Plastics identification through burning (with odor and flame table)

I don't know how I could forget, during all these years that I keep this website, talking about something as important as the identification of plastics through burning. This is a very common process in recycling companies and aims to identify, for prior separation, the different types of polymers present in a shipment.


The process has no secret, a candle and / or a lighter, tweezers or pliers, are the necessary tools to perform this work. Depending on the type of plastic, a different effect occurs when the flame comes into contact: yellow flame, blue flame, soot release, flame self-extinguishing, etc. In addition, the smoke from burning has a particular odor for each polymeric family, through which, the most experienced recyclers, can even distinguish between the members of that family (eg: polyamide family - members: polyamide 6, polyamide 6.6 etc).

There has been a table circulating on the internet since the early 2000s that shows these burning characteristics, the problem is that it has a series of errors (eg, saying that polyacetal has a styrene monomer odor). In 2004, Hélio Wiebeck and Ana Magda Piva used this table in the book "Reciclagem de Plásticos" (Plastic Recycling), correcting some errors and keeping a few others.

I reformulated the table and added illustrations (just for visual reference), the result is this:

Polymers Burning test behavior Smoke odor Burning illustration
(L)LDPE, MDPE, HDPE Blue flame with yellow apex. Drips like a candle Paraffin
PP Blue flame with yellow apex. Drips like a candle Paraffin but a little tastier than PE
PMMA Blue flame with yellow apex. Bubbles in the piece, burns slowly, and does not carbonize Garlic
PVC Yellow flame with green vertex. Self-extinguishing flame Chlorine
ABS Yellow flame. It carbonizes and produces smoke with a lot of soot. Burns a little more slowly than PS and SAN Burnt rubber and styrene monomer*
PS Yellow flame. Carbonizes and produces smoke with a lot of soot Styrene monomer*
SAN Yellow flame with glow. Produces sooty smoke and carbonizes more than PS Styrene monomer*
PC Hard to burn, self-extinguishing yellow flame, carbonizes and produces soot "Medicine" (imagine the smell of a concentrated pharmacy)
PET Yellow flame. Produces a little black smoke Characteristic. Use the odor of a burnt bottle as a reference
POM Low, round blue flame, almost invisible, without soot Extremely strong odor to the point of causing a momentary headache if the smoke is breathed in deeply
PU Produces a lot of smoke Characteristic. Use as a reference the odor of burnt mattress foam
PA (all) Blue flame with yellow apex. It takes time to catch fire, does not generate soot and drips if you keep the fire for a long time Burnt hair
Cellulose acetate Yellow flame. Ignites Acetic acid
Cellulose butyrate acetate Blue flame with sparks. Ignites Rancid butter
PTFE Does not catch fire, chars As it does not burn, it does not emit odor

* this monomer, when liquid, smells like a thinner, but when polymerized and burned it has a smoother and sweeter odor


Bibliography:
HARPER, Charles A.; PETRIE, Edward M. Plastics Materials and Process: A Concise Encyclopedia. Hoboken: John Wiley & Sons, Inc., 2003.
WIEBECK, Hélio; HARADA, Júlio. Plásticos de Engenharia: Tecnologia e Aplicações. São Paulo: Artliber Editora, 2005.
Article posted in Apr 13, 2020
About the author: Daniel Tietz Roda is Plastics Technologist graduated from the FATEC/ZL and Mechanical Design Technician from ETEC Aprígio Gonzaga, in São Paulo, Brazil. Roda worked 5 years with technical assistance and development of plastics in industries and nowadays is the publisher of this website.
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