Plastic Identification with the Burn Test
I’m going to start by saying that I do NOT recommend testing and identifying plastic types this way. The burn test involves burning a piece of plastic with a heat source such as a lighter and carefully inspecting the way it burns, the color of flame, the smell, and other characteristics. The issue with conducting the burn test is it releases chemicals in the air that is possibly carcinogenic. Since on-site plastic identification is sometimes required for plastic scrap trading, it sometimes gets overlooked as being hazardous to your health.
I’m not going to lie to you, I never conduct the burn test, instead, I hire experts to do this for me. For instance, burning ABS plastic releases black smoke with soot (black ashes). Inhaling this is probably worse than smoking a pack of cigarettes. Therefore, I’m going to warn you again, I’m writing this guide for educational purposes only. Do this at your own risk!
The proper protocol for conducting the plastic burn test is to NOT do it near other plastics. That is, most plastic storage areas are filled with flammable plastics, you need to bring the plastic sample you collect into an office or ask an on-site worker where the best place is to conduct the test. Most buyers coming to my facility know not to smoke cigarettes or conduct the plastic identification tests anywhere in my storage shed. I have a large conference area for this.
Step one of the plastic burn test is to find a suitable piece of plastic. You want something that is relatively large, at least the size of a quarter (so your fingers can hold on to it while it burns). For plastic pellets or small flakes, you can bring along a small metal clip to hold the plastic sample. Although most people in the China plastic scrap industry carry around a jet lighter, a regular lighter will do the trick.
With your lighter on, start by putting the piece of plastic near the flame, it should start to melt and or catch on fire. Observe the color of the flame, the nature of the flame, if there is soot, and whether or not the melted plastic drips. Blow out the flame and using your hands, fan some of the smoke toward your nose to get an idea of smell. Again, I don’t recommend conducting the plastic identification burn test. It is not an exact science, that is, it’s not an accurate way of identifying plastics. For 100% accurate testing, bring your sample to a lab.
Below is a list of common plastics and its burn test characters. I will provide videos of various plastics burning for you in the future, so stay tuned!
Polyethylene (including HDPE & LDPE)
- Blue, yellow tipped flame
- Burns slowly
- Plastic drips
- Smells like candle wax (paraffin)
- Floats in water
- Blue, yellow tipped flame
- Burns slowly
- Plastic drips
- Has sweet odor
- Floats in water
- Yellow flame
- Burns quickly
- Plastic drips
- Illuminating gas odor (naphtha)
- Dense black smoke w/ soot (floating particles)
- Yellow flame w/ green spurts
- Plastic does not drip
- Self extinguishing
- Smells like hydrochloric acid
- Plastic chars
Polyethylene Terephthalate (PET / PETE)
- Yellow flame
- Plastic drips
- Burns slowly
- light smoke
- Orange flame
- Self extinguishing
- Plastic drips
- Black smoke w/ soot (floating particles)
- Faint, sweet aromatic odor
Acrylonitrile Butadiene Styrene (ABS)
- Orange flame
- Plastic drips
- Burns slowly
- Black smoke w/ soot (floating particles)
- Acrid odor
As you will notice, the plastic types mentioned above have similar flame properties, however, the smell when ignited is different. This makes smelling the odor an essential (not recommended) part of the burn test.
I’ve only provided properties for the most commonly seen plastics. Remember that adding additives to augment plastic properties such as flame-retardants may affect results. Usually speaking, experienced plastic traders will run a plastic burn test several times to confirm their findings.
There are many other plastic types not listed above. In fact, there are literally hundreds if not thousands of plastic variations. I suggest that if the above is not enough for plastic identification, bring the sample to a proper lab for testing. While prices differ from one country to another, lab tests in China is only around 200-300 RMB per sample.
Good luck to you!