Thermal Drawing of Fibers
Two variations of protein fibers were produced: gelatin and zein.
We developed fibers comprised of gelatin and glycerol at ratios of 70:30 and 50:50, respectively, by weight. Gelatin is a protein obtained from denatured collagen. Collagen, found in connective tissues, is animal-derived.
Why did we use a material that is not a plant protein to make fibers?
The concept of thermally drawing protein fibers was demonstrated in a paper by Sordo et al., in which gelatin glycerol fibers were thermally drawn. After constructing our device, we wanted to put it to the test with materials that had already shown to be capable of thermal drawing. The other material in the preforms, glycerol, is an edible liquid that acts as a plasticizer in our fibers. A plasticizer decreases the viscosity of a material, increasing its flexibility.
The gelatin mixture started as a hydrated powder, which solidified after heated centrifugation. This method of preparation enabled us to create a preform in a conical tube which could be removed prior to drawing. We found that holding the preform with pliers was the most effective method to stabilize it during the drawing process.
Once the preform was heated enough to soften, it could be manually pulled to a thin fiber. Due to heat dissipation within the hollow of the heating block, the preform had to make contact with the side of the block to heat sufficiently for pulling.
The other version of fibers we produced were zein and glycerol, with 55% zein and 45% of an aqueous solution of 33% glycerol. After demonstrating the efficacy of our device at thermal drawing, we tested it with plant-derived materials. Zein is a bright yellow protein found in corn. It is edible and previously demonstrated success in being drawn into fibers.
The zein powder became a moldable dough after an initial heating. However we found that it dehydrated quickly during drawing attempts, becoming hardened and resistant to drawing. We had success with containing the zein powder mixture in a plastic syringe which was placed within the hollow of the drawing device.
Once the powder became a dough, the syringe could be pressed to extrude the material. We continued to pull the extruded material manually to create a thinner fiber.
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