茂金属催化线性低密度聚乙烯的光氧化稳定性

茂金属催化线性低密度聚乙烯的光氧化稳定性;茂金属线性低密度聚乙烯;Ziegler-Natta线性低密度聚乙烯; 光氧化降解     

三种芳烃溶剂在低密度聚乙烯膜材料中无限稀释扩散系数的测定

用气相色谱法测定了苯、甲苯和乙苯在固定液低密度聚乙烯中的保留时间和半峰宽,运用vanDeemter模型进行数据处理,得到3种芳烃小分子在低密度聚乙烯膜材料中的无限稀释扩散系数.     

结晶聚合物的辐射效应：多官能团单体对LDPE的结晶成核作用

根据x射线、电镜、DSC和凝胶分数的测试结果,讨论了多官能团单体结构对低密度聚乙烯聚集态结构的影响以及结晶度与辐射交联(或剂量)的关系。发现由于单体的存在导致低密度聚乙烯结晶度增加而结晶尺寸变小(即结晶成核效应);成核效应越大,增强辐射交联的效果也越大。添加具有高结晶成核作用的单体有利于低密度聚乙烯的辐射交联,同时也加速其结晶结构的破坏。     

湿度及无机填料对低密度聚乙烯热释电流谱的影响

 我们将低密度聚乙烯试样暴露在湿空气中一定的时间,不管在用直流高压极化的前后,甚至在极化后对其经过72h的真空干燥处理,在中温区也存在一个附加的湿致热释电流峰,它可能是由俘获在晶区-非晶区界面的离子热释放所致。 由分析在极化前对含无机填料(经表面处理的高岭土)的低密度聚乙烯试样进行干燥或润湿处理后的热释电流谱表明,聚乙烯中的无机填料与吸收的水分子都可作为电子的受主,前者为电子深陷阱,后者为电子浅陷阱。     

结晶聚合物的辐射效应——多官能团单体对LDPE的结晶成核作用

根据x射线、电镜、DSC和凝胶分数的测试结果,讨论了多官能团单体结构对低密度聚乙烯聚集态结构的影响以及结晶度与辐射交联(或剂量)的关系。发现由于单体的存在导致低密度聚乙烯结晶度增加而结晶尺寸变小(即结晶成核效应);成核效应越大,增强辐射交联的效果也越大。添加具有高结晶成核作用的单体有利于低密度聚乙烯的辐射交联,同时也加速其结晶结构的破坏。     

茂金属线性低密度聚乙烯的组成均匀性

茂金属线性低密度聚乙烯的组成均匀性徐旭荣徐君庭封麟先陈伟（浙江大学高分子科学与工程学系杭州３１００２７）（中国石化总公司石油化工科学研究院北京１０００８３）关键词线性低密度聚乙烯，组成均匀性，茂金属催化剂８０年代以来，茂金属催化剂得到迅速发展．...     

线性低密度聚乙烯的结构、形态与热行为研究进展

介绍了近年来包括藏金属ＬＬＤＰＥ在内的线性低密度聚乙烯的结构、形态、结晶、熔融和物理性质等方面研究工作的最新进展。     

线性低密度聚乙烯/橡胶共混体系的相容性研究

本文用FTIR-ATR方法考察了线性低密度聚乙烯与天然橡胶(NR)及丁苯橡胶(SBR)两个共混体系,发现NR的835cm~(-1)和SBR的964cm~(-1)两个吸收峰因与聚乙烯共混而增高变窄,说明聚乙烯的非晶链段和橡胶分子之间存在一定程度的相互作用。     

线性低密度聚乙烯和聚苯乙烯共混物的原位增容及其形态、结构和性能

反应挤出;线性低密度聚乙烯和聚苯乙烯共混物的原位增容及其形态、结构和性能     

线性低密度聚乙烯／乙烯醋酸乙烯共聚物共混体系的相容性及性能

线性低密度聚乙烯／乙烯醋酸乙烯共聚物共混体系的相容性及性能杨毓华＊白春霞花荣于李三喜（中国科学院长春应用化学研究所长春１３００２２）（沈阳化工学院高分子科学与工程系沈阳）关键词线性低密度聚乙烯，乙烯醋酸乙烯共聚物，共混，相容性，ＤＳＣ，ＷＡＸＤ，力...     

低密度聚乙烯/乙丙烯三元共聚(LDPE/EPO)共混体系的结晶动力学

用DSC方法研究了LDPE/EPO共混体系的等温及非等温结晶动力学,对LDPE/EPO共混体系的等温结晶动力学研究表明,共混物是三维生长的异相成核,共混物在各个结晶温度下的结晶过程都是以方式K_g(Ⅱ)进行的.采用联系Avrami方程和Ozawa方程导出的新非等温结晶动力学方程,处理了LDPE/EPO共混体系,得到了非等温结晶过程的一些基本参数,新方程很好地描述了此共混体系的非等温结晶动力学过程.     

Crystallization of irradiated polyethylene

This study compares the effects of radiation dose on the isothermal and non-isothermal crystallization of LLDPE, LDPE and HDPE by differential scanning calorimetry (DSC). It includes qualitative comparison of the non-isothermal data and quantitative calculations of Avrami parameters for crystallization rate and nucleation mode. The isothermal crystallization allowed the observation of the changes in the crystallization rate, related to the decrease in the crystallization temperature caused by the crosslinking of the polymer. It was also observed by the non-isothermal crystallization, the development of crystallites of very different sizes in the polymer.     

Nucleation Activation and Spherical Crystals Morphology of LLDPE/LDPE/TiO2 Nanocomposites Prepared by Non-Isothermal Crystallization

The nucleation activation of TiO₂ nanoparticles in the linear low-density polyethylene (LLDPE)/low-density polyethylene (LDPE)/TiO₂ nanocomposites prepared by non-isothermal crystallization, the spherical crystals morphology of the etched LLDPE/LDPE and LLDPE/LDPE/TiO₂ composites were investigated by differential scanning calorimetry (DSC) and field-emission scanning electron microscopy (FE-SEM), respectively. The results showed that the heterogeneous nucleation activation of TiO₂ nanoparticles was accelerated by the fast cooling rate. The spherical crystals in the LLDPE/LDPE and LLDPE/LDPE/TiO₂ composites were ascribed to the same crystal structure. It was worth to note that there was distinct difference between the morphology of the cocrystallization LLDPE/LDPE crystals and that of the independent crystallization LLDPE/LDPE crystals.     

An experimental method for studying nonisothermal crystallization of polymers at very high cooling rates

A new technique based on light depolarizing microscopy was developed for studying non-isothermal crystallization of polymers at average cooling rates up to about 5000°C/min. The polymer is cooled down by a gaseous cooling medium supplied at a constant temperature. The temperature of polymer is measured by a thermocouple imbedded directly in the sample. A heat transfer analysis was used to establish appropriate sample geometry to assure that, under the applied cooling condition, the temperature distribution along the sample thickness can be neglected. A light-scattering effect, which occurs when crystallization is carried out under high cooling rates, was observed. This required the development of a method to correct the depolarized light intensity for the effect of light scattering. An appropriate correction method was developed based on both a theoretical and an experimental analysis of the light intensity measurement. This provided a means to measure the overall crystallization kinetics. Examples of such measurements for iPP, HDPE, and LDPE are presented. In addition to the overall crystallization kinetics, the developed technique includes a video camera and VCR system used for measurements of spherulite growth rates during crystallization under high cooling rates. Constant spherulite growth rates were observed for isotactic polypropylene crystallized under very non-isothermal conditions. © 1996 John Wiley & Sons, Inc.     

Non-Isothermal Crystallization of Poly(vinylidene Fluoride)/Multiwalled Carbon Nanotube Composites

Poly(vinylidene fluoride)/multiwalled carbon nanotube (PVDF/MWCNT) composites were prepared by the method of solution blending. The non-isothermal crystallization of PVDF and its composites was investigated by differential scanning calorimetry (DSC). The results showed that the crystallization peaks shifted to lower temperature and the exothermic trace became wider when cooling rate increased for PVDF and its composites. The MWCNTs caused an increase in crystallization temperature and initial crystallization temperature. In addition, the Jeziorny and Mo methods were used to analyze the non-isothermal crystallization kinetics. The results showed that the crystallization rate rose with an increase in cooling rate, however, the MWCNTs decreased the crystallization rates of PVDF.     

水性聚氨酯/功能化石墨烯纳米复合材料的非等温结晶动力学

采用差示扫描量热法DSC研究了水性聚氨酯/功能化石墨烯(WPU/FGNs)纳米复合材料的非等温结晶行为,分别采用Ozawa方程、莫志深方程研究复合材料的非等温结晶动力学,并通过Kissinger方程计算了结晶过程中的活化能。 结果表明,石墨烯在复合材料的结晶过程中起到异相成核剂的作用,提高了复合材料的结晶起始温度、峰值温度和结晶速率;增加石墨烯的质量分数,复合材料的结晶维数增加;石墨烯增加至0.3%,复合材料的活化能从-47.74 kJ/mol降低至-53.60 kJ/mol,继续增加石墨烯至1.0%,复合材料的活化能增加至-41.74 kJ/mol。     

一种研究聚合物非等温结晶动力学的方法

作者基于多年对聚合物结晶动力学方面研究的工作积累,联合Avrami方程和Ozawa方程,提出了一种研究聚合物非等温结晶动力学的新方法.该方法既克服了使用Ozawa方程所获得的数据点过少,常常出现非线性,不能获得可靠的动力学参数的缺点,又克服了使用经Jeziorny修正的Avrami方程所获得的表观Avrami指数无法准确预测非等温过程成核生长机理的缺点.该方法已成功用于多种聚合物体系,被国内外学者引用数百次,已成为研究聚合物非等温结晶动力学一种有效方法.     

PA13N的合成和非等温结晶动力学研究

采用DSC方法研究了PA13N在不同降温速率下的结晶过程,并利用Avrami方程研究了其非等温结晶动力学。在非等温结晶过程中,随着降温速率的增大,结晶温度向低温偏移。综合利用Avrami方程得到Avrami指数为1.35~1.88和结晶速率常数Zc≈1;并求得其结晶活化能为-58.42kJ/mol。结果表明,PA13N的结晶能力小于其他脂肪族尼龙。     

Non-isothermal crystallization kinetics of β-nucleated isotactic polypropylene

Isotactic polypropylenes (iPP) samples were incorporated with two β-nucleating agents (NT-A and NT-C), respectively, and their non-isothermal crystallization and subsequent melt behaviors were investigated by means of differential scanning calorimeter. Jeziorny, Ozawa, and Mo methods were used to analyze non-isothermal crystallization kinetics of pure iPP and β-nucleated iPP samples. The activation energies (ΔE) of non-isothermal crystallization were calculated by Kissinger method. And the nucleation activities were calculated according to the Dobreva method. It is found that the crystallization temperature decreases and the crystallization rate increases with increasing cooling rate. The crystallization temperature and crystallization rate of nucleated iPP are higher than those of pure iPP. The order of ΔE is NT-A/iPP > pure iPP > NT-C/iPP. NT-C is more efficient than NT-A as a β-nucleating agent. But the non-isothermal crystallization kinetics of α- and β-phases cannot be determined separately. The present results should be considered with caution.     

Space charge distribution and crystalline structure in polyethylene blended with EVOH

The space charge distribution in polyethylene samples under direct current (DC) electrical field was measured by pulsed electro-acoustic (PEA) method. It was found that by blending with 5 wt.% of poly(ethylene-co-vinyl alcohol) (EVOH) in low-density polyethylene (LDPE) the amount of accumulated space charges decreased and the field distribution of space charge improved. The differential scanning calorimetry (DSC) study showed that crystallization of LDPE/EVOH started at a higher temperature than LDPE. The results of wide-angle X-ray diffraction (WAXD) and small-angle light scattering (SALS) for LDPE/EVOH indicated that the crystal forms did not change, whereas the spherulites became smaller and imperfective. It can be seen from the results that EVOH played a role of nucleation during the crystallization of LDPE in the blend. The observation of scanning electron microscope (SEM) showed that the domains of EVOH were dispersed in LDPE as particles in diameter of 1 μm. The reduction of space charges in the blend sample can be explained as the results of the trapping of homo-charges at the interface and the dissipation of charges through LDPE matrix consisting of smaller spherulites.