Materials and Properties
WANG Jie, ZHANG Weimeng, HU Jing
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335 )
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Three⁃dimensional porous poly（lactic acid） （PLA） scaffolds with a porosity of 61.7 % and good connectivity were prepared by using a 3D⁃printing technology. Then， PLA/poly（lactic acid⁃co⁃hydroxyacetic acid） copolymer （PLGA） composite scaffolds were prepared by coating PLGA on the surface of the PLA scaffolds with different concentrations of PLGA using a dip⁃coating method. The effects of PLGA concentrations on the properties of PLA scaffolds such as cross⁃sectional microscopic morphology， scaffold surface hydrophilicity， mechanical strength， and the cell proliferation activity on the scaffolds were investigated by using scanning electron microscopy， contact angle analyzer， universal testing machine， and cell counting Kit⁃8. The results indicated that the PLGA⁃coated PLA scaffolds presented a significant decrease in contact angle compared to the PLA scaffolds without a PLGA coating. They exhibited the smallest contact angle of 64.7 ° ± 1.1 ° at a PLGA mass fraction of 6 %. The cell activity on the surface of PLGA/PLA composite scaffolds was enhanced significantly after the cell inoculation for 24 h.
DUAN Kaige, ZHU Hui, NI Jia, PAN Hao, ZHOU Chaoxi, CHEN Xiaodie, MEI Zhenwei, YU Dongming
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363 )
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Polyethylene with raised temperature resistance （PERT） was modified through micro⁃crosslinking to obtain a new type of cross⁃linked thermoplastic polyethylene （TPEXa） pipes. The resultant PERT pipe not only retained good thermoplasticity but also obtained an improvement in heat resistance and creep resistance due to partial crosslinking in the PEX pipes. The influence of the content of crosslinking agent on the melt mass⁃flow rate and crosslinking degree of TPEXa material was investigated， and the hydrostatic properties， hot melt recovery performance， and mechanical properties of the recycled TPEXa pipe material were characterized. The results indicated that the TPEXa material obtained a melt mass⁃flow rate of 5.6 g/10 min （190 ºC， 21.6 kg）， a crosslinking degree of 2.3 %， and a heat deformation temperature of 78 ºC （Tf0.45） at a crosslinking agent content of 0.08 wt%. The prepared pipe passed 22 h， 165 h and 1000 h hydrostatic tests at 95 ºC. The ring stress applied in the tests exceeded the requirements of the ring stress of PERT II pipe and was close to the ring stress of PEX pipes. The TPEXa material exhibits good temperature resistance and creep resistance. This material can be melted and recycled， and the recycled material presents good mechanical properties.
ZHANG Hengyuan, LIU Jianye, WANG Shaojie, XU Yaohui, ZHANG Shijun
Abstract (
302 )
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The isothermal crystallization behaviors of polypropylene （PP） in two different solvents were analyzed by using differential scanning calorimeter （DSC）， and its isothermal crystallization kinetics was studied by using the Avrami's equation. The results indicated that the crystal growth rate decreased with an increase in crystallization temperature. Meanwhile， the reduction of nucleation constant （Kg） and end surface free energy （σe） indicated that the crystallization rate of PP in solution was higher than that of pure PP according to the Lauritzen–Hoffman's theory.
LI Yi, FAN Guiqi, WU Tianyu, YE Haimu
Abstract (
387 )
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Polychlorotrifluoroethylene （PCTFE）/graphite micro⁃sheets （GMS） composites were prepared through melt blending， and the effect of GMS content on the crystallization behavior， mechanical properties， microstructure， dynamic thermo⁃mechanical properties， and barrier properties of the composites were investigated. Meanwhile， the mechanisms for the variation of the properties were discussed. The results indicated that the addition of GMS improved the mechanical strength and rigidity of the composites. The PCTFE/GMS composite exhibited tensile strength of 50.5 MPa at a GMS loading of 0.3 wt%. This result is 22 % higher than that of pure PCTFE. When 2 wt% of GMS was added， the PCTFE/GMS⁃2 composite obtained an elastic modulus of 1 091 MPa and a loss modulus of 1 233 MPa， which increased by 36 % and 60 %， respectively， compared to pure PCTFE. Moreover， the glass transition temperatures of the composites were also improved significantly， which was 7~12 ℃ higher than that of pure PCTFE. The change of mechanical properties is attributed to the reinforcing effect of high⁃strength GMS on the PCTFE matrix. Simultaneously， GMS could promote the nucleation of PCTFE， and a small amount of GMS enhanced its crystallinity. In addition， GMS enhanced the barrier performance of PCTFE effectively， and its hydrogen permeation coefficient decreased gradually with an increase in the GMS content. When 2 wt% of GMS was added， the PCTFE/GMS composites obtained a permeation coefficient of 2.78×10-15 cm3·cm/（cm2·h·Pa）， which was 49 % lower than that of PCTFE.
LI Shouchao, FANG Yingchun, TANG Xinqiang
Abstract (
425 )
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Four types of polyethylene powders prepared by using different production processes were selected to prepare the polyethylene powders with different particle size ranges using vibrating screen machine equipped with different pore size screens. The melt mass⁃flow rate （MFR） of these powders was measured by melt index instrument， and the difference of the MFR of polyethylene powders in different particle size ranges and the relationship between the MFR and particle size distribution of polyethylene powders were investigated. The relationship between the repeatability of MFR test results and particle size distribution of the powders was analyzed. A method for reducing the test errors of MFR in the test process was proposed， which provided guidance for the measurement of the MFR of the powders. The results indicated that the particle size distribution of polyethylene powders had a great influence on MFR. The repeatability of MFR can be improved by pretreatment and regular sampling.
SHEN Yirui, ZHOU Wenbin, ZHANG Jingjing, ZHAO Chengzhong, GAO Huakun, SHEN Shuguang, LIU Dekai, JIANG Pingping
Abstract (
393 )
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Medium⁃long carbon chain chlorine paraffin （chlorine paraffin⁃52， CP⁃52） was added in the poly（vinyl chloride） （PVC） products plasticized with bis（2⁃ethylhexyl） phthalate （DEHP）. The performance of PVC products before and after the addition of chlorine paraffin was investigated. The thermal weight analyzer was used to evaluate the thermal stability of PVC films before and after the addition of chlorine paraffin. The mechanical properties of PVC films were measured by using a servo⁃control tension test machine， and the migration resistance of plastic system in PVC films was analyzed. The results indicated that the thermal stability of PVC specimens was improved with the addition of CP⁃52 and DEHP， and its onset decomposition temperature increased by 7.4 ºC from 251.6 ºC （0⁃CP⁃52/DEHP） to 259.0 ºC （40⁃CP⁃52/DEHP）. The addition of chlorine paraffin enhanced the aging resistance of PVC. In addition， the fracture elongation and tensile strength of PVC products were improved greatly. When the addition amount of chlorine paraffin was 30 wt%， the fracture elongation and tensile strength of the PVC films were increased by 4.7 times and 4 times， respectively. Their extraction resistance， volatile resistance， and migration resistance in food simulation liquid were improved. The addition of CP⁃52 can reduce the cost of PVC products， thus providing low⁃cost and high⁃performance formulations for PVC products.
ZHANG Weicheng, HU Xiang, LUO Hongxing, JIN Hui, YOU Feng, JIANG Xueliang, YAO Chu
Abstract (
416 )
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A series of soft polyurethane （PU）/tricresyl phosphate （TCP）， PU/TCP/hollow glass beads （HGB）， PU/TCP/HGB/azodicarbonamide （AC） composites were prepared by melt blending method using TCP as a plasticizer， HGB as a filler， and AC as a foaming agent. The effects of the contents of TCP， HGB and AC foaming agent on the sound absorption and dynamic mechanical properties of PU composite materials were investigated. The results indicated that the addition of TCP， HGB， and AC foaming agent enhanced the sound absorption properties of the composites significantly. The composites obtained optimal performance at a TCP mass fraction of 25 wt%， a HGB mass fraction of 10 wt%， and an AC mass fraction of 2 wt%. Their average sound absorption coefficient and maximum sound absorption coefficient reached 0.29 and 0.55， respectively， at a frequency of 1 714 Hz. Based on the half⁃peak width of sound absorption frequency， the addition of TCP was found to reduce the length of half peak width of the composites with an increase in the amounts of HGB and AC foaming agent. Through analyzing the dynamic mechanical properties of PU/TCP， PU/TCP/HGB composites， the rationality of the addition of 25 wt% TCP and 10 wt% HGB in the composites was verified.
JIAO Ruimin, HE Xiaofang, DONG Qingsong, WANG Lin, CAO Xinxin
Abstract (
291 )
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Pulverized coal powders were modified jointly with KH⁃560 and a vulcanization accelerator （CZ）， and then the modified coal was added to SBR as a reinforcing filler to prepare the modified coal/SBR composites. The optimal experimental ratio was explored for the co⁃modified coal⁃reinforced SBR by setting different loadings of co⁃modified coal in the composites. The results indicated that the optimum addition amount of KH⁃560 was 5 wt% in the composite， resulting in optimal mechanical properties for the coal⁃KH560/SBR composite. KH⁃560 and CZ modified coal can obviously reduce the agglomeration of coal and disperse uniformly in SBR. When the addition amount of Coal⁃KH560⁃CZ is 40 %， compared with pure SBR， the tensile strength increases from 1.66 MPa to 2.9 MPa， the elongation at break increases from 295 % to 390 %， and the tear strength increases from 7.1 N/mm to 11.6 N/mm. The mechanical properties and thermal stability of the composite are improved， and the processability is also greatly improved.
ZHOU Xinxing, ZHENG Yuying, CHEN Chengxin, KONG Fansheng
Abstract (
324 )
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To address the problems of low strength， poor durability， and brittleness at low temperatures of ordinary polyurethane （PU）， a low⁃density， high⁃strength， fast⁃hardening thermoplastic PU （TPU）/graphene⁃modified PU grouting material was prepared by using TPU and graphene as composite modified together with the addition of small amounts of fly ash， bottom slag， and alkaline activator. The density， expansion ratio， compressive strength， flame retardancy， permeability coefficient， and microscopic morphology of the resultant grouting materials were characterized by using density tester， universal material testing machine， permeability coefficient tester， and fluorescence microscope. The effects of the type and dosage of graphene and TPU on the basic physical properties， mechanical properties， and microstructure of the grouting material were investigated. The results indicated that the prepared grouting material had a density of 0.24~1.25 g/cm3， its expansion ratio reached up to 38 times， and its compressive strength was 15.0~43.8 MPa. The compressive strength of the grouting material was almost doubled compared to the unmodified grouting material. The alcohol lamp combustion experimental results indicated that the flameless combustion time was less than 20 s. Both graphene and TPU can improve the strength， durability， and microscopic morphology of PU. The resulting grouting material exhibits good strength， durability， and elasticity to meet the requirement of various applications as a grouting material.
Processing and Application
WANG Dejian, YU Pengfei, DING Yumei, YANG Weimin
Abstract (
280 )
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To explore the extrusion flow process and mixing characteristics of natural polymers in the stacked flow channel， a three⁃dimensional physical model and a finite element mesh model of the stacked flow channel were established. The POLYFLOW software was used to calculate the flow rate of the food melt and the distributions of pressure， velocity， and shear rate during the extrusion process. The results indicated that the pressure decreased in a gradient along the extrusion direction， and the pressure difference at the middle position increased with an increase in the inlet flow rate. There is a significant change in shear rate in the flow channel. The shear rate tended to decrease from the middle position of the flow channel to the periphery and from the wall surface to the surrounding area. The speed increased at first and then decreased along the extrusion direction in the flow channel. The speed presented a small value near the wall surface. The structure and size design of the stacked twist flow channel can help to improve the mixing effect of natural polymers. The mixing effect in the 1st and 4th layer runners was better than that in the 2nd and 3rd layer runners. An increase in the inlet flow was also beneficial to the improvement of mixing effect.
XUE Peng, ZHANG Yu, ZHOU Guofa
Abstract (
233 )
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In general， the in⁃mold micro assembly molding of micro⁃fine universal direction spherical mechanical kinematic pair is difficult to meet the technical requirements of manufacturing dimensional tolerances. To address this common technical bottleneck， the technology of the functional self⁃lubricating liquid film⁃assisted in⁃mold micro assembly molding was proposed to realize its high⁃precision micro forming and assembly. The synergistic evolution law between the manufacturing diameter dimensional tolerances of spherical micro assembly interface and the slip coefficient of functional self⁃lubricating liquid film was simulated and studied. The results indicated that the diameter tolerance of the micro assembly interface had a positive correlation with the slip coefficient. The diameter tolerance also had a positive correlation with the near surface coupling temperature， the thickness of the continuous phase⁃transformation evolution zone， the thermal fluid structure coupling pressure， the elastic normal stress， and the viscous drag shear stress in the micro spherical assembly interface. When the slip coefficient decreased from 1×109 to 1×103， the diameter dimensional tolerance of the micro assembly interface decreased from 211 μm to 19 μm along with an improvement in the manufacturing accuracy by 91 %， and meanwhile its maximum coupling temperature decreased by 4.7 %. The maximum thickness of the continuous phase change zone decreased by 23.8 %， and its thermal⁃fluid⁃solid coupling pressure， elastic positive stress， and viscous drag shear stress decreased by 73 %， 72.8 %， and 56.3 %， respectively. This was attributed to the mechanism to realize the precision micro assembly of micro⁃fine universal direction spherical mechanical kinematic pair.
GAO Yonghong, CHEN Lingfeng, JIN Qingping
Abstract (
263 )
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The purpose of this study is to evaluate the effects of different freeze⁃thaw agents and freeze⁃thaw cycles on the axial compression performance of concrete⁃filled GFRP tube columns. A freeze⁃thaw cycle experiment and an axial compression experiment were conducted on 21 concrete⁃filled GFRP tube columns and 21 plain concrete columns in aqueous solution and NaCl solution with a mass fraction of 3.5 %. The ultrasonic experiment for the concrete⁃filled GFRP tube columns after freeze⁃thaw cycles was also performed. The results indicated that the mass loss rate and abnormal points of the GFRP tube columns increased with an increase in the freeze⁃thaw cycles in the same freeze⁃thaw agents， whereas the relative dynamic modulus， bearing capacity， and ultimate strain decreased. At the same freeze⁃thaw cycle numbers， the GFRP tubular columns showed a more significant decrease in the axial ultimate compressive strength after exposed to a saline environment. The GFRP tube columns also presented a decrease in the ultimate compressive strength by 29.45 % after 150 saline freezing⁃thawing cycles. This result is 2.19 times in water under the same conditions. The ultimate strain of the concrete⁃filled GFRP tube columns after the salt freezing cycle was less than that after the water freezing cycle under the same conditions.
LIU Xuejun
Abstract (
233 )
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In this study， two research methods were proposed to assess the heat transfer coefficients at the inner surface of a rotational mold heated by electricity. These two methods were suitable for the heating phase just before the powders started to melt. In the first method， the temperatures at the outer surface and inside of the mold were measured in the four cases. Then， a heat transfer model was established based on the energy conservation law so that these tested temperatures could be converted into heat transfer coefficients at the inner surface of the mold in the four cases by means of the model. In the second method， the actual rotational mold was simplified to a two⁃dimensional cylinder equivalently. The air inside the mold was treated as a main phase， and the powders were treated as a secondary phase. The numerical simulation was conducted to calculate the heat transfer coefficients at the inner surface of the mold with the aid of the Mixture model in the multiphase module of the FLUENT software. The results obtained from these two methods were in good agreement with each other in the three cases. As the volume percentage of powders increased， the heat transfer coefficient at the inner surface of the mold increased rapidly at first and then tended to increase slowly. It started to decrease after reaching a peak value of 61.2 W/（m2·K）. At the inner surface of the mold， the errors of heat transfer coefficients caused by the second method were no more than 10 % when the volume percentage of powders was out of the range of 58 %~74 %.
ZHOU Mei, LI Sijia, XU Weifeng, HUANG Jinbao, LUO Xiaosong, WU Lei
Abstract (
322 )
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The mechanisms for the hydrolysis/alcoholysis/ammonolysis reactions of ethylene terephthalate dimer was studied by using the density functional theory B3P86/6⁃31++G（d，p） method. The possible reaction paths in the hydrolysis/alcoholysis/ammonolysis degradation process were proposed. The geometric structures of various intermediates， transition states， and products involved in the reaction were optimized， and their frequencies were calculated to get the thermodynamic and kinetic parameters. The reaction mechanism for the hydrolysis/alcoholysis/ammonolysis degradation in the acyl⁃oxygen bond position in the backbone chain of ethylene terephthalate dimer was analyzed. The results indicated that the hydrolysis/alcoholysis/ammonolysis reactions reduced the activation energy of the acyl⁃oxygen bond cleavage in the main chain ester bond of ethylene terephthalate dimer， resulting in an easier reaction. The main element reaction in the hydrolysis had the highest energy barrier of 169.0 kJ/mol， whereas the ammonolysis reaction had the lowest energy barrier of 153.0 kJ/mol. The alcoholysis reaction exhibited an energy barrier of 155.0 kJ/mol.
Additive
LIU Qingkun, CONG Chuanbo, MENG Xiaoyu, ZHOU Qiong
Abstract (
301 )
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A reactive macromolecular antioxidant （hereafter named "TMPTMA/MB"） was synthesized through a free radical⁃initiated reaction of trimethylolpropane trimethacrylate （TMPTMA） with 2⁃mercaptobenzimidazole （MB）. The chemical structure of TMPTMA/MB was characterized by using Fourier⁃transform infrared spectroscopy， X⁃ray photoelectron spectroscopy， and elemental analysis. The effect of TMPTMA/MB on the vulcanization characteristics， tensile properties， and oxidation resistance of EPDM were investigated. The results indicated that TMPTMA/MB was grafted onto the EPDM molecular chains， followed by consuming the alkoxy radicals generated by the peroxide decomposition. This slowed down the vulcanization rate of the rubber and reduced its crosslinking degree. The grafted TMPTMA/MB enhanced the internal friction of molecular chains under the action of external forces and therefore improved the tensile properties of EPDM. In addition， the TMPTMA/MB grafted on the EPDM molecular chains has high migration resistance， thus improving the oxidation resistance of EPDM significantly.
Plastic and Environment
ZHAO Weiwei, ZHANG Yong, LIU Zhi, ZHANG Bin, GAO Jian
Abstract (
315 )
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The recycled polyamide gauge baffles were employed by using the original polyamide gauge baffles prepared by using glass fibers with a length of 4.5 mm and a diameter of 10 mm as a reinforcement and POE⁃g⁃MAH as an impact modifier at a loading of 10 wt%. The resultant recycled polyamide gauge baffles could meet the requirement of product size and performance indexes together with good size stability. There was no damage in the parts after the test of assembly fatigue performance， and all the assembly performance could meet the requirements. The results indicated that the waste polyamide parts were good renewable resources after collecting， crushing， cleaning， and modification， and they could be reused in the railway field.
ZHAO Yiquan, DONG Jinghan, ZHANG Tongzhu, WANG Yanmeng, DIAO Shuai, LI Minghe, XU Changzhu
Abstract (
348 )
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In this study， a series of recycled polypropylene （RPP） materials were prepared by adding different amounts of post⁃consumer recycled polypropylene （PCR⁃PP） into virgin polypropylene （VPP）. The effect of the loading of PCR⁃PP on the tensile， bending， compression， and impact properties of RPP materials was investigated. The internal mechanism for the property degradation of RPP materials was studied by DSC， melting flow index， and scanning electron microscopy. The results indicated that the ageing resistance， crystallization performance， and machining properties of RPP materials decreased gradually with an increase in the PCR⁃PP content， resulting in a decrease in the strength properties and plasticity. When the content of PCR⁃PP was less than 30 %， the RPP materials presented strength and plasticity retention rates of above 90 %. The physical properties of RPP material can meet the requirements of automotive industry if reinforcing agents are used in the products. The research results obtained from this work provides an important data support for the practical application of RPP materials in the automotive industry.
YANG Tianxue, YANG Zhe, ZHANG Junping, WANG Ming, GONG Tiancheng, ZHANG Ting, HOU Jiaqi, XI Beidou
Abstract (
398 )
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In this study， a comparative analysis of domestic and foreign studies on biodegradable films （BM） was performed by a combination of bibliometric visualization technology and content analysis to present an objective and systematical overview of global BM research. A total of 1932 English and Chinese literatures related to BM from the China National Knowledge Infrastructure （CNKI） and the Web of Science Core collection were analyzed to elucidate its development history and most influential contributors including countries， institutions， and authors. Furthermore， the domestic and foreign research frontiers and hotspots of BM were identified， including the types of BM， the optimization of the performance of BM， and the application effectiveness of BM in various fields. The development of novel low⁃cost and high⁃performance BM products and their life cycle environmental risk assessment are of great significance in the global future study.
Review
LIU Haoyu, XIN Fei, DU Jiaying, FAN Xiaoling
Abstract (
539 )
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This paper reviewed the research progress in the halogen⁃free flame⁃retardant polyester⁃based composites in recent five years. The variations of mechanical properties， thermal stability， compatibility， smoke suppression， and heat release rate of the composites were discussed after the flame⁃retardant modification was performed by using organic flame retardants like phosphate and phosphonate， inorganic flame retardants like red phosphorus and montmorillonite， and organic⁃inorganic flame⁃retardant systems like aluminum hydroxide/ammonium polyphosphate/expandable graphite composite system. The future development trend of halogen⁃free flame⁃retardant polyester composites with highly efficient and environmentally friendly characteristics was prospected.
