不同高压聚乙烯工艺生产涂覆料性能差异探讨

就两种不同工艺产品——茂名石化管式法生产的涂覆牌号2420M和燕山石化釜式法生产的1C7A涂覆牌号在物性、加工性能、相对分子质量分布、结晶行为等差异进行探讨。经对比发现,管式法产品的分子支化程度过低是造成其性能不佳的主要原因,釜式法生产产品具有相对分子质量分布宽、长支链多、挤出收缩小,因此在生产涂覆料方面要优于管式法。     

反应挤出制备高熔体强度PP

采用反应挤出方法制备高熔体强度聚丙烯,通过凝胶渗透色谱仪、差示扫描量热仪、偏光显微镜等研究了改性产品的结构与性能,并进行挤出发泡应用实验。结果表明：采用特殊的过氧化物引发剂和支化促进剂,与聚丙烯基础树脂共混后通过双螺杆挤出机熔融连续反应挤出,可以直接制备具有长链支化结构的聚丙烯,熔体强度提高300％;挤出发泡试样泡孔均匀,发泡倍率达到50倍,具有较好的可发性能。     

长链支化聚丙烯的流变性能研究

利用反应挤出法制备了长链支化聚丙烯,采用旋转流变仪和毛细管流变仪对纯聚丙烯及其改性聚丙烯进行测试,用流变学理论进行表征。结果表明,聚丙烯加入支化剂后,产生了长支链,分子量增大,分子量分布变宽;在一定范围内,随着支化剂量的增大,其支化程度增加;在低频处,能模量G'比损耗模量G″对长支链的出现及量变更敏感;加入支化剂后熔体强度明显增大,且支化的程度越高熔体强度越大,可拉伸性变小,能有效地改善材料的加工性能。     

长链支化聚对苯二甲酸乙二醇酯的制备及其超临界CO2挤出发泡性能研究

以具有支化结构的多元醇原位聚合改性聚对苯二甲酸乙二醇酯(MPET)为原料，均苯四甲酸二酐(PMDA)为扩链剂，通过反应挤出改性可控制备了不同长链支化程度的聚对苯二甲酸乙二醇酯(PET)。流变测试结果表明长链支化改性MPET熔体黏弹性得到大幅度提升，应变硬化因子也随长链支化程度的增加而增强。在超临界CO₂(scCO₂)挤出发泡过程中，长链支化改性MPET具有优异的挤出可发泡性。采用0.3%(质量分数，下同)PMDA制备得到的MPET-P3具有最佳的挤出发泡性能。当熔体温度为265℃时，其发泡倍率可达14.0倍，泡孔密度为4.81×106个/cm³，平均泡孔直径为153.9μm。     

控制长链支化度对EPDM挤出性能的影响

生产高质量、低成本的ＥＰＤＭ制品需要彻底了解聚合物参数对加工和产品性能的影响。2 0世纪 90年代已有文献报道了对混炼和聚合物参数的研究 ,近年来的热门话题是挤出行为。测量的挤出参数包括 :功率消耗、产量、产量 /机头压力、比能耗、胶料最高温度和口型膨胀率。用化学组分、门尼粘度、相对分子质量分布和长链支化度描述了ＥＰＤＭ的分子结构。最近推出的新一代ＥＰＤＭ的分子结构与普通ＥＰＤＭ有很大不同 ,运用控制长链支化度原理获得了相对分子质量分布与长链支化度的平衡。这种聚合物是为改进混炼和挤出性能并保持较好的物理性能而…     

果酒包装内盖专用LDPE的开发

根据注塑瓶盖制品性能和对产品加工的要求,结合管式法低密度聚乙烯生产装置的工艺特点,确定了果酒包装内盖专用低密度聚乙烯树脂LD607BW的基本物性指标:密度为(0.921±0.002)g/cm3,熔体流动速率为(7.5±1.0)g/10 min,拉伸断裂应力≥8 MPa,断裂标称应变≥80%。根据基本物性指标确定了试生产工艺条件,包括聚合温度、聚合压力和对助剂的要求等。通过提高反应器尾端第四、第五反应区的温度,降低反应压力,使长链支化、短链支化增多,降低了产品的密度和硬度,解决了制品的翘曲问题。产品性能测试及应用表明,工业化试生产的LD607BW满足指标要求且质量稳定。     

长链支化聚丙烯的研究进展

介绍了长链支化聚丙烯制备的成熟技术；阐述了长支链对聚丙烯熔体弹性影响的机理；分析了长链支化对聚丙烯结晶行为和流变行为的影响。当前的研究表明：长支链可以显著提高聚丙烯的熔体弹性。电子束辐射进行聚丙烯的长链支化受到辐射温度、辐射剂量以及辐射的条件和后处理工艺的强烈影响；反应挤出进行聚丙烯的长链支化受到过氧化物用量及其分子结构的影响。长链支化聚丙烯的结晶行为和流变行为与线形聚丙烯存在明显差异，其初始结晶温度要高于线形聚丙烯10℃左右；流变行为表现出显著的“应变硬化”现象，从而可以有效地保证挤出发泡过程中气泡增长的稳定。     

反应挤出制备长链支化聚丙烯：挤出条件对挤出物熔体性能的影响

本文采用在过氧化物和官能团丙烯酸单体共存的情况下通过反应挤出的方法对聚丙烯进行长链支化改性，通过引入一种支化促进剂抑制反应挤出过程中的β-断裂和交联。对制备的长支链聚丙烯进行了流变学研究。研究了原料聚丙烯种类、过氧化物的类型和浓度对挤出物熔体强度的影响。     

二丙烯酸酯参与的反应挤出制备长链支化PP

研究了二丙烯酸酯参与的反应挤出制备长链支化聚丙烯过程,重点考察了二丙烯酸酯双键间链段长度以及单体用量对长链支化程度的影响。结果表明,1,4-丁二醇二丙烯酸酯(BDDA)在聚丙烯分子链上具有较强接枝能力;在接枝率相当的情况下,悬垂双键参与偶合扩链的能力会随双键间链段长度增加而下降。单体接枝率增加以及悬垂双键反应能力增强均会使长链支化程度增大。随着二丙烯酸酯用量增加,长链支化程度增加;单体过量会使大分子自由基偶合扩链程度加重,导致局部交联形成凝胶。     

PP链结构对反应挤出制备长链支化PP的影响

以过氧化二异丙苯(DCP)为引发剂、1,4-丁二醇二丙烯酸酯(BDDA)为接枝单体,通过反应挤出制备长支链聚丙烯(PP),研究了PP链长及主链中乙烯嵌段含量对PP长链支化程度的影响。随着PP树脂分子链长度降低以及乙烯嵌段含量增加,PP大分子自由基发生接枝和双基偶合扩链反应的几率增大,导致BDDA在PP主链上的接枝率提高,反应挤出产物的熔体弹性效应增强以及在Cole-Cole曲线出现上翘所对应的动态黏度降低。黏度降低表明分子链松弛时间增加,PP长链支化程度增大。。     

电缆绝缘专用LDPE的结构与性能

研究了2种国产电缆绝缘专用低密度聚乙烯(LDPE)2220H(分别记作LDPE A,LDPE B)的分子链段结构、动态流变性能、熔融结晶性能、体积电阻率和直流击穿强度.结果表明:LDPE A的相对分子质量和长支链含量高于LDPE B,相对分子质量分布相近;结晶度和熔融温度较高的LDPE A在较高温度条件下的体积电阻率高...     

高速挤出涂覆专用树脂的工业开发

结合市场需求和低密度聚乙烯（LDPE）装置特点,开发了LDPE高速挤出涂覆专用树脂1C7A-1。确定了反应压力、反应温度、引发剂消耗量及链转移剂加入种类。生产的1C7A-1各项指标可满足市场需求,涂覆过程中的膜边缘稳定性得到提高,挤出复合时缩幅较小,且加工速度较高（大于280m/min）,最小涂覆厚度达到6μm,填补了国内无菌包装高速挤出涂覆树脂生产的空白。     

Influence of low density polyethylene quality on extrusion coating processability

In order to obtain explicit information about the influence of different low density polyethylene (LDPE) quality parameters on extrusion coating processability, a test run was made with an autoclave reactor and the products were investigated. All the grades manufactured had melt indices (MI), densities, molecular weight distributions (MWD), and degrees of long chain branching(LCB) typical of commercial extrusion coating grades. The processability characteristics studied were maximum line speed and neck-in. The influence of MI, density, and extrusion melt temperature were systematically investigated. It was found that the maximum line speed rose with increasing MI, density, and extrusion melt temperature, and that an increasing extrusion melt temperature led to a growing difference between the maximum line speed at a constant coating thickness and the maximum line speed at a constant screw speed. Neck-in was found to increase with increasing MI, increasing density, and increasing coating thickness. These effects were more pronounced at higher extrusion melt temperatures. When using the extrusion temperature needed to achieve a certain line speed for each grade, the influence of MI on neck-in was practically non-existent.     

Molecular,rheological, and crystalline properties of low‐density polyethylene in blown film extrusion

The molecular weight and its distribution, degree of long chain branching and cooling rate strongly influence crystallinity during processing, which in turn determines the processability and the ultimate properties of the blown film. Generally a decrease in the number of branches and molecular weight of the polymer and the cooling rate results in an increase of the crystallinity. Length of the main chain and extent of branching in low‐density polyethylene (LDPE) are also factors that affect melt rheology and film crystallinity. Long chain branched polyethylene is suitable in the blown film process due to its better melt strength for bubble stability. The objective of this article is to describe the effect of molecular properties (e.g. molecular weight and its distribution, degree of long chain branching etc) of LDPE on film crystallinity at different cooling rates of blown film extrusion. Two different grades of LDPE were selected to investigate molecular characteristics, crystallinity, and rheology. The resins were processed in a blown film extrusion pilot plant using four different cooling rates. Molecular, rheological, and crystalline properties of the resins were key parameters considered in this study. POLYM. ENG. SCI., 47:1983–1991, 2007. © 2007 Society of Plastics Engineers     

亚磷酸酯抗氧剂PEPQ及168对LDPE加工性能和热稳定性的影响

通过双螺杆5次挤出加工试验,考查了亚磷酸酯类抗氧剂对低密度聚乙烯(LDPE)树脂的加工性能和热稳定性能的影响。结果表明,抗氧剂PEPQ在保持LDPE的熔体流动性能和力学性能上优于抗氧剂168,但对抑制LDPE黄变效果不如抗氧剂168。     

Phase structural analyses of polyethylene coatings on high‐density papers. III. Determination of the crystallite thicknesses by T1 measurements

Two different extrusion‐coating qualities of polyethylene, namely LDPE and HDPE, were coated on high‐density papers. Differences were observed with respect to their response to storage and low temperature heat treatment. HDPE does not respond to storage at ambient temperature and heat treatment in the same way as LDPE. The LDPE‐coating exhibits an increase in the monoclinic crystalline fraction at the paper surface as a result of heat treatment. The nature of this response appears to be a result of adhesion to a paper surface, the properties of this surface, orientation of polymer chains, and chain mobility differences. The increase of the monoclinic fraction is shown to relate to an increase of the mean crystallite thickness and initiation of new crystallites at the paper surface. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 235–241, 2004     

Extrusion coating performances of iPP/LDPE blends

The performance of iPP/LDPE blends in an extrusion coating process was investigated in the terms of coating width and draw‐down ability. It is well known that iPP alone is not proper because of lower draw‐down ability with severe draw resonance in elongational flow. To obtain higher draw‐down ability, iPP was blended with LDPE. Additionally, iPPs having different molecular weight distribution (MWD) were used in this study to find out the effect of MWD of iPP on neck‐in and draw‐down ability. It was observed that iPP/LDPE blend with narrower MWD exhibits narrower coating width and higher draw‐down ability. Neck‐in and draw‐down ability were correlated with shear and elongational properties obtained by several rheological measurements. From this study, the major rheological parameters affecting extrusion performance in iPP/LDPE blends could be assessed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of molecular architecture and melt rheological characteristic on the optical properties of LDPE blown films

A systematic investigation on the origin of the haze of LDPE blown films was conducted, aiming to correlate the film haze with the molecular architecture and melt rheological properties. First of all, the haze measurement indicated that the surface haze, rather than the bulk haze, is the dominating factor for the total haze of the investigated films. No spherulitic crystals or other superstructures were observed for the LDPE blown films, implying that the crystallites formed in the film-blowing process are too small to be responsible for the optical haze. Rheological study revealed that the surface roughness was originated from the irregular flow of LDPE melt during the extrusion process. NMR, GPC and parallel-plate rheology were applied to study the molecular architecture of the LDPE resins. It was found that the LDPE sample with higher haze value exhibits distinctly larger portion of higher molecular weight component, broader molar mass distribution, significantly higher side chain branch density.     

LDPE收缩膜专用树脂性能的研究

研究了低密度聚乙烯收缩膜专用树脂LD163的分子链结构、结晶性能及收缩性能。结果表明,LD163具有较高的相对分子质量、适中的相对分子质量分布,总体支化度低、长链支化度较高,结晶度高、结晶速率快。因此,LD163具有优良的力学性能,良好的加工性能,其薄膜制品的收缩性能及综合性能优异。     

管式法LDPE产品浊度影响因素及改进措施

通过在管式法低密度聚乙烯装置上控制反应压力和各反应区压降、调整反应温度器分布、合理设定引发剂注入压力、优化反应器流量分配和比例控制、调整添加剂用量等,降低了树脂薄膜制品的浊度值。提高了膜制品的光学性能,改进了高档膜料树脂的质量,其中控制引发剂注入压力比对应点反应压力高25MPa,反应器流量分配调整为正面进料为41．8％,第一侧流为28．7％,第二侧流为29．5％。