Apparent density refers to the ratio of the mass of a material to its apparent volume. Apparent volume is the actual volume plus the closed pore volume. It refers to the ratio of the space occupied by a material under the action of an external force to the mass of the material, usually expressed in kilograms per cubic meter (kg/m³). It can reflect the porosity, hardness, elasticity and other properties of the material. For materials with regular shapes, the volume can be measured directly; for materials with irregular shapes, the pores can be sealed with wax sealing, and then the volume can be measured by drainage. The apparent density is usually measured in the natural state of the material, that is, the dry state stored in the air for a long time. For foamed rubber and plastic insulation materials, the ratio of closed-cell bubbles to rubber and plastic components varies, and there is a density range with the lowest thermal conductivity.
High porosity can effectively insulate; but too low density can easily lead to deformation and cracking. At the same time, the compression strength increases with the increase in density, ensuring the long-term stability of the material. In terms of thermal conductivity, the smaller the density, the lower the thermal conductivity and the better the thermal insulation; but if the density is too high, the internal heat transfer increases and the thermal insulation effect decreases. Therefore, when selecting thermal insulation materials, it is necessary to comprehensively consider their apparent density to ensure that the various properties are balanced to meet the needs of different usage scenarios.
Bulk density refers to the density of the material itself, that is, the ratio of the space occupied by an object to its mass. In thermal insulation materials, it usually refers to the ratio of the internal pore air and the actual mass per unit volume, expressed in kilograms per cubic meter (kg/m³). Similar to apparent density, bulk density is also one of the important parameters for evaluating the performance of thermal insulation materials, which can usually reflect the weight, water absorption, thermal insulation and other characteristics of the material.
Therefore, although both apparent density and bulk density reflect the density and porosity of thermal insulation materials, they have some obvious differences:
1. Different meanings
The apparent density of thermal insulation materials mainly evaluates the properties of the material such as porosity and elasticity, and can reflect the proportional relationship between the air and the actual mass inside the material.
Bulk density refers to the density of the insulation material itself, and does not involve any properties of the internal structure.
2. Different calculation methods
The apparent density of insulation materials is usually calculated by measuring the mass and volume of the sample, while the bulk density is calculated by measuring the weight of a material sample of known volume.
3. There may be errors
Since the calculation of the apparent density of the insulation material is based on the volume occupied by the compressed sample, it cannot well represent the overall structure of the material. At the same time, when there are cavities or foreign matter inside the material, the calculation of the apparent density may also have errors. Bulk density does not have these problems and can accurately reflect the density and weight of the insulation material.
Measurement method
Displacement method: For materials with regular shapes, the volume can be measured directly; for materials with irregular shapes, the pores can be sealed with wax sealing method, and then the volume can be measured with the displacement method.
Pycnometer method: For some materials, such as carbon materials, the pycnometer method can be used, with toluene or n-butanol as the standard solution for measurement, or the gas medium displacement method can be used to fill the micropores with helium until it is almost no longer adsorbed.
Application areas
Apparent density has a wide range of applications in materials science. For example, in flexible foam rubber and plastic insulation products, the main purpose of the apparent density test is to evaluate its density performance and ensure that its thermal insulation and mechanical properties meet the standards. In addition, apparent density is also used to evaluate the physical properties of materials and the performance of materials in engineering applications.
If the density increases and the rubber and plastic components increase, the material strength and wet rent factor may increase, but the thermal conductivity will inevitably increase and the thermal insulation performance will deteriorate. Kingflex finds an optimal total balance point in the mutually restrictive relationship between the lower thermal conductivity, the higher wet rent factor, the most suitable apparent density and the tear strength, that is, the optimal density.
Post time: Jan-18-2025
