Gas barrier properties of PP/EPDM blend nanocomposites
Introduction
Polyolefins, such as polypropylene and polyethylene find extensive use in packaging. Improvements in poor barrier properties of polyolefins will be beneficial for the current applications and should also lead to applications in pharmaceuticals, electronic packaging and particularly packaging of food products, which are sensitive to oxygen. Most schemes to improve polyolefins gas barrier property involve either addition of higher barrier plastics via a multilayer structure or high barrier surface coatings, however, these approaches are not cost effective. The emerging field of polymer-layered nanocomposites is unique in that it addresses shortcomings of polyolefins for both packaging and engineered applications requiring desirable mechanical, thermal as well as good barrier properties. Polymer-layered silicate nanocomposites are plastics containing low levels of dispersed platelet minerals with at least one dimension in the nanometer range. A small clay loading does not affect the processibility and does not substantially increase the specific gravity of the polymer. Also, due to the fine particle size of the fillers, the film clarity, for all practical purposes, will not be reduced. The most common mineral used in nanocomposites is montmorillonite. Nonpolar, hydrophobic polyolefins, such as polypropylene and polyethylene lack a strong interaction with polar, hydrophilic clay particles of montmorillonite. To improve the interaction between polymer and clay, montmorillonite is treated usually with ammonium alkyl compounds and the treated clay is called organoclay. Many approaches have been tried to prepare organoclay/polyolefin nanocomposites, including in situ polymerization of ethylene in the presence of layered silicates [1], [2], solvent blending [3] and melt compounding [4], [5], [6], [7], [8]. However, melt blending is the most convenient process for preparation of the nanocomposites. Although, in situ polymerization may form an exfoliated nanocomposite but the clay platelets would recover the stacked structure in the subsequent melt forming process and mechanical properties would not significantly improved [1], [2]. Only one recent article was found on the solvent blending of polyethylene/montmorillonite reporting a good dispersion of clay in polyethylene [3]. Compatibilizers (usually maleated PP or PE) are believed effective for melt blending of clay and polyolefin in order to enhance the interaction between clay and polymer [9], [10]. In solvent blending process that was used for preparation of nanocomposites in our study, maleic anhydride grafted polypropylene was unsuccessful, and indeed, it caused agglomeration of the clay instead of resulting in good dispersion. One recent report used an antioxidant as compatibilizer for polypropylene/montmorillonite in a melt compounding process claiming a relatively successful result [11]. So far, most papers on clay/polyolefin nanocomposites concentrate on the state of dispersion of nanoclay in melt compounding and mechanical properties in particular [2], [5], [6], [8], [12], [13], [14], [15], [16]. However, to our best knowledge none of these reports have studied the barrier properties. In this paper, we have studied diffusion of oxygen and carbon dioxide gases across the 50:50 blend of polypropylene (PP) and ethylene-propylene-diene (EPDM) rubber membranes containing organophilic montmorillonite nanoclay and an antioxidant as compatibilizer. The nanocomposite was prepared in a solvent blending process. The effect of nanoclay content and presence of compatibilizer on the state of dispersion are discussed by using XRD and a gas permeation model. The effect of nanoclay in barrier improvement of PP/EPDM blend against oxygen and carbon dioxide was investigated. Crystallinity of polypropylene and morphology of PP/EPDM/organoclay systems are discussed.
Section snippets
Materials
The layered silicate used in this study was Nanolin DK4 from Zhejiang Fenghong Clay Chemicals, Inc. It is an alkyl ammonium modified montmorillonite with cation-exchange capacity of 115–120 mmol/100 g (115–120 meq/100 g). Polypropylene with MFI = 7 g/10 min and density = 0.9 g/cm3 was used. EPDM was a product of Montell (Italy) with MFI = 0.41 g/10 min and density = 0.86 g/cm3. Xylene was used as solvent. The compatibilizer was an antioxidant from Ciba Specialty Chemicals, generally known as Irganox 1010. It has
Results and discussion
XRD measures the degree of dispersion by estimating the distance between individual platelets after mixing with polymer. A shift to lower angles of the characteristic diffraction peak suggests an increase in interlayer spacing or gallery of the clay, which is referred to as intercalation. A disappearance of the clay interlayer diffraction peak indicates possible exfoliation of the clay platelets and a broadening of the peak is considered to be the result of partial exfoliation. The XRD spectra
Conclusions
The degree of dispersion in PP/EPDM/nanoclay nanocomposite prepared by solvent blending was studied by XRD method. The clay gallery separation or d-spacing calculated from Bragg's law. These results suggested that 3 and 5 wt% clay nanocomposites are intercalated. Presence of compatibilizer induced even more intercalation of nanoclay. State of nanoclay dispersion was also examined by evaluation of aspect ratios of nanoclay platelets from permeability measurements and using a permeability model.
References (22)
- et al.
Polyethylene-layered silicate nanocomposites prepared by the polymerization-filling technique: synthesis and mechanical properties
Polymer
(2002) - et al.
Influence of clay exfoliation on the physical properties of montmorillonite/polyethylene composites
Polymer
(2002) - et al.
Melt compounding of syndiotactic polypropylene nanocomposites containing organophilic layered silicates and in situ formed core/shell nanoparticles
Polymer
(2002) - et al.
3D hierarchical orientation in polymer–clay nanocomposite films
Polymer
(2003) - et al.
Synthesis and characterization of maleated polyethylene/clay nanocomposites
Polymer
(2001) - et al.
Preparation and characterization of polypropylene/layered silicate nanocomposites using an antioxidant
Polymer
(2004) - et al.
Polydisperse flakes in barrier films
J. Membr. Sci.
(2004) - et al.
Barrier membranes with different sizes of aligned flakes
J. Membr. Sci.
(2005) - et al.
Synthesis and characterization of polypropylene/clay nanocomposites
J. Appl. Polym. Sci.
(2001) - et al.
Study on the solvothermal preparation of polyethylene/organophilic montmorillonite nanocomposites
J. Mater. Chem.
(2002)
Morphology evolution and anisotropic phase formation of the maleated polyethylene-layered silicate nanocomposites
Macromolecules
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