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,
-----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.