VOLATILITY OF TITANIUM DIOXIDE PIGMENTS IN POLYETHYLENE FILM EXTRUSIONS

摘要

TiO2 grades absorb moisture in direct relationship to both their level of surface alumina and silica and the level of ambient humidity. Addition of surface organics slightly reduce the degree of moisture absorption. Once absorbed, the moisture can not be completely removed by simple drying at 120 degrees C but continues to volatilize as the processing temperatures are increased. Even if devolatilized during concentrate production, the permeability of LDPE allows the TiO2 to return to its equilibrium level of moisture. At low extrusion temperatures and /or TiO2 loadings, most TiO2 grades can produce acceptable film without visual defects due to volatility. However the presence of Lacing defects is a function of TiO2 grade selection, ambient storage humidity, film loading and extrusion temperature. For demanding applications such as extrusion coating of paper, TiO2 grades without surface alumina or silica treatments are required.