Plastics Density and Burn test results



Plastics Density and Burn test results

Density. Cut small (approximately 3- to 5-mm square) pieces of each sample. Determine the approximate density by the behavior in the fluids provided.

 

|Polymer |Water |10% w/v NaCl |46% v/v Isopropanol |Vegetable Oil |

| |(s.g = 1.00) |(s.g = 1.07) |(s.g = 0.940) |(s.g = 0.918) |

|PETE |sinks |sinks |sinks |sinks |

|HDPE |floats |floats |sinks |sinks |

|PVC |sinks |sinks |sinks |sinks |

|LDPE |floats |floats |floats |sinks |

|PP |floats |floats |floats |floats |

|PS |sinks |floats |sinks |sinks |

 

An efficient way for a team to distinguish the polymers is to use water to make the first cut, then follow a flow chart. For example:

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Copper wire flame test. Using tongs or forceps, hold a 5-cm length of copper wire in the flame of a gas burner. Touch the hot wire to a sample of polymer and place it back in the flame. A green flame indicates the presence of halogen such as the chlorine in PVC.

Burn test. Using clean forceps, briefly hold a 1- to 2-cm strip of each sample in the flame of a match, lighter, or gas burner. Observe the behavior of the material in the flame and after removing it from the flame. If the sample continues to burn after removal, blow out the flame and observe the condition of the material. After observations are complete, quench the residue in a beaker of water.

|Polymer |Behavior |

|PETE |Melts and bubbles first; burns slowly with some black soot; pungent odor of acetaldehyde |

|HDPE |Burns rapidly and cleanly; drips flames; white smoke when extinguished |

|PVC |Melts; may burn, but extinguishes on removal from flame |

|LDPE |Burns rapidly and cleanly; drips flames; white smoke when extinguished |

|PP |Burns more slowly than PE; may drip flames |

|PS |Burns rapidly; large amounts of black soot |

 

 

Teams identify the polymers by their densities and their behavior in two burn tests. Other characteristics such as hardness (can a sample be scratched by a fingernail?) and flexibility should be noted. Hardness and flexibility are somewhat ambiguous, as they are affected by molecular weight, sample thickness, presence of plasticizers and impact modifiers among other considerations. Care in observation and a basic knowledge of polymer properties should lead to the correct identification of the unknown samples.

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