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.