Jinggang Gai’s research while affiliated with Sichuan University and other places

Polyethylene glycol (PEG 200) was used as an eco-friendly plasticizer for preparing thermoplastic cellulose acetate (CA) by a twin-screw extruder. The plasticization efficiency of PEG 200 was compared with that of triethyl citrate (TEC). The interaction between polyethylene glycol and CA was investigated by Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). Both FT-IR and DSC proved that PEG 200 could form stable and strong hydrogen bonds with CA molecules. Scanning electron microscopy (SEM) revealed that the CA granules were completely disrupted during the extrusion and a continuous and homogeneous phase was observed. The PEG 200-plasticized cellulose acetate (PCA) showed greater viscosity reduction than triethyl citrate-plasticized cellulose acetate (TCA) at the same additive levels. Furthermore, the Izod-notched impact strength and elongation at break of PCA were higher than those of TCA. The tensile strength, Izod-notched impact strength and elongation at break of PCA containing 25wt% PEG 200 reached 31.6 MPa, 20.9 KJ/m2 and 80.5%, respectively, as compared to 39.2 MPa, 10.9 KJ/m2 and 32.3% for 25wt% TEC plasticized CA.

Large amount of work has been published on the isotacticity–properties relationship of isotactic polypropylene (iPP). However, the stereo-defect distribution dependence of morphology and mechanical properties of iPP injection molding samples is still not clear. In this study, two different isotactic polypropylene (iPP) resins (PP-A and PP-B) with similar average isotacticity but different stereo-defect distribution were selected to investigate the morphology evolution and mechanical properties (tensile and notching) of their injection molding samples using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), 2D wide angle X-ray diffraction (2D-WAXD), and scanning electron microscope (SEM). The results of DMA showed that the molecular movement ability of PP-A (with less uniform distribution of stereo-defect) was stronger than that of PP-B, meanwhile the analysis of DSC and SEM suggested that after injection molding, smaller spherullites, and crystals with higher perfection had formed in the specimens of PP-A. The resulting of tensile properties of PP-A were found to be better than that of PP-B. The results of morphology evolution by SEM observation and 2D-WAXD showed that PP-A is more likely to occur interspherulite deformation and can disperse the tensile stress more efficiently, and therefore, its crystal structure can withstand a greater force when tensile stress is applied. On the other hand, PP-B has larger spherulites and boundaries, and low perfection of lamellaes, and the intraspherulte deformation tend to take place. It is easier for the crystal of PP-B to be broken up and reoriented along the tensile direction. Copyright © 2014 John Wiley & Sons, Ltd.

Large amount of work has been published on the tacticity-properties relationship of isotactic polypropylene (iPP). However, the stereo-defect distribution dependence of morphology and mechanical properties of β-nucleated iPP (β-iPP) is still not clear. In this study, two different iPP resins (PP-A and PP-B) with similar average isotacticity but different uniformities of stereo-defect distribution were selected, their β-iPP injection molding specimens were prepared, and the morphology evolution and tensile behaviors were studied by means of differential scanning calorimetry (DSC), 2D wide-angle X-ray diffraction (2D-WAXD) and scanning electron microscope (SEM). DSC results showed that with the same concentration of β-nucleating agent (0.3 wt % WBG-II), PP-B with more uniform stereo-defect distribution exhibited more amount of β-phase than that of PP-A with less uniform stereo-defect distribution, indicating that PP-B is more favorable for the formation of β-phase. SEM results showed that PP-B formed more amount of β-crystals with relatively high structural perfection, while in PP-A a mixed morphology of α- and β-phase with obviously higher amount of structural imperfection emerges. The results of room-temperature tensile test indicated that the yield peak width of PP-B was obviously wider, and the elongation at break of PP-B was higher than that of PP-A, showing a better ductile of PP-B. The morphology evolution results of SEM, 2D-WAXD and DSC suggest that, a combination of lamellar deformation and amorphous deformation occurred in PP-A, while only amorphous deformation mainly took place in PP-B, which was thought to be the reason for the different tensile behaviors of the samples. In the production of β-PP products via injection molding, the uniformity of stereo-defect distribution was found to be an important factor. PP with more uniform distribution of stereo-defect favors the formation of large amount of β-phase with high perfection, which exhibit superior ductile property. The related mechanism was discussed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 40027.

The selectivities of different β-nucleating agents might be quite different from each other, which is important in determining the crystallization and properties of the obtained β-isotactic polypropylene (β-iPP). However, the relationship between molecular structure and dynamic crystallization behavior of β-iPP nucleated by dual-selective β-nucleating agent (DS-β-NA) is still not clear. In this study, the dynamic crystallization and melting behavior of two β-iPP with nearly same average isotacticity but different stereo-defect distribution, nucleated by a DS-β-NA (N,N′-dicyclohexyl-2,6-naphthalenedicarboxamide; trade name TMB-5), were studied by differential scanning calorimetry, wide-angle X-ray diffraction, and scanning electronic microscopy. The results indicated that in the presence of TMB-5, the dynamic crystallization and melting behavior of the samples are quite different because the joint effects of the dual selectivity of TMB-5 and stereo-defect distribution of the iPP under different cooling rates. Two important roles were observed: (i) slow cooling rate favors the formation of high β-fraction; and (ii) high crystallization temperature favors the crystallization of α-phase accelerated by TMB-5. Generally, the dual selectivity of the DS-β-NA, the stereo-defect distribution of iPP, and the cooling rate were important factors in determining the formation of β-crystal. Copyright © 2013 John Wiley & Sons, Ltd.

Detailed characterization of the crystallization behavior is important for obtaining better structure property correlations of the isotactic polypropylene (iPP), however, attributed to the complexity in ZN‐iPP polymerization, the relationship between crystallization behavior and the stereo‐defect distribution of iPP is still under debate. In this study, the crystallization kinetics of the primary nucleation, crystal growth and overall crystallization of two iPP samples (PP‐A and PP‐B) with nearly same average isotacticity but different stereo‐defect distribution (the stereo‐defect distribution of PP‐B is more uniform than PP‐A) were investigated. The results of isothermal crystallization kinetics showed that the overall crystallization rate of PP‐A was much higher than that of PP‐B; but the analysis of self‐nucleation isothermal crystallization kinetics and the polarized optical microscopy (POM) observation indicated that the high overall crystallization rate of PP‐A was attributed to the high primary nucleation rate of the resin. The stereo‐defect distribution plays an important role in determining both the nucleation kinetics and crystal grow kinetics, and thus influence the overall crystallization kinetics. A more uniform distribution of stereo‐defects restrains the crystallization rate of iPP, moreover, it has more influence on nucleation kinetics, comparing with the crystal growth. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Organic vermiculite (OVMT) prepared from vermiculite (VMT), with high aspect ratio and orderly arranged platelets intercalated by octadecyl trimethyl ammonum bromide (OTAB), was used as a synergistic agent on the flame retardancy of a polypropylene/intumescent flame retardant (PP/IFR) system. The flammability and thermal stability of PP/IFR/OVMT composites were investigated by limiting oxygen index (LOI), UL-94 testing, cone calorimetry tests, and thermogravometric analysis. The results of LOI and UL-94 testing showed that low loading of OVMT improved the flame retardancy and retarded dripping for PP/IFR composites. OVMT, with 1% loading, increased the char residue of PP/IFR composites and could act as an effective additive for improvement in flame retardancy, which was confirmed by the cone data. The char layer morphological structures observed by scanning electron microscopy (SEM) showed that OVMT with 1% loading can promote formation of a continuous and compact intumescent char layer. Raman spectroscopy results indicated that the OVMT or its pyrolytic products led to a decrease in size of the carbonaceous micro-domain during combustion, resulting in formation of more compact charred layers. Thus, OVMT with 1% loading showed a synergistic effect with IFR in the combustion of the PP/IFR composites.

Large amount of work has be published on the dynamic crystallization and melting behavior of β-nucleated polypropylene (β-PP). However, the relationship between molecular structure and dynamic crystallization behavior of β-PP is still not clear. In this study, the dynamic crystallization and melting behavior of two β-nucleated isotactic polypropylene (β-iPP) with nearly same average isotacticity but different stereo-defect distribution, were studied by differential scanning calorimetry (DSC), wide angel X-ray diffraction (WAXD) and temperature modulated DSC (TMDSC). The results indicated that stereo-defect distribution of iPP can significantly influence the dependence of the β-crystal content and thermal stability on the cooling rate. NPP-A with less uniform stereo-defect distribution favors the crystallization at higher temperature region and the formation of β-crystal with high thermal stability in all cooling rates concerned, moreover, the β-crystal content is influenced by cooling rate; for NPP-B with more uniform distribution of stereo-defect, the crystallization temperature and the regular insertion of molecular chains can be reduced in a larger extent. NPP-B is more suitable for the formation of high proportion of β-crystal in both low and high cooling rates, meanwhile, the thermal stability of crystal is sensitive to the cooling rate. This work provides a new insight into the design of β-iPP in dynamic crystallization.