EPS is a thermoplastic material

EPS is a thermoplastic material, after heating foam, the volume per cubic decimeter containing 300 to 600 million independent airtight, containing more than 98% of the volume of air, so that it has many features of the structure.
First, thermal insulation performance
EPS has good insulation performance because it consists of completely closed polyhedral-shaped honeycomb structure, honeycomb diameter of 0.08 ~ 0.15mm, honeycomb wall thickness of 0.001mm. EPS consists of about 98% air and 2% polystyrene. Air entrapped in the honeycomb is a poor conductor of heat, and thus the thermal insulation of EPS (insulation) performance plays a decisive role. And other gases containing the foam, the air long-term stay in the honeycomb, so the insulation effect is stable.
(A) thermal conductivity
Thermal conductivity depends on density and temperature. EPS thickness decreases, heat radiation transmittance increases, when the thickness is less than 10mm is particularly evident. The water content of the EPS has a significant effect on the thermal conductivity. For every 1% volume of water absorbed, the thermal conductivity increases by 3.4%. Therefore, in any wall structure, the insulation must be kept away from condensate.
As the ambient temperature decreases, the thermal conductivity of the EPS foam will decrease. EPS foam is suitable for low temperature environments. Because the conduction and radiation to varying degrees with the density of the workpiece (ie cell wall thickness) and change, when the EPS density is too large or too small, its thermal conductivity will increase. At room temperature, when the density of EPS foam in the 30 ~ 40kg / m 3, the lowest thermal conductivity.
According to the above characteristics, if we want to choose EPS foam as insulation material, first, the ambient temperature should be less than 75 , the lower the ambient temperature, the lower the thermal conductivity, the better insulation performance. Secondly, we should also choose the density of EPS foam as a thermal insulation material. If we only from the thermal conductivity of the starting, you can choose the density of 30 ~ 40kg / m 3 or so of the EPS foam is better, with the increase in the density of EPS, EPS strength will rise, but the material consumption, cost Will rise. Therefore, we choose the density of EPS foam, we should consider its thermal conductivity, strength and cost of production and many other factors.
It is to be noted that, in addition to the above-mentioned density of the EPS foam, the molecular weight of the EPS (generally expressed as the relative viscosity value), the size of the EPS particles, the degree of adhesion (sintering) after the foaming process, Foam after its own aperture, etc., these factors are also the number of EPS foam plastic thermal conductivity has an impact. Obviously, we require EPS products after molding, the degree of bonding to a good degree of granularity requirements of smaller, and generally optional between 10 to 25 mesh, and should make the particle diameter is relatively uniform. As for the EPS after the pre-made aperture, that is, its internal with the pores, the more detailed the better. The size of EPS beads after pre-emission is mainly related to the process characteristics of EPS raw materials. The fine-grained foamed EPS beads can reduce convection, conduction and radiation heat transfer, so that the EPS bead shaped products can have good thermal insulation properties.
From the above, a variety of EPS raw materials, the thermal conductivity may be slightly different, but the difference is not large.
(B) the use of temperature
The maximum allowable temperature of the EPS foam depends mainly on the time and magnitude of the stress experienced under thermal conditions. Under the premise of not undermine the stress, styrofoam recycling short-term high temperature can reach more than 95 . However, in some cases, such as asphalt spreaders or hot melt adhesives, the contact temperature can be as high as 110 ° C for a short time and EPS foams can be tolerated. As the molding density is increased, the thermal stability is improved, while the maximum allowable temperature does not change. In the absence of any stress, EPS foam can be used at a maximum temperature of 85 .
Polystyrene foam structure is a non-crystalline plastic, from -180  to 95  glass transition temperature does not show a fundamental structural changes, so long-term use at very low temperatures.
Second, the mechanical properties
EPS foam deformation is increased with the load time increases. Only after two days of production can it reach its carrying capacity. The part just emerging from the mold is pressure sensitive because the condensation of steam and residual blowing agent in the cell causes a partial vacuum until the cell is sucked into the air to achieve pressure balance. It is necessary to allow the residual blowing agent to diffuse for a period of time because the blowing agent has a softening effect on the article.
EPS foam is a rigid foam class. In the case of a load, it exhibits viscoelastic properties, which are characteristic of a brittle material. Flexural strength, compressive strength and tensile strength are proportional to the apparent density of EPS foam.
Third, water absorption
Unlike many other foams, EPS foams are not hygroscopic and, even when immersed in water, absorb only a very small amount of water. Since the honeycomb walls are impermeable to water, the water can only move from the fused cells to the tiny cells It is understood that the amount of water absorbed (the amount of water penetrated) depends on the performance and processing conditions (especially when foaming) of EPE foam recycling raw materials during processing. As the density of EPS foam increases, water absorption and water vapor transmission rate decrease, and the diffusion coefficient of water vapor increases. For a certain density of molded parts, the better the sintering between the beads, the greater the water vapor diffusion resistance.

Oznake: EPS foam