Expert knowledge from A-Z
Permeability of a layer to gaseous substances; requires a pressure gradient.
Glass transition temperature
The temperature at which the ability of a plastic to deform experiences its greatest variation. The glass transition separates the brittle, energy-elastic area (=glass area) from the soft, entropy-elastic area (=rubber-elastic area). The glass transition temperature increases with the cross-link density of the plastic. Semi-crystalline plastics have both a glass transition temperature at which the amorphous phase "freezes" (becomes brittle) if the temperature goes lower, and a melting temperature at which the crystalline phase breaks down. PP has a glass transition temperature of 0 to −10 °C and becomes brittle at low temperatures. The upper working temperature is between 100 and 110 °C. The crystallite melting range is between 160 and 165 °C.
The gloss of films stems from their ability to reflect light. Measurement in accordance with DIN 67530 determine a reflectometer value, which represents the gloss of a surface (reflection characteristic). Depending on the film's surface properties, different angles of incidence are used to distinguish between measured values. For high-gloss surfaces, as an example, an angle of incidence of 20° should be used; high measured values (= high gloss) mean the surfaces reflect more light (or have less turbidity).