Spinnability of Polymer Melts – a Complex Problem in Basic Research¹⁾

Abstract

Melt spinning of polymer melts is a formation process makingextremely high demands on the material's continuous deformation ability by highest deformation speeds. The structural conditions of a thermoplastic polymer which are necessary for spinnability have not been exactly cleared up yet. But this knowledge gap must be closed especially with regard to the many efforts to spin fibers with new properties made from modified polymers or polymer blends. The article is begun with a pragmatic definition of the spinnability of a polymer melt. The discussion of a structural rheological model shows a correlation between dynamic rheological measurement datas of polymer melts and experimental experience about their spinnability. Proceeding from a comprehensive description of possible failure cases (fiber beak problems), results of rheological measurement of a number of different polymers, which are spinnable well, not as well or not at all, are compared. The article is concluded by some comments on open problems which have to be solved by basic research in the near future.

High‐speed melt spinning of various grades of polylactides

“…This ratio may be seen as one important factor for the spinnability of polymers. For commercially used spinnable polymers, the ratio is about 10 16. The master curves of G ″ versus G ′ of the single PLA types are shown in the so‐called modified Cole–Cole plot (Fig.…”

Rheological and Theoretical Estimation of the Spinnability of Polyolefines

“…In the melt spinning process a short time load occurs for the polymer with rapid increase of the extensional strain and simultaneous extreme cooling between spinneret and winding point [1]. From the point of view of rheology this uniaxial extension is a`strong¯ow' because it tends to generate a high degree of molecular stretching and orientation [2].…”

“…

Melt spinning is a polymer processing technique that makes great demands on the extensibility of the polymer melt in the distance between die exit and solidi®cation point [1]. The polymer material is exposed to a rapidly growing deformation rate over a large range of deformation within a short time of about 100 milliseconds.

…”

Melt-Spun Fibers for Textile Applications

“…Note that the maximum allowed extrusion temperature can fall well below the decomposition temperature T d quoted in Table 2 , while some polymers have their melt-processing window near T d . In addition, such thermoplastic polymers should ideally have the following properties to ease processability and to yield sufficient fiber properties [ 8 , 9 , 10 ]: withstand extrusion temperature and shear strain at minimal degradation and without crosslinking (thermal stability); have sufficiently high molecular weight and thus enough melt-strength to prevent filament break under draw-down strain (too high molecular weight and thus too high viscosity can hamper processability); exhibit small polydispersity (narrow molecular weight distribution) to ensure consistent melt flow rheology (constant flow); have high enough mobility of the molecular chains to disentangle and unfold under stress and to orient in fiber direction under strain (linear polymers are most suitable); show high uniformity and purity to prevent fluctuations and blockage in processing. …”

“…The degree of orientation in the filament depends on the extent of spin-line stress, which increases with decreasing melt temperature, with increasing molecular weight of the polymer, as well as with progressing quench and stretch rates [ 7 , 145 ]. However, too high viscosity and too fast cooling can subdue the drawability of the filament and prevent the necessary degree of deformation before the start of solidification [ 10 ]. Thus materials with long relaxation times and low spinnability are often spun into a post-heater (hot shroud) installed under the spinneret to improve stability, lower pre-orientation and reduce the solidification rate [ 7 , 146 ].…”