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The aim of the work was to investigate the combined effect of Sepiolite and Cloisite 30B on the morphology and properties of PHBV/PLA 50/50 w/w blend. Scanning electron microscopic analysis showed that the morphology of PHBV/PLA blend was relatively regular and homogeneous in the presence of Cloisite 30B and Sepiolite compared to the virgin blend, indicating a better compatibility between the two base polymers. The thermal stability of PHBV/PLA blend was enhanced by the clay fillers. Modulus and hardness were also increased in comparison with the virgin blend. The rheological measurements showed a significant increase in both the complex viscosity and storage modulus of the filled blend due to interactions between the clays fillers and the PHBV/PLA blend. [ABSTRACT FROM AUTHOR]

The present article reports a study of oxidative degradation under eBeam irradiation of neat PHBV, neat PLA and PHBV/PLA blend (50/50 w/w) with and without Cloisite 30B (C30B) (3 wt%) at absorbed doses of 1 and 10 kGy. The changes in the chemical structure, the molecular weight, the thermal, mechanical and barrier properties as well as the morphology were evaluated. The data showed that eBeam irradiation of PHBV/PLA blend leads to oxidation reactions involving ester groups in both neat PLA and neat PHBV resulting in the formation of hydroperoxides groups. The presence of C30B in the polymer blend has no influence on the nature of the degradation process. However, the good dispersion of C30B nanoparticles provides more stability to the molar mass and the thermal, mechanical and barrier properties of PHBV/PLA blend. At absorbed dose of 10 kGy, the irradiated samples are completely safe. Furthermore, ecotoxicity testing of both non irradiated and irradiated samples clearly showed no toxicity. [ABSTRACT FROM AUTHOR]

Abstract: This work focuses on the effect of repeated processing cycles on the structure and properties of PS/Cloisite 15A (5% w/w) nanocomposite through a series of eight extrusion cycles using a co-rotating intermeshing twin screw extruder. For comparison, neat PS was also reprocessed as a reference material. Changes in the nanostructure were studied by wide angle X-ray scattering (WAXS) and rheological measurements. Molecular weight change was determined by size exclusion chromatography (SEC). Chemical changes were studied by Fourier transform infrared spectroscopy (FT-IR). Furthermore, the mechanical properties were investigated by a nanoindentation test method, whereas colorimeter techniques were used to analyze yellowness during reprocessing. The results of the WAXS analysis show that the d001 peak of the PS nanocomposite shifts to lower angles with increasing the number of reprocessing cycles indicating intercalated-delaminated structure. The rheological data reveal an enhancement of G′ in the melted state with reduction of the terminal slope of the nanocomposite samples over the PS matrix, thus confirming the occurrence of strong interaction between the silicate sheets and the polymer and their tendency to form a three dimensional superstructure. Further, in contrast to neat PS which undergoes a large reduction of molecular weight with increasing the number of cycles due to chain scission; in PS nanocomposites, the SEC data shows however that the degradation involves two mechanisms: chain scission as the most prevalent one, with the probability of occurrence of some crosslinking after 8 reprocessing cycles as demonstrated by the increase in both and . Repeated reprocessing globally yield colour changes in both the neat PS and PS nanocomposites whereas, the chemical structure and nanomechanical properties remain stable during reprocessing for PS nanocomposite. [Copyright &y& Elsevier]

Abstract: The effects of reprocessing cycles on the structure and properties of isotactic polypropylene (PP)/Cloisite 15A (OMMT) (5 wt. %) nanocomposites was studied in presence of maleic anhydride-grafted-polypropylene (PP-g-MA) (20 wt. %) used as the compatibiliser to improve the clay dispersion in the polymer matrix. The various nanocomposite samples were prepared by direct melt intercalation in an internal mixer, and further they were subjected to 4 reprocessing cycles. For comparative purposes, the neat PP was also processed under the same conditions. The nanocomposite structure and the clay dispersion have been characterized by wide angle X-ray scattering (WAXS), transmission electron microscopy (TEM) and rheological measurements. Other characterization techniques such as Fourier transform infrared spectroscopy (FT-IR), tensile measurements, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) have also been used to evaluate the property changes induced by reprocessing. The study showed through XRD patterns that the repetitive reprocessing cycles modified the initial morphology of PP/OMMT nanocomposites by improving the formation of intercalated structure, especially after the fourth cycle. Further, the addition of PP-g-MA promoted the development of intercalated/exfoliated silicate layers in the PP matrix after the second cycle. These results are in agreement with TEM observations indicating an improved silicate dispersion in the polymer matrix with reprocessing cycles displaying a morphology with both intercalated/exfoliated structures. The initial storage modulus (G′) of the nanocomposites, which was highly improved in presence of PP-g-MA seems to be less affected by reprocessing cycles at very low frequencies exhibiting a quasi-plateau compared to pristine PP/OMMT and PP. In contrast, the complex viscosity was found to decrease for the whole samples indicating that the main effect of reprocessing was a decrease in the molecular weight. Moreover, the thermal and mechanical properties of the nanocomposites were significantly reduced after the first cycle; nevertheless they remained almost unchanged during recycling. No change in the chemical structure was observed in the FT-IR spectra for both the nanocomposites and neat PP samples after 4 cycles. [Copyright &y& Elsevier]

Abstract: The degradation of polylactide (PLA)/Cloisite 30B nanocomposites under natural weathering was investigated as a function of clay loadings (1, 3 and 5wt.%) for up to 130 days using Fourier transform infrared (FT-IR) spectroscopy, size exclusion chromatography (SEC), nanoindentation measurements, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). For comparative purposes, the neat PLA was also considered. The FT-IR results showed that the photo-oxidation mechanism of PLA was not modified in the presence of Cloisite 30B, but only the degradation rates were accelerated. Moreover, the photo-oxidative degradation of PLA nanocomposite samples led to the formation of vinyl unsaturation, carbonyls, anhydrides and hydroperoxides groups as a result of the occurrence of several chemical mechanisms simultaneously. The decrease of the weight-average molecular weight, and the number-average molecular weight associated with an enhanced polydispersity of the nanocomposite samples indicated that chain scission was the most prominent phenomenon in natural weathering. The thermal degradation of the PLA was faster in the presence of clay. Modulus and hardness measured by nanoindentation increased slightly with exposure time for both neat PLA and PLA nanocomposite samples; the increase is also a function of the clay content. Finally, the weathering effect on the morphology of exposed samples observed by SEM revealed that the fractured surfaces exhibited many voids and cracks. These defects were much more pronounced for the PLA nanocomposites. [ABSTRACT FROM AUTHOR]

The effect of hindered amine stabilisers (HAS) on the thermal oxidation of low-density polyethylene (LDPE) films subjected to various gamma radiation doses in the range of 68–812 kGy, was studied by chemiluminescence (CL) at 190 °C in the presence of air. Different types of HAS were used, commercially known as Tinuvin 123, Sanduvor PR31 and Uvasil 299. It was found that under CL conditions, an antioxidative effect occurs for all unirradiated samples, being more relevant in the case of Sanduvor PR31. Our results indicate a specific decrease in the stability (depending on HAS nature) of irradiated materials with increasing irradiation dose. The initial intensity of CL emission (I0), which is related to the concentration of radiation-induced peroxy species was plotted as a function of dose and led to straight line dependence with the slope values placing the HAS effectiveness in the sequence: Tinuvin 123 > Sanduvor PR31 > Uvasil 299 ≫ none. [Copyright &y& Elsevier]

Blends of poly (3-hydroxybutyrate- co -3-hydroxyvalerate) (PHBV) and poly (butylene succinate) (PBS) (50:50 w/w) were prepared by melt mixing. 5 wt% of compatibilizing agent, obtained by grafting of maleic anhydride onto PHBV, was used to improve the miscibility between the blend components. The influence of the presence of both sepiolite and compatibilizer was studied by evaluating the effect of repeated extrusion cycles (up to 6) on the morphology and the functional properties of materials. Changes in thermal, morphological, rheological and mechanical properties were investigated. All the results showed that PHBV is the more sensitive component towards recycling due to thermomechanical degradation, but PBS as well as sepiolite and compatibilizer play a stabilizing role on PHBV due to improved morphology. The mechanical characteristics measured at different scales remain more or less constant compared to the initial ones revealing the preservation of the mechanical properties of the different samples after reprocessing. This paper highlights a synergistic effect induced by the presence of both compatibilizer and sepiolite leading to an improved recyclability of the resulting materials compared to neat polymers. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: The oxidative degradation of neat polylactide (PLA) and PLA-Cloisite 30B (C30B) nanocomposites under gamma irradiation was studied for irradiation doses ranging from 0 to 200 kGy. The morphologies and the properties of neat PLA and PLA-C30B nanocomposites (5 wt.%) were investigated using Fourier transform infrared spectroscopy (FT-IR), size exclusion chromatography (SEC), differential scanning calorimetry (DSC), thermogravimetric analysis (ATG), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nanoindentation measurements. The results were analysed by comparing the C30B influence on the PLA degradation. Results show neat PLA is strongly degraded by gamma irradiation while PLA-C30B nanocomposites are less affected because gamma irradiation promotes the C30B layer distribution within the PLA matrix. The morphological defects were much less more pronounced for the PLA nanocomposites compared to neat PLA, for which many voids and cracks were observed after irradiation. [Copyright &y& Elsevier]

The aim of this study was to assess the effect of various surface treatments on Aloe Vera fibers (AVF) used as reinforcement in PHBHHx biocomposites prepared by melt compounding. AVF were subjected to various surface treatments including alkaline, organo-silanes and combined alkaline/organo-silanes treatments. Both untreated and treated AVF were added to PHBHHx at filler content of 20 wt% and the resulted biocomposites were characterized using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), water absorption test and rheological measurements. The study showed that the combined alkaline/organo-silanes treatment of AVF resulted in better morphology and properties of PHBHHx biocomposite compared to untreated AVF and those treated either with alkaline or with organosilanes. Indeed, SEM analysis of the fracture surface of PHBHHx/AVF treated with combined alkaline-organosilanes showed better fiber-matrix interactions compared to the other samples. As a result, rheological properties, i.e., complex viscosity (η∗), storage modulus (G′) and loss modulus (G″) were increased. Higher resistance to water absorption was observed for PHBHHx/AVF treated with combined alkaline-organosilanes. Whereas, the various surface fiber treatments led to no noticeable change in thermal characteristics of the biocomposites. This study highlights the effectiveness of combined alkaline/organo-silanes treatment of AVF over alkaline and organo-silanes and their applications in PHBHHx biocomposites as an interesting source of cellulosic reinforcing materials. • Effect of surface treatments on Aloe Vera fibers (AVF) used as reinforcement in PHBHHx biocomposites. • Morphological and properties characterization of AVF and PHBHHx/AVF: 80/20 (w/w) biocomposite before and after treatments. • Improvement in fiber-matrix interface achieved by the combined alkaline-organosilanes treatment of AVF. • Interesting AVF source of cellulosic reinforcement materials. [ABSTRACT FROM AUTHOR]