawdust) ... 

Heat-Stabilized Compressed Wood (Staypak). Pressures of 400-4000 psi are applied to the wood after it has been heated. Both heat and pressure plasticize wood. At 160 °C and 12% moisture content, the maximum plastic yield per increment of pressure occurs at 1100 psi. Pressures of 1500-2500 psi are required to yield a specific gravity of 1.3. Highly densified wood must be cooled in the press. Some strength properties, such as impact strength and hardness, are increased in direct proportion to the density. Staypak finds limited application for silverware handles and desk legs (6). 

R. A. Currier, "Manufacturing Densified Wood and Bark Fuels." Report 490, Oregon State University Extension Service, July 1977. 

Compressed wood is also called densified wood or laminated wood. It is wood that has been subjected to high compression pressure to increase its density with or without plastics. It is usually supplied in the form of a laminate in which plastics have been incorporated by drying... 

The Aero grade was made for two different end-users the water-proof plywood manufacturers and those companies making densified wood — laminated wood where, due to the laminating pressure used and the actual constmction of the plywood, the final product had a density significantly above that of the timber species used in its constmction. 

As has already been indicated, the water-proof plywood was used extensively for the constmction of aircraft and gliders and the densified wood was used in propeller manufacture for such aircraft as the Avro Lancaster, the Handley Page Halifax, the Supermarine Spitfire and the Hawker Typhoon. 

Baling has long been used to densify hays, straws, and other agricultural crops such as cotton to simplify removal from the field and to reduce storage space and transportation costs. Baled straw has a density of 70 to 90 kg/m at 10 to 15 wt % moisture content, whereas the bulk density of piled straw is about 5 to 15% of this density range. When straws are compressed to form pellets, briquettes, or cubes in specially designed dies and presses, the density can be increased to 350 to 1200 kg/ml In contrast, dried wood has a density of 600-700 kg/m and a bulk density of about 350 to 450 kg/m, whereas the bulk densities and densities of wood briquettes are 700 to 800 kg/m and up to 1400 kg/m, respectively. 

The heating value depends on the moisture and ash contents of the densified material and is usually in the range of 15 to 17 MJ/kg. The use of asphaltic binders or pelletizing conditions that result in some carbonization can yield densified products that have higher heating values. Pellets, briquettes, and logs have been manufactured by densification methods from biomass for many years. Prestologs made from waste wood and sawdust were marketed before 1940 in North America, and the market for pellet fuels made from wood... 

The types of fuel that will be considered for use in vehicle mounted gasifiers include wood chips ( 30 weight percent H2O) and densified fuel pellets ( 10 weight percent H2O) produced from agricultural residues. 

The mechanical properties of Wood-Plastic-Composites substantially depend on the quality of the raw material, the composite and the manufacturing process. The density of WPC lies between 0.9 and 1.4 g cm and is higher than that of one of the two components, plastic and wood, alone. The porous wood structure is densified during the production process and plastics and additives partly penetrate into the cavities. Thus, water absorption is made harder, and the material swells less and more slowly. ... 

Most natural fibers have a maximum density of about 1.5 g/cm. Though some natural fibers, such as wood, are hollow and have low densities in their native state, they are often densified during processing. Nevertheless, even the maximum density of these fibers is considerably less than that of inorganic fibers such as glass fibers. As such, their low density makes them attractive as reinforcement in applications where weight is a consideration. 

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