High-modulus

Carbon and Graphite Fibers. Carbon and graphite fibers (qv) are valued for their unique combination of extremely high modulus and very low specific gravity. Acrylic precursors are made by standard spinning conditions, except that increased stretch orientation is required to produce precursors with higher tenacity and modulus. The first commercially feasible process was developed at the Royal Aircraft Fstablishment (RAF) in collaboration with the acrylic fiber producer, Courtaulds (88). In the RAF process the acrylic precursor is converted to carbon fiber in a two-step process. The use of PAN as a carbon fiber precursor has been reviewed (89,90). 

Spandex fibers are available as fine as 1.1 tex (10 den), and the finest extmded latex thread available is about 16 tex (140 den). The availabihty of spandex fibers in such fine sizes and their unique properties compared to mbber, eg, dyeabiUty, high modulus, abrasion resistance, and whiteness, has allowed extensive penetration into hosiery and sportswear markets. 

Transparent, homogeneous hybrids using a 50 50 PVAc-to-TEOS mixture and an acid-catalyzed reaction have been produced and characterized by dsc and dms (46). Dsc indicated only a slight increase in the T of the hybrid with incorporation of sihca. Dynamic mechanical tan 8 responses indicate a strong interaction between the organic and inorganic phases and, hence, weU-dispersed phases that lead to high modulus mbbery plateaus. 

Properties. As prepared, the polymer is not soluble in any known solvents below 200°C and has limited solubiUty in selected aromatics, halogenated aromatics, and heterocycHc Hquids above this temperature. The properties of Ryton staple fibers are in the range of most textile fibers and not in the range of the high tenacity or high modulus fibers such as the aramids. The density of the fiber is 1.37 g/cm which is about the same as polyester. However, its melting temperature of 285°C is intermediate between most common melt spun fibers (230—260°C) and Vectran thermotropic fiber (330°C). PPS fibers have a 7 of 83°C and a crystallinity of about 60%. 

W. B. Black andj. Pteston, High Modulus Mromatic Polymers, M tcelDeRket, Inc., New York, 1979. 

Molybdenum, a typical transition element, has the maximum number, five, of unpaired Ad electrons, which account for its high melting point, strength, and high modulus of elasticity. There are many similarities between molybdenum and its horizontal and vertical neighbors in the periodic system. 

Because of its high modulus of elasticity, molybdenum is used in machine-tool accessories such as boring bars and grinding quills. Molybdenum metal also has good thermal-shock resistance because of its low coefficient of thermal expansion combined with high thermal conductivity. This combination accounts for its use in casting dies and in some electrical and electronic appHcations. 

Cydohexanedimethanol can be the comonomer. TerephthaHc acid can also be the diacid in specialty nylons (see Polyamides). Specialty fibers, including certain high modulus aramid fibers, are made from terephthaHc acid—dimethyl terephthalate derivatives. 

Polymers from the meta isomer are useful for their heat and flame resistance polymers from the para isomer are noted for high tensile strength and high modulus. 

Vitahium FHS ahoy is a cobalt—chromium—molybdenum ahoy having a high modulus of elasticity. This ahoy is also a preferred material. When combiaed with a properly designed stem, the properties of this ahoy provide protection for the cement mantle by decreasing proximal cement stress. This ahoy also exhibits high yields and tensile strength, is corrosion resistant, and biocompatible. Composites used ia orthopedics include carbon—carbon, carbon—epoxy, hydroxyapatite, ceramics, etc. 

Fig. 19. Generalized modulus—temperature curves for polymeric materials showing the high modulus glassy state, glass-transition regions for cured and uncured polymers, plateau regions for cross-linked polymers, and the dropoff in modulus for a linear polymer.

Component High modulus sealant, % Low modulus sealant, %... 

Using both condensation-cured and addition-cured model systems, it has been shown that the modulus depends on the molecular weight of the polymer and that the modulus at mpture increases with increased junction functionahty (259). However, if a bimodal distribution of chain lengths is employed, an anomalously high modulus at high extensions is observed. Finite extensibihty of the short chains has been proposed as the origin of this upturn in the stress—strain curve. 

Sometimes cemented carbide tools are used not only for hardness and wear resistance but also for high modulus or stiffness. For example, in end mills used in high speed machining of aluminum alloys, the deflection of the tool can affect the performance of the tool considerably. This includes chatter... 

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