How to identify plastic?
Industrialists and technical staff working in production may need to know which plastic is used in a piece. This is important for knowing both the cost of the piece and the characteristics of the material.
As a matter of fact, identifying plastics is pretty hard. In practice, there are many different types of plastic that may be used. Various ingredients might have been added in order to alter the characteristics of these plastics. In order to obtain the desired characteristics, plastics may have been used in the form of alloys or mixtures.
In spite of all these, it might be possible to determine which polymer is used in the production of a plastic piece through some simple tests. These tests should only be used as preliminary information and the exact type of the material should be determined in result of advanced lab tests.
CAUTION! Wrong usage of these tests may be dangerous. Some vapors may be very dangerous. Extreme care should be given while applying these tests. Extreme care should be given especially in burning and vapor smelling tests. The burning piece should be held 20-30 cm away from the nose and should be inhaled just enough to get the smell. Vapor should not be inhaled deeply and directly. Attention should be paid to dripping polymer, it is caustic and very hot.
The most simple tests for identifying plastics;
- Inspecting the sample with the eyes
- Inspecting its structure by touching
- Sculpting pieces from the sample
- Seeing whether it floats on water or not
- Checking its flame and smell after burning
These tests may roughly give an idea about the polymer.
NOTE: These tests are never sufficient for definite identification. Some ingredients (delaying burning/putting out the flame etc.) may alter the known structure of the product.
- Inspecting the sample with the eyes;
For example, the color of the plastic gives you certain information. For example, the colors of certain polymers are limited, especially in Thermosets. Some have more bright colors, such as polypropylene. Some are both more bright and flat like glass, such as acrylics.
- Inspecting its structure by touching;
You can feel that the touch of some plastics are different. For example, polyolefins (polyethylene, polypropylene) give a different feeling when touched. If there is any fiberglass or similar ingredients in the material, these ingredients manifest themselves.
- Sculpting pieces from the sample;
- Sculpting pieces from the sample A;
With this test, we can tell a lot about the plastic we are trying to identify. Here we may run into two different situations.
a) Bits and pieces fall out in dust form (most probably this is a thermoset). You burn the edge of the sample with a lighter or match and you smell (if it burns but when you pull away the match or lighter it stops burning; if it lets out an odor of phenol (smells similar to tar) the sample is generally brown or black. Phenol Formaldehyde Resin (Bakelite)). If it lets out a sharp and bitter odor and the sample is in light colors; Phenol Formaldehyde based Epoxy Resin. If it burns and lets out an odor of fish, the sample is in general bright colored or white. You apply the test of scratching with your fingernails. If it is scratched with fingernails: Urea Formaldehyde Resin; If it not scratched with fingernails: Melamine; Characteristic polystyrene odor - Polystyrene; Characteristic polystyrene odor + a bitter odor - Styrene Acrylonitrile; Characteristic polystyrene odor + rubber odor - Acrylonitrile Butadiene Styrene
- You cut a straight film from the sample. Generally this is thermoplastic. In order to make sure, you heat a piece of wire with a match and touch it to the plastic. If there is any melting or softening at the point of contact, it is thermoplastic. Otherwise, it is thermoset.
- Throwing to the ground test. You let the sample fall to a hard surface. If there is a metallic sound while falling, most probably this is a styrene-based polymer. If there is no metallic sound, this is not a styrene-based polymer (if it is a foamed polystyrene a metallic sound may not be heard.
- Floating Test;
A) If the sample floats on water most probably it is polyolefin (you apply the scratching test and burning test). If the surface is bright, it is not scratched, it burns and when it burns it lets a paraffin odor - Polypropylene. If the surface is bright, it is lightly scratched, it burns and drips like a candle - Polyethylene (High density). If the surface is not very bright, it is easily scratched, it burns and when it burns it lets a paraffin odor - Polyethylene (Low density).
B) If the sample does not float on water - most probably it is not polyolefin.
- Flame Test;
Burn the edge of the sample with a match;
*It burns and when the match or lighter is pulled away it continues to burn with a bright flame. There is a fruity odor in its vapor - Acrylic (most probably PMMA); There is a paper odor in its vapor - Cellulose Acetate or Cellulose Propionate. There is a bad oil odor in its vapor - Cellulose Acetate Butyrate
*It burns hardly and when the match or lighter is pulled away it stops burning (pay attention to the color of the flame and how hard it burns). If the sample burns with a green flame, there is a bitter and sour odor, the material is soft and elastic - Soft PVC; There is a bitter and sour odor, the material is rigid and bright - Hard PVC
The sample burns with a yellow flame, smells of formaldehyde - Polyacetal; No specific odor, feels like a slippery surface. Press a cold metal to the hot surface of the sample. If the material becomes stringy - Polyamide (Nylon); There is no flame, the sample changes to a cellular form, decomposes - Polycarbonate. Does not burn - PTFE