Wood, recycled

In both the materials used and the construction process, sustainability and efficiency will become standard. Improvements mjob site management and building design will reduce waste and cost of construction. Materials such as engineered wood, recycled carpeting, and cellulose insulation, which have lower environmental impact, will become cheaper and more widely available. Not only are buildings constructed with such material friendlier to the environment, they also provide higher-quality, lower-cost solutions. 

Chromated copper arsenate (CCA) is still used in the USA in home construction and renovation, and also in commercial applications. It may pose risks if wood recycling products such as mulch and GCA-treated wood boards are used, as these might release Cu, Cr and arsenic into the environment. Arsenic-release studies with GCA-treated wood surfaces (Stillwell et al. 2003) and wood mulch (Townsend et al. 2003) showed some, but not very toxicologically significant effects. However, the US EPA announced in early 2002 that the wood industry had voluntarily decided to eliminate arsenical wood preservatives just from residential applications by year-end 2003 (US EPA 2002b). Despite not eliminating all uses, this decision is expected to reduce significantly the future consumption of... 

In the past, lawn and garden trimmings have made up approximately 12% of the waste in municipal landfills. Much lower amounts can be expected from most Army installations. Also, many installations and municipalities are no longer disposing of yard or garden wastes in sanitary landfills instead the waste is land farmed or disposed in non-sanitary landfills, such as approved fill areas. To further reduce the waste streams, many installations now bum wood, recycle metal and other materials, and use dirt, concrete, and brick for erosion control projects. The make-up of landfills vary, but if an installation limits solid wastes to what would normally be placed in a municipal landfill, the composition should compare with table 1-1. 

Insulation Boa.rd. The panel products known as insulation board were the earliest commodity products made from fibers or particles in the composite panel area. These are fiber-base products with a density less than 500 kg/m. Early U.S. patents were obtained in 1915 and production began soon thereafter. The initial production used wood fiber as a raw material, but later products were made of recycled paper, bagasse (sugar cane residue), and straw. Schematics of the two major processes still ia use are shown ia Figure 4. 

Closed-Mill Concept. The closed-mill concept, or water circuit closure, has been studied by the pulp and paper industry for many years. In some parts of the paper manufacturing process, up to 98% of the water is recycled within the process, eg, the wet end of the paper machine. However, in the pulp mill, especiaUy kraft mills, effluents are produced owing to the need to purge from the system various metals that come in with the wood, as weU as organic by-products from the pulping process, additives, and especially chloride ions that originate in the bleach plant. 

Refining and Fractionation. These processes are used to alter and select cellulose properties so the final sheet has the desired properties (51). Properties of recycled fibers differ from those of fibers prepared directly from wood. For example, recovered chemical fibers have lower freeness, an apparent viscosity leading to different water drainage characteristics on paper machines. Recovered fibers also have iacreased apparent density, lower sheet strength, iacreased sheet opacity, inferior fiber—fiber bonding properties, lower fiber sweUiag, lower fiber flexibiUty, lower water reteatioa, reduced fiber fibrillatioa, and much lower internal fiber delamination. 

Another furnace that does not require fuel preparation is the stoker boiler, which was used by New York State Electric Gas Corporation (NYSEG) in its TDE tests. At NYSEG, the stoker boiler, which has a 1649°C (3000°E) flame temperature (as does the cyclone boiler), has routinely blended low quaUty coal, and more recently, wood chips with its standard coal to reduce fuel costs and improve combustion efficiency. In the tire-chip tests, NYSEG burned approximately 1100 t of tire chips (smaller than 5x5 cm) mixed with coal and monitored the emissions. The company determined that the emissions were similar to those from burning coal alone. In a second test-bum of 1900 t of TDE, magnetic separation equipment removed metal from the resulting ash, so that it could be recycled as a winter traction agent for roadways. 

The forecasts made in 1985 (77) of 8—8.5% worldwide aimual growth have not materialized. The 2 x lOg + /yr engineering plastic production reported for 1985—1986 has remained fairly constant. Whereas some resins such as PET, nylon-6, and nylon-6,6 have continued to experience growth, other resins such as poly(phenylene oxide) have experienced downturns. This is due to successhil inroads from traditional materials (wood, glass, ceramics, and metals) which are experiencing a rebound in appHcations driven by new technology and antiplastics environmental concerns. Also, recycling is likely to impact production of all plastics. 

Manual Component Separation The manual separation of solid-waste components can be accomplished at the source where solid wastes are generated, at a transfer station, at a centralized processing station, or at the disposal site. Manual sorting at the source of generation is the most positive way to achieve the recoveiy and reuse of materials. The number and types of components salvaged or sorted (e.g., cardboard and high-quality paper, metals, and wood) depend on the location, the opportunities for recycling, and the resale market. There has been an evolution in the solid waste indus-tiy to combine manual and automatic separation techniques to reduce overall costs and produce a cleaner product, especially for recyclable materials. 

In chemical activation processes, the precursor is first treated with a chemical activation agent, often phosphoric acid, and then heated to a temperature of 450 -700 °C in an activation kiln. The char is then washed with water to remove the acid from the carbon. The filtrate is passed to a chemical recovery unit for recycling. The carbon is dried, and the product is often screened to obtain a specific particle size range. A diagram of a process for the chemical activation of a wood precursor is shown in Fig. 3. 

Adhesives and resins are one of the most important raw materials in wood-based panels. Thus, each question concerning the life cycle assessment and the recycling of bonded wood panels does bring into question the adhesive resins used. This includes, for example, the impact of the resin on various environmental aspects such as waste water and effluents, emission of noxious volatile chemicals during production and from the finished boards, or the reuse for energy generation of wood panels. The type of resin has also a crucial influence on feasibility and efficiency for several material recycling processes. 

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