Plastic compaction

In order to reduce the volume stream and to optimize the efficiency of the following processing units the plastics have to be compacted mechanically before heat/pressure treatment starts. Bales of compacted wet plastics reach bulk densities of about 450 kg/ m3, they are put into moulds which will be transported into autoclaves. During the autoclave process plastics are heated and plastified under saturated steam conditions. Autoclave process is within a wide range independent from changing compositions of the plastics. The process temperature (about 170°C) does not provoke decomposition of plastics, used for household packaging materials. Hydrothermal autoclave conditions lead to further compaction and a stable product (bulk density up to 700 kg/m3) of the mixed different kinds of plastics. Fig. 1 shows a compacted plastic block after finishing the autoclave process. 

Expansion of the strip after pressure release is influenced by the physical characteristics of the material to be compacted (plasticity, brittleness, particle size and distribution, particle shape, etc.), the roll diameter, the speed of rotation, and the surface configuration of the rollers. With increasing roll diameter and/or decreasing speed the expansion of compacted material is reduced due to better deaeration during densification and a more complete conversion of elastic into permanent, plastic deformation. 

The microstructure of p-BN during the a-BN p-BN phase transition [13 to 15] and the formation of multilayer polytypes of p-BN (deformation-induced polytypism) [16] have been studied by electron microscopy. Besides the phase transformation, structure compaction, plastic deformation, and structural relaxation stages have been detected. The chemical composition of the surface of p-BN, as studied by X-ray photoelectron spectroscopy (XPS), has a higher content of oxygen than the original a-BN annealing of p-BN at 800°C results in the depletion of N and the enrichment of oxygen and carbon in the surface layer [17]. 

Secondary porosity is the result of mechanical processes (compaction, plastic and brittle deformation, fracturing) and geochemical processes (dissolution, precipitation, volume reductions by mineralogical changes, etc.). 

Besides this, the new system has also bear introduced successfully as a compact plasticizing unit for injection molding machines (8, 9). 

Ceramic fonning typically involves using pressure to compact and mould particles to the desired size and shape. Ceramics can be fonned from slurries, pastes, plastic bodies (i.e. such as a stiff mud), and from wet and dry powders. 

Working Treatments. Restricted plastic deformation takes place entirely within the confines of a closed die cavity. A sintered part may be placed in the die cavity and pressure appHed to the part. This pressure generally is of the same magnitude as the original compaction pressure. This second apphcation of pressure can be categorized as follows. 

Tempeh. DehuUed cooked soybeans are inoculated with the mold, Thi pus oligosporus packed in perforated plastic bags, and allowed to ferment for 18 h. The mold mycelium overgrows the soybean cotyledons and forms a compact cake. When sHced and deep-fried in oil, a crisp and golden brown product is obtained. Although native to Indonesia, tempeh has become popular with vegetarians in the United States and other Western countries (93). 

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