Omar Khalid
Plastic density is calculated by dividing the mass of the material by its volume. The standard unit for density is grams per cubic centimeter (g/cm3), although it can also be expressed in kilograms per liter (kg/L) or pounds per cubic foot (lb/ft3). To determine the density of a plastic material, you can either test it in water or another liquid. First, obtain a piece of the plastic, weigh it, and then measure its volume. Finally, calculate the density using the bulk density formula, which divides the mass by the volume.
| Characteristics | Values |
|---|---|
| Definition of Density | Total mass of the material divided by the total volume of the material |
| Formula | Density = Mass/Volume |
| Units | Kilograms per cubic meter (kg/m3), grams per cubic centimeter (g/cm3), pounds per cubic feet (lb/ft3), gram per cubic centimeter (g/cc), pounds per cubic foot (b/cu ft), kilogram per liter (KG/L) |
| Calculation Steps | 1. Obtain a piece of the plastic. 2. Weigh the sample. 3. Measure the volume of the sample. 4. Calculate density using the formula. |
| Bulk Density | Weight of material per specific volume |
| Testing Methods | Testing solid plastics in water or another liquid |
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What You'll Learn
Obtain a piece of plastic
To find the density of a piece of plastic, you will first need to obtain a piece of plastic. The type of plastic you obtain will depend on the purpose of your experiment. For example, if you are testing the density of LDPE (low-density polyethylene), a common plastic used in household objects, you will need to obtain a piece of LDPE. You can do this by cutting a sample from an object made with LDPE, such as a "Jif" lemon juice container, a disposable pipette, or a plastic film.
If you are testing the density of plastics to identify an unknown plastic, as in a crime lab experiment, you will need to obtain a sample of the unknown plastic. This may be a sample from a crime scene or another source.
In a classroom setting, students may be asked to bring in samples of plastic polymers for testing. These could be everyday plastic items, such as plastic bottles, food packaging, or disposable containers, which are likely to carry a recycling symbol and identification code. Students should cut their samples into small pieces, approximately 0.5 cm in diameter, so they can easily fit into the test tubes or beakers.
In some experiments, you may need to obtain multiple pieces of plastic of the same type for testing in different solutions. For example, you may need to place a piece of plastic into each of three test tubes containing liquids of known densities, such as an ethanol/water mixture, lab water, and a 10% NaCl mixture. In this case, you would need to cut the plastic into three parts, with each part large enough to be placed into the test tubes.
Once you have obtained your piece of plastic, you can proceed to the next steps of weighing the sample and measuring its volume to calculate its density.
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Weigh the sample
To find the density of a plastic sample, you must first weigh it. Here is a step-by-step guide to this process:
Obtain a piece of the plastic you want to test. If the composition is uniform, a small piece will have the same density as a larger piece. For example, you could cut a sample from an object made with LDPE (low-density polyethylene), a common plastic used in household objects.
Next, weigh the plastic sample using a balance or scale. Ensure you are using the correct units for your measurements. For example, you may need to convert pounds to grams. If the sample weighs 0.15 lb, the mass in grams is 0.15 lb × 453.6 g/lb = 68.04 g.
It is important to note that you should verify the density of your specific plastic material. While most plastics have a density of around 1 g/cm³, slight variations can occur between manufacturers.
Additionally, be aware of bulk densities. Different materials have different bulk densities, so the weight of the plastic material will depend on its specific volume. For example, the virgin PET density differs from PET sheets. You can express bulk density in g/cc (gram per cubic centimeter), b/cu ft (pounds per cubic foot), or KG/L (kilogram per liter).
By following these steps, you can accurately weigh your plastic sample and proceed to the next steps of measuring volume and calculating density using the bulk density formula.
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Measure the volume
Measuring the volume of a plastic object is a crucial step in determining its density. Here are four detailed methods to help you accurately measure the volume of plastic:
Method 1: Using a Graduated Cylinder
If you have a plastic block or a regular three-dimensional plastic object, you can use a graduated cylinder to measure its volume. Here's how:
- Fill a graduated cylinder with a known volume of water.
- Carefully insert the plastic object into the cylinder.
- Observe the increase in the liquid level. The rise in water level indicates the volume of the plastic object.
- Make sure to use a cylinder that can accommodate the plastic object and is marked with volume units.
Method 2: Displacement Method
Archimedes famously discovered the principle of displacement, which is still used today to measure the volume of irregular objects. Here's how you can apply this method:
- Choose a container larger than the object whose volume you want to measure. It can be a bucket, measuring cup, beaker, or graduated cylinder with a scale.
- Pour water into the container and note the volume.
- Submerge the object completely in the water.
- The difference in volume before and after submerging the object is the volume of your plastic object.
Method 3: Calculation for Rectangular Objects
If your plastic object has a rectangular or cuboid shape, you can calculate its volume using the following formula:
Volume = Length x Width x Height
- Measure the length, width, and height of the rectangular plastic object using a ruler.
- Multiply these three dimensions together to obtain the volume.
- You can use an online calculator that accepts your preferred units of measurement and provides the volume in cubic units.
Method 4: Weighing the Object
In some cases, you can determine the volume of a plastic object by weighing it. This method is especially useful when comparing the densities of different plastics:
- Weigh the plastic object in grams.
- Divide the weight by the density of the plastic type to find the volume.
- For example, if a plastic object weighs 100 grams and the density of the plastic is 0.5 g/cm³, the volume is 200 cm³.
Remember, the density of plastic is typically expressed in grams per cubic centimetre (g/cm³) or grams per cubic metre (g/m³). These methods will help you measure the volume accurately, which is essential for calculating the density of plastic.
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Calculate density
To calculate the density of plastic, you need to first understand what density is. Density is the mass per unit volume under normal pressure and temperature. In the metric system, density is measured in kilograms per cubic meter (kg/m3) or grams per cubic centimeter (g/cm3). In the English system, it is measured in pounds per cubic feet (lb/ft3).
To calculate the density of plastic materials, you have two options. The first option is to test the solid plastics in water, and the second is to test the solid plastic in a liquid other than water. The first choice is the more common test and can be performed with plastic sheets.
- Obtain a piece of the plastic: If the composition is uniform, a small piece will have the same density as a large piece. You can use a smaller sample for easier measurement, but a larger sample enables more accurate measurements of mass and volume.
- Weigh the sample: Record the mass in grams. If the scale measures pounds, multiply the result by 453.6 g/lb to convert pounds to grams.
- Measure the volume of the sample: This can be done by measuring the difference in water level before and after immersing the plastic sample in a graduated cylinder.
- Calculate the density: Divide the measured mass by the measured volume. This will give you the density of the plastic in g/cm3.
It is important to note that different materials have different bulk densities, which is the weight of the material per unit volume. Bulk density is crucial in drying operations and material flow. It can be expressed in g/cc (grams per cubic centimeter), b/cu ft (pounds per cubic foot), or kg/l (kilograms per liter).
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Bulk density
The bulk density of a substance is its mass per unit volume. It is usually expressed in grams per cubic centimeter (g/cm^3 or g/cc) for plastics, although it may also be written as kilograms per liter (kg/l) or pounds per cubic foot (lb/cu ft). The bulk density of a material is calculated by dividing its mass by its volume.
In the context of plastics, bulk density is a critical metric that has a significant impact on various phases of processing and production. It is used to determine the best way to treat specific materials throughout the production process, from blending and conveying to drying and storage. For example, bulk density is essential for determining the drying time and equipment sizing for a given material. Materials with lower bulk densities may require longer drying times and special measures to ensure smooth material flow during processing.
Additionally, bulk density affects the amount of material that can be stored in a container of a fixed size. Containers of the same size can hold dramatically different weights of material depending on their bulk density. This property is crucial for optimizing storage space and transportation efficiency.
To measure the bulk density of a plastic material, one can perform the following steps:
- Obtain a piece of the plastic. If the composition is uniform, a small piece will suffice, but a larger sample allows for more accurate measurements.
- Weigh the sample and record its mass in grams.
- Measure the volume of the sample. This can be done by measuring the displacement of water when the sample is submerged or by directly measuring the dimensions of the sample.
- Calculate the bulk density by dividing the measured mass by the measured volume.
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Frequently asked questions
The density of plastic is calculated by dividing the mass of the material by its volume. This is normally expressed in grams per cubic centimetre (g/cm3) or kilograms per cubic meter (kg/m3).
You will need a balance or scale to weigh the plastic sample, and a graduated cylinder to measure the volume of the sample.
Place a heavy weight at the bottom of the cylinder and fill it with water to a certain level. Remove the weight and tie it to the plastic sample with a thread. Drop them together into the water so the sample is completely submerged. The difference between the new and original water levels is the volume of the object.
