Effects of organo-modified clay addition and temperature on the water vapor barrier properties of polyhydroxy butyrate homo and copolymer nanocomposite films for packaging applications
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Polymer nanocomposites, based on bacterial biodegradable thermoplastic polyester, poly(hydroxy-butyrate) (PHB), poly(hydroxyl-butyrate-co-hydroxy-valerate) (PHBHV), and commercial organo-modified montmorillonite (OMMT-Cloisite 10A) were prepared by solution casting method. This work aims to investigate the effect of Cloisite 10A type clay addition on the water vapour permeability properties of PHB/OMMT, and PHBHV/OMMT nanobiocomposite films. Temperature dependence of water vapor permeabilities of the films were also evaluated at various temperatures, and semi empirical permeability models were used to predict the permeability of polymer systems as a function of clay concentration and aspect ratio of nanoplates. Moreover, thermal, optical, and mechanical properties of the composites were examined by using varieties of techniques including differential scanning calorimeter (DSC), thermogravimetric analyzer (TGA), scanning electron microscope (SEM), and thin-film X-ray diffractometer (TF-XRD) respectively. Test results indicated that addition of highly intergallery swollen Cloisite 10A to the PHB/PHBHV, reduced the water vapor permeability up to 41 and 25% compared to native PHB and PHBHV films, respectively. Regarding the all mechanical properties measured, the maximum improvement was achieved for 3 wt% clay loaded samples for both PHB and PHBHV polymer composites. An increase of about 152 and 73% in tensile strength and of 77 and 18% in strain at break was achieved for PHB and PHBHV polymers, respectively. As a result of X-ray diffraction analysis, exfoliated structure was achieved at low clay loaded sample (1% w/w), however at higher concentration (3% w/w) the structure found as intercalated. Therefore, it is an evident that enhancement of characteristic properties highly depend on the dispersion level of clay particles in polymer matrix. The results obtained in this study show the feasibility of improvement of the properties of PHB based polymers with incorporation of nanoclay.