When a part takes 15 hours to print and it breaks, a little chemistry can come in handy. Besides, who doesn’t want take two parts and want to stick them together. Want to know if/how to solvate a polymer? Skip the gnarly home cocktails of ABS & turpentine and learn how to make a good chemical bond below.
Chemical Bonding: Adhesives to English description
[Acrylic] =>Super Glue [Cyanoacrylate]– water [a weak base] on the surface of the part neutralizes the stabilizer [a weak acid] in the super glue and causing to set quickly [aka anionic polymerization]
When to use Super Glue [cyanoacrylate] generally if it has the word acrylic in the name. Cyanoacrylate and acrylic [PMMA, MMA, etc] based polymers can get good bonding at the molecular level.
[ABS, PVC, HIPS] => Acetone and Methyl Ethyl Ketone [MEK aka 2-Butanone] will dissolve both ABS and PVC and chemically rebuild the joint in a less ordered manner as the solvents dries. It essentially adds enough chemical energy to allow the polymer to move around an re-order itself for several minutes before the polymer runs out of energy and sets.
More explanation here: ABS plastic & Solvents: 4 good ideas
Sidenote: Acetone can often instantaneously dissolve polymers with lots of styrene. Styrene [Benzene] groups are prone to ring opening. This is when the benzene ring breaks open and releases a fair amount of energy. ABS will not have this behavior, but it is good to do a test piece before address other styrene polymer eg. “High Impact PolyStyrene”[HIPS]
Bonds to other silicones.
Rubber and Latex
Both rubber and latex are important for 3D printing allow parts to be designed with flexible joints, gaskets, sleeves etc. Rubber cement can work surprisingly well. However latex and many robust rubbers need to be primed or dissolve with N- heptane is a good solvent for latex and most rubbers. Bestine makes a good rubber (with N-Heptane) cement that can bond to both.
Ninjaflex is a good example of a flexible polyurethane. Polyurethane based adhesive can bond on a molecular level with polyurethane parts. Gorilla glue is cheap effective and readily available, flooring and wood finishes offer a mixture for finer applications.
PP [#5] will fuse to most of the polyethylenes. It is fairly solvent resistant, but polyurethanes will interact with the polymer.
It is best to avoid these polymer solvents
Nalgene /Poly Carbonate[PC] – Methylene Chloride dissolves this along with a long list on MeCl based cocktails. [Which means use gloves, goggles, proper ventilation and/or a good respirator] A better alternative for polycarbonate friction fusion. PC has a pretty good friction/heat fusion like PLA.
PolyLactic Acid [PLA] can be dissolved in Bases like, weak concentrations of Lye and Isopropyl Alcohol … however this mix can cause damage to the nervous system. [Which means use gloves, goggles, proper ventilation and/or a good respirator]
These polymers just don’t dissolve. [except with superacids and other complex chemistry.
Kinetic bonding– polymers that can’t be chemically bonded easily, can be fused with ultrasonic welding or with high heat. Layer to layer fusion with heat is one of the main principles that many 3D printers rely on. The extrusion temperature for the polymer is also the welding/fusion temperature. Parts can be bonded manually with the appropriate application of heat.
These polymers are all extremely resistant to acids/bases and solvents.
#1 Poly Ethylene Terephthalate [PET]
#2 High Density Poly Ethylene [HDPE]
#4 Low Density Poly Ethylene [LDPE]
High Molecular Weight Poly Ethylene [HMWPE]
Five rules to help a reader answer their own solvent questions.
There are some solvents you should avoid, teratomas [tumors] and liver toxicity are not worth it. Don’t risk your health and don’t waste your time.
[Chemists out there… stop cringing at the gross generalizations… the DIY folks will be fine].
Rule 1: Read the back of the label… that is where the real information is.
Business often gets in the way of industry information by creating catchy buzz words and brand names. On the back of any product there should be a list of ingredients. This will inform the reader about what family of polymer, adhesive, etc that a product belongs to. The if the warning labels and ingredients don’t explicitly tell the contents check the MSDS sheets for the product. Often the name of the solvent with sound similar to the material name…[Thank you scientific naming conventions]
e.g. cyanoacrylate (super glue) & methylmethylacrylate (acrylic)
Rule 2: Like dissolves Like… this is one of the universal axioms that holds our universe together.
Greasy things are solvated by greasy things, polar things are dissolved by polar things. Think oil and water, they don’t really dissolve each other, they create an emulsion. Where does your polymer lie on the greasy to polar spectrum.
Thanks again Wikipedia you are worth every penny.
Rule 3: Acid Base Chemistry Exists… Deal with it.
Things like PolyLactic Acid are dissolved in Bases like, weak concentrations of Lye and Isopropyl Alcohol. Get cozy with the periodic table. The electronegativity arrangement and electron shell information comes in handy. Polar groups bond to polar solvents. Hydrogen bonding is the giant electromagnet of the polymer world. This means water [super polar] and alcohols [polar but greasy] are good at dissolving things. Why does acetone work well? It is so tiny it fits into most small polymeric crevices. It has a free proton due to resonance, but it is still greasy enough to hang out with the other cool polymers.
Rule 4: Wikipedia and Google images… Learn to love them
Rule 3 describes a substitution reaction. SN1 or SN2 reactions are chemistry “terms” that will help improve search-ability for the necessary solvents. It will be important to be able to classify similar solvents and plausible way for chemistry to happen.
Rule 5: Read the MSDS sheets…Methyl Chloride is not your friend … and neither is Toluene.