It always seems to end up in a mess.
Try to squeeze a little from a tube and a whole glob comes out.
Then after I’ve squeezed out what I need, the glue just keeps on coming…
What a waste!
Or it gets everywhere and it feels like I’m stuck to everything!
So if I can, I avoid it like the plague.
But sometimes we have no choice. We’ve just got to get those parts glued together no matter what.
So what glue should we use?
There are so many types of glues out there its really hard to know which to choose.
So to make it easier for you, I’m going to focus here on the types of adhesive generally used to glue plastic.
Hey, that’s what we’re here for, isn’t it?
There are essentially five types of adhesives and adhesive methods commonly used to adhere plastic to itself and to other materials.
This class of adhesives are specifically formulated for thermoplastics such as ABS, acrylic (Plexiglass®), polycarbonate, styrene (Lexan®) and rigid uPVC.
Cements use a solvent to soften and slightly ‘melt’ the surfaces being joined.
The solvent contains dissolved resin (plastic) of the same type as the material under repair or construction.
The dissolved plastic resin combines with the softened plastic pieces to produce a clear, strong, generally seamless, cemented joint. When you use cement, unlike normal glue, the plastic resin monomers in the cement crosslink with the two joining surfaces to form a welded bond that has the strength of the original material.
Solvent-based adhesives may lose up to 50-70% of layer thickness during drying. In this way they produce very thin glue lines.
In general these types of solvent-based cements are water-thin and fast flowing. They tend to work by capillary action, working themselves between pieces of plastic already fitted together.
Gluing Lego blocks is a perfect example. Say your child just finished that Lego dinosaur and you don’t want all that concentrated work to be lost forever so you decide to glue it all together.
You know, for posterity.
Using thin ABS cement allows you to glue the whole thing without having to glue each piece separately.
The cement works itself into the spaces between the Lego blocks cementing them all together. It all sets once the solvent has evaporated off.
A permanent testimony to your child's creative genius!
Note: acrylic and ABS cement may discolour or deform the plastic. It is recommended that you test the cement on other peices before using.
It's often a good idea to use a primer/cleaner to properly prepare the surface so that there is no contamination from other sources such as grease and oil.
All thermoplastic solvent cements give off strong toxic fumes during use so adequate ventilation is needed.
If good ventilation is not possible then a well-sealed mask with organic vapour canisters is highly recommended.
Don’t take a chance. Protect yourself! You'll need those brain cells for the next project!
A particularly strong class of adhesive, epoxy glues were first developed for the construction of aircraft components. They work well on many hard-to-glue plastic surfaces as well as glass, metal and concrete.
Epoxy glue cures by virtue of a chemical reaction between two components mixed together rather than by drying or by the evaporation of solvents as with cements.
Gluing with epoxy can get quite messy, though, since two parts have to be
added to each other to activate the chemical process.
The first part is a plastic resin that gives the glue its body.
The second part is a catalyst that activates the resin and causes it to cure and harden.
The performance of any particular epoxy adhesive depends on the type of hardener used to activate and cure the resin.
To get a proper cure it’s usually best to mix the two parts in equal measure. However, it is possible to vary the proportions by as much as 60% hardener and 40% resin and vice versa.
Increasing the amount of hardener increases the bond’s flexibility. Adding more resin than hardener will increase the bond’s strength but will render it more brittle and less impact resistant.
Epoxy glues are made to cure quickly as with the 5min variety or they can be made to take longer to cure as needed.
When I first came to use cyanoacrylate or Superglue® I made sure I was well protected with gloves and goggles. I had heard all these warnings about how it could glue my eyelids and fingers together. Instantly!
It may seem a bit silly but I wanted to be safe rather than sorry. Needless to say if you’re careful there is no need to worry but it’s always a good idea to be protected.
Cyanoacrylate glues adhere quickly because they cure in the presence of moisture and in the absence of oxygen.
So when you press two items together with superglue the oxygen is squeezed out and the moisture in the air sets the glue in a matter of minutes.
Cyanoacrylates are only effective on non-porous surfaces such as most plastics, metal, glass, china, ceramics and rubber.
They form strong, durable bonds very quickly but tend to be somewhat brittle and aren’t particularly good where a lot of flexing, bending or shearing (sideways movement) is expected.
In the world of plastics, which is our concern here, cyanoacrylates are particularly good when used on heat-formed or thermoplastics including acrylic, ABS, PLA, polycarbonates and PVC.
Unfortunately cyanoacrylate adhesives don’t have a very long shelf life, making them quite expensive.
I’m sure we’ve all had that experience. We use the superglue once and put it away carefully closing the tube and locking it away in its container far from the reach of the children. A few months later when we need it again, nothing comes out. It’s as hard as a rock.
If you leave the tube of superglue unopened after purchase you’ll still be able to use it for up to a year. But once the tube is opened and exposed to the humidity in the air, it won’t last more than a month.
So it’s often best to store superglue in the freezer where humidity is lower and the curing process is significantly slowed. For more information on storing and preserving cyanoacrylate glues please see the Wikipedia entry on cyanoacrylates.
Hot Melt Adhesive or HMA is thermoplastic in stick form which liquifies when heated. Applied to two surfaces it adheres upon cooling. HMAs are usually clear or translucent, colorless, tan, or amber.
Coloured versions are also available. Glue sticks are generally either 4in or 10in in length and 7/16in in diameter. There are also mini glue sticks, which have a smaller 5/16in. diameter.
Most popular HMAs for arts and craft projects are those based on ethylene-vinyl acetate. It's easy to use and adheres to a wide range of materials including plastic, of course. It works well at both high and low temperatures (see Glue Guns below).
Specialty HMAs are also made to join specific plastics such as acrylics.
HMA’s wide applicability stems from the variety of additives used to change the nature of the melted plastic making it suitable for different surfaces, longer or shorter cooling and setting times and plasticity.
Hot melt adhesives are often preferred because they're also safer. They don't use volatile organic compounds like those used in solvent-based adhesives. Some surfaces such as styrene foam react poorly to solvents. Low-temperature HMA is a better alternative for gluing Stryrofoam®.
Since the HMA solidifies rapidly upon cooling, the drying or curing stages necessay with other glues is eliminated. It also has a longer shelf life unlike, for instance, superglue which barely lasts a month once opened.
One of the benefits of hot glue is that it sets quite quickly, about 15–30 seconds, and dries in about 5–10 minutes. This is also one of its drawbacks since there is not a lot of time to position the pieces being glued before the glue cools and sets. So you have to work quickly.
Some HMAs are engineered to take longer to cool allowing more positioning time.
Hot glue guns are needed to apply hot melt adhesive glue sticks. They operate at both low-temperature ~120 °C (248 °F) and high-temperature ~190 °C (374 °F).
Dual temperature glue guns are equipped with a switch to move between both temperatures.
Some glue guns are equipped with an adjustable reostat to allow the user to select a range of temperatures between Low and High. This permits creater control over the flow of the glue from the tip.
Low-temperature guns are best for more delicate materials such as foam, lace, paper etc.
High-temperature glue guns produce a stronger bond.
Welding plastic, as opposed to gluing it, is similar to welding steel. The substrates to be joined are heated with the tip of the welder. As it heats the surfaces the tip simultaneously melts the end of a plastic welding rod into the joint between the softened surfaces fusing the two parts together.
Plastic welders are often used for difficult to join plastics like polypropylene and polyethylene. With polypropylene the plastic of the welding rod needs to be combined with the plastic of the material being joined.
Thermoplastic welding rods come in a variety of colours to make it easier to match the original material being repaired.
The quality of the rods is based on the amount of air bubbles or voids in the plastic rod. This its degree of porosity. The lower the porosity the higher the quality of the weld.
Bondic welders operate on a different principle from heat based welders. Bondic supplies a liquid plastic which is applied to the parts to be repaired.
Once in place the plastic is hardened with an LED light. In this way layers can be built up to make the repair.
It can be used for joining, filling, sealing and even to build up plastic moulds. Bondic does not use heat or solvents.
The resultant plastic mend is clear. It can be moulded, milled, filed, painted, polished and sanded.
Great for fixing eye glasses!
For a summary table matching plastic types with suggested adhesives go now to Plastic by the Numbers.
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