Modulus of LCP

Fig. 4.4 Relaxation modulus of LCP-A Unfilled at 350 °C and LCP-B Unfilled at 330 °C according to Maxwell model and shear relaxation experiment (Rahman 2013)...

Several studies (Yi et al. 1996 Zachariades and Porter 1983) have reported that the modulus of LCP fibers is a function of the fiber aspect ratio that increases monotonically with fiber length, and more rapidly as the fiber diameter decreases. Yi et al. (1996) gave an approximate linear function to describe the relationship between the modulus and aspect ratio of Vectra A950 fiber in the form ... 

During heat treatment of an LCP fiber the molecular weight, orientation and crystallinity of the polymer are increased leading to improved tensile strength. The modulus of LCP fibers may also be improved by heat treatment. For 4,4 -biphenol containing LCPs the... 

Figure 8. Tensile and impact strengths, and Young s modulus of LCP versus ultrasonic amplitude for extruded (filled symbols), and as-received (open symbols) samples.

Figure 20.12 The tensile modulus of the LCP/PEN blends as a function of the LCP content at draw ratios of 10 ( ) and 20 ( ) [13]. From Kim, S. H., Hong, S. M., Hwang, S. S. and Yoo, H. O., J. Appl. Polym. Sci., 74, 2448-2456 (1999), Copyright (1999, John Wiley Sons, Inc.). This material is used by permission of John Wiley Sons, Inc...

Let us remember that the properties of LCPs are dependent on processing shear and, consequently, creep modulus varies with sample geometry. 

Figure 4.127 shows the creep modulus of several grades of glass fibre reinforced LCPs in various conditions of sample geometry, loading and temperature. The two samples tested... 

As seen from Figure 16, the torsional modulus of the Ultem/Vectra 70/30 blend sheets increased as the draw ratio was increased. This trend is observed no matter what composition ratio (Ultem/Vectra 90/10, 80/20, and 50/50) is used and in which zone the drawing occurs. Hence, there is a significant indication that the LCP fibrils lead to a reinforcement of Ultem. 

Although liquid crystalline polyesters (LCP s) are interesting polymers exhibiting high mechanical strength and modulus due to a high degree of selforientation, no commercial blends of LCP (except with PPS) are available. LCP blends have been... 

Thermotropic polyesters are melt-spun from the nematic phase and orient easily in an elongational flow field (moderate drawdowns/forces are sufficient). In the fiber case, highly oriented fibers form easily with an initial modulus close to theory—typical values range from about 70 to 150 GPa. Ward [46] has shown that the tensile modulus may be described by an aggregate model, i.e., the modulus is a function of the inherent chain modulus, the molecular chain orientation, and the shear modulus (which described the stress transfer between chains). The tensile strength of LCP fibers follows the prediction of the lag-shear model [47]. Both the aggregate model and the lag shear model treat the LCP as though it... 

The unifying feature of all fibers spun from LCPs is the very high axial molecular orientation, which leads to extreme anisotropy of microstructure and mechanical properties. In the transverse direction, the strength is only about 20% of the axial strength and the modulus is typically less than 10% of the axial value. The microstructure of LCP fibers reflects the very... 

LCPs maintain a highly-oriented molecular structure in both the molten and solid states. In general, such polymers are known as rodlike polymers, and exhibit extremely strong mechanical properties in the direction of molecular orientation. For example, unfilled grades of Type II LCPs exhibit tensile strength of 200 MPa and flexural modulus of 9 GPa (both values are of 3 mm thickness), which are values that cannot be reached even with glass filled conventional polymers. 

The final experiment that may be of value in characterizing the flow characteristics of LCP is that of stress relaxation following a suddenly imposed shear strain. In this experiment various strain amplitudes are imposed very rapidly. In this way no flow occurs. At low strain levels intermolecular forces which can result in yield stresses may be more readily identified. From this type of experiment we determine the strain dependent relaxation modulus defined as follows ... 

The tensile moduli of unorientated and orientated polyethylene fiber are 1.67-4.18 and 117 GNm , respectively [20]. These values may seem quite high for thermoplastic materials, but the theoretical tensile modulus (334 GNm ) is much higher than these values [20]. The large difference is because the polymer chains are not fully aligned and extended. In contrast, the tensile modulus of aromatic polyester LCP fibers is 125-175 GNm. These values approach the theoretical value 188 GNm [20]. 

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