In melt spinning, the polymer is melted and this liquid is extruded into fiber as it hardens. In dry spinning, the polymer is dissolved into solution, and the solution is evaporated out as the fiber is drawn. In wet spinning, the polymer is extruded into a coagulent bath, which either extracts the solvent or else catalyzes a crosslinking reaction to form a fiber. In each of these processes, fibers will typically be extruded through a spinneret. The cross section of the fibers can be fairly precisely controlled by changing the shape of the spinneret extrusion holes, and different material properties correspond to different shapes. For example, a fiber with a more star/gear shaped cross section made of a hydrophobic material will perform better wicking than a circular cross-section will.
The top row are natural fibers (cotton, wool, silk) and the bottom row are synthetic fibers. These fibers are extruded as filament (on the order of many km in length), though are not typically used at this length. Instead, post processing steps such as chopping are performed, and the resultant shorter lengths will be spun into yarns for material qualities more similar to natural fibers. Other post processing steps such as crimping can also be done (see below image). Crimping can be done to improve the thermal insulation of the yarn (more space occupying) or to incorporate mechanical stretch/elasticity into the resultant yarn. Some synthetic fibers will not be chopped, for example aramid (twaron, kevlar) fibers will be spun at longer lengths to preserve the high strength of the yarn (breaking fibers requires more strength than sliding them past each other). ### yarns Once we have a bunch of nice, oriented fibers, we want to produce yarn or thread. (The term thread is more commonly used to refer thread :p heading toward sewing applications, while it seems yarn is more standard for things headed toward getting turned into fabric). The production of yarn typically occurs through a process of twisting and plying. Twisting and plying are similar processes; twisting usually refers to going from fibers to yarn while plying refers to combining yarn. Twisting and plying will both have directionality, referred to as either S or Z twist (see image below). It is very common for yarns to be combined with each other using the opposite twist to help prevent unraveling (e.g. we have made 3 S twist yarns, which we will now spin together into one thicker Z twist yar). This image from the 2019 recitation illustrates this well: If you look closely at the inset, it looks like a bundle of three Z twist yarns plied with a S twist. [Studio Hilo](https://www.studiohilo.com/) has an open source CNC yarn twister that's very cool.
![alt text](https://media.springernature.com/lw685/springer-static/image/art%3A10.1038%2Fs41586-021-03295-8/MediaObjects/41586_2021_3295_Fig1_HTML.png?as=webp)#### Bio-fibers and electrospinning - [Electrospinning](https://en.wikipedia.org/wiki/Electrospinning#)
This shows the basic topologies for weaving, weft knitting, and warp knitting. ## weaving Weaving! (for a more coherent overview of weaving, I would go to here)
This diagram shows a traditional loom set up. Individual yarns run along the length of the loom (the warp) and are pulled up and down using heddles. The space formed by one set of warps pulled up is the called the shed (this step is called shedding). The weft yarn runs through the shed (called weft insertion, traditionally, it is moved as a spool (shuttle)) and is packed using a reed (called beating up). As the cloth is formed, it gets collected in the chest beam and more warp is released from the warp beam. This image (sourc: here) shows the structure of the most common weave patterns. These structures can result in very different fabrics! E.g., satin weave is designed to produce glossy fabrics by having longer sections of "floating yarn" (continuous runs of yarn). In Jaquard looms, each heddle is individually addressable and the process for choosing them is programmed and automatic. This enabled the production of cloth in a variety of highly complex patterns, with much less overhead for setting up new patterns. This video shows the operation of a historical Jaquard loom:
A resource for different sewing machines explained A resrource for how to sew, making sewing patterns, etc. ### Embroidery We have an embroidery machine! Camron's tutorial: https://gitlab.cba.mit.edu/camblackburn/inkstitch Here is a #produced video on machine embroidery that emphasizes a few interesting techniques that could be of interest to you: Some examples of cool stuff: http://fab.cba.mit.edu/classes/863.18/Harvard/people/lara/week13.html [Embroidered Speakers Without Permanent Magnets](https://www.media.mit.edu/publications/sonoflex/)