How to Identify Polypropylene Plastic

Polyethylene Plastic Products

A wide variety of plastics are available in the market, and each has unique characteristics, advantages, disadvantages, etc. In this case, identifying the plastic type is crucial for professionals and users.

By considering the higher degree of importance and use of Polypropylene Plastic, we inform you how to identify Polypropylene Plastic in this article. Using this beginner’s guide, you can correctly differentiate Polypropylene Plastic from others.

Basics of Polypropylene Plastic

Polypropylene (PP) plastic is a versatile thermoplastic polymer. It belongs to the polyolefin family. The polymerization of propylene monomers creates this material. Polypropylene is a widely used plastic in various industries due to its superior characteristics.

Characteristics of Polypropylene

  • Polypropylene is lightweight.
  • Though it is lightweight, Polypropylene possesses remarkable strength and toughness. This property confirms greater durability and resilience to impact.
  • Polypropylene is highly resistant to various chemicals, acids, and bases. Following this, the plastic material is highly suitable for applications that encounter corrosion.
  • PP possesses good flexibility and can be molded into various shapes.
  • Polypropylene plastic has a relatively high melting point: 171 °C.
  • This construction material absorbs very low water content.
  • It accommodates excellent electrical insulator capability.

A Comparison between PP, PE, and PVC

Differential criteriaPPPEPVC
DensityRanges from 0.895 and 0.92 g/cm³Ranges between 0.910 and 0.940 g/cm3Ranges between 1.1 to 1.45 g/cm³
Chemical ResistanceHigher than PE and lower than PVCLower than PP and PVCHigher in this group
Heat ResistanceHigher than PE and lower than PVCLower than PP and PVCHigher in this group
FlexibilityHigher than PVC and lower than PEHigher in this groupLower in this group
RecyclabilityResin identification code #5Resin identification code #1Resin identification code #3
The table provides you with in-depth information in terms of PP vs. PE vs. PVC.

How to Identify Polypropylene Plastic

To correctly identify Polypropylene plastic, consider performing at least two examination methods mentioned below.

Method 01: Physical Inspection

In this plastic identification method, your first task is to look for the “International Code” on the plastic. This code consists of three arrows forming a triangle (often known as a recycling sign), and in between it is a symbol indicating the plastic’s name. Note the below symbols to identify Polypropylene.

  • Low-density Polypropylene: This category of Polypropylene contains symbol number 4.
  • High-density Polypropylene: This category of Polypropylene contains symbol number 2.

Next, check the color and appearance of the respective plastic. In general, Polypropylene plastic is translucent or semi-translucent. It comes in various colors; white, black, and various shades of blue, green, or beige.
Finally, check the flexibility of the plastic material. If it is made of Polypropylene, it will bend without breaking easily. Below are the two points that need to be considered.

  • Low-Density Polyethylene (LDPE): It exhibits a delicate nature; easy to crumble by hand. In the handled process, it produces crackling sounds.
  • High-Density Polyethylene (HDPE): It shows remarkable resistance against deformation. Most HDPE items feature a translucent and milky white coating. However, if it is not colored, it comes with a waxier appearance.

Method 02: Identification of Polypropylene Plastic Using Float Method

Follow the stepwise guidelines.

Step 01: Arrange a clean container.

Step 02: Fill the container with clean water. We suggest the water must not contain any impurities, increasing its density.

Step 03: Take a small piece of the respective plastic.

Step 04: If the plastic is made of Polypropylene, then it will float due to having a low density. Most essentially, low-density polyethylene even remains above the water.

Method 03: Testing the Plastic Chemically

This method consists of two approaches: burning and solvent tests.

Burning Test: Take a piece of examining plastic and fire it up. If it generates dirty engine oil and undertones of candle wax, it indicates that the material is Polypropylene Plastic. However, upon burning, PP produces water vapor and CO2.

Solvent Test: At first, put a piece of the examining plastic in isopropyl alcohol or mineral spirits. If the plastic is made of Polypropylene, it won’t get dissolved or react with the solvent. Again, to be more sure, Second, put a piece of the respective plastic in benzene and acetone. Polypropylene plastic will get dissolved in the solvents of benzene and acetone.

Method 04: Laboratory Test

Many laboratories and survey companies perform plastic identification testing on individual clients. They usually use Fourier-transform infrared (FTIR) spectrometers, Gas Chromatography-Mass Spectrometry (GC-MS) machines, etc., to identify the plastic category. However, this testing method is subject to a fee.

Final Words

Understanding how to identify Polypropylene plastic is certainly essential. This knowledge facilitates the right construction material use, responsible recycling, etc. You can confidently differentiate Polypropylene from other plastics by using the mentioned methods, like visual inspection, density tests, float tests, and chemical tests.

Finally, experience in plastic material use and handling also contributes to its identification process.

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