Fiber formation melt spinning process

Aromatic polyesters had been successfully synthesized from the reaction of ethylene glycol and various aromatic diacids but commercialization awaited a ready inexpensive source of aromatic diacides. An inexpensive process was discovered for the separation of the various xylene isomers by crystallization. The availability of inexpensive xylene isomers allowed the formation of terephthalic acid through the air oxidation of the p-xylene isomer. DuPont produced polyester fibers from melt spinning in 1953, but it was not until the 1970s that these fibers became commercially available. 

For this comparison, a melt-spinning process was chosen. Each special thermoplastic process influences the structure and thus the properties of the obtained polymer samples differently. This is particularly pronounced for fibers, since especially melt spinning is a process which makes extremely high demands on the deformation ability of the polymer melts at high deformation speeds. Particularly the tensile stress within the fiber formation zone is a very important factor to reach a high orientation of the macromolecules along the fiber axis and a stress-induced crystallization. This crystallization should be discussed in relation to PLA and PHB multifilaments, and at the same time the general property spectrum of these polymers should be represented. 

LiuRG, Shen YY, Shao HL, WuCX, HuXC (2001) An analysis ofLyocell fiber formation as a melt-spinning process. Cellulose 8 13-21... 

Figure 6. Double crucible melt spinning process depicting the outer and inner crucible, the air flow and the void or hollow fiber formation. Redrawn from M. L. Nice, Apparatus and process for fiberizing fluoride glasses using a double crucible and the compositions produced thereby, US Patent 4,897,100, Jan. 20,1990.

One inviscid melt spinning process, the containerless laser heated melt process (Chapter 4.4.4) is believed to facilitate the formation of fibers by increasing the viscosity of the inviscid melt (and jet lifetime) at a normal quench rate of IC K/s, i.e., without increasing the quench rate to -10 K/s. 

A viable process for the formation of continuous, self-supporting fibers such as hydrogen from liquefied gases has emerged over the past two decades [74]. Like all prior process iterations [74], it appears to be an inviscid melt spinning process (IMS) and not a rapid solidification (RS) process. 

The poor dyeability of PP fibers was overcome by blending PP with a second polymer (e.g., polyester) at high temperature, in the melt state, followed by its formation into a filament through a melt spinning process. It is possible to obtain light, medium, and dark colors with the new fibers. 

Mechanical Properties. Polyester fibers are formed by melt spinning generally followed by hot drawing and heat setting to the final fiber form. The molecular orientation and crystalline fine stmcture developed depend on key process parameters in all fiber formation steps and are critical to the end use appHcation of the fibers. 

The primary fabrication process in the production of synthetic fibers is the spinning—i.e., the formation—of filaments. In every case the polymer is either melted or dissolved in a solvent and is put in filament form by forcing through a die, called spinneret, having a multiplicity of holes. Spinnerets for rayon spinning, for example, have as many as 10,000 holes in a 15-cm-diameter platinum disc, and those for textile yarns may have 10-120 holes industrial yarns such as tire core might be spun from spinnerets with up to 720 holes. 

Ternary blends from a thermotropic liquid crystalline polymer, PEN, and PET were prepared by melt blending and melt spinning to fibers. The mechanical properties of ternary blend fibers could be significantly improved by annealing at 180°C for 2 h. This is attributed to the development of more ordered crystallites and to the formation of more perfect crystalline structures. The interfacial adhesion between PEN and liquid crystalline polymer phases is enhanced when the blends are processed with dibutyl-tindilaurate as a reactive catalyst to promote transesterification. 

The typical spun-bonding process includes a spinneret with a means of conveying the continuous filaments out into the form of a web, or else several spinnerets arranged in a row whose length may approximate the width of the web to be produced. In either case, the process of melting and fiber formation is identical to that used in conventional melt spinning. 

For fiber formation from a polymer, it is necessary for the polymer to either melt at an elevated temperature or dissolve in a solvent. The first commercially produced PVC fiber (monofilament) was made by a method of melt-spinning [144]. However, melt-spinning of PVC is not an agreeable process because of its high melting point, its high melt viscosity, and its low thermal stability. 

One distinct advantage of oxide fibers in terms of processing is that several alumina precursors suitable for forming fibers are available. The aqueous chemistry of aluminum allows for the formation of viscous basic aluminum salt solutions that can be made into fibers by dry-spinning. Polymeric aluminoxanc precursors have also been used to produce alumina-based fibers. Recently, aluminoxanes that can be melt-spun into fibers have been produced. Details of both types of chemical precursors arc given below. 

---