Bingjie Wang

Thermo-mechanical properties of the composite made of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) and acetylated chitin nanocrystals

Acetylated chitin nanocrystals were prepared through surface modification, and biodegradable poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/chitin nanocrystals films were produced via solution-casting method. Transmission electron microscopy observations and X-ray diffraction profiles revealed that the rod-like morphology and crystal structure of chitin nanocrystals were maintained. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy results showed that the hydroxyl groups were partly replaced by the acetyl groups on the surface of chitin nanocrystals. The hydrophobic performance of the acetylated chitin nanocrystals was significantly increased according to the contact angle measurements. Differential scanning calorimeter results indicated that the influence of chitin nanocrystals on the crystallization behaviors of PHBV matrix was changed from suppression to assistance after the surface modification. Tensile test showed that the tensile strength and Youngs modulus of PHBV/acetylated chitin nanocrystals composites were improved by 44% and 67%, comparing to the improvement of 24% and 43% for PHBV/chitin nanocrystals composites with the addition of 5.0 wt.% nanocrystals into PHBV.

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.