Effect of Highly Exfoliated and Oriented Organoclays on the Barrier Properties of Polyamide 6 Based Nanocomposites

Abstract

The influence of the incorporation of nanoparticles (organo-modified montmorillonite Cloisite 30B) in polyamide 6 (PA6) on the transport of small molecules was investigated. Nanocomposites were prepared by melt blending followed by cast extrusion for obtaining film-forming materials. The nanoclay content of the materials was varied from 0 to 5 vol%. Differential scanning calorimetry measurements, electronic microscopy, X-ray diffraction, and rheology were used for characterizing the nanocomposite structure. Because of the presence of nanofillers, a high barrier effect to nitrogen and water was clearly evidenced and mainly attributed to the increase of tortuosity because of the increase of the diffusion pathway generated by impermeable nanofillers. In this study, the high barrier effect was attributed to the very good dispersion of montmorillonite platelets in the PA6 matrix resulting from a twostep melt processing. This peculiar processing has induced a good exfoliation and an orientation parallel to the film surface of lamellar montmorillonite platelets which is clearly demonstrated from transmission electron microscopy analysis. The permeation results were evaluated on the basis of geometrical models proposed by Nielsen and Bharadwaj, and by analyzing the plasticization phenomenon in the case of water permeation involving a concentration-dependence diffusivity correctly approached by an exponential law.

A review of the water barrier properties of polymer/clay and polymer/graphene nanocomposites

“…Of the studies reviewed in Table 1, some have measured the aspect ratio using transmission electron microscopy (TEM) [16,50,51,56] whereas others have calculated the value from fitting experimental data to one of the models [33,50,51,54,56,66]. Comparing the studies where aspect ratios have been measured, modest values (of 20, 38 and 52) were reported for samples prepared by melt processing.…”

“…Bharadwaj [22] can be successfully applied [50,56,62]. Other models are claimed to be more suitable for predicting behaviour at high filler aspect ratios.…”

“…This result was surprising but was thought to be due to reduced mobility of polymer chain segments because of the large number of clay platelets at high clay concentration. Therefore, the authors [33] concluded that around the filler particles and aggregated filler, there was an interfacial layer, the properties of which were different from the bulk polymer when Alix et al [50] found that in PA6 based nanocomposites, the plasticization phenomenon was greater in the intercalated polymer clay nanocomposite than in the neat polymer and increased with clay content. This revealed that the sorbed water, due to the plasticization phenomenon, is associated with the intercalated structure of the montmorillonite clay in the nanocomposite.…”

“…Polymer / clay nanocomposites, such as PE and nylon nanocomposites, are used as barrier materials in packaging and storage applications [43,46,50,52]. Recently, biodegradable and bio-based polymer / clay nanocomposites, for example PLA, PCL and PBS, have been used as packaging, especially for food and also for short shelflife products, such as containers, beverage cups and blister packages [16,57,63,65,66,116].…”

“…TEM was used in a couple of studies and values of 800 and 500 were reported [94,95]. These values are at least an order of magnitude higher than the aspect ratios reported from polymer-clay nanocomposites that were processed by melt blending [16,50,51], although more comparable to polymer/clay nanocomposites prepared by polymerisation and casting [56]. Atomic force microscopy (AFM) has also been used and gave a value of 150 in one study [102] and was found to corroborate the TEM results of another [94].…”