Poly(propylene)‐Layered Silicate Nanocomposites: Gas Permeation Properties and Clay Exfoliation

Abstract

To monitor the mineral surface coverage and energy, the inorganic cations of two clays (montmorillonite) with different surface area/cation have been exchanged by alkylammonium ions, carrying alkyl chains of different number and length. The prepared OMs were free of unreacted organic ions. With increasing length and number of the alkyl chains, an increase in the basal‐plane spacing (d‐spacing) of the OM was observed. The d‐spacing also increased with increasing CEC of the clay (decreasing available area/cation). The OMs were compounded with PP and their effect on the crystallinity and gas‐barrier properties of the polymer was investigated. The OM had no influence on the degree of crystallinity of PP under the processing conditions used. Oxygen permeation through the composites decreased, depending on the cross‐sectional area of the exchanged organic cation and the CEC of the clay. These parameters control the mineral surface coverage (consequently the surface energy) as well as the tilt angle of the alkyl chains to the mineral surface, and hence the d‐spacing. Increasing the length of the alkyl chains and their number per cation enhanced the d‐spacing, clay exfoliation, and the gas‐barrier properties of the composites. A mixed morphology, consisting of delaminated aluminosilicate layers and OM tactoids of varying thickness was observed but no intercalation took place. The oxygen permeation coefficient of the nanocomposites was found to be a non‐linear function of the volume fraction of the inorganic part of the OM.magnified image

Polypropylene-Layered Silicate Nanocomposites: Filler Matrix Interactions and Mechanical Properties

“…The inorganic content of the OMMT was always kept constant to 3 vol.% in the composites in order to have comparison of the properties among each other. The prepared OMMT were ensured to be free of any excess molecules of the surface treatment by using high resolution TGA and extensive washing protocols [21]. As the organic modifications used in the study have onset of degradation in the range of 200-2158C and the peak degradation temperatures in the range of 260-3008C, therefore, the compounding temperatures during composite formation were also kept low in order not to degrade the modification and as well as the polymer, but high enough to ensure homogenous mixing.…”

“…The aluminosilicate surface was rendered organophilic by exchanging the inorganic cations with organic ammonium ions as described earlier [21]. Both the degree of exchange and the purity of the surface were monitored by hi-res thermogravimetric analyzer [21].…”

“…The aluminosilicate surface was rendered organophilic by exchanging the inorganic cations with organic ammonium ions as described earlier [21]. Both the degree of exchange and the purity of the surface were monitored by hi-res thermogravimetric analyzer [21]. If the TGA thermogram indicated the presence of unreacted surfactant molecules on the surface owing to their degradation at lower temperatures than the reacted ammonium ions, the washing step was repeated by resuspending the modified clay in solvent, sonication for 10 min and stirring overnight followed by filtration, washing and drying at 708C under reduced pressure.…”

“…Scintag XDS 2000 diffractometer (Scintag Inc., Cupertino, CA) was used to collect wide-angle X-ray diffraction patterns using Cu Ka radiation ( ¼ 0.15406 nm) in reflection mode as previously described [21].…”

“…It has been reported that a partial delamination can still be achieved without compatibilizer, if the filler matrix interactions are efficiently enhanced by optimizing the modification of the surface supplemented by shear forces during compounding [20,21]. The surface coverage, chemical structure of the coating and basal plane spacing have been observed to determine the surface energy of the organically modified montmorillonite and its tendency to exfoliate [22].…”