Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/organo-modified montmorillonite (OMMT) nanocomposite films were prepared by melt compounding and cast-film extrusion at various loading rates, i.e. 1, 3 and 5 wt. %. The effect of OMMT on the biodegradability of produced PHBV nanocomposite films was investigated under controlled conditions in aqueous medium (20 C for 28 days) by monitoring the biochemical oxygen demand (BOD), and under laboratory-scale composting conditions (58 C for 70 days) by monitoring the weight and surface loss. The microstructural and macromolecular changes were monitored during the biodegradation process by means of scanning transmission electron microscopy (STEM), differential scanning calorimetry (DSC) and size exclusion chromatography (SEC) analysis. The initial microstructure of the nanocomposites samples exhibited an intercalated structure with a good clay/matrix affinity. BOD evolution in aqueous conditions as well as surface and weight loss in composting conditions indicated that the biodegradation rate of PHBV nanocomposites was lower than neat PHBV, which supports a barrier effect of OMMT. This was confirmed by the surface erosion observed through SEM accompanied by a significant decrease of the average molecular weight in the bulk of the films. Our results demonstrated that the biodegradation of PHBV and nanocomposite films occurred by combined hydrolytic and enzymatic processes, at the surface as well as in the bulk of the material. DSC analysis also revealed no change in the degree of crystallinity, which suggests that the amorphous and crystalline phases were degraded at same rate.

No abstract

In this paper, the effects of gamma irradiation on Cast poly(3hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and PHBV/Cloisite 30B (C30B) (3 wt%) bionanocomposite prepared by melt compounding, were evaluated at various doses, i.e., 5, 15, 20, 50 and 100 kGy at room temperature in air. Changes in molecular weight, morphology and physical properties were investigated. The study showed that the main degradation mechanism occurring in gamma irradiation in both Cast PHBV and C-PHBV/3C30B bionanocomposite is chain scission, responsible for the decrease of molecular weight. Differential scanning calorimetry (DSC) data indicated a regular decrease in crystallization temperature, melting temperature and crystallinity index for all irradiated samples with increasing the dose. Further, DSC thermograms of both Cast PHBV and PHBV bionanocomposite exhibited double melting peaks due probably to changes in the PHBV crystal structure. Tensile and DMA data showed a reduction in Young's modulus, strength, elongation at break and storage modulus with the radiation dose; the decrease was however more pronounced for Cast PHBV. The morphological damages were much less pronounced for the PHBV bionanocomposite sample compared to Cast PHBV, for which some irregularities and defects were observed at 100 kGy. This study highlighted the ability of C30B to counterbalance the detrimental effect of radiolytic degradation on the functional properties of PHBV up to 100 kGy, thus acting as a potential anti-rad.

Hygrothermal aging of neat poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and PHBV filled with an organomodified montmorillonite (C30B) at 3wt. was investigated at 65 C and 100% relative humidity (RH) up to 100 days. FT-IR data indicated that the carbonyl intensity index decreased with exposure time for both samples, while the main degradation mechanism occurred through hydrolysis reaction. This led to chain scissions resulting in a decrease in molar mass. Water absorption increased with exposure time for both neat PHBV and PHBV/C30B (3wt%) bionanocomposite. Differential scanning calorimetry measurements showed a decrease in both crystallinity index and melting temperature after hygrothermal aging and thermogravimetric analysis data indicated also a decrease in thermal stability. Mechanical and viscoelastic properties were also altered, being, however, more pronounced for the neat PHBV. Overall, the PHBV bionanocomposite exhibited a better resistance toward hygrothermal aging at 65 C and 100% RH.