交叉分级技术在高密度聚乙烯支链结构研究中的应用

以高密度聚乙烯（PE HD）为研究对象,采用多种不同的分级方法对树脂进行了分级,研究了树脂的支链结构及其分布,通过升温淋洗分级法与其他技术结合的交叉分级法,建立了短链支化含量、淋洗温度、相对分子质量的三维关系图,反映了PE HD支链结构的分布特征。结果表明,PE HD树脂由4部分构成：含有一定数量支链的低分子蜡部分;短支链数目较多的线形低密度聚乙烯部分,此部分随相对分子质量的增大支化度增加,且分布在高相对分子质量部分的支链含量较高;短支链数目较少的高密度聚乙烯部分,此部分短支链在不同相对分子质量区域的分布较为均匀;几乎不含支链的线形聚乙烯部分。     

低密度聚乙烯长支链含量的测定

针对低密度聚乙烯(LDPE)支化度计算困难的问题,采用旋转流变法及核磁共振碳谱(~(13)C-NMR)法分别计算Basell管式法装置生产的系列LDPE的长支链含量。结果表明:随着LDPE熔体流动速率的提高、相对分子质量的降低,其长支链含量降低;探讨了旋转流变法和~(13)C-NMR法的差异,采用~(13)C-NMR法计算得到的长支链数差异小,无法准确表征支化结构接近的工业化LDPE各批次间的差异;采用旋转流变法测定的LDPE长支链数具有检测时间短、长支链敏感性高的特点,适合工业上快速、准确地表征LDPE支化结构。     

PE-LD电缆料支链的表征及其对加工性能的影响

研究了不同低密度聚乙烯电缆料的力学性能差异,并对其支链结构进行了研究。通过动态流变性能分析和表征各电缆料的长支链含量指数（LCBI）,进一步采用拉伸流变对长支链含量进行了表征和验证,同时利用红外分析法测定了不同电缆料的总支链含量。结果表明,在相对分子质量、总支链含量相近的前提下,短支链含量的增加有利于降低反应活化能,提高加工性能,有利于交联;而长支链可增加缠结点,增大反应活化能,不利于交联。     

电缆绝缘用LDPE的结构与性能

选用3种国内商品化的电缆用低密度聚乙烯(LDPE),利用凝胶渗透色谱仪、升温淋洗仪、红外光谱仪、差示扫描量热仪研究了其链结构和交联性能,探讨了相对分子质量及其分布、链支化、双键等因素对树脂结晶行为和交联性能的影响.结果表明:支链含量越少,亚甲基序列越长,结晶能力越强,其结晶度越高;端双键含量越高,其交联反应速率越快;凝...     

核磁共振对高聚物短链支化的研究

高聚物主链上支化的类型和数量是决定低密度聚乙烯(高压聚乙烯)和高密度聚乙烯(低压聚乙烯)物理性能差异的主要原因。短链支化影响聚合物的形态和半结晶聚合物的固态性质,而长链支化对溶液的粘度和熔体流变行为产生深远的影响。长链支化是由于分子间链转移反应产生,短链支化是分子内链转移反应引起的。在这类聚合物的结构测定中,除了分子量和分子量分布之外,支化度是一个重要的结构参数。     

α-二亚胺氯化镍/mMAO/AlR3制备支化聚乙烯

介绍了用2,6-二异丙基苯基苊二亚胺氯化镍／改性甲基铝氧烷(mMAO）催化乙烯制备支化聚乙烯(PE),讨论了mMAO中三甲基铝(TMA)含量、外加三异丁基铝(TIBA)以及铝镍摩尔比对催化活性,PE相对分子质量、熔点、支化度及支链类型的影响。PE的核磁共振碳谱表明,当mMAO中TMA摩尔分数小于20％时,产物的支链绝大多数为甲基支链;TMA摩尔分数增大,PE支化度增大,长支链增多;外加TIBA导致产物的长支链(支链长度大于或等于6)增多。     

聚硅氧烷结构对车用内饰聚丙烯复合材料性能的影响

通过硅氢加成反应制备了长链烷基支化聚硅氧烷和交联聚硅氧烷,采用衰减全反射红外光谱(ATR)、能谱仪(EDS)、扫描电镜(SEM)对比分析了线性结构、支化结构和交联结构聚硅氧烷在车用内饰聚丙烯复合材料中的含量分布和微观形貌,考察了不同结构聚硅氧烷对聚丙烯复合材料耐刮擦、应力发白和力学性能的影响。结果表明,不同结构聚硅氧烷均匀地分布在复合材料表层和内层,线性聚硅氧烷的耐刮擦性能优于交联聚硅氧烷,可明显改善复合材料的耐刮擦性能,但会引起复合材料应力发白和力学性能的下降;长链烷基接枝后,耐刮擦性能提升不明显,但复合材料应力发白和力学性能下降问题得到明显改善。     

盘天化制定聚乙烯树脂企业标准

<正> 盘锦天然气化工厂聚乙烯装置是从英国BP 公司引进并于1990年10月投产的线性低密度聚乙烯(LLDPE)生产线(也可生产高密度聚乙烯,代号 HDPE)。LLDPE 是乙烯与1—丁烯烃的共聚物,其分子的主链呈线性结构,并带有短支链。LLDPE 与具有长支链的 LDPE(低密度聚乙烯)不同,但其密度范围又与 LDPE 相似。LLDPE 的分子结构特点使它具有独特的物理性能和机械性能,例如:优良的抗撕裂强度、耐穿刺性和拉伸强度等。正因为如     

白色母粒的组分对其遮盖力的影响

遮盖力是白色母粒的重要性能指标,母粒中钛白粉是影响其遮盖力的主要因素,但其他组分也对其遮盖力有重大影响。通过考察白色母粒载体的种类及含量、分散剂的种类及含量、第四组分种类的变化来研究这些因素对白色母粒遮盖力的影响。研究表明:在以聚乙烯为载体的母粒中,选用具有短支链结构的线性低密度聚乙烯为载体树脂,更有利于母粒的分散;在研究体系中,不同分散剂效果不一,效果并不是越多越好,在研究体系中,12%>分散剂的含量>6%较合适。     

核磁共振波谱表征弹性体支化结构方法的研究进展

综述了利用核磁共振波谱(NMR)表征弹性体类高聚物的支化度、支链长度、支链序列分布的方法。核磁共振氢谱可通过甲基的化学位移表征短链支化(6 C)的支化密度,而核磁共振碳谱可以通过支链点附近C原子的化学位移判断支链类型并计算支化密度,不仅适用于短链支化,还可表征较长链支化(≥6 C)的支化结构,及支链在主链上的序列分布。超长链支化的表征是NMR研究支化结构的盲区。针对文献中报道的某些接枝型支化高聚物的NMR结果,总结并提出了利用核磁共振氢谱计算支化密度及支链长度的方法。     

Thermal and mechanical properties of silane‐grafted water crosslinked polyethylene

The effects of linear low density polyethylene (LLDPE) grafting with vinyltrimethoxysilane by different types and contents of peroxide were studied. When grafting silane onto LLDPE, with 0.10 phr of Dicumyl peroxide (DCP) or 0.05 phr content of 2,5‐Dimethyl‐2,5‐di (tert‐butyl‐peroxy)‐hexane (DHBP), it was found that the grafting effect was improved; however, as Di(2‐tert‐butylperoxypropyl ‐(2))‐benzene (DIPP) or excess DHBP was used, LLDPE was supposed to cause self‐crosslinking, which reduced the grafting effect of silane and was invalid in the processing of extrusion. In this study, vinyl trimethoxysilane (VTMS) was grafted onto various polyethylenes (HDPE, LLDPE, and LDPE) using DCP as an initiator in a twin screw extruder. The grafted polyethylenes were able to crosslink utilizing water as the crosslinking agent. The effects of varied crosslinking time on the mechanical properties of the crosslinked polyethylenes were studied. It was found that the HDPE and LLDPE were apt to crosslink during the grafting process and thus decreased the grafting ratio. Multiple melting behavior was observed for crosslinked LDPE and LLDPE. Mechanical and thermal properties of the crosslinked PE are much better than that of uncrosslinked PE. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2383–2391, 2005     

硅烷接枝交联LDPE、LLDPE及其共混物的结构研究

利用红外光谱、凝胶渗透色谱、热延伸试验、差示扫描量热法、扫描电子显微镜等方法研究了低密度聚乙烯（LDPE）、线型低密度聚乙烯（LLDPE）及其共混物的乙烯基硅烷接枝及交联产物的分子结构、熔融行为和形态。结果表明：硅烷接枝后，LDPE、LLDPE的重均摩尔质量小幅增加；硅烷接枝交联能力为：LLDPE〉LDPE／LLDPE共混物〉LDPE；接枝和交联使LDPE、LLDPE及其共混物的结晶度降低，晶粒变得不均匀；硅烷接枝和交联能增加LDPE／LLDPE共混物的相容性；交联结构提高了LDPE、LLDPE及其共混物的抗冲性。     

Thermal characteristics and temperature profile changes of structurally different polyethylenes with peroxide modifications

Crosslinking and processing characteristics of polyethylenes (PEs) with different molecular architectures, namely high‐density polyethylene (HDPE), linear low‐density polyethylene (LLDPE), and low‐density polyethylene (LDPE), were studied with regard to the effects of peroxide modifications and coolant flow rates. Dicumyl peroxide (DCP) and di‐tert‐butyl peroxide (DTBP) were used as free‐radical inducers for crosslinking the PEs. The characteristics of interest included normalized gel content, real‐time temperature profiles and their cooling rates, exothermic period, crystallinity level, crystallization temperature, and heat distortion temperature. The experiments showed that LDPE exhibited the highest normalized gel content. The real‐time cooling rates, taken from the temperature profiles for all PEs before the crystallization region, were greater than those after the crystallization region. The cooling rate of the PEs increased with the presence of DCP, whereas the crystallization temperature of the PEs was lowered. The HDPE appeared to show the longest exothermic period as compared with those of the LLDPE and LDPE. The exothermic period showed an increase with increasing coolant flow rate, but it was decreased by the use of DCP. As for the effect of peroxide type, the gel content and cooling rate of the PE crosslinked by DCP were higher than those for the PE crosslinked by DTBP. The DTBP was the more effective peroxide for introducing crosslinks and simultaneously maintaining the crystallization behavior of the PE. J. VINYL ADDIT. TECHNOL., 20:80‐90, 2014. © 2014 Society of Plastics Engineers     

A molecular dynamics study of the effects of branching characteristics of LDPE on its miscibility with HDPE

The effects of branching characteristics of low-density polyethylene (LDPE) on its melt miscibility with high-density polyethylene (HDPE) were studied using molecular simulation. In particular, molecular dynamics (MD) was applied to compute Hildebrand solubility parameters (δ) of models of HDPE and LDPE with different branch contents at five temperatures that are well above their melting temperatures. Values computed for δ agreed very well with experiment. The Flory-Huggins interaction parameters (χ) for blends of HDPE and different LDPE models were then calculated using the computed δ values. The level of branch content for LDPE above which the blends are immiscible and segregate in the melt was found to be around 30 branches/1000 long chain carbons at the chosen simulation temperatures. This value is significantly lower than that of butene-based linear low-density polyethylene (LLDPE) (40 branches/1000 carbons) in the blends with HDPE computed by one of the authors (polymer 2000; 41:8741). The major difference between LDPE and LLDPE models is that each modeled LDPE molecule has three long chains while each modeled LLDPE molecule had only one long chain. The present results together with those of the LLDPE/HDPE blends suggest that the long chain branching may have significant influence on the miscibility of polyethylene blends at elevated temperatures.     

HDPE/LDPE复合交联物的热降解研究

采用热重分析仪（TG）考察了高密度聚乙烯（HDPE）／低密度聚乙烯（LDPE）复合交联物的热稳定性。结果显示，HDPE／LDPE复合交联物的热稳定性低于HDPE／LDPE共混物。FTIR分析证实，交联反应使聚乙烯（PE）的支化程度提高，取代基的位阻效应在一定程度上影响了PE的热降解过程。在N2气氛下，HDPE／LDPE共混物及交联物的热降解过程均为一步降解反应。Kissinger法求解HDPE／LDPE共混物及其复合交联物的热降解活化能发现，LDPE质量分数在20％～30％之间变化时，HDPE／LDPE交联物的热降解过程对温度的敏感性发生了突变。     

Cocrystallization and miscibility studies of blends of ultrahigh molecular weight polyethylene with conventional polyethylenes

Ultrahigh molecular weight polyethylene (UHMWPE) was mechanically mixed with conventional polyethylenes (LLDPE, HDPE, and LLDPE) using an internal mixer. Rheological studies of these blends suggest that UHMWPE seems to be miscible with LLDPE, HDPE, and LDPE in the melt state. Yield characteristics are observed in all blend systems, particularly in high UHMWPE blend compositions. Differential scanning calorimetry and small-angle light scattering studies show that cocrystallization takes place in the blends of UHMWPE/LLDPE and UHMWPE/HDPE blends. However, separate crystals are formed in UHMWPE/LDPE. The formation of separate crystals may be attributed to long chain branching of conventional low-density polyethylene. Tensile properties of the former two blends vary almost linearly with blend compositions, while deviations are seen in the latter UHMWPE/LDPE blends.     

Silane grafting and moisture crosslinking of polyethylene: The effect of molecular structure

The silane grafting and moisture crosslinking of different grades of polyethylene have been investigated. Three types of polyethylene (HDPE, LLDPE, and LDPE) with different molecular structures and similar melt flow indices were selected. The initiator was dicumyl peroxide (DCP), and the silane was vinyltrimethoxysilane. The grafting reaction was carried out in an internal mixer. The extent of grafting and the degree of crosslinking were determined, and hot‐set tests were carried out to evaluate the crosslink structure of the different polyethylenes. The LLDPE had the highest degree of grafting, while the LDPE had the least. The rate of crosslinking for LDPE was higher than that of HDPE and LLDPE. The gel content of LDPE was higher than that of HDPE and LLDPE. Hot‐set elongation and the number‐average molecular weight between crosslinks (M_c) were lower for LLDPE and LDPE than for HDPE. Increasing the silane/DCP percentage led to peroxide crosslinking, thereby decreasing the M_c and hot‐set elongation. The number‐average molecular weight (M_n), molecular weight distribution, and number of chain branches were the most important parameters affecting the silane grafting and moisture crosslinking. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers     

硅烷接枝热水交联聚乙烯共混物的研究

本文介绍了采用过氧化二异丙苯（ ＤＣＰ） 为引发剂,二月桂酸二丁基锡（ ＤＢＴＬ） 为催化剂,在双螺杆挤出机中硅烷（ ＶＴＥＳ） 与聚乙烯（ＰＥ） 共混物的接枝反应,以及通过热水交联获得硅烷交联聚乙烯共混物。研究了不同牌号聚乙烯的选取,正交实验优化配方以及热水交联时间对产品性能的影响。结果表明：选取适当的高密度聚乙烯,低密度聚乙烯及线性低密度聚乙烯共混物进行硅烷接枝交联,可获得具有良好的力学性能和良好的加工性能的交联ＰＥ 共混物;正交实验获得ＤＣＰ、ＶＴＥＳ 及ＤＢＴＬ 的最佳用量分别为０ ．１０ 份、２ ．５ 份、０ ．１５ 份;热水交联的合适时间约为１２ 小时,在此之前拉伸强度、维卡软化点及凝胶率随交联时间而升高,断裂伸长率随时间而降低,此后,几者均趋于稳定。     

聚乙烯反应挤出接枝马来酸酐的研究

以过氧化二异丙苯(DCP)为引发剂,使用反应挤出机研究了不同种类聚乙烯及其共混物接枝马来酸酐的反应规律。实验结果表明:产物的接枝率和熔体流动速率(MFR)变化与聚乙烯的种类有直接关系,接枝性能从优到差的顺序为:LDPE>LLDPE>HDPE;引发剂DCP对LDPE接枝产物的MFR影响显著,对LLDPE次之,对HDPE的MFR几乎没有影响;聚乙烯共混物的接枝性能取决于组成共混物的聚乙烯种类和用量。接枝产物及纯化后样品的红外光谱分析表明,酐基是以化学键连接到聚乙烯分子链上,接枝产物几乎不含游离态的马来酸酐。     

不同密度聚乙烯共混物性质的研究

讨论了HDPE与LDPE及HDPE与LLDPE共混物的性质。研究表明共混物的力学性能、结晶度、熔点及维卡软化点都随密度ρ的变化呈规律性变化,由此总结出综合性能较好的共混物密度范围。