PVA or polyvinyl alcohol is a relatively rare material in industry and is usually very difficult to process. Water acts like a plasticizer for PVA and the material is water soluble. This means that any humidity can adversely affect its performance and even eventually break it down. PVA is used in glues and also in bait bags for fishing carp for example. Bait is inserted in the bag and this is put into the water to attract fish. Once the bait bag dissolves in water, the bait spreads around the hook leading to more fish more likely to bite. The fact that PVA is water soluble and considered safe means that for a number of years it has been seen as the ideal support material for FDM 3D printing.
Fused Depositioning Modeling (FDM, also called FFF) systems use a nozzle to extrude and lay down plastic filament such as ABS or PLA. A build platform is then lowered and a new layer is applied. Industrial 3D printing systems have long used a second nozzle to extrude a sacrificial support material to support overhangs in the 3D print. This material is later removed. Sometimes supports can be a breakaway support structure or a material that has a lower head deflection temperature or strength than the build material. Stratasys, the company that invented FDM, has a wax support material for example. The company also has a PPSF support material (polyethersulfone), a polystyrene support material which is meant to be removed manually and a water soluble support material called 2-Propenoic acid, 2-methyl-, polymer with methyl 2-methyl-2-propenoate which is an acrylic and another which is a Terpolymer of Methacrylic Acid, Styrene, and Butylacrylate. Depending on the 3D printing process, the build material and the requirements of the part, many different supports are available.
For the desktop 3D printing community however PVA is the most researched and most coveted. PVA’s environmentally friendly characteristics coupled with the ease of use in removing the supports have lead to many companies looking into it. PVA is however notoriously difficult to keep. It must be dried before use. Even then, in a normal room PVA can quickly be adversely affected by water. In some cases a mere 12 hours in a room may degrade the material considerably. During normal 3D printing operations the material can also degrade much faster than other materials. What we discovered in our experiments with the material is that in addition to these issues care must be taken when extruding it. Any PVA remnants inside nozzles for example can wreak havoc on subsequent 3D prints and extrusions. Tricky stuff, PVA. This is also one of the reasons (along with nozzle lifting and software) while dual extrusion and support material on desktop 3D printers is so difficult to do. Many companies have researched dual extrusion and are trying to implement it. The difficulty of working with the engineering, software and material however has lead to only precious few 3D printing companies actually being able to make dual extrusion with PVA a reality. Even of those who say they can do several can not reliably do it.
After drying out and extruding the material we were able to create good PVA filament with it in less than half a day of testing. The material was tested in prints and as a support and performed well. We will share our learnings with customers who are interested in making or developing their own PVA filaments.