Spinnability

What makes a polymer melt- or solution-spinnable A theoretical prediction is hardly possible [6]. Laboratory tests are in fact small spinning trials. This is the way most fiber producers will test newly developed polymers, or modifications and new grades of known polymers on a small spinning machine, which may be a one-hole laboratory machine. The reason is that in the initial stage of development often only small amounts of material are available. 

Obviously, the use of a high molecular weight polymer grade will be preferred. It gives increased melt strength, and will usually give better yam properties. Problems with die swell and melt fracture can make a compromise necessary, however. 

For wet spinning there is an additional factor influencing spinnability. The thread formation process is complicated it involves diffusion of solvents out of 

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Isopropenyl acetate gives spinnable fibres on copolymerization with vinyl chloride. 

Also in 1972 (6), Carbomdum researchers described a family of aromatic copolyesters which were recognized later to form Hquid crystalline melts. The polymers are based on a bisphenol monomer. In 1976, in a patent assigned to Carbomndum, a hydroxybenzoic acid—terephthaHc acid—bisphenol system, modified and softened with isophthaHc acid, was reported to be melt spinnable to produce fiber. 

Another type of experiment involves a fluid filament being drawn upward against gravity from a reservoir of the fluid (101,213,214), a phenomenon often called the tubeless siphon. The maximum height of the siphon is a measure of the spinnabiUty and extensional viscosity of the fluid. Mote quantitative measures of stress, strain, and strain rate can be determined from the pressure difference and filament diameter. A more recent filament stretching device ia which the specimen is held between two disks that move apart allows measurements ia low viscosity Hquids (215). AH of these methods are limited to spinnable fluids under small total strains and strain rates. High strain rates tend to break the column or filament. 

To date, there has been relatively little work reported on the mesophase pitch rheology which takes into account its liquid crystalline nature. However, several researchers have performed classical viscometric studies on pitch samples during and after their transformation to mesophase. While these results provide no information pertaining to the development of texture in mesophase pitch-based carbon fibers, this information is of empirical value in comparing pitches and predicting their spinnability, as well as predicting the approximate temperature at which an untested pitch may be melt-spun. 

Wojtkonski [185] has also reported on three series of melt spinnable thermotropic aromatic-aliphatic polyimines. The polyimines were prepared by reaction of 1,2-bis(4-formylphenoxy) ethane, terephthalaldehyde, or 4,4 -biphenyldicarboxaldehyde, respectively, with l,n-bis(4-amino-3-methylphenoxy) alkanes where n = 1-10, 12, 14, and 16 in dry DMAC containing 5% dry lithium chloride. The polymers decomposed at 400°C, and as the length of the flexible aliphatic segments increased, melting points decreased. Polymers with an odd... 

Melt spinning of the E-plastomers has been the source of a commercial development directed to woven cloth of cross-linked E-plastomers [16]. Recent work on the rheological and theoretical estimation of the spinnability of polyolefins is a part of this development. 

That fall, Carothers assistant Edgar W. Spanagel discovered polyethylene terephthalate, the polyester that Du Pont later manufactured under license as Dacron fiber and Mylar film. Carothers had made most of the polyesters, but he and others in his group assumed that Spanagel s polyester, like their earlier ones, melted at too low a temperature to be practical. As a result, Carothers did not have this one tested for spinnability. British scientists later used it to make Terylene. When Du Pont executives had to buy a license from the British to make Spanagel s fiber, their faces were bright red with embarrassment. 

On February 28, 1935, Carothers project succeeded beyond anyone s wildest dreams. The cheerful, lively Frenchman Berchet produced a superpolymer made from chemicals derived from cheap benzene, a by-product of coal later they would be made from petroleum. A filament teased from Berchet s polymer was, despite its lowly origins, pearly and lustrous. And when it was tested, it proved to be spinnable. Its code name was 6-6 because both its reactants—hexamethylene diamine and adipic acid—had six carbon atoms. Technically, the filament was polyhexamethylene adipamide, a long-chain polymer similar in structure to proteins. It became world-famous as nylon. 

It was shown (1-3) that the silicon alkoxide solutions become spinnable when an acid is used as catalyst and the water content of the starting solution is small at less than 4 or 5 in the water to silicon alkoxide molar ratio. Recently, it has been found that this rule for the possibility of drawing fibers is only valid for the solutions reacted in the open system and no spinnability is found in the solutions reacted in the closed system (4). It has also been found that the addition of very large amounts of acid to the starting solution produces relatively large round-shaped particles, preventing the occurrence of spinnability (4). These will be discussed in the first half of this paper. 

Tetraethoxysilane-water-alcohol-hydrochloric acid solutions of appropriate compositions become viscous and spinnable in the course of hydrolysis and condensation of SiCCX Hs). Fig.l shows the time change of the viscosity of a Si(0C2H5)4 solution with the [H2O]/... 

It was assumed that linear polymeric particles are formed in the low water content solutions which show spinnability on the way of progressing hydrolysis-polycondensation reaction. In order to confirm this, the molecular weights and intrinsic viscosities of the solutions listed in Table 1 have been measured (2.). Figure 2 shows the log Mjj versus log[ri] plots. The slope of the plot a is larger than 0.5, that is, 0.75 and 0.64 respectively for solutions 1 and 2 of... 

It has been shown that the spinnability occurs in the silicon alkoxide solution when an acid is used as catalyst and the water content is small at less than 4 in the water to metal alkoxide ratio. 

Further examination has shown that the acid content should be small in order for the solution to become spinnable in the course of hydrolysis and polycondensation. It has been found (4 ) that very large concentrations at more than 0.15 in the [HCl]/[Metal alkoxide] ratio of acid catalyst produce round-shaped particles in the tetra-ethoxysilane (7) and tetramethoxysilane solutions, and so no spinnability appears. 

So far the results have been shown in which the metal alkoxide solutions are reacted in the open system. It has been shown that the metal alkoxide solutions reacted in the closed container never show the spinnability even when the starting solutions are characterized by the low acid content and low water content (4). It has been also shown from the measurements of viscosity behavior that the solution remains Newtonian in the open system, while the solution exhibits structural viscosity (shear-thinning) in the closed system. 

In our research,16171819 we first prepared a series of tris(/i-alkylamino)borazines that possess different pendent groups. This allowed us to investigate the effect of the nature of the /i-(alkylamino) substituents on both the viscoelastic behavior of the thermal properties and, therefore, the melt spinnability of the resulting poly[/i-(alkylamino)-borazines] polymers. 

Conversely, we have also confirmed that the presence of bridge-type bonds in po I y (/i-a I ky I am i n oboraz i nes) confer flexibility and improve processability, thus leading to the conclusion that melt spinnability increases going from polymers derived from 1 to polymers derived from 4. 

Copolymerisation is also possible (Fig. 4). Dimethyldisilane reacts with diphenylsilane with formation of a copolymer with the composition H[(MeSiHx)(PhSiHy)]nH. This copolymer is a viscous liquid and is spinnable. By heating to 180° C the polymerization continues and a solid results [23]. The presence of branched structures, which were not found with the polymerization of monosilanes, the very rapid polymerization rate achievable, and the observable SiSi cleavage points to another mechanism, as was postulated for monosilanes. 

The earliest work on silicon carbide fibers was done by Yajima and co-workers [3]. Yajima applied the Kumada [4] rearrangement to Burkhard s [5] dimethylpolysilane - an insoluble and infusible compound - (Eq. 1) and obtained by thermolysis at 400 - 450°C or by catalysis with polyborodiphenyl-siloxane at 350°C a melt spinnable and soluble polycarbosilane (Eq. 2). 

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