3D printing is becoming more and more prevalent in this day and age as it allows for detailed 3D models to easily come to life in a matter of hours using a 3D printer. For engineers as well, this tool is proving to be immensely powerful for quickly developing design prototypes and test parts. 3D printing falls under the umbrella of additive manufacturing, where raw material can be added to a growing object layer by layer until a desired geometry is achieved. This raw material can exist in many forms of metals and plastics, sometimes even as gases or vapours. In the case of 3D printing, most of these raw materials are often in the form of polymers or polymer solutions known as thermoplastics and thermosetting plastics. Thermoplastics are commonly used in manufacturing since they possess the ability to endure numerous melting and solidifying cycles. These cycles are reversible since no chemical bonding takes place in the melting process, allowing the material to easily be recycled and reused. On the other hand, thermosetting plastics remain permanently solid once cured. These plastics begin as a blend of monomers and polymers that are then linked together with the help of heat, light, or some other form of radiation. This process is not reversible and thus the material cannot be recycled and reused.
The two most common forms of 3D printing come in the form of fused deposition modelling (FDM), where thermoplastic is melted and extruded through a nozzle which deposits material layer by layer, and stereolithography (SLA), which uses a laser to photopolymerize thermosetting polymers. SLA printing uses polymer and monomer blends known as resins. Using such blends allows for an ever growing library of printable materials and for custom material properties, depending on the individual components within the resin mixture.
Developing new SLA resins can be research intensive and can take months of experimenting to really fine tune the properties of the printed material. However, the majority of SLA resin mixes ultimately involve a few key components: a blend of macromolecules (monomers, oligomers, and polymers), a photoinitiator, and, in some cases, pigments. Varying the types of macromolecules can tailor the material to be soft and flexible, hard and brittle, and anywhere in between! Using these basic concepts, scientists have developed a number of custom resins such as ones that are flexible, tough, heat resistant, impact resistant, and more recently, springy materials that can be used in 3D printed shoes! Though it can take months to develop a new material, there is bound to be a custom material waiting to be made for new 3D printing applications.