Size exclusion chromatography of photo-oxidated LDPE by triple detection and its relation to rheological behavior
Size exclusion chromatography of photo-oxidated LDPE by triple detection and its relation to rheological behavior
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DOI：
10.1016/j.polymdegradstab.2014.10.022
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发表时间：
2015
影响因子：
5.9
通讯作者：
V. H. Rolón-Garrido;M. Kruse;M. Wagner
中科院分区：
文献类型：
--
作者：
V. H. Rolón-Garrido;M. Kruse;M. Wagner
在空气存在下，使用氙灯照射样品 1 天至 6 周，对低密度聚乙烯 (LDPE) 片材进行光氧化。通过流变表征、傅里叶变换红外光谱和溶剂萃取方法，研究了长达 1 周的降解过程中长链支化 (LCB) 的形成以及较长辐射期间断链和交联之间的竞争（Rolón-Garrido 和 Wagner. Polym Degrad Stabil 2014, 99: 136，Rolón-Garrido 和 Wagner. J Rheol 2014, 58: 199）。在本贡献中，使用三重检测（浓度、光散射和粘度）通过尺寸排阻色谱表征来研究相同的样品。通过过滤然后分析可溶性聚合物部分来测定凝胶含量。讨论了光氧化时间对分子量分布（摩尔质量和多分散性）、均方回转半径和特性粘度收缩因子的影响。结果与分子应力函数（MSF）理论的模型参数（β和f max 2）相关，用于定量描述单轴伸长的流变数据。经证实，LCB 作为一种旁路过程发生，在凝胶化发挥关键作用之前，长达一周的降解比断链占主导地位。证实模型参数β与凝胶含量相关，凝胶含量反映了断链和交联之间的竞争，而f max 2 与实验确定的收缩因子相关。通过将本研究的数据与先前获得的具有明确结构的聚苯乙烯梳状熔体的数据进行比较，支化频率（即每1000个碳原子的支化点数量）对f max 2 的影响变得明显。
Sheets of low-density polyethylene (LDPE) were subjected to photo-oxidation in the presence of air using a xenon lamp to irradiate the samples for times between 1 day and 6 weeks. The formation of long-chain branching (LCB) up to one week of degradation and the competition between chain scission and crosslinking at longer periods of radiation were investigated by rheological characterization, Fourier transform infrared spectroscopy, and the solvent extraction method (Rolón-Garrido and Wagner. Polym Degrad Stabil 2014, 99: 136, Rolón-Garrido and Wagner. J Rheol 2014, 58: 199). In the present contribution the same samples are studied by size exclusion chromatographic characterization using triple detection (concentration, light scattering and viscosity). The gel content is determined by filtration followed by the analysis of the soluble polymer fraction. The influence of photo-oxidation time on the molecular weight distribution (molar masses and polydispersity), the mean square radius of gyration and the intrinsic viscosity contraction factors is discussed. The results are correlated with the model parameters (β and f max 2) of the molecular stress function (MSF) theory, used to describe quantitatively the rheological data in uniaxial elongation. It is verified that LCB occurs as an aside process, which up to one week of degradation dominates over chain scission, before gelation plays a critical role. It is confirmed that the model parameter β correlates with the gel content, which reflects the competition between chain scission and crosslinking, while f max 2 is found to correlate with the experimentally determined contraction factors. By comparing the data of this study with those obtained earlier for polystyrene comb melts with well defined structure, the influence of the branching frequency (ie the number of branch points per 1000 carbon atoms) on f max 2 becomes evident.