Omar Khalid
Plastic is everywhere, and recycling it is essential for the well-being of our planet. There are several ways to identify different types of plastic, including appearance, feel, float tests, and burn tests. The easiest way is to look for the international plastic identification code, which is a triangle of arrows with a number in the middle. Plastic #1, or PET, is one of the most commonly used plastics, often found in food and beverage containers, and it is safe for food and drink packaging. However, it should only be used once and must not be heated, as it can leach toxic chemicals.
| Characteristics | Values |
|---|---|
| Identification code | 1 |
| Chemical makeup | Polyester and PET plastics |
| Common uses | Plastic bottles, clothing, materials used for insulation |
| Buoyancy | Sinks in water |
| Flammability | Flammable |
| Burning smell | Burnt sugar, candy floss, or sugar candy |
| Appearance | Smooth texture, flexible, may leave marks |
| Sound | Makes a loud noise when crumbled |
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What You'll Learn
- Float test: Plastic will sink or float depending on its type
- Burn test: How the plastic burns, smells and what it looks like can indicate the type
- Solvent test: Using a knife, mush a small drop of solvent on the plastic's surface
- Discolouration: Rubbing with a paper towel can cause ABS plastic to discolour
- Infrared analysis: This can determine whether it is ABS or Polypropylene
Float test: Plastic will sink or float depending on its type
The float test is a simple method to determine the type of plastic. The test is based on the principle that plastics with a density greater than water will sink, while those with a lower density will float. This test is particularly useful when trying to distinguish between different types of plastics, such as ABS and polypropylene.
ABS, or Acrylonitrile Butadiene Styrene, is commonly used for items like Lego toys and computer keyboard keys. When placed in water, ABS tends to sink. However, it's important to note that other plastics also sink in water, so this test may not provide a definitive identification. To enhance certainty, a secondary test using glycerin can be performed. Since glycerin is denser than ABS, if the plastic floats in glycerin, it is likely ABS.
On the other hand, polypropylene, often coded as PP, is known for its buoyancy. It has a density of less than 1.0 g/cm3, causing it to float in water. Additionally, polypropylene exhibits unique characteristics when exposed to a flame, emitting an acrid smell and a yellow flame, followed by a sweet smell as it continues to burn slowly.
It is worth noting that the presence of bubbles or voids in a sample of ABS could impact its buoyancy, potentially making it as buoyant as polypropylene. Therefore, while the float test is a useful initial assessment, it may not always provide conclusive results.
Other plastics, such as PET (polyethylene terephthalate), PVC (polyvinyl chloride), and PS (polystyrene), also tend to sink due to their higher densities. These plastics have various applications, with PET commonly used for single-use drink bottles, PVC in flooring and medical tubing, and PS in disposable cups.
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Burn test: How the plastic burns, smells and what it looks like can indicate the type
While the burn test is a good way to rule out certain types of plastics, it is difficult to use this method to specifically identify a plastic with complete certainty. This is because the presence of additives like flame retardants can modify how a plastic behaves when burned. Nevertheless, the burn test is a rapid preliminary identification technique that can provide initial information about the material. To perform a burn test, hold a sample of the plastic near the edge of a flame from a source such as a cigarette lighter, gas burner, or torch. Hold the material in the flame for a maximum of ten seconds if it fails to ignite right away. Here are some characteristics to observe during the burn test:
Flame colour: The flame colour during combustion can indicate what the material is made of. A blue flame usually suggests thorough combustion with fewer impurities, while yellow or orange flames demonstrate the presence of carbon or other contaminants in the material.
Soot presence: Soot production during combustion demonstrates incomplete burning, which occurs frequently in plastics containing high carbon content and various additives.
Smoke characteristics: Observe the type and amount of smoke emitted during the burn test. Thermoplastics, for example, drip during combustion because they become pliable when exposed to heat. On the other hand, thermosets maintain their form and do not drip when exposed to flame.
Odour: Each plastic material produces a unique smell when burned. For example, PVC emits a sharp acrid smell when burned, while polyethylene releases a sweet and gentle odour.
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Solvent test: Using a knife, mush a small drop of solvent on the plastic's surface
One way to identify plastic is by looking at the three arrows that form a triangle with a number in the middle. This is an international code that indicates the chemical makeup and grading for recycling. For example, Symbol 1 denotes polyester and PET plastics, which are commonly found in clothing, plastic bottles, and insulation materials.
However, if you want to specifically identify whether a plastic item is made of ABS or polypropylene, you can perform a solvent test. This test involves using a knife to mush a small drop of solvent on the plastic's surface. The solvents that can be used for this test include acetone, methyl ethyl ketone (MEK), 2-butanone, and methylene chloride. These solvents will dissolve ABS but not polypropylene. So, if you see the plastic softening and diluting when you mush the solvent, it is likely ABS.
It is important to note that this test may not be suitable for all items, as some plastics may be damaged by the solvent. Therefore, it is recommended to choose a non-critical location on the plastic item for testing. Additionally, this test may not be effective if the plastic item has bubbles or voids, as this can impact the buoyancy of the material.
Before performing any tests, it is important to understand the potential risks and take the necessary precautions. Some plastics may release toxic chemicals when heated or burned, so it is crucial to ensure adequate ventilation and safety measures.
Other methods to identify plastics include visual inspection, feeling the material, and the floating method. Visual inspection involves observing the appearance of the plastic, such as its colour, texture, and flexibility. Feeling the material can also provide clues, as different plastics have distinct tactile characteristics. For example, low-density polyethylene (LDPE) is thin and crumbly, while high-density polyethylene (HDPE) is tougher and has a waxy appearance. The floating method involves placing the plastic in water to determine its density based on whether it sinks or floats. However, it is important to remember that these methods may not always provide conclusive results, and further analysis may be required for complex plastic compounds.
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Discolouration: Rubbing with a paper towel can cause ABS plastic to discolour
Discolouration is a common issue with ABS plastic, often resulting from exposure to ultraviolet (UV) light. A flame retardant added to the plastic during the manufacturing process can cause this discolouration when exposed to UV light. This typically manifests as a yellowing of the plastic, as observed in the case of a Stormtrooper helmet.
To address this issue, several methods can be employed to restore the original colour of the ABS plastic. One approach involves scrubbing the affected areas with diluted dish soap and a toothbrush, followed by wiping it off with a paper towel. This method can effectively remove the discolouration in small sections. Alternatively, you can use a product called Retr0bright, an open-source formula made from ingredients available at your local grocery store. It is designed to reverse the process of UV discolouration in ABS plastic.
For a more technical solution, you can try irradiating the ABS plastic with UV light in the presence of additional hydrogen atoms, such as hydrogen peroxide. This process breaks the bonds between oxygen and bromine, allowing the bromine to bond with the hydrogen instead, thus reversing the discolouration. However, it is important to exercise caution when handling chemicals like hydrogen peroxide.
While these methods can be effective in reversing UV damage, it is worth noting that paint may not adhere well to ABS plastic. As a result, you might need to repaint the surface after treating it for discolouration. Additionally, when working with chemicals or cleaning agents, it is always recommended to wear protective gear, such as rubber gloves, to avoid any potential harm to your skin.
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Infrared analysis: This can determine whether it is ABS or Polypropylene
Infrared analysis is a highly effective method to determine whether a plastic is ABS or Polypropylene. This technique is also known as infrared spectroscopy, and it is a commonly used method to identify plastics.
Infrared analysis can be performed in two ways: transmission measurement and ATR (Attenuated Total Reflectance). Transmission measurement is used when the plastic material is thin enough for infrared light to pass through. However, if the material is too thick, ATR can be used to measure a few microns inside the solid.
Infrared spectroscopy is particularly useful for analysing polymers, which are common in plastics. This technique can identify the functional group structural information of the plastic. Each type of polymer has a unique infrared spectrum, which can be used to distinguish between different plastics. For example, high-density polyethylene (HDPE) has a different spectrum compared to low-density polyethylene (LDPE).
In the context of distinguishing ABS from Polypropylene, infrared analysis can identify the chemical structure and functional groups of the plastic. ABS and Polypropylene have different chemical resistances, with Polypropylene being more resistant. Infrared analysis can detect the presence of functional groups that are characteristic of each plastic's chemical structure, allowing for their differentiation.
In conclusion, infrared analysis is a reliable and non-destructive method to determine whether a plastic is ABS or Polypropylene. By examining the functional groups and chemical structure through infrared spectroscopy, these two types of plastics can be accurately identified.
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Frequently asked questions
The easiest way to identify plastic #1 is by locating three arrows forming a triangle with the number 1 inside. This international code offers clarity for plastic identification based on chemical makeup and recycling grading.
Plastic #1, or PET plastic, is generally considered safe for use in food and beverage packaging. It is often used for plastic bottles and food containers, and while it is recyclable, it is important to ensure that it is properly recycled to prevent environmental contamination.
One way to physically test for plastic #1 is through the float test. Chop a small piece off a product, if it floats, it is likely HDPE (high-density polyethylene), and if it sinks, it could be PET, which is plastic #1.
Plastic #1, or PET, typically has a clear and glossy appearance, resembling glass. It is strong and resistant to breaking, with a smooth surface that can sometimes feel slightly textured due to the manufacturing process.
