不同聚乙烯辐致凝胶效应的比较研究

Comparative Study on Radiation-Induced Gel Effect of Different Polyethylene

研究比较了不同聚乙烯的辐致凝胶效应。实验表明 ,聚乙烯的辐致凝胶效应与其分子的线性程度和结晶度有关。分子的线性程度越高 ,则辐射过程中产生的自由基在相互耦合形成交联时所遇到的空间阻力将愈小。同时 ,线性程度的增加 ,将使聚乙烯的结晶度提高 ,被束缚在晶区边界处的相互靠近的链段也就愈多。晶区自由基存在向边界迁移的趋势 ,这就使该区域的自由基浓度增加 ,所以就越容易形成交联。但是 ,结晶度越高 ,聚合物中的缺陷就越多 ,在空气氛中辐射时就越容易发生氧化。更高的剂量率可以抑制空气氛辐射时伴随的氧化反应 。

Comparative study has been done on radiation-induced crosslinking of different polyethylene. It was revealed that radiation-induced crosslinking effect of polyethylene is relevant to the linearity degree of its molecule and crystallinity. When radiation-induced free radicals couple, the more linear polyethylene molecule is and the fewer side groups are on main chains of polyethylene molecules, the less the space resistance to formation of crosslinks is. At the same time, improvement in linearity of molecule means enhancement in crystallinity of polyethylene. Meanwhile, chain fragments increase those bound in neighborhood of crystalline regions, inerease where distance between them is smaller than that of those in other regions of amorphous phase. For diffuse of radicals in crystalline region to surface of crystal, concentrations of radicals rise in these regions. For these reasons, increase in linearity of molecule and crystallinity will improve sensitization of polyethylene on radiation. But the higher crystallinity increases flaw in polyethylene, which facilitates oxidation accompanying with radiation-induced crosslinking when radiation is carried out in air, while higher dose rate can restrain this oxidation, especially when dose accumulates rather high.