The degradation and stabilization of an extensive range of unstabilized and stabilized polyethylenes during multiple extrusions are examined in order to investigate and determine their chemical and structural changes and inter-relationship with different commercial antioxidant/stabilizer packages including nondust blends. Unsaturation changes were also assessed after each extrusion. Oxidative stability was also evaluated by hydroperoxide analysis and carbonyl index. Metal catalysts residues of the neat polymers were determined and their contribution toward the overall oxidative stability of the polymers assessed along with the activity of the phenolic/phosphite antioxidants (as determined by HPLC). All the chromium-based HD polyethylenes and the metallocene LLDPE crosslinked during multiple extrusions. The HDPE with high Cr/Ti and Al levels underwent chain scission after the second extrusion. The results indicated that crosslinking reactions during processing were initiated at the unsaturated groups. Melt flow index (MFI) changes observed during processing were accompanied by vinyl disappearance and trans-vinylene formation. The addition of alkyl radicals to vinyl unsaturations appears to be the main reaction. All stabilized packages effectively inhibited carbonyl growth during multiple extrusions but did not inhibit MFI change due to the crosslinking reactions, except for one LLDPE.

中文翻译：

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多重挤出过程中催化剂对不同聚乙烯稳定性影响的研究前景和进一步研究：氧化化学和抗氧化活性的相互关系

为了研究和确定它们的化学和结构变化以及与包括无尘共混物在内的不同商业抗氧化剂/稳定剂包的相互关系，研究了广泛的不稳定和稳定聚乙烯在多次挤压过程中的降解和稳定性。每次挤出后也评估不饱和度变化。还通过氢过氧化物分析和羰基指数评估了氧化稳定性。测定了纯聚合物的金属催化剂残留物，并评估了它们对聚合物整体氧化稳定性的贡献以及酚类/亚磷酸酯类抗氧化剂的活性（通过 HPLC 测定）。所有铬基 HD 聚乙烯和茂金属 LLDPE 在多次挤压过程中交联。具有高 Cr/Ti 和 Al 含量的 HDPE 在第二次挤压后发生断链。结果表明，加工过程中的交联反应是在不饱和基团处引发的。在加工过程中观察到的熔体流动指数 (MFI) 变化伴随着乙烯基消失和反式亚乙烯基的形成。将烷基加成到乙烯基不饱和键上似乎是主要反应。除了一种 LLDPE 外，所有稳定的包装都有效地抑制了多次挤压过程中的羰基生长，但由于交联反应而没有抑制 MFI 变化。