Measurement of Diffusion Coefficient of Monomers in Polymers

在这项工作中，氮气和乙烯在高密度聚乙烯（HDPE）和两个线性低密度聚乙烯（LLDPE）具有不同的1-己烯含量的溶解度和扩散系数进行了测量。在333.2，353.2，403.2和433.2K的温度和3.5MPa的压力下，用电天平法测量了样品的温度和压力。此外，测得的溶解度和扩散系数分别与Sanchez-Lacombe状态方程和Vrentas-Duda理论。通过调查发现：1.对于氮-聚合物系统，溶解度随着温度的升高而增加，显示出对于具有低临界温度的气体常见的所谓的逆溶解度。由亨利常数的温度依赖性确定的结晶度随着温度的升高而降低。扩散系数几乎没有浓度依赖性。扩散系数的温度依赖性也很小，在所研究的温度范围内，扩散系数随温度的升高而增加约一个数量级.对于乙烯-聚合物体系，溶解度随温度升高而降低，表现出通常的温度依赖性.尽管1-己烯含量不同，乙烯在两种LLDPE无定形区的溶解度几乎相同。乙烯在聚合物中的溶解度比氮气大7倍。乙烯的扩散系数具有明显的温度依赖性。在低温下，扩散系数的浓度依赖性也很大。

In this work, solubilities and diffusion coefficients were measured for nitrogen and ethylene in high-density polyethylene (HDPE) and two linear low-density polyethylenes (LLDPE) having different 1-hexene contents. The measurement was carried out using an apparatus based on the electricbalance method at temperatures of 333.2,353.2,403.2 and 433.2 K and at pressures up to 3.5 MPa. Moreover, measured solubilities and diffusion coefficients were correlated with Sanchez-Lacombe equation of state and Vrentas-Duda theory, respectively. From the investigations, the followings wree found :1. For the nitrogen - polymer systems, solubilities increased with increasing temperature, showing so-called reverse solubility that is common for gases with low critical temperatures. Degree of crystaliinity, that was determined from temperature dependence of Henry's constants, decreased with increasing temperature. Diffusion coefficients represented little concentration dependence. Temperature dependence of the diffusion coefficients was also small in the temperature range examined, where the diffusion coefficients increased about one ordr of magnitude with an increase in temperature.2. For the ethylene - polymer systems, solubilities decreased with increasing temperature, showing a usual temperature dependence. The solubilities of ethylene in amorphous regions of two LLDPE were almost the same despite different 1-hexene content. Ethylene showed about 7 times larger solubilities in the polymers thatn nitrogen. Diffusion coefficients of ethylene **vcaled remarkable temperature dependence. Concentration dependence of diffusion coefficients was also large at low temperatures.