Frontiers in Chemical Engineering Research Needs and Opportunities (1988) / Chapter Skim
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5 Polymers, Ceramics, and Composites
5 Polymers, Ceramics, and Composites
Pages 61-78
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From page 62... ...
In this chapter, five additional classes of materials are covered: polymers, polymer composites, advanced ceramics, ceramic composites, and composite liquids. CHALLENGES TO CHEMICAL ENGINEERS The revolution in materials science and engineering presents both opportunities and challenges to chemical engineers.
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From page 63... ...
In 1985, Union Carbide and Shell Chemical successfully extended the UNIPOL process to the manufacture of polypropylene, another major polymer commodity. Interestingly, the first two licensees for the new polypropylene process were a Japanese chemical company and a Korean petroleum company.
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From page 64... ...
The resulting materials, known as composites, usually have one of the structures depicted in this figure. Clockwise from the upper left, reinforcement may be accomplished by embedding randomly oriented fibers, by orienting fibers along a particular axis, by assembling reinforced layers into laminates, or by embedding fabrics of reinforcing fibers in the material.
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From page 65... ...
For example: · Conventional ceramics are made from natural raw materials such as clay or silica; advanced ceramics require extremely pure manmade starting materials such as silicon carbide, silicon nitride, zirconium oxide, or aluminum oxide and may also incorporate sophisticated additives to produce specific microstructures. · Conventional ceramics initially take shape on a potter's wheel or by slip casting and are fired (sintered)
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From page 66... ...
FRONTIERS IV Cl~iE.~L 3ElYGIlYEERING strength / Optical condensing F I uorescence Transl ucence ., ~ .,.,./ ,' Optical , ~ cow conductivity .,.,.,.~.,..,y. ~ ~ Electrical \ Electrical conductivity Semiconductivity Piezoelectric Dielectric Magnetic am FIGURE 5.3 The myriad functions, properties, and applications of advanced ceramics.
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From page 67... ...
Chemical Additives in Ceramic Processing Another area to which chemical engineers can contribute is the use of chemical additives
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From page 68... ...
Ceramic metal-matrix composites are fabricated by infiltrating arrays of fibers with molten metal so that a chemical reaction between the fiber and the metal can take place in a thin layer surrounding the fiber. As with advanced ceramics, chemical reactions play a crucial role in the fabrication of ceramic composites.
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From page 69... ...
Composite Liquids A final important class of composite materials is the composite liquids. Composite liquids are highly structured fluids based either on particles or droplets in suspension, surfactants, liquid crystalline phases, or other macromolecules.
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From page 70... ...
Polymers and Polymer Composites The Panel on Advanced Materials of the NSF Japanese Technology Evaluation Program (JTECH) issued a report in 1986 assessing the status and direction of Japanese research and development efforts in several high-technology polymer areas.' The panel noted that the major Japanese chemical companies already manufacture most of the commercially available poly mers and that "since 1970, there has been an increasing flow of upgraded technology from Japan to the United States." For engineering plastics and resins, the panel judged the United States to be ahead in basic research (although the lead is diminishing)
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From page 71... ...
The situation is less clear for liquid crystals and adhesives, where there is greater competition from Europe and Japan. INTELLECTUAL FRONTIERS A wide variety of chemical engineering research frontiers involve advanced materials and belong in the mainstream of academic chemical engineering departments.
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From page 72... ...
Inasmuch as polymerization processes are influenced by the diffusion of free radicals from initiators and from reactive sites, and because free radicals FRONTIERS iN CHEMICAL ENGINEERING can be deactivated when they are intercepted at solid boundaries, the high interracial area of a prepolymerized composite represents a radically different environment from a conventional bulk polymerization reactor, where solid boundaries are few and very distant from the regions in which most of the polymerization takes place. The polymer molecular weight distribution and cross-link density produced under such diffusion -- controlled conditions will differ appreciably from those in bulk polymerizations.
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From page 73... ...
Fluid mixtures flowing into a mold of complicated geometry may exhibit large temperature gradients from the highly exothermic chemical reactions taking place and significant spatial variations in viscosity and molecular weight distribution.
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From page 74... ...
Information on the response to rapid shear flows and extensional flows, even in simple polymer solutions, is very limited. Thus, we are far from having dependable equations from which models of such fluids could be developed and farther still from a generalized molecular understanding of the structure-property relations of these fluids and from extrapolations of the flow patterns and stress distributions in such fluids in geometries close to those in which they are used.
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From page 75... ...
Process Design and Control Because processing conditions and history have such an important influence on the conformation and properties of materials, there is a need to develop models and systems for the measurement and control of materials manufacturing processes so that processes can be better designed, more precisely controlled, and automated. Opportunities for chemical engineers in process design and control, including advanced mathematical modeling of polymer processing, are explored in depth in Chapter 8.
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From page 76... ...
In a number of situations, joining and fabrication processes involving chemical reactions with the material will be needed in systems fabrication. Fundamental research to support materials assembly and fabrication probably centers on the science and technology of adhesion, although research on mechanical assembly driven by chemical action, such as the self-assembly FRONTIERS IN CHE.~ICAL ENGINEERING of large molecules or particles, also holds promise for solving some fabrication problems.
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From page 77... ...
All the scientific and engineering disciplines involved in materials research are in need of better instrumentation and facilities. Suitable equipment for chemical engineers interested in materials questions might include the following: solid-state NMR spectrometry; spin-echo NMR spectrometry; Raman spectroscopy; secondary ion mass spectrometry; X-ray photoelectron spectroscopy; laser light scattering; advanced dynamic rheometers; computer-controlled, fully equipped poly- 2 mer~zation reactors; · directional irradiation devices; and · dynamic mechanical property measure ment equipment.
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From page 78... ...
New Structural Materials Technologies: Opportunities for the Use of Advanced Ceramics and Composites A Technical Memorandum (OTATM-E-321. Washington, D.C.: U.S.
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