As-spun fibers

Since PVA fiber as spun is soluble in water, it is necessary to improve the water resistance of the as-spun fiber (10). Heat treatment followed by acetalization is a classic method to provide high water resistance. 

A report130 of DSC measurements on polybenzimidazole fibers describes important differences for the glass transition temperature depending on die mechanical treatment of the fiber. An as-spun fiber exhibits a Tg at 387°C instead of 401°C for a drawn fiber free to shrink or 435°C for a drawn fiber widi fixed length. 

At speeds beyond 4000 m/min, inertial and air drag effects become the dominant contributors to fiber stress. Sufficient orientation can be induced so that significant crystallization occurs in the as-spun fiber. The structure begins to partition into either highly oriented crystalline regions, or amorphous regions of relatively low orientation. There is relatively less oriented-amorphous structure. 

The orientation functions (F-values) of as-spun fibers were calculated according to the following equation ... 

The morphologies of the tensile-fractured as-spun fibers and the flexural-fractured injection molded specimens were studied by scanning electron microscopy (SEM). 

The liquid crystallinity and the moduli of as-spun fibers of polyarylates from substituted HQs and substituted PECs could be controlled by the substituents shown in Table 19.1. Polyarylates derived from /-butyl HQ (fBu-HQ) and PEC (fBu-HQ/PEC), and phenyl-HQ (Ph-HQ) and PEC (Ph-HQ/PEC), showed decreased liquid crystallinity when compared to chloro-HQ (Cl-HQ) and PEC (Cl-HQ/PEC), and methyl-HQ (Me-HQ) and PEC (Me-HQ/PEC), because of the bulky substituents on the HQ units. 

Therefore, the moduli of as-spun fibers of fBu-HQ/PEC and Ph-HQ/PEC were lower than those of Cl-HQ/PEC and Me-HQ/PEC [18, 22, 23], Tensile-fractured as-spun fibers of f Bu-HQ/PEC and Ph-HQ/PEC exhibited decreased orientation of fibrils when compared to Cl-HQ/PEC and Me-HQ/PEC. 

Polyarylates prepared from cyclohexyl-HQ (Ch-HQ) and PEC (Ch-HQ/PEC) did not show liquid crystallinity due to the more bulky substituent on the HQ unit compared to those on f Bu-HQ and Ph-HQ. As-spun fibers of Ch-HQ/PEC exhibited lower moduli than those of fBu-HQ/PEC and Ph-HQ/PEC. Therefore, in order to obtain high-modulus as-spun fibers, the stability of the liquid crystalline state (7j — 7j,) is an influential factor, as shown in Table 19.1. 

On the other hand, the moduli of as-spun fibers of polyarylates from Cl-HQ and l,2-bis(2-chlorophenoxy)ethane-4,4/-dicarboxylic acid (Cl-PEC) (Cl-HQ/ Cl-PEC), and Me-HQ and Cl-PEC (Me-HQ/Cl-PEC), were higher than those of Cl-HQ/PEC and Me-HQ/PEC. The reason for the higher moduli seemed to be the increased rigidity of the polymer chain caused by the restricted rotation of the ether linkage of Cl-PEC as a result of the steric hindrance of the Cl atoms. However, the moduli of polyarylates from fBu-HQ and Cl-PEC (fBu-HQ/Cl-PEC), and Ph-HQ and Cl-PEC (Ph-HQ/Cl-PEC), were lower than those of fBu-HQ/PEC and Ph-HQ/PEC, because the Cl atoms on the PEC units prevent... 

The reason for the lower liquid crystalline (LC) temperature of the BB model compound seems to be that the biphenyl unit of this compound was adopting a twisted structure in the LC state [26], Therefore, we prepared various polyarylates containing the BB unit and determined their thermal properties and the moduli of the as-spun fibers, as shown in Table 19.3. 

However, as-spun fibers of the polyarylates derived from Me-HQ and BB (Me-HQ/BB) exhibited a lower modulus than that of Me-HQ/Cl-PEC in spite... 

Figure 19.1 SEM images of tensile-fractured as-spun fibers of (a) Me-HQ/BB (5 GPa F, 0.62 Tg, 175 °C) (100x) [19], and (b) Me-HQ/CI-PEC (72 GPa F, 0.90 Tg, 129°C) (300x) [31]. (a) 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, (b) 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...

Although as-spun fibers of Cl-HQ/BB/TA with m/n = 70/30 exhibited a modulus of 95 GPa, as-spun fibers of Cl-HQ/BB/TA with m/n = 80/20 exhibited a lower modulus of only 11 GPa in spite of the more rigid chemical structure due to the decreased elongational flow orientation, as shown in Figure 19.3.1 Tensile-fractured as-spun fibers of Cl-HQ/BB/TA with m/n = 70/30 exhibited many fibrils when compared to those of Cl-HQ/BB/TA with m/n = 80/20. 

The lower modulus seemed to be referred to the lower elongational flow orientation. Tensile-fractured as-spun fiber of Me-HQ/BB/NDA with m/n = 92.5/7.5 exhibited many fibrils when compared to Me-HQ/BB/NDA as-spun fiber with m/n = 95/5, as shown in Figure 19.5. 

Figure 19.6 shows the relationship between the moduli of as-spun fibers and the F-values of substituted HQs/BB and substituted HQs/BB modified with... 

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. 

Figure 19.8 F-values of as-spun fibers and injection molded specimens [19]...

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. 

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. 

---