View Full Version : Plastic help needed

09-18-2010, 07:05 PM
Without going into a long story (yet) Im looking for a machinable plastic that hot glue will stick to.

Hot glue sticks fairly well to injection molded plastics, I made the parts out of delrin and pvc, it does not stick so well. Any ideas?

09-18-2010, 07:52 PM
PET-G should work well. It softens at about 215F and doesn't become liquid until around 400F. It fire polishes better than any other plastic and is very machinable. Surprisingly it doesn't have a tendency to melt when machined and it doesn't shatter at all. It is also as tough as Lexan but doesn't turn white when bent and is much less sensitive to solvents. It glues easily with most glues and heat welds well.

Here is an item made with PET-G:


09-18-2010, 07:54 PM
Thanks Evan..... What about a plastic that glue will stick to and be really strong, like delrin?

I guess Im trying to figure out why it does or doesnt stick to certain types....

09-18-2010, 08:00 PM
Delrin has too high a melting temperature for hot melt glue. Polyethelene has too few surface bonds to hold onto most glues. Acrylic (PMMA) could work but it is a pain to machine as it grabs, shatters and melts easily. Nylon also melts too high as does Lexan or polycarbonate. Holt melt glues are formulated with low melting temperatures for safety. There are industrial hot melt glues that have much higher melting temperatures but the application equipment is expensive.

BTW, PET-G IS really strong. That is what they use to make the blister packaging that you need a band saw to open.

09-18-2010, 08:05 PM
That makes since. Why does it stick to injection molded plastic? Low melting temp?

I want it to stick, but not melt into it also....

09-18-2010, 08:33 PM
Injection molding plastic isn't a single type of plastic. All the plastics I mentioned are used for injection molding. Whether the glue will stick depends on melting temperature and the type of plastic and it's chemical makeup. It also depends on the type of hot melt glue you use. There are different types with different purposes. Most of the hot melt glues are probable a styrene monomer which will stick very well to injection molded styrene or ABS parts.

Liger Zero
09-18-2010, 08:47 PM
Evan speaks the truth.

Delrin is a *unt to bond under most circumstances. Nylon can be tricky too.

HDPE can be "treated" with a flame to accept adhesive. Just "kiss" the spot you want to bond with a flame for a split second... not long enough to melt... hard to explain I'd have to show you. This site will now accept adhesive.

If we knew more about your application we could give you better advice. There are other factors besides the ones Evan mentioned and if we know what you are trying to make we can suggest a material.

09-18-2010, 09:44 PM
Too high a melting point? I did'nt know hot melt glue relied on melting the target to stick.

Liger Zero
09-18-2010, 09:46 PM
Too high a melting point? I did'nt know hot melt glue relied on melting the target to stick.

It does in some plastic applications. We use this principle to ensure a very very strong bond.