Fiber crystallinity/orientation, effect

Parameter Effect on Spinning Stress Effect on Filament Temperature Time Spent in Spinning Line Fiber Orientation Fiber Crystallinity Remarks... 

XRD studies by Fischer et confirm the increase in crystallinity with drawing of EB fibers. The increase in crystallinity was attributed to the nucleation of new crystallites, rather than by growth of existing crystals. These workers also noted an orientation effect of the amorphous phase, so that highly drawn (L/Lq = 4.5) EB has an amorphous phase analogous to the nematic liquid crystal structure. 

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. 

Figure 13.3 Crystalline (fc) and amorphous (fa) orientation factors as a function of take-up speed for the three PET samples described in Table 13.1 , branched , linear (IV, 0.66) A, linear (IV, 0.61) [13]. From Some effects of the rheological properties of PET on spinning line profile and structure developed in high-speed spinning, Perez, G., in High-Speed Fiber Spinning, Ziabicki, A. and Kawai, H. (Eds), 1985, pp. 333-362, copyright (1985 John Wiley Sons, Inc.). Reprinted by permission of John Wiley Sons, Inc.

In the above, the variable R is the radius between center to center fiber spacing, while r is the fiber radius. The shear modulus (Gm) can be approximated as Em/3. The matrix modulus is effected by the level of crystallinity and it is important that the samples are fully crystallized to ensure reproducibility. The value of (> for 30wt% glass-fiber-reinforced PET has been calculated as 3.15 x 104. Using the mathematical analysis shown above, the orientation function of the glass fiber... 

Local Crystallinity. The "azimutal correction" previously mentioned should be applied only in the second case discussed above, i.e., when the variation of the local orientation is the main factor in affecting the observed diffraction pattern. In this specific case, the diffracted intensity is spread over the whole interference. As a result, the correction should be made for 66 polyamide and not for PETP. This correction could have a large effect and would result in lowering the crystallinity differences between the two kinds of fibers. This azimutal correction gives a better account of the whole azimutal intensity than the normalization of the half-height width value as proposed in another paper (10). 

Oda, T., Makino, K., Yamashita, I., Namba, K., and Maeda, Y. (1998). Effect of the length and effective diameter of F-actin on the filament orientation in liquid crystalline sols measured by X-ray fiber diffraction. Biophys. J. 75, 2672-2681. 

The higher thermal conductivity of inorganic fillers increases the thermal conductivity of filled polymers. Nevertheless, a sharp decrease in thermal conductivity around the melting temperature of crystalline polymers can still be seen with filled materials. The effect of filler on thermal conductivity for PE-LD is shown in Fig. 2.5 [22], This figure shows the effect of fiber orientation as well as the effect of quartz powder on the thermal conductivity of low density polyethylene. 

Poly((3-PL) has been hydrolytically degraded in a buffered salt solution (pH 7.2) at 37 °C [125,175], Oriented fibers and unoriented fibers showed different mechanical properties on degradation. The changes in tensile strength were slower for the oriented material. The molecular weight decreases rapidly during the first 50 days while the crystalline phase increases, probably due to an anneal-ing-like effect caused by the temperature at which the degradation was performed and rapid water absorption [175]. 

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