Team:UGent Belgium/Filament
Filament
Overview
The general idea is to dissolve PLA and biotin in a solvent that allows good dissolvement for both components without destructing or changing their inherent character. After dissolving the PLA and biotin, the PLA (and hopefully the attached/included biotin) must be solidified again. The solidified PLA should be melted and formed into pellets that subsequently can be fed to an extruder to make PLA filament with biotin. The PLA-biotin filament can then be used to print our awesome water collector whereon proteins can be adhered via the well known biotin-(strept)avidin interaction.
Dissolving
From literature, we found that heated DMF (dimethylformamid) could be a good option for dissolving solid PLA and biotin, without disrupting the polymer or destroying the biotin. Due to the momentarily lack of biotin in the lab, we already went out and test the solubility of PLA in hot DMF and succeeded to dissolve 0,55g PLA in 8ml (68,75 g/l) without reaching its maximum, although the viscosity did increase by the end, by heating DMF in a hot oil bath (80-90°C) with a reflux column for safety (see set-up in picture on the left).
Solidifying
After dissolving the PLA, we wanted to precipitate it. Since DMF is miscible with water and ethanol, and PLA is not, we wanted to alter the polarity of the DMF by mixing it with either of those, and doing so, forcing the PLA out of solution. Since PLA is hygroscopic, we used room temperature ethanol and just added the hot DMF directly to it, resulting in a cotton-like debris (PLA). This was washed again with ethanol and dried in a 70°C oven.
Melting
Since PLA pellets for extrusion should be solid and not bigger than 4mm³, and not like a ball of cotton, we tried to melt it in a test tube using a Bunsen flame. This resulted in baking, discoloring and thus destroying of the polymer, probably due to too direct and too hot.
Another setup we tested (not with the cotton, since it was already spent, but with normal PLA filament) is a very controlled increase of temperature using a hot oil bath and calmly increasing the temperature up until melting of the PLA without baking. A completely see-through solution was obtained. We cooled it down and obtained a solid pellet which can be reduced in size by simple mechanical force (mixing, cutting...).
Upcoming
- When the biotin arrives, redoing the steps with biotin in mixture
- Testing biotin availability after solidifying
- Making filament when extruder is finished
