Jie Zhang

Sichuan University, Hua-yang, Sichuan, China

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Publications (19)30.17 Total impact

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    ABSTRACT: This study investigates the influence of length scale effects (micro- and macro-injection molded parts) and mold temperature on the epitaxial growth and morphological characteristics in injection-molded bars of isotactic polypropylene (iPP)/high-density polyethylene (HDPE) blends. After preparing the blends with an iPP content of 70 wt% via melt extrusion, the injection-molded bars were formed using both micro and conventional injection molding. Samples were subsequently prepared from the moulded components to allow investigation of the internal morphology using wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and polarized light microscopy (PLM). The results indicated that the matching of micro scale and appropriate mold temperature was most favorable for epitaxial crystallization. The micro-parts had a large fraction of shear layer compared with macro-parts. The SEM observations showed that the shear layer of the former consisted of a highly oriented shish-kebab structure. Moreover, the effects of different methods of injection molding on the morphological characteristics of the micro-parts and macro-parts in different layers were elucidated in detail using PLM and SEM.
    Polymer Testing 04/2014; DOI:10.1016/j.polymertesting.2014.01.006 · 1.82 Impact Factor
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    ABSTRACT: In optical printed Chinese character recognition (OPCCR), many classifiers have been proposed for the recognition. Among the classifiers, support vector machine (SVM) might be the best classifier. However, SVM is a classifier for two classes. When it is used for multi-classes in OPCCR, its computation is time-consuming. Thus, we propose a neighbor classes based SVM (NC-SVM) to reduce the computation consumption of SVM. Experiments of NC-SVM classification for OPCCR have been done. The results of the experiments have shown that the NC-SVM we proposed can effectively reduce the computation time in OPCCR.
    PLoS ONE 05/2013; 8(3):e57928. DOI:10.1371/journal.pone.0057928 · 3.53 Impact Factor
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    ABSTRACT: To compare the difference of morphological evolution of HDPE micropart and macropart, micropart with 200 μm thickness and macropart with 2000 μm thickness were prepared. The PLM images of micropart and macropart exhibited a similar “skin–core” structure, but the micropart showed a much larger fraction of orientation layer. The SEM observation of core layer of micropart featured an unoriented lamellae structure and shear layer of micropart showed a highly oriented shish‐kebab structure. The 2D‐WAXD patterns of shear layer of macropart indicated twisted oriented shish‐kebab (KM‐I) structures, however that of micropart indicated untwisted oriented shish‐kebab (KM‐II) structures which was firstly found in microinjection molding. The diffraction pattern of the micropart exhibited stronger azimuthal dependence than the shear layer of macropart, indicating the most pronounced orientation of HDPE chains within lamellae. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
    Journal of Applied Polymer Science 10/2012; 126(2). DOI:10.1002/app.36698 · 1.64 Impact Factor
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    ABSTRACT: Micro-injection molding is attracting much attention nowadays. Characterization of the morphological distribution in parts prepared by micro-injection molding is thus of growing importance. The morphological features of micro-parts may strongly differ from those of the macro-parts prepared by conventional injection molding, resulting in specific physical properties. In the present study, β-nucleated isotactic polypropylene micro-parts (μPPB) with 200 μm thickness, as well as macro-parts (PPB) with 2000 μm thickness, were prepared. Polarized light microscopy (PLM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) were used to investigate their morphological features. The results show that the morphology distribution in μPPB had many differences from that of the PPB. The 1D WAXD and DSC analysis showed similar results; the degree of crystallinity of the μPPB was higher than that of the PPB. However, the content of β-crystals of μPPB was lower than that of the PPB. This can be explained by the restraining effect for the formation of β-crystals in β-nucleated iPP under the strong shear field. The through-the thickness-morphology of both μPPB and PPB exhibited a ‘skin-core’ structure from PLM observations, but the former had a large fraction of shear layer in comparison to the latter implied. The SEM observations showed that the shear layer of μPPB consisted of a highly oriented shish-kebab structure while that of the core layer consisted of deformed spherulites structure. The 2D WAXD pattern of the core layer of PPB, showing full Debye rings, indicated an overall random orientation of the iPP chains, while the arcing indicated a pronounced orientation in the shear layer. The more pronounced arcing of the μPPB indicated a more pronounced orientation.
    Journal of Macromolecular Science Part B 08/2012; DOI:10.1080/00222348.2011.649663 · 0.62 Impact Factor
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    ABSTRACT: Microwave heating technology has numerous advantages compared with the traditional heating methods and has been widely used to process materials. However, most thermoplastics do not possess a sufficiently high dielectric property to be heated by microwaves. In this study, carbon black (CB) was utilized as the microwave absorber to improve the microwave heatability of isotactic polypropylene (iPP). Effects of CB contents on the microwave heatability of iPP/CB composites were studied. The temperature of iPP/CB composites with relatively low CB content (5% and 10%) increased slowly and tended to remain unchanged after 120 seconds of microwave exposure. In contrast, iPP/CB composites with relatively high CB content (15% and 20%) presented a much faster heating rate and the temperature of the sample kept increasing with the prolongation of exposure time. On the basis of the fact that iPP/CB composites with different CB contents have different microwave heatability, a novel oriented structure, in which the core layer has relatively high orientation and the surface layer has relatively low orientation, was prepared by selective microwave heating. Two-dimensional wide angle X-ray diffraction (2D-WAXD) analysis indicates that the orientation parameter calculated by the (040) plane of the surface layer (0.45) was lower than that of the core layer (0.83). The novel oriented structure is different from the common skin-core structure formed in the samples of semicrystalline polymers by traditional polymer processing methods, in which orientation of the skin layer is higher than that of the core layer. The novel oriented structure has not been reported before to our knowledge and its formation mechanism is also discussed in this paper.
    Journal of Macromolecular Science Part B 08/2012; DOI:10.1080/00222348.2012.657105 · 0.62 Impact Factor
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    ABSTRACT: The morphological feature of microparts evolved during micro-injection molding may differ from that of the macroparts prepared by conventional injection molding, resulting in specific physical properties. In this study, isotactic polypropylene (iPP) microparts with 200 µm thickness and macroparts with 2000 µm thickness were prepared, and their morphological comparison was investigated by means of polarized light microscopy (PLM), scanning electron microscopy (SEM), differential scanning calorimeter (DSC), and wide-angle X-ray diffraction (WAXD). The results presented some similarities and differences. PLM observations showed that the through-the thickness-morphology of micropart exhibited a similar “skin–core” structure as macropart, but presented a large fraction of shear layer in comparison to the macropart which presented a large fraction of core layer. The SEM observation of shear layer of micropart featured highly oriented shish-kebab structure. The micropart had a more homogeneous distribution of lamellae thickness. The degree of crystallinity of the micropart was found to be higher than that of the macropart. High content of β-crystal was found in micropart. The 2D WAXD pattern of the core layer of macropart showed full Debye rings indicating a random orientation, while the arcing of the shear layer indicates a pronounced orientation. The most pronounced arcing of the micropart indicates the most pronounced orientation of iPP chains within lamellae. Copyright © 2011 John Wiley & Sons, Ltd.
    Polymers for Advanced Technologies 03/2012; 23(3):686 - 694. DOI:10.1002/pat.1946 · 1.96 Impact Factor
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    ABSTRACT: In optical printed Chinese character recognition (OPCCR), support vector machine (SVM) is thought to be a good classifier. However, the recognition rate of SVM depends on the features extracted and the time consumption of it is large. For this reason, we propose statistic features (SF) and local nearest neighbor SVM (LNN-SVM) to promote the recognition rate and to reduce the computational time of SVM. Experiments have been done and the results showed that SF and LNN-SVM can promote the recognition rate and reduce the computational time in OPCCR.
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    ABSTRACT: Flow-induced crystallization has long been an important subject in polymer processing. Varying processing conditions can produce different morphologies, which lead to different properties. Recent studies have indicated that the final morphology is, in fact, dictated by the formation of crystallization structures under flow. This study deals with the influence of processing parameters on the polymorphism and crystallization orientation of isotactic polypropylene (iPP) in microinjection molding. Crystallinity and polymorphism were investigated by means of differential scanning calorimeter (DSC) and one-dimensional wide-angle X-ray diffraction (1D-WAXD). Crystalline orientation was characterized by two-dimensional wide-angle X-ray diffraction (2D-WAXD). Herman's orientation functions determined from the flat-plate wide-angle X-ray diffraction patterns were used to evaluate the orientation level of microparts. It was found that the effect of processing parameters on the crystallinity was not obvious, but these processing parameters had a great influence on the β-modification content of microparts. When the mold temperature was 150°C, β-modification still formed in microparts because the thermal stability of the β-modification was enhanced with increasing the mold temperature; The β-modification content of microparts decreased obviously when the injection time was 1 s compared to the longer injection time. However, the β-modification content of microparts increased with increasing the injection pressure. In addition, the γ-modification existed in the microparts at the mold temperatures of 150 and 160°C. From Herman's orientation functions, we know that the influence of processing parameters on α-crystalline orientation in microparts was small. But the processing parameters can affect the degree of the β-modification orientation. A shish-kebab structure was observed in some regions throughout the longitudinal sections of all the microparts by the SEM analysis.
    Journal of Macromolecular Science Part B 11/2011; Part B(Vol. 50):2227-2241. DOI:10.1080/00222348.2011.562839 · 0.62 Impact Factor
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    ABSTRACT: To study the effect of vibration field on the electrical conductivity properties of nanocomposites, isotactic polypropylene (iPP)/multiwalled carbon nanotubes (MWCNT) composites were prepared by conventional injection molding and vibration injection molding. Results showed that the electrical conductivity of iPP/MWCNT composites was significantly promoted by vibration injection molding. Vibration injection molded samples had a percolation threshold of about 2.7 wt% compared with the threshold of about 4.5 wt% for conventional injection molded samples. The effects of test locations and vibration frequency on the electrical conductivity of composites were investigated. The samples exhibited an inhomogeneity along the injection direction. The electrical conductivity of the samples was different at different test locations and increased with increasing vibration frequency. Polarized light microscopy (PLM) results indicated that vibration injection molding can induce MWCNT aggregates to be stretched and oriented along the flow direction, which could form conductive networks and greatly enhance the electrical conductivity of iPP/MWCNT composites.
    Journal of Macromolecular Science Part B 11/2011; Part B(Vol. 50):2193-2202. DOI:10.1080/00222348.2011.563193 · 0.62 Impact Factor
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    ABSTRACT: In this study, isotactic polypropylene (iPP) samples were prepared by conventional injection molding (CIM) and pressure vibration injection molding (PVIM), in which a periodical shear field was imposed on the iPP melt during the cooling solidification. The distribution of supermolecular structures of samples was investigated by Polarized Light Microscopy (PLM) and Scanning Electron Microscopy (SEM). Results show that the through-the thickness-morphology of sample prepared by CIM features a typical skin-core structure, as a result of general shear-induced crystallization. This structure can be divided into three layers, including a skin layer in which the shish–kebab structure was found, a transition region with deformed spherulite structure and a core layer with spherulitic structure. However, the morphology of the sample prepared by PVIM, as a result of periodical shear-induced crystallization, features a richer and fascinating supermolecular structure and can not be roughly divided into three layers. A region full of shish–kebab-like cylindrulite structures was found between the transition region and the core layer, which is rare to be seen in conventional injection molding. Based on their various core structures, two kinds of shish–kebab-like cylindrulites were defined: one is multi-fibril-core cylindrulite of which core is an assembly of multiple fibrils, and the other is single-fibril-core cylindrulite of which the core just contains a single fibril. Based on the investigated results, a schematic illustration is proposed to depict the through-the thickness-distribution of supermolecular structure of iPP sample prepared by PVIM. The mechanism of the formation of the two kinds of shish–kebab-like cylindrulite structures is also depicted by a schematic illustration, and it was discussed in terms of periodical shear-induced crystallization.
    Polymer 06/2011; 52(13):2970-2978. DOI:10.1016/j.polymer.2011.05.002 · 3.77 Impact Factor
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    ABSTRACT: Microwave heating has several advantages over traditional methods of heating, including rapid and uniform heating, greater penetration depth of heat into material, lower power costs and selective heating within the material and so on. In this paper, effects of microwave heating on the properties of high-density polyethylene/carbon black (HDPE/CB) composites were studied. The results show that the HDPE/CB composites can be heated via microwave irradiation, and composites with different CB concentration exhibit different microwave heatability. The 20 wt% CB composites have the most rapid heating rate, and its temperature reaches 78°C after 10 sec, and 159°C after 150 sec, respectively. Meanwhile, microwave heating improves the mechanical properties of HDPE/CB composites. Scanning Electron Microscopy (SEM) analysis shows a better combination between CB particles and HDPE after microwave irradiation. Furthermore, selective heating of microwave was used to prepare a novel oriented structure, which the core layer has preferential orientation and the surface layer has little orientation. Characterization of the novel oriented structure was also studied. Wide angle X-ray diffraction (WAXD) analysis of 25 wt% CB composites with the novel oriented structure shows that the diffraction peaks of the surface layer are obviously weaker than those of the core layer, which indicates that orientation in the core layer is more intensive than that in the surface layer. The novel oriented structure is different to the traditional skin-core structure, in which the surface layer has preferential orientation and the core layer has little orientation. Copyright © 2009 John Wiley & Sons, Ltd.
    Polymers for Advanced Technologies 06/2011; 22(6). DOI:10.1002/pat.1582 · 1.96 Impact Factor
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    ABSTRACT: A self-designed pressure vibration injection molding device was used to study the effect of vibration frequency and vibration pressure on tensile strength and impact strength of PP/HDPE (70/30) samples prepared by vibration injection molding. Furthermore, DSC and scanning electron microscopy (SEM) observations were conducted. The tensile strength and impact strength increase with increasing vibration frequency and vibration pressure. SEM micrographs show that the orientation degree of the vibration sample obtained at 190°C obviously increases compared with the static sample, and the clusters of lamellae are stretched along the flow direction, whereas their lateral sizes decrease correspondingly. There is no evident orientation in the core layer of the vibration sample obtained at 230°C. DSC testing results show that the degree of crystallinity of vibration samples are higher than those of static samples.
    Journal of Macromolecular Science Part B 01/2011; Part B(1-Vol. 50):41-50. DOI:10.1080/00222341003609401 · 0.62 Impact Factor
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    ABSTRACT: Microwave processing has numerous advantages over traditional methods of heating. Most thermoplastics, such as high-density polyethylene (HDPE), are nearly transparent to electromagnetic radiation. Carbon black (CB) filled HDPE was prepared in order to improve the microwave heatability of HDPE. The heating response of HDPE/CB composites to microwave exposure and the effects of this exposure on the mechanical and physical properties of material were investigated. The addition of CB particles improved the microwave heatability of HDPE, and microwave heatability of composites varied with CB content, in which an average temperatures of up to 139 °C above ambient were measured for 20 wt% CB composites after a exposure duration of 150 s. Microwave exposure had no obvious effect on rheological property of HDPE/CB composites. Mechanical properties of HDPE/CB composites are relatively improved after microwave exposure. Scanning electronic micrograph (SEM) analysis presented that the interface defects between CB particles and HDPE matrix are significantly reduced and a better combination was found after microwave exposure. Differential scanning calorimetry (DSC) analysis showed that the melt point of HDPE with CB shifted toward high temperature and degree of crystallinity increased after microwave exposure.
    Journal of Materials Processing Technology 11/2010; 210(14):1991-1996. DOI:10.1016/j.jmatprotec.2010.07.014 · 1.95 Impact Factor
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    ABSTRACT: Summary A self-designed pressure vibration injection device was used to study the effect of vibration frequency and vibration pressure on tensile strength and impact strength of iPP F401 vibration injection molding samples. Furthermore, vicat softening temperature, WAXD measurements and polarized microscopic observation were conducted. According to the results, tensile strength and impact strength increase with increasing vibration frequency and vibration pressure. The maximum increment of tensile strength is 26.1%. Under certain process conditions, there is a transition of the impact strength, whose maximum increment is 85%. The vicat softening temperatures have a significant increase of 6∼8 �C for the samples obtained at high vibration frequencies compared with that of static samples. According to pole figures, α-PP of vibration samples orientates much stronger than that of static samples. PM micrograghs show that vibration changes the crystal structure of samples and enhances their orientation.
    Polymer Bulletin 01/2008; 59(6):855-864. DOI:10.1007/s00289-007-0831-4 · 1.49 Impact Factor
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    ABSTRACT: A vibration–injection molding equipment was developed to prepare isotactic polypropylene injection samples to investigate their crystal form and orientation. Wide-angle X-ray scattering experiments (WAXD) were conducted in two modes: theta–theta mode and tube-fixed mode. Through vibration–injection molding, in additional to α form, β form, or γ form can be obtained under different conditions. At high melt temperature (230), β-PP can be induced and the core of the sample contains more β-PP than the surface. At low melt temperature (190), γ-PP can be induced and the core and the surface of the sample contain approximate same proportion of γ-PP. Pole figures show that α-PP of a static sample just orientates slightly along M direction, while that of vibration samples orientate much stronger. The orientation of the normal of (040)α plane of the sample obtained at T = 230°C, f = 0.5 Hz, and Pv = 75MPa is preferred in M direction, and the orientation of the normal of (040)α plane of the sample obtained at T = 190°C, f = 1.5 Hz, and Pv= 35 MPa is preferred in N direction. β-PP and γ-PP do not show obvious orientation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
    Journal of Applied Polymer Science 11/2007; 106(3):1456-1461. DOI:10.1002/app.26554 · 1.64 Impact Factor
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    ABSTRACT: A new type of extrusion apparatus with a hydraulic vibration field was self-developed to study the effects of vibration on the rheological behavior, mechanical properties, and morphology of high-density polyethylene (HDPE) during the process of extrusion. In the research, the morphology and mechanical properties of specimens produced by conventional extrusion molding were used for comparison with specimens obtained via vibration extrusion molding. The research showed that the extrusion property of the HDPE melt was improved under a vibration field, and the apparent viscosity decreased. The maximum decrement of the apparent viscosity was 37.98%. The change in the apparent viscosity of the HDPE melt corresponded to the vibration frequency and amplitude, die temperature, and rotational speed of the extruder screw. Both the longitudinal and transverse yield strengths of the HDPE specimens increased under the vibration field. The increment of the longitudinal yield strength (11.5%) was bigger than that of the transverse yield strength (6.9%). According to scanning electron microscopy micrographs, the vibration field made the crystallites orient and become smaller, and the crystal size became more homogeneous. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007
    Journal of Applied Polymer Science 10/2007; 106(1):552 - 557. DOI:10.1002/app.26551 · 1.64 Impact Factor
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    ABSTRACT: A pressure vibration injection machine with vibration frequency of 0–1.5 Hz and vibration pressure of 0–75 MPa was developed to investigate self-reinforcement of high-density polyethylene (HDPE). The effect of vibration frequency and vibration pressure on tensile strength and elongation of HDPE DGDA6098 vibration molding samples, which were obtained at different melt temperatures, was studied, and SEM and WAXD measurements were conducted. Experimental results showed that vibration changed the crystal structure of vibration samples and enhanced their orientation. Instead of spherulites of static samples, crystal structure of vibration samples was lamellae that was orientated along melt flow direction. When vibration frequency was high, lamella size was small and orientation degree was low. When vibration pressure was high, lamella size was large and orientation degree was high. Therefore, vibration samples were self-reinforced with increasing vibration frequency and vibration pressure, where the maximum increment of tensile strength was 41.0 %.
    Polymer-Plastics Technology and Engineering 06/2006; 45(5-5):601-606. DOI:10.1080/03602550600554117 · 1.48 Impact Factor
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    ABSTRACT: To better understand the formation of different crystal structures and improve the mechanical properties of high-density polyethylene samples, melt vibration technology, which generally includes shear vibration and hydrostatic pressure vibration, was used to prepare injection samples. Through melt vibration, the crystal structure changed from typical spherulites of the traditional injection sample to obviously orientated lamellae of vibration samples. Sizes and orientation degrees of lamellae were different according to different vibration conditions. Crystallinity degrees of vibration samples increased notably. Therefore, the tensile strength of vibration samples increased with increasing vibration frequency and vibration pressure, whereas elongation of vibration samples decreased during the first stage and then continued to increase as the vibration frequency increased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 818–823, 2005
    Journal of Applied Polymer Science 05/2005; 96(3):818 - 823. DOI:10.1002/app.21034 · 1.64 Impact Factor
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    ABSTRACT: In order to understand the formation of different crystal structures and improve the mechanical properties of isotactic polypropylene (iPP), melt vibration technology, which generally includes shear vibration and hydrostatic pressure vibration, was used to induce the change of crystal structure of iPP. iPP forms α crystal structure in traditional injection molding. Through melt vibration, crystal orientated and its size became smaller, and a change of crystal structure of iPP from α form to β form and γ form was achieved. Therefore, the mechanical properties of iPP were improved. At high melting temperature (230 °C), only β form can be induced. At low melting temperature (190 °C), either β form or γ form can be induced, depending on the combination of frequency and vibration pressure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2385–2390, 2004
    Journal of Polymer Science Part B Polymer Physics 06/2004; 42(12):2385 - 2390. DOI:10.1002/polb.20110 · 2.55 Impact Factor