Coagulation bath temperatures

From the morphology and mechanical properties of these as-spun PANI fibers, it is obvious that the size and number of macrovoids must be reduced. Therefore, the effects of the temperature and composition of the coagulation bath were subsequently investigated. The coagulation bath temperature should affect the morphology of the as-spun PANI fibers. From theoretical calculations, a high bath temperature is expected to accelerate the diffusion and the demixing processes. From the above study, we... 

Using a 25 wt% EB/NMP/HPMI solution, we also spun a batch of fiber into a 20 wt% NMP aqueous bath. The PANI fibers were processed using coagulation bath temperature of 20°C with a take-up speed on the first godet of 10 m/min. Typically, in the water bath, the nascent fiber formed within a few minutes. In order to remove any residual solvent (NMP and HPMI) from the as-spun fiber, we usually kept the fibers in a water bath for 24 h. However, for the same dope solution, which was spun into the... 

GUO Guo, Y., Feng, X., Chen, L., Zhao, Y., and Bai, J., Influence of the coagulation-bath temperature on the phase-separation process of poly(vinylidene fluoride)-grq -poly(V-isopropylacrylamide) solutions and membrane structures, J. Appl. Polym. Sci., 116, 1005,2010. 

Temperature is another important parameter in wet spinning. The temperatures of the extmded fluid and of the coagulation bath are controlled separately. Usually, the dope temperature is kept higher to avoid fluid flow problems, while the coagulation bath temperature is kept lower to control the coagulation rate and improve the cohesiveness of the spinning line. 

For polymeric hollow fiber membranes, spinning parameters are crucial factors that must be controlled during the preparation of membranes. These parameters include the amount and type of polymers, solvents, additives mixed into the spinning dope solution, the dope and bore fluid rate, the kind of bore fluid, the fiber take-up velocity, the air-gap distance (unless wet spinning is used), and the coagulant bath temperature and the kind of coagulant bath. 

As a semicrystalline polymer, the kinetics of phase separation for PVDF are more difficult to comprehend than other amorphous polymers such as polysulfone (Wienk et al. 1996). The immersion temperature is proven to affect the crystallinity of PVDF membranes. For example, in a PVDF/DMA/water system (12% PVDF concentration), Buonomenna et al. (2007a) found that a crystal type was more dominant than p type at high coagulation bath temperature (60°C) and vice versa at 25°C. They explained the importance of the kinetic aspect. At higher temperature, solution viscosity is lower, which affects the two-phase separation process by increasing the mass transfer between the solution and precipitation bath, favoring the liquid-liquid demixing. 

Isotropic solutions (12-15% by weight) of XVI in m-cresol were dry-jet wet spun into a coagulation bath of water/methanol. The as-spun fibers were drawn at temperatures above 380 °C to give fibers having a tensile strength of about 3.2 GPa and a modulus of 130 GPa. The annealed fibers displayed distinct wide-angle X-ray patterns from which a monoclinic unit cell was determined. 

Dopes like these exhibit mesomorphic behaviour they are solid at room temperature, but at higher temperature become less viscous and show optical anisotropy. If heated further, the clearing temperature (Td) is reached at which a phase transformation takes place from an anisotropic solution to an isotropic solution. With increasing polymer concentration both Ta and the melting point of the dope (T ) increase. Fibres of the highest quality (tenacity) are obtained by spinning at temperatures between and Ta, but as low as possible, The spun filament is solidified in a coagulating bath, preferably at temperatures below 5 °C. 

---