Density of Plastics: Technical Properties
Introduction
In bulk plastic, density is a substance’s mass per unit volume. It is a crucial determinant of putting plastics away in a box, Equipment sizing for drying, and Material progression. There is a wide range in the bulk density of plastic materials. Bulk density can be represented in three different ways:
- Lbs./cu.ft. Means pounds per cubic foot.
- (g/cc) is the unit of mass density.
- Liters per kilogram (kg/l)
Importance of Density in Plastics
- Mechanical Properties: Researchers found that molecular density significantly affects the polymer matrix’s mechanical strength, stiffness, and hardness. In general, the density of the material is directly proportional to its mechanical strength and rigidity.
- Weight Considerations: Ideally, the density of a specific type of Plastic determines the weight of the manufactured end product. Industries like automobiles and aircraft prefer porous plastic products for their lighter densities.
- Thermal Insulation: Some plastics have better thermal insulating capacity and low density, which is ideal for applications involving heat preservation and heat resistance.
- Buoyancy: Plastic density defines the probability of floating or sinking in water, which is critical in marine applications or buoyancy considerations.
- Cost: The density of the plastics plays a significant role in the cost because the higher density ensures that more raw material is used, yielding massive and costly products.
Densities of plastic types:
Some of the accepted density of plastic are:
- The density of polyethylene plastic is 0.92 g/cm3
- The density of recyclable plastics is 0.94-0.965 g/cm3 ( for R-HDPE)
Measurement of Density
The techniques used to measure the density of plastics is summarized below:
| Particulars | Details |
| Hydrostatic Weighing | One of the most used techniques for determining a sample’s density is where the sample’s weight in air and water is taken and compared. |
| Density Gradient Column | Refers to a procedure where one sinks the plastic sample into a fluid and then uses the force exerted by the liquid to determine the density. |
| Pycnometer | It uses the amount of liquid displaced by the sample to quantify its mass to determine the density of the sample. |
| Archimedes Principle | It uses the amount of liquid displaced by the sample to quantify its mass and determine the density of the sample. |
Application of Density in Material Testing
Failure Analysis:
In the case of a plastic part’s service failure, density testing can determine whether the plastic material was within specification, which can help in the root-cause material analysis.
Regulatory Compliance End Uses:
Many industries require density within certain limits for various materials based on safety and performance. Density testing ensures that the materials meet these requirements.
Product Development:
The density of plastics plays a major role in the formulation of materials during the development of new plastic products for optimizing properties.
Read more: ASTM D1505: The Density of Plastics by the Density-Gradient Technique
Conclusion
The density of plastics is critical for material selection, product design, and performance improvement. It directly impacts how a plastic material performs under different situations, its processing properties, and its applicability for specific applications.
FAQs
How is specific gravity and density related? Specific gravity is directly proportional to density. If you know the density of a material, you can calculate its specific gravity by dividing it by the density of water.
What are the factors influencing plastic density? The factors affecting plastic density are: Polymer Composition, Filler Content, Porosity & Crystallinity.
What are the typical applications of density in plastic selection? Automotive, construction, medical devices, and packaging.
