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Imagine this: you stumbled upon a box of material with no identifiable label or documentation. What do you do? Would you scrap the material or try to identify it? Whether you’re a researcher, material scientist, engineer, student, or a curious individual, identifying an unknown polymer. This blog will guide you through the steps of polymer material characterization.

Rudimentary Polymer Characterization:

Sophisticated analytical equipment is not always necessary or available for characterizing an unknown polymer. While advanced instruments offer enhanced precision and benefits in polymer identification, there are simpler and more cost-effective methods that can be utilized without the need for high-cost capital equipment. This section will help outline the process of identifying a polymer material without relying on costly analytical equipment.

1. Obtain a Material Sample: The sample should be of the raw material, meaning either pellets or powders for thermoplastic materials to be used for the following test methods.
   
   
2. Visual and Physical Inspection: Start by examining the physical properties of the polymer. Make note of the appearance, color, transparency, texture (flexibility/softness), and any distinctive features. could provide preliminary clues about the type of polymer. For example, if a material has a rubber-like feel to it, it could be either a TPE, TPV, or TPU. If the material is clear, chances are it might be an amorphous material. However, if a material is opaque, it could be a colored amorphous material or semi-crystalline. If the material feels ‘waxy’ then the material could be in the polyolefin family.
   
   
3. Solubility Test: Take two of the unknown material and place each pellet into a test tube. Fill the first test tube about halfway with toluene and fill the second test tube about halfway with acetone and then cap both test tubes. Carefully, mix each test tube of polymer pellet and solvent and observe any changes in the size/shape of the pellet. Does the pellet swell, dissolve, crack/craze or is there no effect? Do take note that this test should be done with a polymer pellet, however, if you are trying to identify powder you might only be able to observe the level of dissolution due to the small particle size of the powder.
   
   

Table 1. Effect of Polar and Non-Polar Solvents on Various Polymers

Swelling: An increase in volume of the polymer pellet

Dissolution: The formation of a solution when a solute dissolves in a solvent

Crazing: Intermediate stage between yielding and fracture observed visually as whitening of the polymer

4. Density Test: A simple water test can help determine the density of a material. Water has a density of 1 g/cm³, meaning if an unknown polymer floats, it must have a density < 1 g/cm³ and if the pellet sinks, then the density of that polymer is > 1 g/cm³.
   • Note: Polyolefin materials (typically PE & PP) have a density < 1 g/cm³ and therefore should float.

5. Beilstein Flammability Test for (most) Halides (Cl, Br, I): Heat a few inches of solid copper wire. Once hot, press the hot wire into the sample material long enough to get some sample material to stick to the wire. Heat the copper wire again and note the color of the flame. Changes in the flame color are due to the formation of volatile copper halide salts.
   1. Chlorine ⇒ Bright Green
   2. Bromine ⇒ Bright blue-green
   3. Iodine ⇒ Deep blue-purple
      
      

Figure 1. Beilstein Flammability Test^[1]

6. Thermal Behavior Testing: Expose the polymer to heat using a hot plate, oven, or flame (with caution). Observe behaviors such as softening, melting, burning, and charring behavior. This will help to identify specific thermal transitions.

Stay tuned for Part 2 of Identifying Unknown Polyers with Advanced Polymer Characterization.

View what Technical Solutions Nexeo Plastics can provide you here.

[1] Nichols, Lisa. “6.4D: Individual Tests.” Chemistry LibreTexts, Libretexts, 7 Apr. 2022, chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_Lab_Techniques_%28Nichols%29/06%3A_Miscellaneous_Techniques/6.04%3A_Chemical_Tests/6.4D%3A_Individual_Tests.