Sparse Long-chain Branching's Effect on the Film-casting Behavior of PE
Sparse Long-chain Branching's Effect on the Film-casting Behavior of PE
复制标题
稀疏长链支化对PE流延性能的影响
DOI：
10.3139/217.2184
复制
发表时间：
2009
影响因子：
1.3
通讯作者：
D. Baird
中科院分区：
文献类型：
--
作者：
C. W. Seay;D. Baird
摘要分析了三种不同程度稀疏长链支化的聚乙烯（LLDPE）在流延过程中的膜宽减小或颈缩程度。所述树脂包括三种稀疏LCB聚乙烯（PE）材料，所述材料具有范围从线性到0.57 LCB/10000 CH 2的不同LCB含量，沿着齐格勒-纳塔聚合的LLDPE和管状自由基聚合的低密度聚乙烯（LDPE）。最后两种树脂用作参比物质。本分析的主要目的是评估是否单轴拉伸流变特性，特别是应变硬化，这是由于LCB影响的膜颈缩性能。在最低的压下比，颈缩被观察到减少与增加LCB，从而应变硬化特性。在更高的拉伸比下，观察到LCB不再减少颈缩，并且曲线与线性PE的结果合并，除了在LDPE的情况下，其在所有拉伸比下均显示出减少的颈缩。此外，还对膜颈缩进行了比较，以分离分子量分布、MWD和LCB的影响。结果表明，加宽MWD和添加稀疏LCB都降低了颈缩程度，但在加宽MWD的情况下降低程度较小。的单轴拉伸和动态剪切流变与pom-pom本构模型的分析表明，分支沿着较短的松弛时间模式的分布是重要的，在减少颈缩在较高的压降比。剪切粘度效应、挤出物溶胀和非等温行为等因素作为影响因素被排除。
Abstract The degree of film-width reduction or necking during film-casting is analyzed for three metallocene-catalyzed linear low density polyethylenes, LLDPE, with varying degrees of sparse long-chain branching, LCB. The resins included three sparsely LCB polyethylene, PE, materials with varying LCB content ranging from linear to 0.57 LCB/10000 CH2 along with a Ziegler-Natta polymerized LLDPE and a tubular free-radical polymerized low density polyethylene, LDPE. The last two resins are used as reference materials. The primary objective of this analysis is to evaluate whether uniaxial extensional rheological characteristics, in particular strain-hardening, that are a result of LCB influence the film-necking properties. At the lowest drawdown ratio, necking is observed to be reduced with increasing LCB, and thus strain-hardening characteristics. At the higher drawdown ratios it is observed that LCB no longer reduces necking and the curves merge to the results found for linear PE, except in the case of LDPE, which shows reduced necking at all drawdown ratios. Furthermore, comparisons of film necking are also made to separate the effects of molecular weight distribution, MWD, and LCB. The results indicate that both broadening the MWD and the addition of sparse LCB reduce the degree of necking, but to a lesser degree in the case of broadening the MWD. Analysis of the uniaxial extensional and dynamic shear rheology with the pom-pom constitutive model reveals that a distribution of branches along shorter relaxation time modes is important in reducing necking at higher drawdown ratios. Factors such as shear viscosity effects, extrudate swell, and non-isothermal behavior were eliminated as contributing factors.