Plastics generally

Some design factors, however, work against composites. For example, glass fiber-reinforced plastics generally have lower modulus (stiffness) than metals. Thickness and shape adjustments are requited where stiffness is a critical design requirement. With appropriate reinforcement, any modulus, even greater than that of metals, can be achieved. However, it may become expensive and uneconomical to do so. 

The effective interfacial area depends on a number of factors, as discussed in a review by Charpentier [C/j m. Eng.J., 11, 161 (1976)]. Among these factors are (1) the shape and size of packing, (2) the packing material (for example, plastic generally gives smaller interfacial areas than either metal or ceramic), (3) the liquid mass velocity, and (4), for smaU-diameter towers, the column diameter. 

Because most plastics may be fabricated in the melt and at quite low temperatures (e.g. 200°C) the energy requirements for processing are low. Since plastics generally have low densities, costs of transportation and general handling are also relatively low. 

In general adding reinforcing fibers significantly increases mechanical properties. Particulate fillers of various types usually increase the modulus, plasticizers generally decrease the modulus but enhance flexibility, and so on. These RPs can also be called composites. However the name composites Utterly identifies thousands of different combinations with very few that include the use of plastics (Table 6-18). In using the term com-... 

Like metals, plastics generally expand when heated and contract when cooled. Usually, for a given temperature change many TPs have a greater change than metals. The coefficient of linear thermal expansion (CLTE) is the ratio between the change of a... 

The flow of plastics is compared to that of water in Fig. 8-5 to show their different behaviors. The volume of a so-called Newtonian fluid, such as water, when pushed through an opening is directly proportional to the pressure applied (the straight dotted line), the flow rate of a non-Newtonian fluid such as plastics when pushed through an opening increases more rapidly than the applied pressure (the solid curved line). Different plastics generally have their own flow and rheological rates so that their non-Newtonian curves are different. 

Plastic materials manufacturing is primarily a large-volume, low-cost, low-unit profit margin business with great overall economies. The plastics generally compete with each other on a money value basis in which an economic analysis takes into account the differing densities of the various plastics in order to judge them on a cost per pound or volume basis. 

In some databases, material-specific data are present for various waste treatment options. Plastics generally are among the materials included. However, no specific data on additives are found. In case of incineration, organic additives break down and therefore are not expected. In case of landfill, some leaching of evaporation would be probable, but cannot be found in the data. 

Table 2 presents the results of tests to measure the calorific power, ash content, and chlorides concentration of some of the materials obtained from the separation process, such as polystyrene, aluminum foil, plastic foam, and other plastics (general, clear, colored, black, and vinyl). Polystyrene and clear plastic have very high calorific power and low levels of chlorides, but polystyrene has very high ash content. Figures 10-17 present the samples of waste components from the separation and composting plant of Cantagalo. 

A considerable number of alternative techniques have been suggested for measuring vapour permeability of plastics, generally with the aim of making the measurement more convenient and increasing sensitivity. For water vapour transmission, carrier gas type commercial apparatus using an infrared sensor is now commonly used. This procedure is standardised in ASTM... 

Dunbar of Ontario, Canada and the Wee Piper of Vermont are producing bagpipes and chanters from catalyst-heat wood-plastics supplied by Wing Archery. The wood-plastic composite has replaced the black African wood usually used for bagpipes. Pipers claim that the tone of the new wood-plastic chanter is more mellow. Traditionally, bagpipe parts of ebony wood are black and this intense black has not been duplicated in wood-plastics. Generally, wood-plastic bagpipe parts are made in the natural maple color or dyed a deep brown. 

Plasticizers and flexibilizers are incorporated into an adhesive formulation to provide it with flexibility and/or elongation. Plasticizers may also reduce the melt viscosity of hot melt adhesives or lower the elastic modulus of a solidified adhesive. Similar to diluents, plasticizers are nonvolatile solvents for the base resin, and by being incorporated into the formulation, they separate the polymer chains and enable their deformation to be more easily accomplished. Plasticizers generally affect the viscoelastic properties of the base resin whereas diluents simply reduce the viscosity of the system. Whereas diluents result in brittle, hard adhesive systems, plasticizers result in increased flexibility and lower modulus. The temperature at which polymers exhibit rubbery properties (i.e., the glass transition temperature) can also be modified by incorporating plasticizers. 

The first category consists of unreactive diluents, and they may be considered mainly as plasticizers. Generally they do not increase flexibility, and often they result in the overall degradation of physical properties. The cured resin has reduced strength and hardness and could even exhibit a cheeselike structure. The second category consists of reactive diluents, and they can be considered as true flexibilizers. 

Biaxial orientation of crystalline plastics generally improves clarity of films. This occurs because stretching breaks up large crystalline structures into smaller than the wavelength of visible light. With uniaxial orientation, the result is an anisotropic refractive index and thus birefringence, especially in crystalline plastics. 

The thermoset (TS) plastics and reinforced thermosets (RTSs) are more suitable to meet tight tolerances. With amorphous and crystalline thermoplastics (Chapter 1) reinforced thermoplastics (RTPs), and particularly unreinforced thermoplastics (UTPs) can be more complicated tolerance-wise if the fabricator does not understand their behavior. Crystalline plastics generally have different rates of shrinkage in the longitudinal (melt flow direction) and transverse directions when injection molded. 

Examples of major plastic families Thermoplastic thermal properties are compared to aluminum and steel General properties of thermoplastic General properties of thermoset plastic General properties of reinforced thermoplastic General properties of reinforced thermoset plastic Examples of drying different plastics (courtesy of Spirex Corp.)... 

Dyestuffs are easy to disperse and usually are readily soluble within the polymer matrix. Dyes that have been designed for use in plastics generally are oil or solvent soluble, although some are only resin soluble. While many dyestuffs are water... 

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