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Biodegradable poly(3-hydroxybutyrate) (PHB)/functionalized multi-walled carbon nanotubes (f-MWNTs) nanocomposite was prepared in this work by solution casting method at 2 wt% f-MWNTs loading. Scanning electron microscopy and transmission electron microscopy observations indicate a homogeneous distribution of f-MWNTs in the PHB matrix. Nonisothermal melt crystallization, overall isothermal melt crystallization kinetics, and crystalline morphology of neat PHB and the PHB/f-MWNTs nanocomposite were studied in detail. It is found that the presence of f-MWNTs enhances the crystallization of PHB during nonisothermal and isothermal melt crystallization processes in the nanocomposite due to the heterogeneous nucleation effect of f-MWNTs. Moreover, the incorporation of a small quantity of f-MWNTs apparently improves the thermal stability of the PHB/f-MWNTs nanocomposite with respect to neat PHB. Two methods are employed to study the activation energies of thermal degradation for both the neat PHB and the PHB/f-MWNTs nanocomposite. The activation energy of thermal degradation of the PHB/f-MWNTs nanocomposite is higher than that of neat PHB. Copyright © 2009 John Wiley & Sons, Ltd.

In this work, nonisothermal melt crystallization and subsequent melting behavior of poly(hydroxybutyrate) (PHB) and its nanocomposites at different multiwalled carbon nanotubes (MWCNTs) loadings were investigated. Increasing the MWCNTs loadings has enhanced the nonisothermal melt crystallization of PHB significantly in the nanocomposites when compared with that of the neat PHB; furthermore, increasing the cooling rates shift the crystallization exotherms to low temperature range for both neat PHB and its nanocomposites. Double melting behavior is found for both neat PHB and its nanocomposites crystallized nonisothermally from the melt, which is explained by the melting, recrystallization, and remelting model. Effects of the MWCNTs loadings, cooling rates, and heating rates on the subsequent melting behavior of PHB were studied in detail. It is found that increasing the MWCNTs loadings, decreasing the cooling rates, and increasing the heating rates would restrict the occurrence of the recrystallization of PHB in the nanocomposites. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2238–2246, 2009

Isothermal Melt Crystallization Kinetics Study of Biodegradable Poly(3-hydroxybutyrate)/Multiwalled Carbon Nanotubes Nanocomposites

By using the mathematical uniform design, a new agglomerated flux for high speed and multi-arc submerged arc welding (SAW) has been developed in this paper, which performs excellently in welding process, and the effects of flux composition on the welding characteristics is analyzed as well. The mechanical tests show that the weld metal obtained in SAW with this flux exhibits high toughness at low temperature, and the other mechanical properties of the weld metal also satisfy the technical specifications for the West to East Pipeline Project in China. The microstructures of the weld metal are also examined. Both optical and TEM microphotoes demonstrate that the weld consists mainly of small-sized and uniformly distributed acicular ferrite. These microstructures can effectively prevent the initiation and propagation of micro cracks, resulting in high notch toughness of the weld metal at low temperature.

Biodegradable poly(epsilon-caprolactone) (PCL)/multi-walled carbon nanotubes containing carboxylic groups (f-MWNTs) nanocomposites were prepared via simple melt compounding at low f-MWNTs loading in this work. Scanning and transmission electron microscopy observations indicate a homogeneous and fine distribution of f-MWNTs throughout the PCL matrix. The effect of low f-MWNTs loading on the crystallization, mechanical properties, and controlled enzymatic degradation of PCL in the nanocomposites were studied in detail with various techniques. The experimental results indicate that the incorporation of f-MWNTs enhances both the nonisothermal crystallization peak temperature and the overall isothermal crystallization rate of PCL in the PCL/f-MWNTs nanocomposites relative to neat PCL; moreover, the incorporation of a small quantity of f-MWNTs has improved apparently the mechanical properties of the PCL/MWNTs nanocomposites compared to neat PCL. The enzymatic degradation of neat PCL and the PCL/f-MWNTs nanocomposites at low f-MWNTs loading was studied in detail. The variation of weight loss with enzymatic degradation time, the surface morphology change, the reduced film thickness, the appearance of f-MWNTs on the surface of the films, and the almost unchanged molecular weight after enzymatic degradation suggest that the enzymatic degradation of neat PCL and the PCL/f-MWNTs nanocomposites may proceed via surface erosion mechanism. The presence of f-MWNTs reduces the enzymatic degradation rate of the PCL matrix in the nanocomposites compared with that of the pure PCL film.