Sorption behavior and microcellular foaming of low-density polyethylene/clay nanocomposites by gas dissolution under sub-critical conditions

Abstract

Two of the most interesting properties of polymer composites are their improved gas barrier properties, which make them useful for packaging and protective applications and their ability to generate microcellular structures with interesting applications in the construction sector. In this paper, the batch gas dissolution method has been employed to analyze both the sorption behavior and the microcellular foamability of different formulations based on blends of low-density polyethylene, polyethylene grafted with maleic anhydride, and layered clays. Blends of low-density polyethylene and polyethylene grafted with maleic anhydride have been also produced with the aim of clearly distinguish the role played by the clays. The batch gas dissolution process, employing CO2 as gaseous phase, has been intensively used for the foaming of amorphous polymers; however, it is not common in the case of semi-crystalline polymers like low-density polyethylene. Results indicate that the presence of clays reduces slightly the diffusivity. However, the reduction in diffusivity when the clay content increases from 3 wt.% to 5 wt.% is not as high as expected. The existence of an interface between the clays and the polymer, which allows gas molecules to find faster ways across the composite, could be the reason of this behavior. Regarding the cellular materials, in general the relative density increases when adding nanoparticles and also a deterioration of the cellular structure is observed. The slight improvements in the sorption behavior have not been high enough to overcome the effects related to the worsening of the extensional rheological properties of the polymer composites.