Moduli of injection molded specimens

Because as-spun fibers of Me-HQ/Cl-PEC showed a higher modulus than those of Ph-HQ/Cl-PEC, the flexural modulus of injection molded specimens of Me-HQ/Cl-PEC exhibited a higher flexural modulus than those of Ph-HQ/Cl-PEC due to the liquid crystalline state. Although flexural-fractured injection molded specimens of Me-HQ/Cl-PEC exhibited highly oriented fibrils, Ph-HQ/ Cl-PEC no longer displayed fibrils because of the lack of liquid crystallinity. 

Accordingly, we have evaluated the flexural modulus of injection molded specimens of CP-HQ/BB having higher F-values than those of Me-HQ/BB polyarylates. The flexural modulus of injection molded specimens of Me-HQ/BB 

The average cross-sectional area (S) of the repeating unit can be calculated according to the following equation  

According to Equation (19.3), the average cross-sectional area (S) of Me-HQ/ BB was 24.9 A2, compared to the value of 32.8 A2 in the case of CP-HQ/BB. Thus, to improve the packing density of Ph-HQ/BB, we have attempted to synthesize Ph-HQ/HQ/BB copolymers. 

As-spun fibers of Ph-HQ/HQ/BB with m/n = 50/502 exhibited a much higher modulus (100 GPa) than Ph-HQ/BB (40GPa) due to the increased F-value and rigidity of the polymer chain. Injection molded specimens of Ph-HQ/HQ/BB with m/n = 50/50 exhibited a much higher modulus than those of Ph-HQ/BB due to the increased rigidity and packing density of the polymer chain upon copolymerization with HQ. However, the F-value of injection molded specimens of Ph-HQ/HQ/BB (m/n = 50/50) was not much higher than those of Ph-HQ/BB, as shown in Table 19.4. 

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HIGH-PERFORMANCE LIQUID CRYSTAL POLYESTERS 4.2 MODULI OF INJECTION MOLDED SPECIMENS... 

The moduli of as-spun fibers of polyarylates depend highly upon the stability of the liquid crystalline state, the rigidity of the polymer chain, and the degree of elongational flow orientation (F-value). On the other hand, the moduli of injection molded specimens of polyarylates depend upon the stability of the liquid crystalline state, and the rigidity and packing density of the polymer chain. 

Thus, both the rigidity and packing density of the polymer chain seem to be more influential factors than the F-values in achieving a high modulus of injection molded specimens. Figure 19.10 shows the variation of the flexural moduli as a function of the F-values for various substituted-HQs/BB and substituted HQs/BB modified with DHB, HQ, 2,6-dihydroxynaphthalene (DHN), NDA, Cl-PEC and TA [31,32], We could find no relationship between them. 

Figure 19.10 Flexural moduli and F-values of injection molded specimens O, Me-HQ/BB and copolyarylates O, Ph-HQ and copolyarylates x, CP-HQ/BB [31 ]. From Inoue, T., Tabata, N. and Yamanaka, T., Polym. J., 28,424-431 (1996), and reproduced with permission of The Society of Polymer Science, Japan...

Thus, the influential factors in obtaining high moduli for injection molded specimens are as follows (1) tlte stability of tlte liquid ciystalline state, (2) tlte rigidity of the polymer chain, and (3) tlte packing density of tlte polymer chain. 

Anisotropic materials have different properties in different directions (1-7). 1-Aamples include fibers, wood, oriented amorphous polymers, injection-molded specimens, fiber-filled composites, single crystals, and crystalline polymers in which the crystalline phase is not randomly oriented. Thus anisotropic materials are really much more common than isotropic ones. But if the anisotropy is small, it is often neglected with possible serious consequences. Anisoiropic materials have far more than two independent clastic moduli— generally, a minimum of five or six. The exact number of independent moduli depends on the symmetry in the system (1-7). Anisotropic materials will also have different contractions in different directions and hence a set of Poisson s ratios rather than one. 

Many researchers have reported the structure-thermal property correlations in LCPs from substituted hydroquinones (HQs) and dicarboxylic acids. Lenz and co-workers have investigated the liquid crystallinity of the polyarylates obtained from substituted HQs and terephthalic acid (TA) [6-10], substituted HQs and l,10-bis(phenoxy)decane-4,4/-dicarboxylic acid [8], and substituted HQs and a,oo-bis(phenoxy)alkane-4,4/-dicarboxylic acid [11], Kricherdorf and Schwarz [12] and Osman [13] reported the liquid crystallinity of the polyarylates obtained from substituted HQs and 1,4-cyclohexanedicarboxylic acid, while Krigbaum el al. [14], Heitz and co-workers [15] and Kricherdorf and Engelhardt [16] investigated the liquid crystallinity of the polyarylates synthesized from substituted HQs and substituted TAs. In addition, Jackson reported the liquid crystallinity and the moduli of fibers and injection molded specimens of the polyarylates... 

Table 19.4 Thermal properties and moduli of as-spun fibers and injection molded specimens of Ph-HQ/BB and Ph-HQ/HQ/BB (m/n = 50/50) polyarylates [19] From Inoue, T. and Tabata., N., Mol. Cryst. Liq. Cryst, 254, 417-428 (1994), and reproduced with permission of Gordon and Breach (Taylor and Francis) Publishers...

The polyamide 66 composites exhibit sinular property trends and more evidence of fiber degradation. Injection molded specimens could not be tested due to too much degradation. The flexural properties of polyamide 66 conposites are shown in Table 4. Conqjared to neat polyamide 66 there is a drop in flexural strength and an increase in flexural modulus. The flexural moduli of polyamide 6 and 66 composites are similar whereas the strengths of the polyamide 66 composites are lower. These trends are consistent with the lower quality of the polyamide 66 composites. 

The specimens for measurements of the flexural moduli were prepared by injection molding using a Sumitomo NESTAL injection molding machine (0.5 ounce).1... 

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