Key Laboratory of Advanced Materials Processing and Mold

Laboratory of, China

Key Laboratory of Advanced Materials Processing and Mold

Laboratory of, China
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Wang K.,Zhengzhou University | Wang K.,Key Laboratory of Advanced Materials Processing and Mold | Jiao T.,Zhengzhou University | Jiao T.,Key Laboratory of Advanced Materials Processing and Mold | And 8 more authors.
Materials Letters | Year: 2013

Cast films of poly(butylene succinate) (PBS) were prepared by extrusion followed by stretching using a chill roll. The effects of extrusion temperature and take-up speed on the microstructures of the PBS cast films were investigated by two-dimensional wide angle X-ray diffraction (2D-WAXD) and small angle X-ray scattering (2D-SAXS) techniques. It was found that the processing conditions had almost no influence on the degree of crystallinity and the long period of the lamellae of the films, whereas the orientations at both crystal and lamellar levels increased with increasing take-up speed and decreasing extrusion temperature. In addition, the 2D-SAXS patterns revealed the formation of the shish-kebab structure at a lower extrusion temperature and higher take-up speed. © 2012 Elsevier B.V.


Wang Y.,Zhengzhou University | Tong B.,Key Laboratory of Advanced Materials Processing and Mold | Hou S.,Zhengzhou University | Li M.,Key Laboratory of Advanced Materials Processing and Mold | Shen C.,Zhengzhou University
Composites Part A: Applied Science and Manufacturing | Year: 2011

The focus of this work was to evaluate the transcrystalline effects at poly(lactic acid) (PLA) matrix caused by various sisal fibres, which were untreated (U-sisal), or treated with alkali (A-sisal) and silane (S-sisal). Isothermal crystallization was performed at temperatures between 123 and 130 °C using polarized optical microscopy. Results showed that the sisal fibres untreated or treated all had a nucleating ability to transcrystallize in PLA matrix. Based on the theory of heterogeneous nucleation, the interfacial free energy difference functions Δσ were determined to be 0.68, 0.65, and 0.65 erg/cm2 for PLA/U-sisal, PLA/A-sisal and PLA/S-sisal, respectively. This suggests that the fibre surface modification by using alkali or silane has little or no influence to the nucleation ability of sisal fibre in PLA matrix. © 2010 Elsevier Ltd. All rights reserved.


Li M.,Zhengzhou University | Li M.,Key Laboratory of Advanced Materials Processing and Mold | Hu D.,Zhengzhou University | Hu D.,Key Laboratory of Advanced Materials Processing and Mold | And 4 more authors.
Polymer Engineering and Science | Year: 2010

The nonisothermal crystallization behavior of poly(lactic acid) (PLA) in the presence of talc with poly(ethylene glycol) (PEG) was performed by using differential scanning calorimetry (DSC) and polarized optical microscopy. It was evidenced that talc together with PEG had a synergistic effect on enhancing the crystallization rate of PLA, despite the fact that the two additives had an opposite effect on the size and density of the spherulites. The nonisothermal crystallization data were analyzed by using three different kinetics models, namely, the Avrami, Ozawa, and Mo models. It was found that the Avrami method and the Mo model could describe the experimental data of the nonisothermal crystallization fairly well for all the specimens, whereas the Ozawa analysis failed to provide an adequate description of the nonisothermal crystallization of the PLA formulations comprising talc with PEG. The difference in the values of the Avrami exponent between neat PLA and its mixtures with talc and PEG suggested that the nonisothermal crystallization of the mixtures corresponds to a three-dimensional growth with heterogeneous nucleation. The activation energy for nonisothermal crystallization of PLA formulations was evaluated based on the differential isoconversional method of Friedman. © 2010 Society of Plastics Engineers.


Zhang R.,Zhengzhou University | Zhang R.,Key Laboratory of Advanced Materials Processing and Mold | Wang Y.,Zhengzhou University | Wang Y.,Key Laboratory of Advanced Materials Processing and Mold | And 8 more authors.
Polymer Bulletin | Year: 2013

Poly(lactic acid) (PLA) is a well-known biodegradable and biocompatible polyester with intrinsically slow crystallization rate. To extend its applications to the field where heat resistance is required, increasing the crystallization rate of the material becomes critical. In this note, the nucleation effect of supramolecular inclusion complex (IC), organized by non-covalent interactions through threading α-cyclodextrin molecules onto PLA chains, on the crystallization of PLA was investigated by differential scanning calorimetry (DSC) and polarized optical microscopy. The formation of IC was confirmed by wide-angle X-ray diffraction and DSC measurements. It was found that the presence of PLA-IC significantly promoted the crystallization of PLA from both the non-isothermal and isothermal crystallization experiments. The nucleation mechanism was also discussed to some extent. © 2012 Springer-Verlag.


Shen C.,Zhengzhou University | Shen C.,Key Laboratory of Advanced Materials Processing and Mold | Wang Y.,Zhengzhou University | Wang Y.,Key Laboratory of Advanced Materials Processing and Mold | And 4 more authors.
Journal of Polymer Science, Part B: Polymer Physics | Year: 2011

The crystal modifications and multiple melting behavior of poly(L-lactic acid-co-D-lactic acid) (98/2) as a function of crystallization temperature were studied by wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). It was found that the disorder (α′) and order (α) phases of poly(L-lactic acid) (PLLA) were formed in cold-crystallized poly(L-lactic acid-co-D-lactic acid) samples at low (<110 °C) and high (≥110 °C) temperatures, respectively. A disorder-to-order (α′-to-α) phase transition occurred during the annealing process of the α′-crystal at elevated temperatures, which proceeded quite slowly even at the peak temperature of the exotherm Pexo but much more rapidly at higher temperature close to the melting region. The presence or absence of an additional endothermic peak before the exotherm in the DSC thermograph of the α′-crystal was strongly dependent on the heating rate, indicating that a melting process involved during the α′-to-α phase transition. © 2010 Wiley Periodicals, Inc.


Wang K.,Zhengzhou University | Wang K.,Key Laboratory of Advanced Materials Processing and Mold | Wang Y.,Zhengzhou University | Wang Y.,Key Laboratory of Advanced Materials Processing and Mold | And 6 more authors.
Polymer Composites | Year: 2012

Novel biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)]/organoclay nanocomposites were prepared via solution casting. Exfoliated nanocomposite structure was confirmed by wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) for the nanocomposites with low organoclay loadings (≤3 wt%), whereas the mixtures of exfoliated and unexfoliated organoclays were appeared in the nanocomposite with an organoclay content of 5 wt%. The organoclay fillers accelerated significantly the cold crystallization process of P(3HB-co-4HB) matrix. The thermal stability of the nanocomposites was in general better than that of pristine P(3HB-co-4HB). Considerable increase in tensile modulus was observed for the nanocomposites, especially at an organoclay content of 3 wt%. These results demonstrated that the nanocomposites improved the material properties of P(3HB-co-4HB). © 2012 Society of Plastics Engineers.


Wang Y.,Zhengzhou University | Wang Y.,Key Laboratory of Advanced Materials Processing and Mold | Li M.,Zhengzhou University | Li M.,Key Laboratory of Advanced Materials Processing and Mold | And 2 more authors.
Materials Letters | Year: 2011

Cast poly(lactic acid) (PLA) films were prepared by extrusion followed by stretching using a vertical threepinch roll at various take-up speeds from 100 to 1000 cm/min. These cast films were found to be amorphous and unoriented regardless of the take-up speeds applied, using two-dimensional wide angle X-ray diffraction (2D-WAXD), polarized Fourier transform infrared (FTIR), and differential scanning calorimetry (DSC) techniques. However, upon constrained annealing, oriented crystalline structures developed for the films cast at 400 cm/min and over, and the orientation level and crystallization rate of the films increased with the take-up speed at which the film was cast. The findings could be explained by the presence of global orientation during film casting and stress-induced crystallization upon constrained annealing. © 2011 Elsevier B.V. All rights reserved.

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