Abstract
Vacuum drying can dehydrate materials further than dry heat methods, while protecting sensitive materials from thermal degradation. Many industries have shifted to vacuum drying as cost- or time-saving measures. Small-scale vacuum drying, however, has been limited by the high costs of specialty scientific tools. To make vacuum drying more accessible, this study provides design and performance information for a small-scale open source vacuum oven, which can be fabricated from off-the-shelf and 3-D printed components. The oven is tested for drying speed and effectiveness on both waste plastic polyethylene terephthalate (PET) and a consortium of bacteria developed for bioprocessing of terephthalate wastes to assist in distributed recycling of PET for both additive manufacturing as well as potential food. Both materials can be damaged when exposed to high temperatures, making vacuum drying a desirable solution. The results showed that the open source vacuum oven was effective at drying both plastic and biomaterials, drying at a higher rate than a hot-air dryer for small samples or for low volumes of water. The system can be constructed for less than 20% of commercial vacuum dryer costs for several laboratory-scale applications, including dehydration of bio-organisms, drying plastic for distributed recycling and additive manufacturing, and chemical processing.
Highlights
Absorbed moisture can only be removed to the point of equilibrium with the air surrounding the material. This means that simple hot-air drying cannot make the plastic any dryer than the air in the room. This can be a major impediment to the successful use of recycled polyethylene terephthalate (rPET) in distributed recycling and additive manufacturing (DRAM) as for example simple air drying does not work in humid environments
The rPET tests each had 3% water by mass added to the sample prior to testing, and every sample showed a reduction in mass to below the initial ‘dry’ mass, indicating that additional pre-existing moisture was removed from the plastic during drying
Uneven heating in the chamber had negative effects on the drying rate while removing large amounts of water from a material because it caused evaporated water to condense on other surfaces in the chamber, rather than leave the chamber via the air ejector. This issue is dependent on the volume of water to be removed from the sample, so the oven is suitable for drying small samples of wet material and larger samples of fairly dry materials that need a deeper dry
Summary
The vacuum oven constructed in this study has two primary components: (1) a vacuum chamber and (2) a heating element. System performance was monitored with an open source precision mass balance [26] and multimeters
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