Printing materials
Contents
PrintingMaterials
In this section we will discuss a number of materials that can be used with RepRap and the ways to use them, as well as the core information needed for their successful application. Many of these materials will fall under the Polymer class (loosely called plastics). In time we will also discuss clays, plasters, cements, gels, and any other materials we think can be of use.
Polymers
Thermoplastic
The term thermoplastics applies to polymers that reversibly change phase with temperature. While keeping within a boundary of temperatures, these phase changes can be done safely and the material returns to it's original solid state after cooling, without any alteration in it's original properties.
See also WorkingWithThermoplastic.
Thermoplastics Data Sheets and where to get them
These are the various suppliers we've found. YMMV.
Polymorph (Polycaprolactone)
A useful plastic with a very low melting point that is hand-workable. You can use it to fashion your own parts without a machine, Its a tad bit expensive, but very handy. Check out the link above for suppliers.
HDPE (High Density PolyEthylene)
This is very common engineering plastic. It is used in a wide variety of consumer goods. Its strong, durable, and has a decent melting point. Its also very cheap. Theres a good chance that this may end up being the main working material of choice for RepRap.
ABS (Acrylonitrile Butadiene Styrene)
ABS is a general purpose, strong, and very resistant type of plastic. It is a bit more expensive than HDPE, but it also is a bit higher quality material than HDPE.
PLA (Polylactic Acid)
Polylactic acid is a cheap, biodegradable polymer, that is produced from Lactic acid, which can be obtained from the maceration of starch and sugars in biotanks.
PP (Polypropylene)
Abbeon Cal $10 / lb
Non-Thermoplastic
Non-Thermoplastic polymers are plastics that once hardened cannot reversibly change phase (molten) through heat. Solvents may dilute them and by evaporation of the solvent they can harden again. This application, very common in solvent based varnishes and paints, is nevertheless not practical for RepRap, as the volatile solvents take a long time to evaporate and in large sections or layer thickness this evaporation cannot be regulated and controlled so as to produce a uniform deposition layer (bubbles, hardening imperfections).
The most common application of Non-Thermoplastics happens through chain reactions between monomer (oligomer) blends, whether initiated by catalysts and radicals that spring from reaction with moisture, oxygen, radiation or heat or auto-intiation with another identical monomer or a suitable copolymer. some polymerisation can be initiated by a simple change in pH, by adding an acidic or basic reactant (furfural resins, phenol-urea, phenol-formaldehide...)
For rapid prototype deposition, Non-Thermoplastic polymers have to fulfill a number of conditions:
1) They have to have a long work time frame, meaning that they have to remain fluid, preferably without any changes in viscosity and state for the whole time frame of the deposition session. Failing to do so would mean that the depositing tool may get clogged and that the deposition process would entail errors due to variations in flow rates.
2) They have to have the correct viscosity and plasticity, so that after deposition they don't sag or change shape noticeably. Additionally, at no moment during the hardening process should the volume of the polymer change severely.
3) After deposition they have to have suitable adhesive properties so that threads glue together with the best resulting bond strength.
4) Once deposited, there has to exist a mechanism by which the polymer will start to set or harden, if possible, on command. this point will be discussed under the section Catalysts and Initiators
These conditions are less restrictive if you want to use the polymers as a casting resin to fill molds built by the deposition technique. The generic term for the largest groups of polymers with the above mentioned properties is Resins.
Dual Component Resins Data Sheets
In this section we will list resins that need to be stored in two separated components for them to remain stable for long periods of time. They have to be mixed in a given proportion just before usage and start the polymerization chain reaction as soon as the two parts are in contact.
Polyester Resins (Isophthalic, Vinyl Ester, Marine, General purpose, Casting Resin, Surfboard Resin, Gelcoat)
Epoxy Resins (Thin coat, thick coat...)
Single Component Resins Data Sheets
In this section we will discuss resin blends that can be mixed in their final composition and still be kept unchanged for long periods of time. They will only start polymerizing after having been given the right trigger effect (see Catalysts and Initiators) [[|]]
For the following list of products I have found this site that provides chemical products all over the globe. They have good prices and seem to be ok at delivering through a global network of retailers:
Go to their web and search for the keywords listed below (you will have to register to get prices and place orders):
Phenol, Cat N� MFCD00002143 (Copolymer to Furfuryl alcohol and Urea) Urea, Cat N� MFCD00008022 (Copolymer to Furfuryl alcohol and Phenol) Furfuryl alcohol Cat N� MFCD00003252 (Copolymer to Phenol and Urea)
Other Additives, Monomers, Fillers
Fillers, Glass spheres, glass strands
For Organic products I have found this site that provides chemical products all over the globe. They have good prices and seem to be ok at delivering through a global network of retailers:
Go to their web and search for the keywords listed below (you will have to register to get prices and place orders):
Benzophenone, catalogue number MFCD00003076 (Photoinitiated catalyst)
Catalysts and Initiators
There are 3 chemical types of catalysts that are of use to RepRap. All of them, independently of their chemical type, fall into two categories. The category they fall in is actually more important to RepRap than the chemical type and these categories will require most of our attention.
[ImmediateCatalysts The first category] starts the polymerization reaction as soon as it comes in contact with the monomer. We could call this type immediate catalysts. They do not need any further external input to fulfill their initiator role, be it heat, moisture, radiation (UV, visible, IR...). There are many examples of dual component polymers available in the market that illustrate this behaviour. Most of them are epoxys and are excellent materials as well as versatile. Some dual polymer mixes are in a 1:1 proportion or similar and could be counted in the auto-initiated sub-category of polymers. Nevertheless, for our purposes, both cases have identical applications and usage parameters.
[TriggeredCatalysts The second category] we could call triggered catalysts. These need a triggering effect to start their initiator role. This is an obvious advantage as they can be blended in the monomer mix and be kept on the shelve for significant amounts of time (days to months). They will not clog any tubings, pumps or dispensers. Also, they offer one more level of control, being able to decide when and where to apply the trigger effect and possibly also when to stop the chain reaction. These triggered initiators are usually more expensive as the first category, if what you are looking for is a rapid reaction producing fast setting times. One example is the acrylic based tooth filling the dentists use, that are triggered by UV light. Many varnishes are also UV triggered but they have a much longer setting time and require hour-long exposures to achieve definitive hardening.
Catalysts for dual-component mixes
Monomers, MEK-Peroxide hardener for polyesters
Benzoyl Peroxide hardner for polyesters
Catalysts for single-component mixes
Glossary of Terms and Definitions
Catalysts
Copolymers
Copolymers are additives that are included in the polymer blends with the intention to add certain properties to the main polymer. All polymers have principal properties that are desired, but bring others that are not. A good example is Styrene, which is clear, has great accuracy when molded into a shape but is very brittle and ages bad under sunlight. In certain commercial varnishes Butadyene can be added to give it some flexibility and UV protectors to make it more durable. The difference between copolymers and fillers is that the first ones participate in the chemical chain reaction and are bonded to the main monomer.
Curing see Setting
Filler
Fillers are solid materials that are added to polymers (or cements) and that do not interact chemically with it. They remain inert but do add special desired mechanical features to the compound. These can range from density alteration (make the compound heavier or lighter) additional strength (fibers...), resistance to abrasion and improved thermal properties (sands...) or simply thinning the compound so as to make it cheaper in average.
Hardening see Setting
Monomer
Oligomer
Oligomers are big molecules composed of monomer bricks, joined together in more or less branched fashion, so as to provide polymerisation seeds for the final polymer. A free analogy would be that monomers are to oligomers what a water molecule is to a snowflake. In commercial resins, oligomers are mixed with their monomer components so as to achieve a polymer of desired properties, due to their ability to spatially organize the polymerization process.
Setting
Viscosity
Viscosity is a property of fluids determining it's resistance to flow. The higher the viscosity, the more difficult a material will be to extrude or dispense (more energy/pressure will be needed). Also, the higher the viscosity, the less the deposited thread of material will sag or change shape until hardening(setting). For a detailed definition see: Wikipedia:Viscosity
