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What happens to fibres in the coagulation bath during wet spinning?
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Figure 1: Three common polymer structures. The linear, branched, and network architectures are represented (from top), respectively, by high-density polyethylene (HDPE), low-density polyethylene (LDPE), and phenol formaldehyde (PF). The chemical structure and molecular structure of highlighted regions are also shown.
In the wet spinning process, the spinnerette is typically submerged in a coagulation bath, also known as a spin bath.1
Within this bath, two simultaneous diffusion processes occur:
* The solvent used to dissolve the polymer diffuses out of the extruded material.1
* A nonsolvent, which is typically water, diffuses into the extrudate.1
This exchange causes the polymer to coagulate, forming a gel. During this stage, the resulting gel may be oriented by stretching, or the freshly formed fibres may be stretched after they are removed from the bath. Following coagulation, the fibres—which still contain solvent and nonsolvent—are washed with additional nonsolvent, treated with a lubricant known as a fibre finish, and dried on heated drum rolls.1