Pre-expansion Technology





The foaming agent for expandable polystyrene is mainly pentane, which is divided into 

n-pentane and isopentane. 

In industrial pentane, the olefin content has a great influence on the processability of 

expandable polystyrene. High olefin content, easy to cause product shrinkage.The EPS 

foaming agent content is not as high as possible. Standard: 4.8%-7% (≤6.8%) is generally 

normal at around 5%.

-----The foaming agent content is too high: the pre-foaming body is flowering, uneven, 

deformation cracking.

-----The content of the foaming agent is too low: the foaming ratio is lowered, the heating 

time is too long, the adhesion between the EPS beads is poor during the molding process, 

and the product is easy to shrink and fall off.





During the pre-expansion process, the beads containing the blowing agent do not foam 

until 80 ° C, except that the blowing agent in the beads spreads outward, and the beads 

do not expand at this time. 

When the temperature is higher than 80 ° C, the beads begin to soften, and the blowing 

agent distributed inside it is heated, and gasification generates pressure, causing the beads 

to start to expand and form mutually unconnected cells. At the same time, steam also 

penetrates into these cells, increasing the total pressure in the holes. As time goes by, the 

steam continues to deepen, the pressure increases, and the volume of the beads increases. 

This process continues, and the volume expansion can be maintained until the thin wall of the 

cell is broken. It can be seen that during the pre-expansion process, steam is continuously 

infiltrated, and it is important to increase the total pressure in the pores. This is the simple 

mechanism of EPS foaming.


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