Why is it so important to choose the correct GMS dosing during the foaming/expansion process to produce high quality PE (polyethylene) or PP (polypropylene) foam material?
Simply because GMS, being an emulsifier and one of the most significant components, has a huge influence on many factors.
Let’s examine the following three main factors that help you to avoid the common mistakes:
GMS is a crucial element in cell formation
Surface tension during foaming - in simple terms, this is the effect that occurs as a result of the expansion of the blowing agent (butane, CO2 and others) when heated in the extruder, precisely when the blowing agent stops flowing and forms a new cell during critical expansion, and stretches the walls of already formed cell. GMS reduces the surface tension during expansion, helps and improves the process of cell’s formation (gas structural element).
GMS affects the diffusion process or called also “degassing”
An increase in the GMS input on the one hand improves the foaming process, but at the same time a large concentration of GMS migrates from the lower layers of the foam to upper layers and creates an obstacle for the replacement of gas with air, which leads to an increase in the conditioning time of the rolls in the warehouse and the rupture of the foam structure (formation of cell), since the gas in the foam structure expands after production. Also, a high gas residue in the foam structure and a high concentration of GMS on the foam surface can have a negative effect on the quality of lamination in the future.
At the same time, an insufficient concentration of GMS contributes to a sharp release of gas before the foam matures and, as a result, collapse of the foam occurs. Therefore, it is very important to control the dosing of GMS through experience and by carrying up tests during production, avoiding excessive or insufficient concentration.
GMS reduces friction and static charges on the foam surface
Reduction of static charges on the surface of the foam during the production process - static charges accumulate on the surface of the foam as a result of friction - thus reducing the risk of fire
The lower the density of the foam (kg/m3) and the saturation/gassing of it, the more the GMS will influence these factors.
The problem of many foam producers/manufacturers working with ultra-light, low density foams is mainly the shrinkage or rapid expansion of the foam during the conditioning process in the warehouse and the resulting formation of "bubbles" and breaks on the surface. The use of various additives "Anticolaps" in addition to GMS does not make a lot sense, because Anticolaps works exactly in the same way as GMS.
The correct dosing of GMS depends on many factors such as foam density, raw material dosage kg/h, ambient temperature, ambient humidity, temperature fluctuation during the day and night, and so on. Therefore, it is very important to choose the correct dosage/concentration of GMS during the foaming process.