氧气在聚丙烯内吸附和扩散的分子模拟

采用巨正则Monte Carlo和分子动力学模拟相结合的方法研究了氧气在不同聚合度的聚丙烯内的吸附和扩散. 模拟结果表明, 随聚丙烯聚合度的增加, 聚丙烯对氧气的吸附量逐渐增加, 而氧气在聚丙烯内的扩散系数减小; 当聚合度增大到一定程度时, 吸附量和扩散系数都趋于一稳定值. 随温度的升高, 氧气在聚丙烯内的吸附量减少, 而扩散系数增大. 本文还应用自由体积理论探讨了氧气在聚合物内扩散的机理, 发现氧气在聚丙烯内以空穴形式存在的自由体积之间扩散, 即氧气先在一个空穴内不停振动, 然后通过聚丙烯链段运动形成的通道跳跃到下一个空穴来完成扩散. 结果表明, 较高聚合度的聚合物材料在常温及低温下使用对于其在食品包装材料中的应用是有利的, 这为食品包装材料行业相关产品的应用开发提供了一定的指导和依据.

Molecular Simulation of Oxygen Adsorption and Diffusion in Polypropylene

Grand canonical Monte Carlo and molecular dynamics simulations were used to study the adsorption and diffusion of oxygen in polypropylene (PP). It is found that at roomtemperature, the loading of oxygen in PP increases and the diffusion coefficient of oxygen in PP decreases as the polymerization degree of PP increases. The loading and diffusion coefficient reach platform values when the polymerization degree of PP is relatively high. The loading of oxygen decreases and the diffusion coefficient of oxygen in PP increases as the temperature increases. The oxygen diffusion mechanism in PP is also discussed according to free volume theory. Oxygen molecules firstly oscillate inside one cavity of PP and then jump from this cavity to another one through a channel formed by the thermal motion of PP chains. In general, simulation results indicate that polymer materials with a high degree of polymerization used at room or low temperatures should be preferred in food reservation technology. This work provides some guidance and basis for developments in food packing materials.