Raw Material Forms

For many fabricators the raw form of the polymers they use is the result of a previous fabrication step. This is true of the sheet formers, since the molder of blister packages or refrigerator door liners seldom makes the original flat sheet but buys it from a separate converter. Builders of ductwork, storage tanks, and luggage commonly buy their raw materials as sheets, tubes, or other extruded shapes. 

Mixing low-viscosity liquids or blending dry powders can be accomplished with conventional equipment. Turbine and propeller agitators are used to mix low-viscosity liquids, and twin-cone blenders or tumblers are used for dry powders. These devices have low power requirements and rather low residence times. At the other extreme, the dispersion of a finely divided solid such as carbon black in a rubber with viscosity of about a million poises presents a situation requiring more power. 

The degree of mixing, the uniformity of dispersion of one phase in another, can be measured in several ways. One could take a series of samples of uniform size 

FIG U RE 13.1 The impeller of the Cowles dissolver. (Data from Nylen, P., and E. Sunderland Modem Surface Coatings, Wiley, New York, 534, 543, 1965. Copyright Wiley-VCH Verlag GmbH Co. KGaA. Reproduced with permission.) 

The mainstays of the rubber industry for over 60 years have been the two-roll mill and the Banbury mixer. RoU mills were first used for rubber mixing over 100 years ago The plastics and adhesives industries adopted these tools later on. The Banbury is often termed an internal mixer since the contents are under pressure as opposed to the roll mills that are open to the atmosphere. 

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Particle Preparation. The initial step in particleboard production is reduction of the wood raw material into the desired configuration for the particular particleboard to be manufactured. The wood may be received from a number of sources and in a variety of forms. Roundwood, chips, planer shavings, plywood trim, and sawdust are the most common raw material forms and rarely does one particleboard plant use more than two or three of the above sources. Different processing steps are required to produce quality particles from each of the above sources consequently, each plant is limited to the source which is compatible with their... 

Farm-level processing operations are the most important unit operations for value addition and product diversification of spices. It is essential that these operations ensure proper conservation of the basic qualities like aroma, flavour, pungency, colour, etc. Each of these operations enhances the quality of the produce and the value of the spice. The clean raw materials form the basis for diversified value-added products. 

An increase of the contact strength with the decrease of water layering is confirmed experimentally. For example, it was stated that the strength of raw material formed from wetted bentonite is determined by the equation ... 

Expandable raw materials form a glass-like pyroplastic") phase at I 100 to I200 C and are expanded by the gases formed at these temperatures... 

Process 2 - Process Description. The impurities in the raw material form azeotropes with tetrahydrofuran and ethylacetate. All the azeotropes had to be separated by a combination of counter current extraction and rectification. The aim was to recover ethylacetate and THF. The following major problems had to be solved by a solvent recovery unit 1) separate the THF/ methanol and the THF/ ethanol azeotropes, 2) dewater the THF and ethylacetate (azeotropes), 3) separate THF (Atmospheric boiling point (Tb) = 65.7°C) from ethylacetate (Tb= 77°C) and methylacetate (Tb = 57.1°C). 

Other raw materials stream The input of these raw materials forms the secondary raw materials. These all end up as residues. The secondary raw materials include the non-recyclable solvents, catalysts and impurities (side components) in the primary raw materials. 

Perhaps the most confusing aspect of plastics to the non-specialist is the profusion of raw material forms and processes involved. These are classified and reviewed in this chapter, together with the all-important questions of economics and The numbers game . Polymers can themselves be classified in a number of ways ... 

Plastic natural ceramic raw materials, consisting predominately of kaolinite, illite and/or montmorUlonite, are accompanied by residual quartz, feldspar, mica, and calcite as well as organic residues. In particular, the hmestone content has been used to distinguish between clay (<4 mass% hme), marly day (4—10 mass% lime), clayey marl (10-40 mass% hme), marl (40-75 mass% hme), calcareous marl (75-90 mass% lime), marly hmestone (90-96 mass% hne), and hmestone (>96 mass% hme). Kaolinitic raw materials formed in situ (autochthoneous) are called kadine, while kaolinitic raw materials found in secondary deposits (aUochthone-ous) are called clays. Marl and marly hmestones are important raw materials for Portland cement production (see Section 5.2.1). 

Composite materials, particularly in the raw material form, present toxic hazards to users and should be handled carefully. Essentially, there is a need for management inputs and controls on the following aspects of composite fabrication ... 

Thermoplastics, by the very definition of the word, denotes polymeric materials which can be made to soften and take on new shapes by the application of heat and pressure. In their original raw material form, themu iastics are available in solid state as chips, granules, or powder. These are melted and reshaped to form various plastic products. For details regarding engineering aspects and properties of plastics, readers could refer to some of the available hancRxwks [168-171]. 

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