As stated in the description, the goal is to create parts that are biodegradable and made from renewable materials. If a part is 80% wood, but bound by a plastic it loses a lot of the advantages. Wood filaments for FDM printing for instance do gain the feel and sometimes smell of wood, but are ultimately still made of plastic with all the drawbacks thereof.

The challenge of creating a 3DP powder that is fully degradable and renewable is that a lot of common solutions do not meet the given requirements. The specific problems that need to be solved are:

Creating a binder

The binder is sprayed into the powder using an inkjet printhead. In my case the HP45. The HP45 is a thermal inkjet (TIJ), so it can handle water based fluids. TIJ heats a fluid to expel it from the printhead. This means that fluids that burn before vaporizing, or leave deposits when they are vaporized are not usable in printhead. Also the boiling point needs to be close to water.

Luckily, while the fluid is called the binder, it usually does little binding itself. Most of the work is usually done by the powder. The binder can therefore be a simple mix of water and alcohol. People have printed with neat vodka or sake with great success.

Other ingredients are surfactants and if the particles are small enough pigments. Binders with glues do exist, but none are specifically known by me.

Creating a powder

The powder consists off several steps.

• The base material: The material which will make up the bulk of the powder. In this case it will be organic powders such as wood flour, ground nuts and maybe coffee grounds.
• The glue: The material which solidifies when it is hit with water, through various mechanisms. Known glues are:
  
  • PVA powder
  • Maltodextrine (a starch)
  • Sugar
  • Urea-formaldehyde (also called plastic resin glue)
• The stabilizer: A material which add extra properties to powders, such as better spreadability, or making the material more hydrophobic of hydrophilic, to prevent wicking from printed parts to unprinted parts. This includes materials like corn starch.

Creating a good powder is getting the mix right on all of the above points. The goal is to create a part which can be handled and cleaned before the next step.

Creating a post processing step

3DP printed parts are notoriously weak. The strength right out of the printer (called green strength) is usually only enough for some basic handling. Parts right out of the printer are rarely strong enough for real work. A few ways to strengthen cleaned parts are:

• Baking the parts in an oven (either household oven or ceramic oven, depending on the powder)
• Infiltrating the part with a glue like CA glue or epoxy
• Infiltrating the part with a molten material which solidifies like wax or metal
• Soaking the part in water or another fluid which activates something in the part
• Subjecting the part to a gas which activates something in the part

The ultimate goal is to make the part strong enough to be actually used. How strong this is depends on what the expected use is.

Bonus points

Given that we want to create a part in wood, there is one more thing which can be done. Do more to make it look like wood. We work in wood powder, which is an even color, but 3DP, being an inkjet based technique, can add color to parts. While Oasis in it's current form cannot print in color, but this would be a great addition.

Previous work

No work gets done in a vacuum, and this is no exception. A great deal of research has been done by open3DP (https://depts.washington.edu/open3dp/). Even wood has been done already, though it has not been perfected yet in my opinion (https://depts.washington.edu/open3dp/2011/04/woodnt-you-know-it-3dp-in-wood/)

Other links of interest are:

• http://www.evillabs.net/index.php/ZCorp_Z310%2B#Materials
• The book "Printing architecture" by Ronald Rael and Virginia San Fratello