Microcellular foaming by using subcritical CO2 of crosslinked and non-crosslinked LDPE/clay nanocomposites

Abstract

The semicrystalline character of low density polyethylene adds severe difficulties to its foamability by a batch process in which the gas is dissolved into the polymer matrix under subcritical conditions. To improve the low density polyethylene foamability, two strategies have been used: the addition of nanoclays and a partial crosslinking of the polymer matrix. On the one hand, the use of nanoparticles is suggested because they act as heterogeneous nucleating sites reducing the cell size and increasing the cell density. On the other hand, crosslinking is also adopted as a solution because both the crystallinity (and hence, the gas solubility and diffusivity) and the extensional rheological properties of the polymer matrix are highly influenced by the crosslinking degree achieved. Results indicate that despite the fact that the presence of nanoclays deteriorates the rheological behaviour of the nanocomposites and, hence, the later foaming behaviour, the use of partially crosslinked polymer matrices allows achieving high expansion ratios (around 7.5) as well as enhanced cellular structures with cell sizes of approximately 15 µm.