期刊文献+
共找到4篇文章
< 1 >
每页显示 20 50 100
The Influence of Ethyl Branch on Formation of Shish-Kebab Crystals in Bimodal Polyethylene under Shear at Low Temperature 被引量:2
1
作者 Zong-Bao Wang Yi-Min Mao +6 位作者 Xu-Ke Li Yi-Guo Li Chatchai Jarumaneeroj Boonyakeat Thitisak Piyawan Tiyapiboonchaiya Wonchalerm Rungswangd Benjamin S.Hsiao 《Chinese Journal of Polymer Science》 SCIE CAS CSCD 2021年第8期1050-1058,I0008,共10页
Formation of shish-kebab crystals using a bimodal polyethylene system containing high molecular weight(HMW)component with different ethyl branch contents was investigated.In situ small-angle X-ray scattering(SAXS)and ... Formation of shish-kebab crystals using a bimodal polyethylene system containing high molecular weight(HMW)component with different ethyl branch contents was investigated.In situ small-angle X-ray scattering(SAXS)and wide-angle X-ray diffraction(WAXD)techniques were used to monitor the formation and evolution of shish-kebab structure sheared at low temperature in simple shear mode and low rate.Only the bimodal PE with no branch formed shish-kebab crystals at the shear temperature of 129℃,and the shish length increased with the crystallization time,while bimodal PE with branch has no observable shish under the same conditions.The degree of crystallization for bimodal PE with no branch increased with time up to above 7%,while those with ethyl branch increased continually up to above 23%.Furthermore,bimodal PE's Hermans orientation factor with no branch increased to 0.60,while those with ethyl branch only increased to a value below 0.15.This study indicated that the shish-kebab crystal formed at the low temperature of 129℃is due to the stretch of entangled chains under shear for the bimodal PE with no branch.Only partly oriented lamellar crystals were formed for the bimodal PE with ethyl branch.All the results at the shear temperatures higher,closed to,and lower than the melting point,the modulation of shish crystals formation owing to different mechanisms of the coil-stretch transition and the stretched network by changing shear temperature was achieved in the bimodal PE samples. 展开更多
关键词 bimodal polyethylene SHISH-KEBAB Ethyl branch SHEAR
原文传递
Modeling and Simulation of Ethylene Polymerization in Industrial Slurry Reactor Series 被引量:4
2
作者 孟伟娟 李建伟 +1 位作者 陈标华 李洪泊 《Chinese Journal of Chemical Engineering》 SCIE EI CAS CSCD 2013年第8期850-859,共10页
A five-site comprehensive mathematical model was developed to simulate the steady-state behavior of industrial slurry polymerization of ethylene in multistage continuous stirred tank reactors. More specifically, the e... A five-site comprehensive mathematical model was developed to simulate the steady-state behavior of industrial slurry polymerization of ethylene in multistage continuous stirred tank reactors. More specifically, the effects of various operating conditions (i.e., inflow rates of catalyst, hydrogen and comonomer) on the molecular structure and properties of polyethylene (i.e.,Mw,Mn, polydispersity index (IPD), melt index, density, etc.) are fully assessed. It is shown that the proposed comprehensive model is capable of simulating the steady-state operation of an industrial slurry stirred tank reactor series. It is demonstrated that changing the catalyst flow rate, changes simultaneously the mean residence-time in both reactors, which plays a significant role on the establishment of polyethylene architecture properties such as molecular mass and IPD. The melt index and density of polyethylene are mainly controlled by hydrogen and comonomer concentration, respectively. 展开更多
关键词 bimodal polyethylene multiple tanks in series SIMULATION POLYMERIZATION
下载PDF
Molecular Mobility in the Amorphous Phase Determines the Critical Strain of Fibrillation in the Tensile Stretching of Polyethylene 被引量:3
3
作者 Rui Li Guo-Xing Yang +2 位作者 Ya-Nan Qin Li Liu Zhi-Yong Jiang 《Chinese Journal of Polymer Science》 SCIE CAS CSCD 2020年第7期740-747,I0006,共9页
The microstructural development of bimodal high density polyethylene subjected to tensile deformation was investigated as a function of strain after annealing at different temperatures by means of a scanning synchrotr... The microstructural development of bimodal high density polyethylene subjected to tensile deformation was investigated as a function of strain after annealing at different temperatures by means of a scanning synchrotron small angle X-ray scattering(SAXS)technique.Two different deformation mechanisms were activated in sequence upon tensile deformation:intralamellar slipping of crystalline blocks dominates the deformation behavior at small deformations whereas a stress-induced crystalline block fragmentation and recrystallization process occurs at a critical strain yielding new crystallites with the molecular chains preferentially oriented along the drawing direction.The critical strain associated with the lamellar-to-fibrillar transition was found to be ca.0.9 in bimodal sample,which is significantly larger than that observed for unimodal high-density polyethylene(0.4).This observation is primarily due to the fact that the bimodal sample possesses a greater mobility of the amorphous phase and thereby a reduced modulus of the entangled amorphous network.The conclusion of the mobility of the amorphous phase as a determining factor for the critical strain was further proven by the 1H-NMR T2 relaxation time.All these findings contribute to our understanding of the excellent slow crack growth resistance of bimodal polyethylene for pipe application. 展开更多
关键词 SAXS bimodal high density polyethylene Molecular mobility
原文传递
Macrocyclic Binuclearα-Diimine Nickel Catalysts for Ethylene Polymerization
4
作者 YANG Jingshuang ZHANG Yuxing JIAN Zhongbao 《Chemical Research in Chinese Universities》 SCIE CAS CSCD 2023年第5期797-802,共6页
Polyolefins are globally important plastics.Molecular weight and molecular weight distribution are two key parameters for determining the properties of polyolefin materials.In this contribution,we develop a strategy f... Polyolefins are globally important plastics.Molecular weight and molecular weight distribution are two key parameters for determining the properties of polyolefin materials.In this contribution,we develop a strategy for combining the macrocyclic framework and the binuclear effect into the benchmarkα-diimine late transition metal catalysts,and thus macrocyclic binuclearα-diimine nickel catalysts(Ni_(2)-Me and Ni_(2)-iPr)are prepared.Compared to the classical Brookhart's acyclic mononuclearα-diimine nickel analogues(Ni_(1)-Me and Ni_(1)-iPr),these nickel catalysts exhibit enhanced thermostability(up to 110℃)and produce polyethylenes with higher molecular weights(up to 7 times)and lower branching densities(as low as 9 branches/1000C)in methylaluminoxane(MAO)activated ethylene polymerization.This translates into the ability of the catalyst to afford more linear high molecular weight polyethylenes.In particular,bimodal polyethylenes with broad molecular weight distributions(Mw/Mn=8.08-14.66)are generated by the sole catalyst.This work affords diverse polyethylenes. 展开更多
关键词 POLYOLEFIN Nickel catalyst Diimine ligand Macrocyclic binuclear strategy bimodal polyethylene
原文传递
上一页 1 下一页 到第
使用帮助 返回顶部