Processing conditions fiber spinning

Post-die processing includes a niunber of operations carried out at the exit of the extruder die in a free-siuface way. Examples of such processes are fiber spinning, film blowing, and sheet forming. The shape and dimensions of the extrudate material are determined by the rheological properties of the melt, the die dimensions, the cooling conditions, and the take-up speed (relative to the extrusion rate). 

Table 8.43. Process Conditions for Spinning Multifilament Perfluoropolymer Fiber ...

The stmcture and properties of viscose fibers can be controlled by selectively modifying the viscos process conditions. Fibers can be made with a symmetrical cross-section or a variety of cross-sectional shapes. By controlling the spinning conditions, the fibers can be spun in a form of skin-core stmcture. By using additives either in the viscose solution and/or in the coagulation bath, high-wet modulus fibers can be produced. 

Process conditions that favor chemical crimp formation are similar to those used for improved tenacity staple (2inc/modifier route). However, spin bath temperature should be as high as possible (ca 60°C) and the spin-bath acid as low as possible (ca 7%). Attempts have been made to overcome some of the leanness of high strength rayons by increasing the crimp levels. ITT Rayonier developed the Prim a crimped HWM fiber (36) and made the process available to their customers. Avtex developed Avdl 111. Neither remain in production. 

Spinnerette Process. The basic spinning process is similar to the production of continuous filament yams and utilizes similar extmder conditions for a given polymer (17). Fibers are formed as the molten polymer exits the >100 tiny holes (ca 0.2 mm) of each spinnerette where it is quenched by chilled air. Because a key objective of the process is to produce a relatively wide (eg, 3 m) web, individual spinnerettes are placed side by side in order that sufficient fibers be generated across the width. This entire grouping of spinnerettes is often called a block or bank, and in commercial production it is common for two or more blocks to be used in tandem in order to increase the coverage and uniformity of laydown of the fibers in the web. 

Depending on the final polymerization conditions, an equilibrium concentration of monomers (ca 8%) and short-chain oligomers (ca 2%) remains (72). Prior to fiber spinning, most of the residual monomer is removed. In the conventional process, the molten polymer is extmded as a strand, solidified, cut into chip, washed to remove residual monomer, and dried. In some newer continuous processes, the excess monomer is removed from the molten polymer by vacuum stripping. 

Meh Spinning. This process is used to produce a broad range of polypropylene fibers ranging from fine, dtex (one denier) staple coarse continuous filaments. Hoiuopolyiners are almost exclusive used to produce fibers, although copolymer blends are used in some special applications. Processing conditions and polymer melt flow vary with the desired fiber type. 

The mathematical formulation of the fiber-spinning process is meant to simulate and predict the hydrodynamics of the process and the relationship between spinning conditions and fiber structure. It involves rapid extensional deformation, heat transfer to the surrounding quenching environment, air drag on the filament surface, crystallization under rapid axial-orientation, and nonisothermal conditions. 

Fig. 14.11 Schematic representation of fiber spinning process simulation scheme showing the multiple scale simulation analysis down to the molecular level. This is the goal of the Clemson University-MIT NSF Engineering Research Center for Advanced Engineering Fibers and Films (CAEFF) collaboration. CAEFF researchers are addressing fiber and film forming and structuring by creating a multiscale model that can be used to predict optimal combinations of materials and manufacturing conditions, for these and other processes.

Extensional viscosity can, depending on process conditions, therefore affect the homogeneity of the film thickness or the evenness of the layer thickness in coating processes. Extremely high extensional speeds can occur in spinning as the fibers are drawn... 

During fiber spinning they can be exposed to different conditions. Different type finishes can be applied after cooling in-line to meet different requirements that include permitting processing improvement... 

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