Co-reporter:Wenju Huang, Kun Dai, Yue Zhai, Hu Liu, Pengfei Zhan, Jiachen Gao, Guoqiang Zheng, Chuntai Liu, and Changyu Shen
ACS Applied Materials & Interfaces December 6, 2017 Volume 9(Issue 48) pp:42266-42266
Publication Date(Web):November 13, 2017
DOI:10.1021/acsami.7b16975
Flexible and lightweight carbon nanotube (CNT)/thermoplastic polyurethane (TPU) conductive foam with a novel aligned porous structure was fabricated. The density of the aligned porous material was as low as 0.123 g·cm–3. Homogeneous dispersion of CNTs was achieved through the skeleton of the foam, and an ultralow percolation threshold of 0.0023 vol % was obtained. Compared with the disordered foam, mechanical properties of the aligned foam were enhanced and the piezoresistive stability of the flexible foam was improved significantly. The compression strength of the aligned TPU foam increases by 30.7% at the strain of 50%, and the stress of the aligned foam is 22 times that of the disordered foam at the strain of 90%. Importantly, the resistance variation of the aligned foam shows a fascinating linear characteristic under the applied strain until 77%, which would benefit the application of the foam as a desired pressure sensor. During multiple cyclic compression-release measurements, the aligned conductive CNT/TPU foam represents excellent reversibility and reproducibility in terms of resistance. This nice capability benefits from the aligned porous structure composed of ladderlike cells along the orientation direction. Simultaneously, the human motion detections, such as walk, jump, squat, etc. were demonstrated by using our flexible pressure sensor. Because of the lightweight, flexibility, high compressibility, excellent reversibility, and reproducibility of the conductive aligned foam, the present study is capable of providing new insights into the fabrication of a high-performance pressure sensor.Keywords: aligned foam; carbon nanotubes; nanocomposite; piezoresistive material; thermoplastic polyurethane;
Co-reporter:Haili Zheng;Bo Wang;Guoqiang Zheng;Kun Dai;Changyu Shen;Zhigang Wang
Industrial & Engineering Chemistry Research April 9, 2014 Volume 53(Issue 14) pp:6211-6220
Publication Date(Web):Publication Date (Web): March 17, 2014
DOI:10.1021/ie500007n
Partially melting high-density polyethylene (HDPE) is investigated by differential scanning calorimetry and in situ Fourier transform infrared spectroscopy (FTIR) measurements. The results show that some incompletely molten crystals can be preserved in the partially melting HDPE, thus accelerating subsequent crystallization. Moreover, quantitative calculation of such incompletely molten crystals has been done based on the FTIR results. Interestingly, the kinetically enhanced crystallization results from the improved nucleation rate because of the incompletely molten crystals. Furthermore, such interesting self-nucleation originating from the partially melting HDPE has been deliberately applied to practical polymer processing, i.e., extrusion, aiming to investigate the influence of partially melting HDPE on the microstructural development and the resultant mechanical properties of the extruded products. Unexpectedly, an increment in tensile strength has been achieved in the sheets extruded from partially melting HDPE compared with that extruded from completely melted HDPE. Wide-angle X-ray diffraction and small-angle X-ray scattering results show that the crystallinity, long period, and lamellar thickness increase for the sheets extruded from the partially melting HDPE. These increases are considered to be responsible for the mechanical increment. This work opens a new gateway for applying the self-nucleating effect of partially melting polymer melt into practical processing with the purpose of preparing high-performance polymer products.
Co-reporter:Yanjun Zheng, Yilong Li, Kun Dai, Mengran Liu, Kangkang Zhou, Guoqiang Zheng, Chuntai Liu, Changyu Shen
Composites Part A: Applied Science and Manufacturing 2017 Volume 101(Volume 101) pp:
Publication Date(Web):1 October 2017
DOI:10.1016/j.compositesa.2017.06.003
Conductive elastomer composites based strain sensors have attracted increasing attention recently. In this paper, flexible composites were prepared by incorporating thermoplastic polyurethane (TPU) with zero-dimensional carbon black (CB) and one-dimensional carbon nanotubes (CNTs), respectively. CNTs/TPU showed a lower percolation threshold (0.28 wt.%) and wider sensing range (0-ca.135% strain), compared with CB/TPU (1.00 wt.% and 0-ca. 90% strain). CB/TPU composites exhibited a higher sensitivity with a GF of 10.8 under 20% strain, while CNTs/TPU showed a lower GF of 6.8. In cyclic loading-unloading test, both the two composites showed non-monotonic ‘shoulder peak’ behaviors. For CB/TPU, the ‘first peak’ was higher than the ‘second peak’; interestingly, CNTs/TPU presented a negative strain effect. The discrepancy was mainly ascribed to the difference of filler dimensionality and the evolution of the conductive network.
Co-reporter:Hu Liu;Mengyao Dong;Wenju Huang;Jiachen Gao;Kun Dai;Jiang Guo;Guoqiang Zheng;Changyu Shen;Zhanhu Guo
Journal of Materials Chemistry C 2017 vol. 5(Issue 1) pp:73-83
Publication Date(Web):2016/12/22
DOI:10.1039/C6TC03713E
Lightweight conductive porous graphene/thermoplastic polyurethane (TPU) foams with ultrahigh compressibility were successfully fabricated by using the thermal induced phase separation (TISP) technique. The density and porosity of the foams were calculated to be about 0.11 g cm−3 and 90% owing to the porous structure. Compared with pure TPU foams, the addition of graphene could effectively increase the thickness of the cell wall and hinder the formation of small holes, leading to a robust porous structure with excellent compression property. Meanwhile, the cell walls with small holes and a dendritic structure were observed due to the flexibility of graphene, endowing the foam with special positive piezoresistive behaviors and peculiar response patterns with a deflection point during the cyclic compression. This could effectively enhance the identifiability of external compression strain when used as piezoresistive sensors. In addition, larger compression sensitivity was achieved at a higher compression rate. Due to high porosity and good elasticity of TPU, the conductive foams demonstrated good compressibility and stable piezoresistive sensing signals at a strain of up to 90%. During the cyclic piezoresistive sensing test under different compression strains, the conductive foam exhibited good recoverability and reproducibility after the stabilization of cyclic loading. All these suggest that the fabricated conductive foam possesses great potential to be used as lightweight, flexible, highly sensitive, and stable piezoresistive sensors.
Co-reporter:Yayun Wang, Xianhu Liu, Meng Lian, Guoqiang Zheng, Kun Dai, Zhanhu Guo, Chuntai Liu, Changyu Shen
Applied Materials Today 2017 Volume 9(Volume 9) pp:
Publication Date(Web):1 December 2017
DOI:10.1016/j.apmt.2017.05.007
•The absorption material (AM) is fabricated by conventional polymer processing method.•The as-prepared AM is prepared using low-cost polyolefins in a solvent-free method.•The as-prepared AM exhibits excellent reusability.•The as-prepared AM shows continuous oil–water separation or oil collection ability.Recently, the development of methods for the cleanup of large-scale oil spills or organic pollutants from water has been attracting global attention. However, traditional techniques suffer from the limits of low efficiency and high operation cost. Herein, we propose a high efficiency, large-scale and easy operation approach to fabricate a hydrophobic and oleophilic high density polyethylene microfiber bundles with interconnected microchannels for oil/water separation. The microfiber bundles with high porosity, excellent absorption capacity and large water contact angle are continuously fabricated by a melt extrusion and leaching technique. More importantly, they are readily cleaned by centrifugation and exhibit excellent shape-recoverable property, which are very promising for the cleanup of large-scale oil spills. This study provides a great promising way to fabricate multifunctional polymer materials by using common polymer molding method.Download high-res image (137KB)Download full-size image
Co-reporter:Weihua Chen;Keming Song;Liwei Mi;Xiangming Feng;Jianmin Zhang;Shizhong Cui
Journal of Materials Chemistry A 2017 vol. 5(Issue 20) pp:10027-10038
Publication Date(Web):2017/05/23
DOI:10.1039/C7TA01634D
SnO2/graphene materials have received extensive attention in broad applications owning to their excellent performances. However, multi-step and harsh synthetic methods with high temperatures and high pressures are major obstacles that need to be overcome. Herein a simple, low-cost, and scalable approach is proposed to construct ultrafine SnO2/graphene nanomaterials effectively under constant pressure and at the low temperature of 80 °C for 4 h, in which ultrafine SnO2 nanoparticles grow on graphene sheets uniformly and firmly via Sn–O–C bonding. This result depends on the synergetic effect of two reactions, the reduction of graphene oxide and formation of SnO2 nanoparticles, which are achieved successfully. More importantly, the constructed SnO2/graphene material exhibits excellent electrochemical properties in both lithium-ion batteries and sodium-ion batteries. As an anode material for lithium-ion batteries, it displays a high reversible capacity (1420 mA h g−1 at 0.1 A g−1 after 90 cycles) and good cycling life (97% at 1 A g−1 after 230 cycles), whereas in sodium-ion batteries, it maintains a capacity of 1280 mA h g−1 at 0.05 A g−1 and 650 mA h g−1 at 0.2 A g−1 after 90 cycles. The proposed synthetic methodology paves the way for the effective and large scale preparation of graphene-based composites for broad applications such as energy storage, optoelectronic devices, and catalysis.
Co-reporter:Junhui Si, Zhixiang Cui, Qianting Wang, Qiong Liu, Chuntai Liu
Carbohydrate Polymers 2016 Volume 143() pp:270-278
Publication Date(Web):5 June 2016
DOI:10.1016/j.carbpol.2016.02.015
•PCL/NC fibrous matrix was successfully fabricated by electrospinning technique.•HA-mineralized on PCL/NC fiber can be prepared by SBF immersion.•NC was successfully used as an additive to induce the deposition of HA nucleus.•The hydrophilicity of PCL/NC/HA scaffolds increases with the formation of HA.A biomimetic nanocomposite scaffold with HA formation on the electrospun poly(ɛ-caprolactone) (PCL)/nanocellulose (NC) fibrous matrix was developed in this study. The electrospun PCL/NC fiber mat was built and then biomineralized by treatment in simulated body fluid (SBF). Using such a rapid and effective procedure, a continuous biomimetic crystalline HA layer could be successfully formed without the need of any additional chemical modification of the substrate surface. The results showed that the introduction of NC into composite fibers is an effective approach to induce the deposition of HA nucleus as well as to improve their distribution and growth of a crystalline HA layer on the fibrous scaffolds. The water contact angle (WCA) of the PCL/NC/HA scaffolds decreases with increasing NC content and mineralization time, resulting in the enhancement of their hydrophilicity. These results indicated that HA-mineralized on PCL/NC fiber can be prepared directly by simply using SBF immersion.
Co-reporter:Xianhu Liu, Yamin Pan, Guoqiang Zheng and Chuntai Liu
RSC Advances 2016 vol. 6(Issue 73) pp:68969-68972
Publication Date(Web):15 Jul 2016
DOI:10.1039/C6RA14921A
The thickness of oriented zones in water-assisted injection moulded β-iPP parts increased with the increasing of β-nucleating agent (β-NA) content. More interestingly, the high β-NA content suppressed the hierarchical structure effectively, which is consistent with the almost invariable crystallinity and orientation. Meanwhile, an unexpected lamellar branching of the β-crystal was observed.
Co-reporter:Shuangyang Liu, Feifei Zhang, Guoqiang Zheng, Kun Dai, Chuntai Liu, Changyu Shen, John Zhanhu Guo
Materials Letters 2016 Volume 172() pp:149-152
Publication Date(Web):1 June 2016
DOI:10.1016/j.matlet.2016.02.111
•iPP fibers containing nano-fibrils are fabricated by high-temperature electrospinning.•Electrospun iPP fibers consist of shish-kebab structure.•Elongational force is responsible for the development of shish-kebab structure.Electrospinning is not only a technique to fabricate macroscopic fiber but also a method to control the microstructure. In this study, high-temperature solution electrospinning was used to prepare isotactic polypropylene (iPP) fibers. Scanning electron microscope (SEM) observation indicates that a single electrospun iPP fiber consists of many nano-fibrils. Based on SEM observation, these nano-fibrils are shish-kebab structure. Electrostatic elongational force involved in the electrospinning process is considered to be responsible for the development of shish-kebab structure.
Co-reporter:Guojie Li, Chao Hu, Wei Zhai, Shuaiguo Zhao, Guoqiang Zheng, Kun Dai, Chuntai Liu, Changyu Shen
Materials Letters 2016 Volume 182() pp:314-317
Publication Date(Web):1 November 2016
DOI:10.1016/j.matlet.2016.07.020
•An approach for tuning PTC characteristics of resistivity was proposed.•The mechanism of tuning PTC is manipulating the size of polymer matrix particles.•The CPCs material with ultra-high PTC intensity was fabricated.•This paper provides an effective route to prepare a tunable temperature sensor.A novel approach, i.e. manipulating the size of incorporated polymer matrix particles, was proposed to tune the positive temperature coefficient (PTC) characteristics of carbon nanotubes (CNTs)/polypropylene (PP) composites with a segregated microstructure. For the conductive properties of CNTs/PP composites, the percolation threshold decreased from 1.32 vol% to 0.44 vol% when the matrix particle size enlarged from 20 to 1200 µm, showing an inverse correlation effect. The controllable PTC characteristics in resistivity are attributed to the microstructure development of conductive pathways and the heat-induced volume expansion of polymer matrix particles. An extremely high PTC material has also been achieved through this method. The present work provides an effective route to acquire a tunable temperature-resistivity sensor.
Co-reporter:Yuanxu Zhao;Bo Wang;Weiwei Chen;An Li;Guoqiang Zheng;Jingbo Chen ;Changyu Shen
Polymer Composites 2016 Volume 37( Issue 6) pp:1914-1923
Publication Date(Web):
DOI:10.1002/pc.23370
Hydroxyl functionalized multiwalled carbon nanotubes (H-MWNTs) were silanized using 3-aminopropyltriethoxysilane (APTES) in order to improve the dispersion and interfacial interaction in composites. MWNT/polycarbonate (PC) composites filled with H-MWNTs and silanized MWNTs (S-MWNTs) were fabricated by melt mixing and injection molding. Fourier transform infrared spectrometry (FTIR) and energy dispersion X-ray spectroscopy (EDS) were employed to prove the presence of APTES on the surface of S-MWNTs. In addition, thermogravimetric analysis (TGA) was used to evaluate the relative amount of introduced APTES. The microstructure and mechanical property of both composites were investigated by scanning electron microscopy (SEM), transmission electron microscope (TEM), tensile test and dynamic mechanical analysis (DMA). The SEM and TEM images showed that S-MWNT/PC composites had better dispersion and interfacial adhesion than H-MWNT/PC composites. A reinforcing and toughening effect on tensile behavior of composites was obtained after silane functionalization. The storage modulus of composites increased markedly as a function of MWNTs content, especially for the composites with S-MWNTs. In summary, the silanization can improve the dispersion of MWNTs and the interfacial adhesion between MWNTs and PC so as to enhance the mechanical properties of composites. POLYM. COMPOS., 37:1914–1923, 2016. © 2015 Society of Plastics Engineers
Co-reporter:Xianhu Liu, Yamin Pan, Cheng Peng, Xiaoqiong Hao, Guoqiang Zheng, Dirk W. Schubert, Chuntai Liu, Changyu Shen
Materials Letters 2016 Volume 172() pp:19-22
Publication Date(Web):1 June 2016
DOI:10.1016/j.matlet.2016.02.127
•Large number of well-developed banded spherulites was observed in the core region.•Shish-kebabs without and with twisted lamellae were found.•The formation of twisted lamellae depends on the level of applied shear stress.A distinct skin-core-water-channel structure was formed in water-assisted injection molded low molecular weight high density polyethylene. A large number of well-developed banded spherulites were observed in core region. Two types of shish-kebabs, i.e., shish-kebabs without and with twisted lamellae, were appeared in both skin and water-channel region. The results imply that the formation mechanisms of twisted lamellae in banded spherulites and shish-kebabs are different, but both depend on the level of applied shear stress.High density polyethylene with low molecular weight was molded by a new polymer processing method, that is, water-assisted injection molding (WAIM), and its crystal morphologies along the thickness direction was studied by two-dimensional small-angle X-ray scattering and wide-angle X-ray diffraction. The scattering intensities of (110) reflection appear two maxima on the off-axis and (200) reflection appear one maxima on the equator, which indicate the formation of twisted kebabs.
Co-reporter:Zhongzhu Liu;Guoqiang Zheng;Kun Dai;Changyu Shen
Journal of Applied Polymer Science 2016 Volume 133( Issue 21) pp:
Publication Date(Web):
DOI:10.1002/app.43454
ABSTRACT
Polymer processing methods generally play a crucial role in determining the development of microstructure in the fabricated product. In this study, isotactic polypropylene (iPP) melt containing 0.05 wt % β-nucleating agent (β-NA) was extruded via a melt flow rate indicator. The molten extrudate was stretched into a fiber upon various take-up velocities (TVs). The microstructures of the fiber were investigated by differential scanning calorimeter, two-dimensional wide-angle X-ray diffraction, and small-angle X-ray scattering. Also, its tensile properties (including tensile strength, modulus, elongation at break, and toughness) were measured by tensile test. Interestingly, the tensile strength (135.0 MPa) of a melt-spun β-nucleated iPP fiber fabricated at 400 cm/min was enhanced by 115.2%, compared with that (62.7 MPa) prepared at 100 cm/min, with a considerable increment in toughness (from 661 to 853 MJ/m3). The enhancement mechanism for tensile properties was discussed based on the microstructures. This work offers a simple approach to prepare β-nucleated iPP fibers with excellent strength and toughness. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43454.
Co-reporter:Junhui Si;Zhixiang Cui;Peng Xie;Lairui Song;Qianting Wang;Qiong Liu
Journal of Applied Polymer Science 2016 Volume 133( Issue 4) pp:
Publication Date(Web):
DOI:10.1002/app.42909
ABSTRACT
In this study, elastic porous polydimethylsiloxane (PDMS) cell scaffolds were fabricated by vacuum-assisted resin transfer moulding (VARTM) and particle leaching technologies. To control the porous morphology and porosity, different processing parameters, such as compression load, compression time, and NaCl particle size for preparing NaCl preform, were studied. The porous structures of PDMS cell scaffolds were characterized by scanning electron microscopy (SEM). The properties of PDMS cell scaffolds, including porosity, water absorption, interconnectivity, compression modulus, and compression strength were also investigated. The results showed that after the porogen–NaCl particles had been leached, the remaining pores had the sizes of 150–300, 300–450, and 450–600 μm, which matched the sizes of the NaCl particles. The interconnectivity of PDMS cell scaffolds increases with an increase in the size of NaCl particles. It was also found that the smaller the size of the NaCl particles, the higher the porosity and water absorption of PDMS cell scaffolds. The content of residual NaCl in PDMS/NaCl scaffolds reduces under ultrasonic treatment. In addition, PDMS scaffolds with a pore size of 300–450 μm have better mechanical properties compared to those with pore sizes of 150–300 and 450–600 μm. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 42909.
Co-reporter:Haili Zheng, Yabo Quan, Guoqiang Zheng, Kun Dai, Chuntai Liu and Changyu Shen
RSC Advances 2015 vol. 5(Issue 74) pp:60392-60400
Publication Date(Web):25 Jun 2015
DOI:10.1039/C5RA07453C
A shear-induced ultrahigh molecular weight polyethylene (UHMWPE) shish-kebab mat (USKM), in which shish-kebabs are well aligned, has been achieved from a dilute UHMWPE solution. Such a USKM is incorporated into linear low density polyethylene (LLDPE) as a reinforcement filler. Isothermal crystallization shows that the USKM acts as an effective nucleating agent for LLDPE crystallization, leading to enhanced crystallinity, long period, and lamellar thickness of the USKM/LLDPE composite. Instead of shish-kebabs, only aligned fibrils are observed in the composite. Such fibrils consist of a shish structure wrapped with LLDPE chains and good bonding at the interface between the fibril and matrix is achieved. Consequently, the interfacial adhesion is expected to improve and favorable stress transfer is realized. Together with good bonding, the superior strength of the shish structure and the above enhanced crystalline parameters contribute to a significant increment in the tensile strength and modulus of the composite, as compared to pure LLDPE.
Co-reporter:Xiaohan Cao, Yan Lan, Yue Wei, Guoqiang Zheng, Kun Dai, Chuntai Liu, Changyu Shen
Materials Letters 2015 Volume 159() pp:276-279
Publication Date(Web):15 November 2015
DOI:10.1016/j.matlet.2015.07.028
•The top test temperature affects the resistivity–temperature behaviors of CPCs.•Resistivity–temperature behaviors were also influenced by the cooling rate.•These results can be elucidated by the FITC and hysteresis effect.•This paper provides an effective route to prepare a tunable temperature sensor.Resistivity–temperature characteristics of conductive multi-walled carbon nanotubes (MWCNT)/epoxy (EP) composite were studied during a heating-cooling run (HCR) with different top test temperatures. The values of Re (room-temperature resistance at the end of a HCR) decrease with increasing the top test temperature. The fluctuation-induced tunneling conduction (FITC) and the hysteresis effect developing in MWCNT/EP composite are responsible for this fascinating phenomenon. In order to understand this result further, resistivity–temperature characteristic at different cooling rates was studied. The values of Re also decrease with rising the cooling rate. This paper provides an effective approach to acquire a tunable temperature sensor.
Co-reporter:Changyan Zhang, Bo Wang, Jingjing Yang, Daowei Ding, Xingru Yan, Guoqiang Zheng, Kun Dai, Chuntai Liu, Zhanhu Guo
Polymer 2015 60() pp: 40-49
Publication Date(Web):
DOI:10.1016/j.polymer.2015.01.026
Co-reporter:Bo Lu, Guoqiang Zheng, Kun Dai, Chuntai Liu, Jingbo Chen, Changyu Shen
Materials Letters 2015 140() pp: 131-134
Publication Date(Web):
DOI:10.1016/j.matlet.2014.10.151
Co-reporter:Linxiang Huang, Zhen Wang, Guoqiang Zheng, John Zhanhu Guo, Kun Dai, Chuntai Liu
Materials & Design (1980-2015) 2015 78() pp: 12-18
Publication Date(Web):5 August 2015
DOI:10.1016/j.matdes.2015.04.001
•Oriented lamellae are formed in core region of injection-molded HDPE upon pre-shear.•Skin–core structure of injection-molded HDPE can be steadily suppressed by pre-shear.•HDPE part is mechanically enhanced if pre-shear was exerted at lower temperature.In the present work, pre-shear was elaborately introduced into melting HDPE and then such pre-sheared melt was injection molded. The hierarchical structure and crystalline morphology of injection-molded HDPE part were investigated by using WAXD and SEM. It was found that pre-shear can enhance the formation of oriented crystals in core region of HDPE part. More interestingly, such enhancing effect becomes more remarkable if pre-shear was exerted at low temperature just slightly above the melting point of HDPE. Naturally, mechanical property was promoted due to the oriented crystals induced by pre-shear at low temperature and the narrowed orientation gap between shear region and core region.
Co-reporter:Zhongzhu Liu;Xianhu Liu;Guoqiang Zheng;Kun Dai
Journal of Materials Science 2015 Volume 50( Issue 2) pp:599-604
Publication Date(Web):2015 January
DOI:10.1007/s10853-014-8618-0
Polymer processing generally plays a crucial role in determining the development of microstructure in the fabricated product. In this paper, isotactic polypropylene (iPP) containing 0.1 wt% β-nucleating agent was extruded via a slit die and immediately melt-stretched upon various stretching rates (SR) at the die exit. The microstructure of β-nucleated iPP samples was investigated using two-dimensional wide-angle X-ray diffraction and small-angle X-ray scatterings (2D-WAXD/SAXS) measurements. It is observed that, no matter what SR is, lamellar branching of β-form crystal is formed in melt-stretched samples, which is scarcely reported in open literatures. A method is proposed to calculate the crystallinity of daughter lamellae in β-crystal (Xβ−D). It is found that Xβ−D decreases with increasing SR, indicating that lamellar branching of β-form crystal is restrained by higher SR. Such case should be attributed to the denser-oriented structures (e.g., shish) induced by higher SR, leaving a confined space between adjacent-oriented structures for the growth of daughter lamellae.
Co-reporter:Baobao Chang;Bo Wang;Guoqiang Zheng;Kun Dai;Changyu Shen
Polymer Engineering & Science 2015 Volume 55( Issue 12) pp:2714-2721
Publication Date(Web):
DOI:10.1002/pen.24078
In this work, isotactic–polypropylene (iPP) specimens were prepared by a modified injection molding machine, in which high temperature preshear (HTPS) can be imposed on the molten polymer during the plasticizing stage. The effect of HTPS on the microstructure and mechanical property of iPP was investigated. It was found that spherulite size in core region of iPP part decreased steadily with the increasing HTPS duration, indicating that HTPS could substantially enhance iPP nucleation. Moreover, β-iPP formation correlated strongly with HTPS duration. That is, in the absence of HTPS, β-iPP existed only in intermediate region; with moderate HTPS duration, β-iPP could be unexpectedly formed in core region; however, long HTPS duration inhibited β-iPP formation in both intermediate region and core region. Based on the relationship between β-iPP formation and HTPS duration, metastable nuclei, instead of α-row nuclei, were proposed to be responsible for the development of β-iPP. Notched Izod impact test showed that moderate HTPS duration enhance the impact strength of injection molded iPP by decreasing the thickness of shear region and elevating β-iPP crystallinity in core region. Dynamic mechanical test indicated that with the increase of HTPS duration, the storage modulus of injection-molded iPP improves drastically. POLYM. ENG. SCI., 55:2714–2721, 2015. © 2015 Society of Plastics Engineers
Co-reporter:Yuezhan Feng, Bo Wang, Fangfang Wang, Yuanxu Zhao, Chuntai Liu, Jingbo Chen, Changyu Shen
Polymer Degradation and Stability 2014 Volume 107() pp:129-138
Publication Date(Web):September 2014
DOI:10.1016/j.polymdegradstab.2014.05.012
Polycarbonate nanocomposites filled with pristine and modified silica were prepared by simple melt compounding. The thermal degradation behavior of composites was investigated by thermogravimetric analysis coupled with differential scanning calorimetry (TGA/DSC). To understand the thermal degradation mechanism, the chemical structures of gaseous and solid degradation products were detected by thermogravimetric analysis coupled with Fourier transform infrared spectrometry (TGA/FTIR) and X-ray photoelectron spectroscopy (XPS), respectively. Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods were employed to analyze the thermal degradation kinetics. High thermal degradation temperature was obtained by incorporating both types of nanoparticles into matrix, but the maximum mass loss rate increased. According to the DSC curves for degradation process, the change of the number and position of absorption peaks meant that the degradation mechanism of composites was different from that of neat PC. The analysis for TGA chars confirmed the presence of alcoholysis reaction between PC and silica nanoparticles during the thermal decomposition. TGA/FTIR results proved that no new degradation volatiles were produced during the thermal degradation of composites, but the total amounts of all gaseous products decreased by adding silica nanoparticles. The degradation activation energies of both composites increased significantly relative to neat PC, especially for the composite with modified silica.
Co-reporter:Shasha Wu, Bo Wang, Guoqiang Zheng, Shuangyang Liu, Kun Dai, Chuntai Liu, Changyu Shen
Materials Letters 2014 Volume 124() pp:77-80
Publication Date(Web):1 June 2014
DOI:10.1016/j.matlet.2014.03.048
•PA66 nanofiber bundles are electrospun using two electrode pins as collector.•The rotating pin significantly influences the arrangement of nanofibers in bundle.•Tensile property and microstructure of bundles are also influenced by rotating pin.•Higher tensile strength can be explained by higher crystallinity and lower porosity.In this study, macroscopic polyamide 66 (PA66) nanofiber bundles were successfully electrospun using two electrode pins as collector. One of the pins can rotate with a speed of 300 rpm. Scanning electron microscope, tensile test, wide-angle X-ray diffraction and differential scanning calorimetry were employed to characterize the arrangement of electrospun nanofibers in bundle, tensile property and microstructure of electrospun nanofiber bundles. Results show that the collector pin׳s rotating speed not only significantly influences the arrangement of nanofibers in bundle but also the crystallinity and porosity of nanofiber bundles, which further influence the tensile strength and failure strain of nanofiber bundles.
Co-reporter:Yamin Pan;Suyu Shi;Wenzhong Xu;Guoqiang Zheng;Kun Dai
Journal of Materials Science 2014 Volume 49( Issue 3) pp:1041-1048
Publication Date(Web):2014 February
DOI:10.1007/s10853-013-7781-z
In this paper, injection-molded isotactic polypropylene (iPP) microparts and macroparts were respectively fabricated by the molds with different thickness under the same processing conditions. Comparative study on microstructure and mechanical property was carried out by means of scanning electron microscopy (SEM), two-dimensional wide-angle X-ray diffraction (2D-WAXD), two-dimensional small-angle X-ray scattering (2D-SAXS), differential scanning calorimetry (DSC) and tensile test. SEM images reveal that the two parts show distinctly different hierarchical structure. An obvious ‘skin–core’ structure is present for the macroparts, while a wide distribution of shish-kebab structure develops in both shear and core layer for microparts, exhibiting a specific ‘core-free’ morphology. 2D-WAXD, 2D-SAXS and DSC results show that microparts have higher orientation degree and crystallinity as compared to macroparts, which are responsible for the remarkably high tensile strength and modulus. Our work provides a good example for better understanding processing structure–property relationship of iPP through tuning their internal microstructure.
Co-reporter:Xianhu Liu, Kun Dai, Xiaoqiong Hao, Guoqiang Zheng, Chuntai Liu, Dirk W. Schubert, and Changyu Shen
Industrial & Engineering Chemistry Research 2013 Volume 52(Issue 34) pp:11996-12002
Publication Date(Web):August 5, 2013
DOI:10.1021/ie401162c
Although both shear flow and β-nucleating agent (β-NA) could separately induce β-crystal in isotactic polypropylene (iPP), their combination, particularly in the typical industrial processes, in fact has received comparatively little attention. In the current study, two-dimensional wide-angle X-ray diffraction and small-angle X-ray scattering (2D-WAXD/SAXS) measurements were performed to investigate the effect of β-NA on the crystalline structure of the oriented shear zone in injection molded iPP. It is observed that, regardless of the β-NA concentration, parent–daughter structure of α-crystal can be formed in iPP. Furthermore, the fraction of daughter lamellae elevates with the increasing concentration of β-NA. Interestingly, unexpected scattering patterns of (300) reflection for β-crystal, which is similar with that for parent–daughter lamellar branching of α-crystal, is exclusively found in iPP with higher concentration of β-NA (1.0 wt %). The most possible explanation is that the addition of high content of β-NA lowers the free energy barrier. Additionally, the same change tendency of long period, crystal lamellar thickness and lateral dimension, d-spacing and crystallite size is found, viz., they first increase and then decrease with the increasing β-NA content. The results demonstrate that the concentrations of β-NA have a significant effect on the crystal grain structure under the practical molding process.
Co-reporter:Xianhu Liu;Changyan Zhang;Kun Dai;Guoqiang Zheng;Changyu Shen
Polymers for Advanced Technologies 2013 Volume 24( Issue 2) pp:270-272
Publication Date(Web):
DOI:10.1002/pat.3071
As a part of continuous efforts to systematically understand the morphological development in water-assisted injection molding, high density polyethylene with different molecular weights was molded in this study. Unexpectedly, it was found that shish kebab with high lamellar and molecular orientations was formed in the sample with a lower molecular weight (LMW) rather than in the higher one, especially in the water channel layer. Present finding is obviously inconsistent with the general consensus, that is, higher molecular weight (HMW) polymer is much easier to form preferential orientation in flow field than LMW one. Such anomalous phenomenon is explained by the fact that even though melts experienced the same processing, lower shear rate is practically achieved in HMW sample due to its high viscosity. The result indicates that the flow history in industrial processing method is far from that in laboratory one. Copyright © 2012 John Wiley & Sons, Ltd.
Co-reporter:Baobao Chang, Mancun Xie, Kun Dai, Guoqiang Zheng, Shiwei Wang, Chuntai Liu, Jingbo Chen, Changyu Shen
Polymer Testing 2013 Volume 32(Issue 3) pp:545-552
Publication Date(Web):May 2013
DOI:10.1016/j.polymertesting.2013.01.012
On the laboratory scale, pre-shear induced orientation at high temperature can considerably influence the subsequent crystallization, which has been intensively investigated by various sophisticated methods. Unfortunately, during conventional polymer processing (e.g., injection molding), the preservation of pre-shear induced orientation is a practical challenge because oriented chains are prone to relax as far as possible. Motivated by the studies on pre-shear induced crystallization, a Mixing-Injection Molding (MIM) machine was designed and built to study pre-shear induced crystallization under practical processing conditions. Its main features contain two aspects: (1) polymer composites or blends can be simultaneously plasticized and melt mixed in the barrel by a rotating screw. Logically, pre-shear is introduced to the homogeneously mixed melt; (2) the pre-sheared melt can be in-situ injected into a mold once the mixing-plasticization process finishes. In the present study, an unusual distribution of β-form isotactic polypropylene (iPP) prepared by the MIM is discovered. That is, in the core region, crystallinity of β-form (Xβ) is unexpectedly equal to that in the intermediate region, while β-form is almost absent in the core region of a conventional injection molded counterpart. Taking into account the main features of MIM and the evidence of supplementary experiments, this interesting result can be attributed to the fact that precursors can be induced by pre-shear. Such precursors are most likely to be short α-row-nuclei, which can act as nucleating sites for the growth of β-spherulites once the material is in-situ injected into the mold cavity.
Co-reporter:Shuangyang Liu, Yanyan Liang, Yabo Quan, Kun Dai, Guoqiang Zheng, Chuntai Liu, Jingbo Chen, Changyu Shen
Polymer 2013 Volume 54(Issue 12) pp:3117-3123
Publication Date(Web):24 May 2013
DOI:10.1016/j.polymer.2013.04.009
Macroscopically aligned isotactic polypropylene (iPP) fibers with different diameters ranging from 0.7 to 13.2 μm were successfully fabricated by high-temperature solution electrospinning using an infrared (IR) heating system. Polarized optical microscope (POM), scanning electron microscope (SEM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and polarized Fourier transform infrared (FTIR) were employed to characterize the surface morphology and microstructure of the electrospun fibers. From SEM images, three macroscopically structural models have been found: (1) cylindrical fibers, (2) twisted fibers and (3) beaded fibers. Interestingly, regardless of fiber's shape and size, they (especially for cylindrical fibers) exhibit well-defined self-similar morphology. That is, the tertiary, secondary and primary morphology are similar with each other. Thermally induced phase separation (TIPS) is the most pertinent origin to explain the formation of self-similar morphology. WAXD and DSC results show that α-form crystal prevails in the electrospun iPP fibers. For comparison, the solution-cast film was also prepared under the same conditions as those adopted in electrospinning except that the voltage was 0 kV. Compared with the solution-cast film, lower crystallinity, smaller average crystallite size and higher melting point are achieved in the electrospun iPP fibers. The results of polarized FTIR spectra demonstrate that the macroscopically aligned electrospun fibers are highly oriented along the fiber's longitudinal axis at molecular level. Furthermore, when the electrospun iPP fibers were embed in iPP matrix, surface-induced crystallization is significantly enhanced and finally develops into transcrystalline layer which can be even revived after recrystallization. As a result, it is logical that long-lived thermodynamically stable structure has been formed in the electrospun iPP fiber. Combined with FTIR result, the α-form crystal formed in the fiber is conjectured to be a kind of oriented structure with thermodynamically long-lived stability which is similar to "shish-kebab" structure.
Co-reporter:Yanyan Liang;Guoqiang Zheng;Shuangyang Liu;Kun Dai
Journal of Materials Science 2013 Volume 48( Issue 6) pp:2326-2333
Publication Date(Web):2013 March
DOI:10.1007/s10853-012-7012-z
The crystallization in isotactic polypropylene (iPP) melt inclusions, encapsulated by transcrystallinity and spherulites, was investigated by polarized light microscope. Generally, owing to the proceeding of crystallization in melt inclusions, a negative pressure will be built up. Up to a critical value, the negative pressure is released by the formation of cavitation in melt. Unexpectedly, β-crystals with different morphologies emerge at different locations in the melt inclusions. For low molecular weight iPP, only smaller β-crystals around bubbles are discernable. Turn to higher molecular weight iPP, apart from the smaller β-crystals, fan-shaped ones can be developed under suitable conditions (e.g., lower than 131 °C) at the growth front of spherulites and transcrystallinity. Considering the characteristics of molecular weight and morphology, it is proposed that β-crystals are induced by different mechanisms. That is, smaller β-crystals are resulted from the stress caused by the appearance of bubbles while the fan-shaped ones are derived due to the temperature gradient during the release of negative pressure.
Co-reporter:Ke Li;Kun Dai;Xiangbin Xu;Guoqiang Zheng
Colloid and Polymer Science 2013 Volume 291( Issue 12) pp:2871-2878
Publication Date(Web):2013 December
DOI:10.1007/s00396-013-3038-2
Carbon black (CB)/poly (lactic acid) (PLA) conductive biopolymer composite were fabricated by casting. A low percolation value (1.25 vol%) is achieved due to the formation of a two-dimensional conductive network in the composite. Vapor sensing behaviors of the CB/PLA conductive composite were studied. A high chemical selectivity with respect to different organic vapors and a good reproducibility to two typical solvents, ethyl acetate and ethanol, during exposure-drying runs have been demonstrated. The variations of the sensing behaviors during exposure-drying processes were associated with the evolvement of CB conductive networks. The results indicate that the Flory-Huggins interactions parameter x12, related to the solubility parameter (thermodynamic factor), molar volume (kinetic factor) and the measurement temperature, affects the vapor sensing behaviors of CB/PLA composite significantly. These results suggest CB/PLA conductive biopolymer composite can be applied as a nice vapor sensor candidate.
Co-reporter:Yanyan Liang;Shuangyang Liu;Kun Dai;Bo Wang
Colloid and Polymer Science 2012 Volume 290( Issue 12) pp:1157-1164
Publication Date(Web):2012 August
DOI:10.1007/s00396-012-2626-x
Polyamide 66 (PA 66) nanofiber bundles were first electrospun and then introduced into isotactic polypropylene (iPP) melts to prepare nanofiber bundle/iPP composites. To reveal the influences of matrix molecular weight (Mn) on the transcrystalline layer, three kinds of iPP with different Mn were adopted. Polarized optical microscope was employed to investigate the transcrystallinity. In the presence of PA 66 nanofiber bundle, the heterogeneous nucleation distinctly happened in iPP melts. Moreover, the higher the iPP Mn, the denser the nuclei. Both a decrease in matrix Mn and an increase in isothermal crystallization temperature led to an increase in the induction time. The maximum temperature at which the transcrystalline layer can be optically observed increased with the increase of Mn. The growth rate of transcrystallinity decreased with the increasing Mn and crystallization temperature. Moreover, selective melting of the transcrystalline layers confirmed that it was merely composed of α form crystal for all composites.
Co-reporter:Guo-Qiang Zheng;Zhenhua Jia;Xianhu Liu;Baochen Liu;Xiaoli Zhang;Kun Dai;Chunguang Shao;Xuejing Zheng;Wei Cao;Jingbo Chen;Xiangfang Peng;Qian Li;Changyu Shen
Polymer Engineering & Science 2012 Volume 52( Issue 4) pp:725-732
Publication Date(Web):
DOI:10.1002/pen.22095
Abstract
The nucleated isotactic polypropylene (iPP) was molded by water-assisted injection molding. The crystalline morphology and orientation distribution were studied. The results show that shear brought by melt filling and pressurized water penetration can separately induce the formation of oriented structures in skin region (i.e., the region near mold cavity wall) and the water channel region. For virgin iPP, slightly oriented lamellae appear exclusively in the above aforementioned regions. However, shish-kebab structure occurs not only in skin and water channel region of the iPP containing moderate content of nucleator (0.2 wt%) but also in the whole region of the iPP containing a higher content of nucleator (1 wt%). It is well known that nucleator cannot directly induce the development of shish-kebab in the absence of shear, thus the results indicate: shear flow actually distributes over a much broader range than expected; in shear field, nucleator is significantly helpful for the shear which is not sufficient to solely induce oriented structure to promote the formation of the oriented structure. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers
Co-reporter:Qingtao Li, Guoqiang Zheng, Kun Dai, Mancun Xie, Chuntai Liu, Baochen Liu, Xiaoli Zhang, Bo Wang, Jingbo Chen, Changyu Shen, Qian Li, Xiangfang Peng
Materials Letters 2011 Volume 65(Issue 14) pp:2274-2277
Publication Date(Web):31 July 2011
DOI:10.1016/j.matlet.2011.04.035
Glass fiber (GF) was immersed in diluted acid solution and corroded for 4 h. The interfacial morphology of isotactic polypropylene (iPP) reinforced by the corroded GF was studied via polarized optical microscope. It was found that the corroded GF exhibits anomalous nucleating ability to induce ringed nuclei, and β-transcrystallinity can be developed unexpectedly from these nuclei during isothermal crystallization. The present work provides a novel approach, via which β-transcrystallinity can arise in static condition from the surface of the acid-corroded GF.The optical picture showing the β-transcrystallinity developed in iPP reinforced by the glass fiber acid-corroded for 4 h.Research Highlights► The acid-corroded GF exhibits anomalous nucleating ability to induce ringed nuclei. ► The β-transcrystallinity can arise in static condition from the ringed nuclei. ► This study provides a facile way to prepare β-transcrystallinity in GF/iPP composites.
Co-reporter:Guoqiang Zheng;Zhenhua Jia;Songwei Li;Kun Dai;Baochen Liu;Xiaoli Zhang;Liwei Mi;Jingbo Chen;Changyu Shen;Xiangfang Peng;Qian Li
Polymer International 2011 Volume 60( Issue 10) pp:1434-1441
Publication Date(Web):
DOI:10.1002/pi.3097
Abstract
At an extremely small extrusion rate, an isotactic polypropylene melt was extruded through a slit die of an extruder. Simultaneously, the extruded melt was stretched at various stretching rates (SRs) at the die exit. The oriented structure and its subsequent recrystallization via self-seeding were investigated using polarized optical microscopy, two-dimensional wide-angle X-ray scattering and small-angle X-ray scattering. As expected, much slenderer and denser oriented structures were formed at larger SR, which indicates that orientation is preferably promoted with increasing SR. In the case of the crystalline morphology developed during recrystallization, a shish kebab-like structure was retrieved via the surviving oriented structure after annealing. Unexpectedly, for the sheet stretched at higher SR, a mainly sparse and short shish kebab structure was observed. For the sheet stretched at lower SR, a dense and long shish kebab structure was observed. This suggests that the oriented structure in the sheet stretched at lower SR has a better thermal stability than that in the sheet stretched at higher SR. This is discussed based on the relaxation of entangled junctions in the stretched networks with respect to varying chain length. Copyright © 2011 Society of Chemical Industry
Co-reporter:Xianhu Liu;Guoqiang Zheng;Kun Dai;Zhenhua Jia
Journal of Materials Science 2011 Volume 46( Issue 24) pp:
Publication Date(Web):2011 December
DOI:10.1007/s10853-011-5764-5
It is well known that water-assisted injection molding (WAIM) process can be fulfilled based on the melt filling stage of conventional injection molding (CIM) process. However, due to the different physical fields involved during WAIM and CIM processes, WAIM part should exhibit unique morphological features compared with the CIM one. In this study, isotactic polypropylene (iPP) parts were prepared by WAIM and CIM, respectively, and their comparative study on morphology were therefore carried out by means of polarized optical microscopy (POM) and two-dimensional (2D) wide-angle X-ray diffraction (WAXD). POM observations illustrated that the WAIM part exhibits a “skin–core–water channel” structure, while the CIM part shows a typical “skin–core” structure. 2D-WAXD results showed obvious arclike reflections in each position along thickness direction of the WAIM part, indicating a pronounced molecular orientation. Furthermore, a parent–daughter model (or branched shish-kebab structure) appears at 0 and 100 μm for both the parts, and the fraction of daughter lamellae for WAIM part is lower than that of CIM part. As for the 1D-WAXD curves, it is noticed that there is a very tiny (300) reflection of β-form in the CIM part, while it is invisible in all positions of the WAIM part. In addition, the crystallinity and crystalline size L of CIM part are found to be higher than that of WAIM part. Those results demonstrate that water penetration and rapid cooling rate have a significant effect on the morphological features of WAIM part.
Co-reporter:Zhongzhu Liu, Xianhu Liu, Guoqiang Zheng, Kun Dai, Chuntai Liu, Changyu Shen, Rui Yin, Zhanhu Guo
Polymer Testing (April 2017) Volume 58() pp:227-235
Publication Date(Web):April 2017
DOI:10.1016/j.polymertesting.2017.01.002
Co-reporter:Yanjun Zheng, Yilong Li, Zeyu Li, Yalong Wang, Kun Dai, Guoqiang Zheng, Chuntai Liu, Changyu Shen
Composites Science and Technology (8 February 2017) Volume 139() pp:64-73
Publication Date(Web):8 February 2017
DOI:10.1016/j.compscitech.2016.12.014
Co-reporter:Yamin Pan, Xianhu Liu, Joachim Kaschta, Xiaoqiong Hao, Chuntai Liu, Dirk W. Schubert
Polymer (24 March 2017) Volume 113() pp:34-38
Publication Date(Web):24 March 2017
DOI:10.1016/j.polymer.2017.02.050
Co-reporter:Hu Liu, Mengyao Dong, Wenju Huang, Jiachen Gao, Kun Dai, Jiang Guo, Guoqiang Zheng, Chuntai Liu, Changyu Shen and Zhanhu Guo
Journal of Materials Chemistry A 2017 - vol. 5(Issue 1) pp:NaN83-83
Publication Date(Web):2016/10/17
DOI:10.1039/C6TC03713E
Lightweight conductive porous graphene/thermoplastic polyurethane (TPU) foams with ultrahigh compressibility were successfully fabricated by using the thermal induced phase separation (TISP) technique. The density and porosity of the foams were calculated to be about 0.11 g cm−3 and 90% owing to the porous structure. Compared with pure TPU foams, the addition of graphene could effectively increase the thickness of the cell wall and hinder the formation of small holes, leading to a robust porous structure with excellent compression property. Meanwhile, the cell walls with small holes and a dendritic structure were observed due to the flexibility of graphene, endowing the foam with special positive piezoresistive behaviors and peculiar response patterns with a deflection point during the cyclic compression. This could effectively enhance the identifiability of external compression strain when used as piezoresistive sensors. In addition, larger compression sensitivity was achieved at a higher compression rate. Due to high porosity and good elasticity of TPU, the conductive foams demonstrated good compressibility and stable piezoresistive sensing signals at a strain of up to 90%. During the cyclic piezoresistive sensing test under different compression strains, the conductive foam exhibited good recoverability and reproducibility after the stabilization of cyclic loading. All these suggest that the fabricated conductive foam possesses great potential to be used as lightweight, flexible, highly sensitive, and stable piezoresistive sensors.
Co-reporter:Weihua Chen, Keming Song, Liwei Mi, Xiangming Feng, Jianmin Zhang, Shizhong Cui and Chuntai Liu
Journal of Materials Chemistry A 2017 - vol. 5(Issue 20) pp:NaN10038-10038
Publication Date(Web):2017/04/24
DOI:10.1039/C7TA01634D
SnO2/graphene materials have received extensive attention in broad applications owning to their excellent performances. However, multi-step and harsh synthetic methods with high temperatures and high pressures are major obstacles that need to be overcome. Herein a simple, low-cost, and scalable approach is proposed to construct ultrafine SnO2/graphene nanomaterials effectively under constant pressure and at the low temperature of 80 °C for 4 h, in which ultrafine SnO2 nanoparticles grow on graphene sheets uniformly and firmly via Sn–O–C bonding. This result depends on the synergetic effect of two reactions, the reduction of graphene oxide and formation of SnO2 nanoparticles, which are achieved successfully. More importantly, the constructed SnO2/graphene material exhibits excellent electrochemical properties in both lithium-ion batteries and sodium-ion batteries. As an anode material for lithium-ion batteries, it displays a high reversible capacity (1420 mA h g−1 at 0.1 A g−1 after 90 cycles) and good cycling life (97% at 1 A g−1 after 230 cycles), whereas in sodium-ion batteries, it maintains a capacity of 1280 mA h g−1 at 0.05 A g−1 and 650 mA h g−1 at 0.2 A g−1 after 90 cycles. The proposed synthetic methodology paves the way for the effective and large scale preparation of graphene-based composites for broad applications such as energy storage, optoelectronic devices, and catalysis.
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