Specific weight, bulk weight and density of plastic
Plastic has become a universal material that is used almost everywhere. It became widely used thanks to its practical advantages. The remarkable strength of plastics has made it possible to replace many more expensive materials.
Specific weight and density of plastics
The density of plastics is much lower than the density of metal, stone and concrete structures. However, only one type of material can compete with plastic in strength — metal. In the process of manufacturing various structures and products, plastic takes different forms and can be stretched and bent well. When certain types of binders are used, plastics can be comparable in strength to wooden structures.
The specific weight of plastic varies depending on the binder used. Thus, the bulk density of polyethylene is 0.9 g/cm³, while the weight of fiberglass plastic will be significantly higher — 1.95 g/cm³.
| Name | Mass of 1 m³ in tonnes | Mass of 1 m³ in kilograms | Specific weight (kg/m³) |
| Weight of 1 m³ of plastic | 0.85 - 1.8 | 850 - 1800 | 850 - 1800 |
Several types of plastics are distinguished depending on their elasticity properties. Their functional characteristics are shown in the table.
| Parameter / type | Rigid | Semi-rigid | Soft |
| Permeability | Impermeable | Affected by gases, vapors, water and air masses | |
| Elasticity | Absent | Low | Very high |
| Resistance to temperature changes | 300 - 400 °C | >70 °C | >50 °C |
| Thermal expansion | Within 25 - 120 · 10⁻⁶ | ||
| Resistance to low temperatures | Very high | Moderate | Low |
| Hardness measurement | 40 HB | 2 - 20 HB | |
| Protection against chemicals | High degree of protection | ||
| Ability to retain heat | They can retain heat well and conduct it poorly | ||
| Electrical conductivity | Used as a dielectric or electrical insulator | ||
| Degree of light permeability | Transmit light well if they are not made with a colored filler | ||
| Ability to retain color | Very high when the correct coloring elements are used (ochre, red lead, etc.) | ||
Based on the data shown in the table, it can be concluded that plastics are resistant to most chemicals. They are often used in the chemical industry to protect structural elements. Particularly resistant plastics include Teflon, polyethylene, polyisobutylene, polystyrene and polyvinyl chloride.
Disadvantages of using plastics
The significant disadvantages of plastics are their ability to ignite quickly, instability at high temperatures and lack of hardness. The softest steel is 2 times harder than plastic. When plastic structures are used inside and outside residential premises, fire risks must be taken into account. They cannot stop burning on their own and can cause significant harm.
There is a concept called plastic aging, which means the loss of some material properties during long-term use. In addition, exposure to sunlight and air gradually destroys plastic products and structures. The following causes start the aging process:
- Breakage of the molecular chain of the polymer substance.
- Rearrangement of the molecular structure.
As a result, strength and elasticity decrease, the color changes, and the product becomes brittle. The most unpleasant process is molecular decomposition, which is accompanied by the release of toxic vapors.
Frequently Asked Questions
Can the density of plastic be used for precise calculations?
The density and weight values for plastic in this article are reference values. They are suitable for preliminary estimates, but design, construction, production and other critical calculations should be checked against standards, material datasheets or measurement results.
Why can the actual weight of plastic differ from the table?
The actual weight of plastic depends on composition, moisture, temperature, porosity, fraction size, material grade and measurement conditions. Because of this, real values may differ from the average table data.
How do you calculate the mass of plastic from density?
For an approximate calculation, use the formula: mass = density × volume. If the density of plastic is given in kg/m³ and the volume is in m³, the result will be in kilograms.