Polyethylene/clay permeability

Table 13 Gas permeabilities of the polyethylene clay nanocomposites and related sam- ...

With up to 40% clay, the compatibilized polymer/clay composites exhibit lower water vapor permeability than typical unfilled polyethylene. The compatibilized composites containing the clay particles were crosslinked, with the anhydride-grafted polyethylene bonded to the clay particles and uncrosslinked polyethylene. The composites exhibited improved flexural modulus, break strength, and notched Izod impact properties. 

The incorporation of clay minerals to polymers is an attractive approach to enhance gas barrier properties, as has been demonstrated with some polar thermoplastic polymers and thermosets [1]. Polyethylene, and especially HOPE, is commonly used in food packaging, where sometimes is needed to achieve an atmosphere with low concentration of oxygen and high of carbon dioxide. Consequently, a high permeability to these molecules is required in HOPE. The understandable idea is that molecules diffusing in the polymer will be slowed by increasing tortuosity as they meet essentially impermeable clay mineral layers in their path through the polymer and have to find a way around them [ 1 ]. 

The influence of the inclusion size, shape, and surface treatment on the gas permeability of polyethylene in its micro- and nanocomposites has been investigated in various papers.Kato et al. report the N2 permeability of nanocomposites based on polyethylene (PE) melt compounded with maleic anhydride grafted polyethylene (MA-g-PE) and octadecylamine (C18-MMT) modified montmorillonite. The gas permeability coefficient for all the prepared samples are reported in Fig. 11.8. Interestingly, polyethylene, maleic anhydride grafted polyethylene, a 70/30 blend of PE/MA-g-PE and a blend of PE/MA-g-PE/MMT have almost the same permeability coefficient. Only the composites obtained by mixing the polymeric matrices with the modified montmorillonite show for PE/MA-g-PE/C18-MMT (PECHl) a decrement of 30% in permeability and for MA-g-PE/C18-MMT (PECH3) a decrement of 35%. The differences in the gas barrier property were attributed to the different dispersion of the clay silicate layers in the matrix. 

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