Solution-spun fibres,

Until the 1970s there was a substantial gap between the theoretical modulus of polymer chains and the practical stiffness achieved in the existing processes. Since then the fibres made by extended chain crystallisation have bridged this gap. Solution spun fibres of high molecular linear polyethylene have been prepared with a Young modulus (at low temperature) of 90% of the theoretical value. Tables 19.9 and 19.10 illustrate the whole extent of elastic moduli in the various materials. 

Although there are no data for the creep behaviour of solution-spun or gel spun fibres of a comparable nature to those for the melt spim and drawn materials, a few results can be presented. 

Fig. 38. Curves fitted to plateau creep data on the basis of the two-process model with no constraint on parameters ( ) Rigidex 50, X = 20 (X) 006.60, X = 20 (A) y-irradiated Rigidex 50, X = 20 (O) H020, >. = 20 (o) Hostalen GUR, solution-spun fibre...

Solution polycondensation, i.e., where the monomers and polymer are soluble in the solvent(s), is also kinetically controlled. It is closely related mechanistically to reactions in the melt, but the choice of the solvent may influence both the rate and equilibrium, and hence the molecular weight. This process is utilized commercially in the production of a variety of organic coatings and certain solution-spun fibres, e.g., certain spandex types and also very high-melting aromatic polymers. 

Although it had been appreciated since the early studies of Meyer and Lotmar 11 in the 1930 s that there was a substantial gap between the theoretical stiffness of the chain in several commercially available polymers and the achievement of stiffness by existing processes, it was not until the 1970 s that this gap was bridged. It is in polyethylene that the results have been most dramatically realised, and oriented fibres and rods have been produced with room temperature Young s moduli in the range from 50-100 GPa 2-7). Solution spun fibres have even been prepared with a Young s modulus at low temperatures of 288 GPa 8), which is very close to the highest theoretical estimate of 324 GPa 9). 

Aramid fibres are aromatic polyamides. Therefore, the presence of the polar and hydrolysable amide group introduces the potential for moisture absorption up to 5%. As a result, these fibres exhibit time-dependent loss of strength or static fatigue in aqueous environments [28,29]. The fibres are spun from sulphuric acid solution so that residuals might be responsible. These fibres are also highly susceptible to hydrolysis in alkaline environments. As with other polymers, aramid fibres are... 

Eling, B., Gogolewski, S. and Pennings, A.J. (1982) Biodegradable materials of poly(L-lactic acid) 1. Melt-spun tmd solution spun fibres. Polymer, 23,1587-1593. 

Hoogsten W., Postema A.R., Pennings A.J., Brinke G., Zugenmair P., Crystal structure, conformation and morphology of solution-spun poly(L-lactide) fibres. Macromolecules, 23, 1990, 634-642. 

In addition to solution-spun textile fibres, granular breaks are also found in some carbon fibres, which reflect their acrylic fibre origin, and in alumina fibres. Granular breaks are also shown in the natural fibres, wool and hair, in cotton at zero moisture content, and in resin-treated, cross-linked cotton at intermediate humidities. 

Fracture Fatigue Defects Cracks Cotton Wool Melt-spun synthetics Solution-spun fibres... 

Regenerated cellulose, cellulose acetate, acrylic and some other fibres are spun from solution, either by dry spinning, with evaporation of solvent, or by wet spinning into a coagulation bath. In viscose rayon, the solute is sodium cellulose xanthate, which is a chemical derivative of cellulose soluble in caustic soda, so that a chemical reaction is involved in fibre formation. 

The synthesis as well as the structure and properties of aromatic polyimides has been reviewed.This combination of synthesis, structure, and properties is a general characteristic of papers in this field. For example, the preparation of polyimides from di-isocyanates, poly(o-amino-o-carbonyl)amides, maleimides, and Af-(4-substituted phenyl)itaconimides, all follow this pattern. The preparation of polyimide fibres, wet spun from solution, has also been given. ... 

Moulded polybenzimidazole has the highest compressive strength of any unfilled resin (400 MPa), of 427 "C and HDT of 435 °C. It can withstand temperatures of 700 °C for several minutes. The LOI is 58%. However, it is degraded in hot aqueous acids. Poly benzimidazole can be solution spun into fibre and is extensively nsed in fightfighters clothing and other fire blocking applications. 

Figure 8 shows the effect of changing the air gap on the wall thickness of hollow fibres. The fibres were spun from a solution of 23% PPO in trichloroethylene with 2% 2-ethyl-1-hexanol, at a flowrate of 1.5 ml/min and a bore liquid flowrate of 2.0 ml/min. They show a reduction in the wall thickness from 0.04 to 0.03 mm as the air gap is increased from 29 to 88 cm. 

Solution processes are used mainly for coating, film casting and fibre spinning, i.e. in processes where the distance the solvent has to diffuse out of the solution once coated, cast or spun is short. Regulation of this diffusion process is important if products of even quality are to be obtained. 

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