Quting Gou

Crystallization behavior, thermal and mechanical properties of PHBV/graphene nanosheet composites

Biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/graphene nanosheet (GNS) composites were prepared via a solution-casting method at low GNS loadings in this work. Transmission electron microscopy revealed that a fine dispersion of GNSs was achieved in the PHBV matrix. The thermal properties of the nanocomposites were investigated by thermogravimetric analysis, and the results showed that the thermal stability of PHBV was significantly improved with a very low loading of GNSs. Nonisothermal melts crystallization behavior, spherulitic morphology and crystal structure of neat PHBV and the PHBV/GNSs nanocomposites were investigated, and the experimental results indicated that crystallization behavior of PHBV was enhanced by the presence of GNSs due to the heterogeneous nucleation effect; however, the two-dimensional (2D) GNSs might restrict the mobility of the PHBV chains in the process of crystal growing. Dynamic mechanical analysis studies showed that the storage modulus of the PHBV/GNSs nanocomposites was greatly improved.

Living lamellar crystal initiating polymerization and brittleness mechanism investigations based on crystallization during the ring-opening of cyclic butylene terephthalate oligomers

The brittleness of polymerized cyclic butylene terephthalate (pCBT) is generally ascribed to its high crystallization degree and perfect crystal structure. Herein, a simple and effective method for improving the brittleness of pCBT is presented. Unlike other published toughening methods, this method did not decrease or destroy any of the natural advantages of cyclic butylene terephthalate oligomers (CBT) and its ring-opening polymerization (ROP). The melting behaviour and crystallization of CBT demonstrated that some CBT crystals were unable to melt completely during ROP. These un-melted crystals served as self-compatible nucleators and reduced the crystallization induction time of pCBT during ROP, they also plant many stress concentration points which result in the brittleness of pCBT, according to mechanical tests and crystallization kinetics. Finally, the “living lamellar crystal” initiating ROP and new brittleness mechanisms were proposed.

Crystallization and morphology of star-shaped polyethylenoxyde-b-polycaprolactone under high pressure carbon dioxide

Atomic force microscopy (AFM), wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry are used to analyze the crystallization morphology and melting behavior of 4-arm PEO-b-PCL under high-pressure CO2. It is demonstrated that CO2 has certain effect on the melting and crystallization behavior of the samples. After crystallization under CO2 at 4 MPa, spherulites with concentric ring-banded structure are formed which are composed of crystals with periodic thickness variation, and the band distance decreases with increasing treatment pressure. Due to the plasticization effect of CO2, depression of the melting temperature is observed with sorption of CO2 in polymers.

Morphology of Poly(Ethylene Oxide)b-Poly(epsilon-Caprolactone) Spherulites Formed Under Compressed CO2

Melt crystallization of PEO-b-PCL thin films was conducted under compressed CO2 and the morphology of the spherulites obtained at various pressures was investigated by polarizing optical microscopy (POM) and atomic force microscopy (AFM). At 3 MPa CO2 classical ring-banded spherulites with periodical twisting lamellae formed. However, in the spherulites with concentric ring-banded structures formed at 5 MPa CO2, the rings were formed due to periodical variations in thickness along the radial direction.