Birefringence melt spun

Preparation of oriented fibers from mixtures of polyvinylidene fluoride with different inherent viscosities (molecular weight) has been reported. [" 1 In one example, two types of PVDF polymers with inherent viscosities of 1.49 and 0.95 dl/g were blended together at a weight ratio of 70%/30%. The mixture had an inherent viscosity of 1.33 dl/g. After pelletization, the PVDF blend was melt spun into monofilaments with a diameter of 520 pm. A single-screw extruder (32-mm diameter) was used to spin the filaments at a temperature of 300°C. Birefringence, which is defined as the difference in refractive index in two selected perpen-... 

Figure 3. Maximum birefringence of melt spun PP/EBM fibers vs PP weight fraction.

Figure 13.5 Birefringence as a function of wind-up speed (a) A, PET control (b) A, PET containing 3% copolyester of 1,4-phenyleneterephthalate and p-oxybenzoate (c) O, PET containing 3% copolymer of 6-oxy-2-naphthalene and p-oxybenzoate [17]. From Orientation suppression in fibers spun from melt blends, Brody, H., J. Appl. Polym. Sci., 31, 2753 (1986), copyright (1986 John Wiley Sons, Inc.). Reprinted by permission of John Wiley Sons, Inc.

The last polymer mentioned in Table 10.9 is poly(p-phenylene terephthalamide). This polymer is spun from its solution in pure sulphuric acid (100%), a dope that exhibits mesomorphic (=liquid crystalline) behaviour it is optically anisotropic and is nematic in character. A number of other polymers, containing rigid elements in the chain have melts of polymer liquid crystals, with a high birefringence and a non-linear optical behaviour in electric fields. 

Nadella et al. [79] studied polypropylenes with a broad range of melt flows. Table 3.25 lists the properties of the melts they studied. These melts were spun from a screw extruder at a temperature of 230°C. In the case of H-0060, filaments were also spun at 200 and 260°C. With the exception of H-0042, the polymers were spun through a single capillary at 2.1 g/min. The H-0042 could not be extruded at that rate because of melt fracture this material was extruded at 0.5 g/min. The filaments were quenched in stagnant air at 25°C and were taken up at speeds of 50,100,200,400, and 550 m/min. X-ray and birefringence measurements were taken along the descending spin-line. 

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