Fibers, tensile moduli

While no direct evidence of liquid crystallinity in PET-BB copolymers has been reported, the high-BB-content copolymers have been shown to possess morphologies similar to those of liquid crystalline polyesters [40], and show major changes in both melt relaxation times and fiber tensile moduli, suggestive of structural organization in a frustrated liquid crystalline polymer (LCP) (Table 6.3 and Figure 6.4) [41, 42],... 

Vf = volume fraction of fibers Vm = matrix volume fraction Ef = fiber tensile modulus Em = matrix tensile modulus... 

Materials (fibers) Tensile modulus (GPa) Tensile strength (GPa) Compressive strength (GPa) Density (g/cm )... 

The compressive stress decreases with increased anisotropy, which can be represented by the ratio of fiber tensile modulus to the torsional modulus (E/jG/) (Figure 20.18). Kumar... 

IM Intermediate modulus fiber. Tensile modulus approximately 300 GPa. 

The Passion s ratios of most isotropic polymers are between 0.3 and 0.4, and hence the E/G ratios of isotropic polymers range from 2.5 to 3.0. However, polymer fibers are anisotropic due to the high molecular orientation. With increase in molecular orientation, the tensile modulus increases, but the shear modulus decreases. This is because the molecular orientation is beneficial for increasing the fiber tensile modulus however, with increased molecular orientation, more fibrils are formed in the fiber and the fibrils are easily separated by twisting although they have excellent tensile properties. Table 15.9 shows the tensile moduli, shear moduli, and their ratios for some fibers. Some fibers have very large E/G ratios due to the high molecular orientation. 

Fiber Tensile Modulus (GPa) Shear Modulus (GPa) Tensile Modulus Shear Modulus... 

Acetate and triacetate exhibit moderate changes in mechanical properties as a function of temperature. As the temperature is raised, the tensile modulus of acetate and triacetate fibers is reduced, and the fibers extend more readily under stress (see Fig. 4). Acetate and triacetate are weakened by prolonged exposure to elevated temperatures in ah (see Fig. 5). 

The copolymer fiber shows a high degree of drawabiUty. The spun fibers of the copolymer were highly drawn over a wide range of conditions to produce fibers with tensile properties comparable to PPT fibers spun from Hquid crystalline dopes. There is a strong correlation between draw ratio and tenacity. Typical tenacity and tensile modulus values of 2.2 N/tex (25 gf/den) and 50 N/tex (570 gf/den), respectively, have been reported for Technora fiber (8). 

Carbon fibers are generally typed by precursor such as PAN, pitch, or rayon and classified by tensile modulus and strength. Tensile modulus classes range from low (<240 GPa), to standard (240 GPa), intermediate (280—300 GPa), high (350—500 GPa), and ultrahigh (500—1000 GPa). Typical mechanical and physical properties of commercially available carbon fibers are presented in Table 1. 

Fibers Tensile strength, GPa Modulus, GPa Density, g/cm Diameter, ]lni Maximum use temperature, °C... 

Applied Sciences, Inc. has, in the past few years, used the fixed catalyst fiber to fabricate and analyze VGCF-reinforced composites which could be candidate materials for thermal management substrates in high density, high power electronic devices and space power system radiator fins and high performance applications such as plasma facing components in experimental nuclear fusion reactors. These composites include carbon/carbon (CC) composites, polymer matrix composites, and metal matrix composites (MMC). Measurements have been made of thermal conductivity, coefficient of thermal expansion (CTE), tensile strength, and tensile modulus. Representative results are described below. 

Kohli et al. [27], for instance, showed that the tensile modulus of a highly drawn PC-TLCP composite could be modeled effectively by the simple additivity rule of mixtures, while the compression molded composite samples with a spherical TLCP morphology had moduli according to the inverse rule. In both cases, the tensile modulus of the TLCP (Ei,c) itself was assumed to be a constant value determined from a tensile test of the pure TLCP samples. But whether or not the dispersed TLCP fibers and deformed droplets have the same modulus as the bulk TLCP samples remains a question. 

It is, therefore, the intention of this section to present the tensile modulus of dispersed TLCP fibers and pure TLCP bulk materials, respectively, both processed by injection molding. 

According to the composite theory, tensile modulus of fiber reinforced composites can be calculated by knowing the mechanical constants of the components, their volume fraction, the fiber aspect ratio, and orientation. But in the case of in situ composites injection molded, the TLCP fibrils are developed during the processing and are still embedded in the matrix. Their modulus cannot be directly measured. To overcome this problem, a calculation procedure was developed to estimate the tensile modulus of the dispersed fibers and droplets as following. 

Fiber Initial modulus (GN/m-) Ultimate tensile strength (MN/m=) Elongation at break (%) Flexural modulus (MN/m-)... 

Figure 6 Effect of fiber orientation on (a) tensile strength and (b) tensile modulus of PALF-LDPE composites.

Extruded composites of plasticized PVC and short cellulose fibers have been investigated by Goettler [103]. Pronounced increases in tensile modulus, yield, and ultimate tensile strength are observed. Single step processing of reinforcement and polymer with good product performance are key characteristics of the material whose field of application lies in the vinyl hose industry. 

Major Constituent Tensile Strength (MPa) Tensile Modulus (GPa) Density (g/cm3) Fiber diam. (pm)... 

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