Melt spinning semicrystalline polymers

The results discussed above indicate that the further study of the spin relaxation parameters possess the potential to develop our understanding of the structure of the non-crystalline regions of semicrystalline polymers. Significant progress has already been made in relating the spin-lattice relaxation parameters with that of the pure melt. The linewidths, or spin-spin relaxation parameters, of semicrystalline polymers have been... 

Variable-temperature NMR experiments provide information about the dynamic processes that occur in solids. It is well known that, for a semicrystalline polymer such as polyethylene (PE), a higher rate of cooling from the melt leads to lower crystallinity C CP/MAS NMR establishes that the cooling rate also affects the structure and motion of the amorphous domain [217]. Many of the dynamic properties of PE, such as jump rates and activation energy, can be explained in terms of chain diffusion between the phases, as detected by 2-D exchange C NMR [218]. Very slow motions in the crystalline a-form of deuterated poly(vinylidene fluoride) have also been detected by exchange NMR [219]. Double-quantum transitions can occur in materials in which spin pairs are only a few bonds apart this... 

The principal forms of spinning are listed in Table 11-1, together with the phase-transformation process as well as the principal commercial fibers formed by each technique. Generally, the selection of a particular type of spinning process is related to the material being spun. For example, nylons are semicrystalline in the solid state and have a definite melting point. Whereas the nature of solid nylon makes it difficult to put it into a solution, it does not prevent a melt from being formed. Hence, nylon is a melt-spun fiber. On the other hand, polyacrylonitrile is an amorphous solid and, as such, is dissolved more readily than a semicrystalline polymer. Here, the result is that polyacrylonitrile is either dry-... 

Recent trends in x-ray diffraction are the increased use of electronic data collection and computer analysis, and in situ or dynamic experiments. These include experiments where the x-ray patterns are obtained while the sample is stretched, heated to its melting point, or aligned with an electric field. Synchrotron radiation is several orders of magnitude more intense than regular laboratory x-ray sources, and its use allows real-time study of deformation or fiber spinning, for example. More synchrotron sources usable for polymer science are currently being built, and although they are limited to national facilities, access should improve in the future. The increased power of computer data analysis permits whole pattern analysis where the crystal structure, orientation and crystallinity are simultaneously determined [10]. More detailed numerical analysis has led to interpretation of x-ray patterns in terms of three phases in semicrystalline polymers instead of the usual two. 

PTT polymer pellets must be dried to a moisture level of <30 ppm, preferably in a close-loop hot air dryer, to avoid hydrolytic degradation during melt processing. Drying is carried out with 130 °C hot air with a dew point of < -40 °C for at least 4 h. Because of the faster crystallization rate, PTT pellets are already semicrystalline after pelletizing, and do not require pre-crystallization prior to drying as with PET. The dried polymer is extruded at 250-270 °C into bulk continuous filaments (BCFs), partially oriented yam (POY), spin-draw yam (SDY) and staple fiber. 

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