LDPE与mLLDPE共混改善mLLDPE的流变性能

通过毛细管流变实验,测定了茂金属催化体系生产的茂金属线型低密度聚乙烯(mLLDPE)/低密度聚乙烯(LDPE)共混物的流变特性.加入LDPE,mLLDPE的临界剪切速率增大;推迟了mLLDPE挤出过程中熔体破裂现象的产生;熔体强度提高,改善了吹膜过程中膜泡的稳定性.     

茂金属聚乙烯蜡对PE共混体系流变行为的影响

用毛细管流变仪研究了茂金属聚乙烯蜡改性聚乙烯共混体系的流变行为，探讨了茂金属聚乙烯蜡用量对共混体系熔体流变行为、熔体黏度、非牛顿指数和流动活化能的影响。结果表明：茂金属聚乙烯蜡对LLDPE／LDPE流动黏度降低明显，增加用量可使黏度逐渐降低；而对MPE／LLDPE／LDPE共混体系流动行为的影响比较复杂，在低剪切应力下黏度随茂金属聚乙烯蜡用量增加而逐渐降低，而在高剪切应力下黏度先增后减；茂金属聚乙烯蜡与MPE／LLDPE／LPDPE的相容性好于LLDPE／LDPE共混体系。     

含氟塑料加工流变剂在mLLDPE中的应用

研究了3种含氟塑料加工流变剂对茂金属线型低密度聚乙烯(mLLDPE)挤出性能的影响;比较了不同流变剂添加到mLLDPE中,在单、双螺杆挤出机中的挤出特性。结果表明:含氟塑料加工流变剂可以明显降低mLLDPE的挤出扭矩,消除挤出熔体破裂,改善薄膜制品的外观质量。     

挤出加工对茂金属聚乙烯性能的影响

由茂金属催化体系制得的高密度聚乙烯(简称茂金属聚乙烯)具有相对分子质量分布窄、支链少等特点。运用核磁共振碳谱(¹³CNMR)测试了挤出加工对茂金属聚乙烯结构的影响。采用差示扫描量热法(DSC)对受到双螺杆挤出加工后的茂金属聚乙烯进行研究,并通过Ozawa法和莫志深法研究了加工前后茂金属聚乙烯的非等温结晶动力学,运用Kissinger法计算了挤出加工前后茂金属聚乙烯的非等温结晶活化能,评价了受到挤出加工影响后的茂金属聚乙烯的结晶能力。采用动态流变学评价了挤出加工对茂金属聚乙烯的影响。结果表明：受到双螺杆挤出加工的影响,茂金属聚乙烯结晶能力降低,结晶峰变宽,结晶峰温度变低,结晶活化能升高;同时,挤出加工也使茂金属聚乙烯的剪切变稀现象更明显,更容易出现熔体破裂。     

茂金属聚乙烯/高流动聚乙烯的共混性能

研究茂金属聚乙烯(mPE)对高流动聚乙烯(HDPE)流变行为、结晶性能和力学性能的影响.研究结果表明:随着mPE含量增加,共混熔体的表观黏度逐渐升高;温度升高,表现黏度下降,加工性能改善.不同共混比例下结晶度和物理机械性能也发生了变化.当mPE质量含量为10%～15%时,茂金属聚乙烯/高流动聚乙烯共混体系的非牛顿流动行...     

茂金属PE LH-113的纺丝流变行为

对中国石油化工集团公司石油化工科学研究院与辽阳石油化纤公司共同中试生产的茂金属淤浆法聚乙烯树脂LH-113的可纺性进行了研究。经流变性能和纺丝性能研究表明,LH-113树脂与一般茂金属聚乙烯一样,在挤出过程中表现出粘度高、压力振荡、粘度和剪切应力对温度反转等流变现象。这些特点对纺丝过程有着重要的影响。由于LH-113为具有较长支链共聚物,所以自由体积大、熔体张力小,这些特点有利于纺丝。     

茂金属气相法聚乙烯中试第一阶段试验获得成功

茂金属气相法聚乙烯中试第一阶段试验获得成功中国石化总公司石油化工科学研究院在“气相法茂金属催化剂”实验室研究工作的基础上，经在兰州化学工业公司、上海Φ气相流化床完成模式聚合评价试验后，又开始与齐鲁石化公司合作进行气相法聚乙烯茂金属催化剂中试聚合试验。...     

茂金属聚乙烯（mPE）／高压聚乙烯（LDPE）共混熔体的流变学

研究了不同比例共混的茂金属聚乙烯（mPE)和高压聚乙烯（LDPE）熔体的流变行为,讨论了共混物组成、剪切速率和剪切应力以及温度对熔体流变曲线、熔体粘度和膨胀比的影响,mPE的加工提供了理论依据。不同共混比的熔体均为假塑性流体,且熔体假塑性随LDPE含量增大而增强。熔体流动活化能随LDPE组成的增加逐渐增大,粘度对温度的敏感性增强,共混物的非牛顿指数随LDPE的增加而降低,改善了mPE的加工性能。     

mLLDPE/EPPE共混体系的流变行为、结晶形态与力学性能研究

研究了不同比例共混的茂金属线性低密度聚乙烯(mLLDPE)和易加工聚乙烯(EPPE)熔体的流变学行为,讨论了共混物组成,剪切速率和剪切应力以及温度对熔体流变曲线,熔体黏度和非牛顿指数的影响。结果表明:随着EPPE含量的增加,共混熔体的黏度呈线性下降,非牛顿指数逐渐减小,黏流活化能先升高后下降,mLLDPE的流动性和加工性能得到改善,而力学性能显示:EPPE在改善mLLDPE流变加工性能的同时可以很好保持mLLDPE的优良性能。     

线性低密度聚乙烯结构与流变特性研究

采用凝胶渗透色谱仪、核磁共振分析仪、旋转流变仪和Rheotens熔体拉伸流变仪分析了线性低密度聚乙烯(LLDPE)和长链支化茂金属线性低密度聚乙烯(mLLDPE)的分子结构与流变特性.结果表明,相对分子质量高、高相对分子质量拖尾和长链支化,可导致聚乙烯(PE)的零切黏度增加、特征松弛时间延长、松弛谱峰变宽、熔体强度提高...     

Effects of the blending sequence in polyolefin ternary blends

Ternary blends of isotactic polypropylene (PP), ethylene–octene copolymer (mPE), and high‐density polyethylene (HDPE) were prepared by melt mixing in a twin‐screw extruder with two different sequences of mixing: the simultaneous mixing of the three components (method I) and the premixing of mPE and HDPE followed by mixing with PP (method II). Regardless of the mixing sequence, mPE encapsulated HDPE in the PP matrix, although better mechanical properties were generally obtained with method II. The domain size was mainly determined by the viscosity ratio of mPE to PP in method I and by the viscosity ratio of the binary blend (mPE/HDPE) to PP in method II. Specimens prepared by injection molding gave much finer dispersions than compression‐molded specimens. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 804–811, 2004     

Hot tack of metallocene catalyzed polyethylene and low-density polyethylene blend

Films made of metallocene catalyzed polyethylene (mPE), low-density polyethylene (LDPE), and their blend were prepared to investigate how LDPE influences the hot tack of film. Experimental results showed hot tack is independent of film thickness. The addition of 30 wt % of LDPE can increase the hot tack of mPE film. The thermograms of differential scanning calorimetry (DSC) suggest the respective partial melting and recrystallization of those smaller size crystals at the bond forming and joint fracture stages play very important roles. The large amount of partial melting and high flow may induce a higher degree of molecular diffusion. Higher residual crystallinity and recrystallization at the hot tack testing process may induce higher resistant to bond fracture. Those two positive influences show that the mPE/LDPE film has the higher hot tack. The evidence from optical (higher optical transmission and lower haze) as well as viscoelastic (higher storage modulus and lower melt viscosity) properties further support this hypothesis. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1769–1773, 1999     

茂金属聚乙烯流变特性的研究

对国产茂金属聚乙烯试验料(mPE)、EXXON公司的茂金属聚乙烯(EXXON)及传统聚乙烯(PE7042)的流变特性进行了对比研究;同时,考察了mPE加入低密度聚乙烯(LDPE)后的流变行为和各种助剂对mPE流变行为的影响,通过研究,发现与PE7042相比,mPE的表观粘度对温度不敏感,容易出现压力振荡,振荡的振幅呈逐渐增加的趋势;LDPE加入量为20%时,mPE的剪切应力、表观粘度明显降低,但LDPE含量继续增加则变化不大.     

气相法mPE的性能剖析

茂金属聚乙烯（mPE)具有优越的力学性能和光学性能，这与茂金属催化剂的催化性能及其聚合物特殊的链结构形式密切相关。对国内开发的mPE进行了结构表征，结果表明：mPE薄膜的力学性能和光学性能明显优于线型低密度聚乙烯产品，其耐穿刺性能明显好于其他聚乙烯产品。     

Rheological,physical, and thermal characterization of single‐site catalyst based polyethylenes for seal layer applications

Four single‐site metallocene catalyst based polyethylenes (mPEs), one ultra low density polyethylene, one conventional linear low density polyethylene (LLDPE), and one low density polyethylene (LDPE) were selected to characterize the effect of side chain branches on physical and mechanical properties. Rheological experiments were carried out to extract complex viscosity and elasticity as a function of frequency. Elongational viscosity tests were also performed to assess long chain branching. For some mPEs, sparse long chain branching improved shear thinning and elasticity of the chains in melt state. During elongation, mPEs with a narrow linear chain distribution showed initially greater melt strength whereas for longer elongation, the mPEs with long chain branching lead over in strength. Cast films were produced from the mPEs and their physical (such as crystallinity, crystal size) and mechanical properties were tested. A double melting peak was observed in the differential scanning calorimetry thermograms of the mPE films. A relatively sharp strain hardening behavior in tensile tests was observed for the mPEs films when compared to LLDPE. Fourier transform infrared was used as an effective and fast method to investigate side chain length. It was found that the positioning of side chain, co‐monomer length, and content influence the melting behavior of mPE films. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Effectiveness of a maleated compatibilizer on the tensile and tear properties of peroxide-cured metallocene polyethylene/clay nanocomposites

Peroxide-cured metallocene polyethylene (mPE)/clay nanocomposites were prepared via melt mixing followed by hot press curing. The maleated compatibilizer, mPE grafted maleic anhydride (mPE-g-MA), was incorporated to improve the dispersion of various amounts of commercial organoclay (denoted as 20A). Experimental samples were analyzed using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results indicated that there was an increase in dispersion with the addition of the compatibilizer. A measurable difference in the crystallization temperature, up to 9.5 °C, can be found for cured mPE reinforced with 5 phr clay in comparison cured mPE, indicating the promotion of crystallization kinetics through the addition of clay moiety. Taking 5 wt% loss as an index of thermal stability, the degradation temperature increased from 375.2 °C in cured mPE to 431.2 °C in the maleated 5 phr-loaded system, the highest improvement in all investigated cases. The Young’s Modulus and tear strength of maleated nanocomposites containing the compatibilizer at 9 phr clay content showed the highest values of up to 2 times increment compared those without clay, reflecting the increased interfacial interaction with the exploit of the compatibilizer.     

茂金属聚乙烯薄膜的工艺研究与应用

塑料包装薄膜向着更薄、更强、更廉的方向发展。５年前发明的基金属聚乙烯树脂具备优异的性能在复合包装材料中发挥了重要作用。如何制得符合使用要求的薄膜，提出了特殊的工艺要求。在抗渗抗污染、抗化学腐蚀、带液快速包装中，茂金属聚乙烯薄膜正在得到广泛的应用。     

Preparation and properties of melt‐mixed metallocene polyethylene/silica nanocomposites

Metallocene polyethylene (mPE)/silica nanocomposites were prepared via melt mixing. Two types of commercial fumed nanosilica, bare silica (A200) and organic modified silica (R974), were incorporated to improve the mechanical properties of the nanocomposites. Transmission electron microscopy, atomic force microscopy, and scanning electron microscopy revealed that the modified silica was dispersed slightly better within the mPE matrix. No distinct effects on the thermal behaviors of the fast‐crystallizing mPE matrix were observed with variations in both the silica dosages and types. Thermal stability was enhanced through the addition of nanosilica, with or without surface treatment. The surface‐modified silica system showed slightly higher tensile strength and Young's modulus compared with the bare silica system, as evidenced by a rheological study using a Cole‐Cole plot to assess enhanced polymer matrix‐dispersed silica interactions, especially for high dosages of organic modified silica. A limited increment in the dynamic storage modulus for modified silica cases, completely opposite of that observed for bare silica cases, was due to the low‐aspect ratio of smaller agglomerates from highly dispersed organic modified silica within the mPE matrix. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers.     

Characterization of an amorphous surface layer on blown polyolefin film

This study concerned an amorphous surface layer on blown polyethylene film with a composition different from that of the bulk. The surface layer was characterized by gentle probing with an atomic force microscope. The demonstration of an amorphous layer uniformly covering the surface of a blown Ziegler–Natta‐catalyzed polyethylene (znPE) film reproduced previous reports. Removing the surface layer by solvent washing confirmed the hypothesis that the layer consisted of lower molecular weight, higher branch content fractions. A blown film of znPE blended with up to 30 wt % impact‐modified high‐melt‐strength polypropylene (hmsPP) also exhibited an amorphous surface layer. In thin films, it was advantageous for the mobile, amorphous fractions of ethylene–propylene rubber (EPR) to locate at the surface rather than at the phase interface. The amorphous EPR tended to segregate into pools on the film surface, and this pointed to a substantial difference between the amorphous surface layers on the znPE and hmsPP/znPE blend films. Surface enrichment best described the compositional gradient that resulted from the concentration of lower molecular weight, higher branch content chains at the surface of the znPE film. Surface segregation was more appropriate for the emergence of EPR fractions as a separate phase on the surface of the hmsPP blend film. Films blown from a blend of a Ziegler–Natta‐catalyzed polyethylene and a metallocene‐catalyzed polyethylene (zn/mPE) and its blend with hmsPP reproduced the primary features of surface enrichment and surface segregation. Some differences between the znPE and zn/mPE films were attributed to the metallocene constituent of zn/mPE. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3625–3635, 2002