Zhi-Cheng Qiu

Unique crystalline/crystalline polymer blends of poly(ethylene succinate) and poly(p-dioxanone): miscibility and crystallization behaviors.

Miscibility and crystallization behaviors of poly(ethylene succinate)/poly(p-dioxanone) (PES/PPDO) blends were investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide-angle X-ray diffraction (WAXD). PES/PPDO blends are completely miscible as proved by the single grass transition temperature (T(g)) dependence of composition and decreasing crystallization temperature of the blends in comparison with the respective component. POM observation suggests that simultaneous crystallization of PES and PPDO components in the blends took place, spherulites of one component can crystallize inside the spherulites of the other component, and the unique interpenetrated crystalline morphology has been formed for the blends in the full composition range. Isothermal crystallization kinetics of the blends was studied by DSC and the data were analyzed by the Avrami equation. The results suggest that the crystallization mechanisms of the blends were unchanged but the overall crystallization rates were slowed down compared with neat PES and neat PPDO. WAXD results indicate that the crystal structures of PES and PPDO did not change in the blends.

A Novel Potential Ecomaterial Based on Poly(p-Dioxanone)/Montmorillonite Nanocomposite With Improved Crystalline, Processing, and Mechanical Properties

Poly(p-dioxanone) (PPDO) is a useful biomaterial and potential ecomaterial due to its biodegradability and good mechanical properties. Like other aliphatic polyesters, however, it has a low crystallization rate and low melt strength; it is difficult to produce thin films from it by blown film processing. In this work, poly(p-dioxanone)/montmorillonite (MMT) nanocomposites have been prepared successfully by in situ ring-opening polymerization of p-dioxanone and MMTs. The novel, biodegradable nanocomposites have a remarkably increased crystallization rate and melt strength; moreover, they can be blown into thin films, which have excellent mechanical properties. A typical sample showed a tensile strength of 59.2 MPa and elongation at break 605%.

PPDO-PU/Montmorillonite Nanocomposites Prepared by Chain-Extending Reaction: Thermal Stability, Mechanical Performance and Rheological Behavior

A two-step approach was employed to prepare Poly(p-dioxanone)-PU/organic montmorillonite (PPDO-PU/OMMT) nanocomposites. In the first step, PPDO diol prepolymers with different molecular weights were synthesized by ring-opening polymerization of p-dioxanone; in the second step, PPDO-PU/OMMT nanocomposites were prepared by coupling PPDO diol melt swollen with organo-modified MMT (OMMT), using 1,6-hexamethylene diisocyanate (HDI) as the chain-extender. The intercalated-exfoliated coexistence morphology of nanocomposites was determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Thermogravimetric analysis (TG), high-pressure capillary rheometer, and mechanical test were performed to investigate the properties of the nanocomposites. The results showed that the thermal stability and mechanical performance of nanocomposites were greatly improved compared to that of pure PPDO. The enhancement of shear viscosity and low temperature sensitivity of the nanocomposite melts enabled it to produce thin films by blowing process successfully.

Thermal Degradation, Crystallization, and Rheological Behavior of Biodegradable Poly(p-dioxanone)/Synthetic Hectorite Nanocomposites

Biodegradable poly(p-dioxanone) (PPDO)/synthetic hectorite nanocomposites were successfully prepared by in-situ ring-opening polymerization of p-dioxanone (PDO) in the presence of organomodified synthetic hectorite (OSHEC). Attachment of poly(ester-ether) chains around the exfoliated clay sheets was found. Influence of clay content on thermal behavior was studied. OSHEC accelerated the thermal degradation of the ester group in the polymer chains. Exfoliated organoclay layers, to some extent, acted as a hindrance to the growth rate of the spherulites instead of as nucleating agents. Inorganic clay played an important role in enhancing the shear viscosity of nanocomposites due to its unique structure and the reasonable interaction between the clay and PPDO matrix.

PROPERTIES OF POLY(p‐DIOXANONE‐URETHANE) COPOLYMERS WITH CONTROLLABLE STRUCTURES

A series of poly(p‐dioxanone‐urethane) (PPDO‐PU) copolymers were produced by chain extending reaction of poly(p‐dioxanone) (PPDO) diol with 1,6‐hexamethylene diisocyanate (HDI) and toluene‐2,4‐diisocyanate (TDI). The chain structure of the copolymers can be easily controlled by varying the molecular weight of PPDO diol and the structure of diisocyanate. Several instruments such as DSC, POM, TG, and Capillary Rheometer have been employed to investigate the structure–properties relationship of PPDO‐PU copolymers. The results show that varying the structure and the content of chain extenders will influence the crystallization behavior, thermal stability, mechanical performance, and rheological behavior of the products significantly. The insertion of urethane groups into PPDO polymer chains enhances the mechanical performance of the copolymers.