Analysis of permeability of low density polyethylene/clay nanocomposite films

The goals of this research were two folds, (i) to study the effects of loading of organoclay and compatibilizer on the permeability of LDPE/PE-g-MA/Org-MMT nanocomposite films, and (ii) to verify the applicability of the modified Nielsen model on prediction of permeability LDPE/PE-g-MA/Org-MIMT nanocomposite films. The LDPE/PE-g-MA/Org-MMT nanocomposites were prepared in the twin screw extruder in three-step mixing procedure and the blown into films. Gallery spacing between clay platelets of the Org-MMT and nanocomposite films were measured by X-ray diffraction. Transmission Electron Microscope (TEM) was used to study the distribution of clays in nanocomposite films. The Oxygen Transmission Rate (OTR) of the nanocomposite films were measured by the Oxygen Permeation Analyzer. The experimental permeability data were fitted by the modified Nielsen model. The experimental results showed that the nanocomposite films of LDPE with Org-MMT and PE-g-MA as compatibilizer having lower oxygen permeability properties than pure LDPE film can be obtained by melt mixing. The obtained LDPE/PE-g-MA/Org-MMT nanocomposite films were mainly the intercalated type. The oxygen gas permeability was reduced by about 50% at 3.14-5.09 wt% inorganic clay loading. The transparency of nanocomposite films slightly decreased with increasing clay content. The 9 wt% PE-g-MA was the optimum loading found. The modified Nielsen model can be used to predict the relative permeability of nanocomposite films providing that the aspect ratio, orientation angle, and volume fraction of inorganic clay could be found accurately.本研究的研究目标分为两点：(i) 探究有机蒙脱土（Org-MMT）与相容剂的负载量对低密度聚乙烯/马来酸酐接枝聚乙烯/有机蒙脱土（LDPE/PE-g-MA/Org-MMT）纳米复合薄膜透气性的影响；(ii) 验证修正的尼尔森模型（modified Nielsen model）在预测LDPE/PE-g-MA/Org-MMT纳米复合薄膜透气性方面的适用性。本研究采用三步混合工艺，通过双螺杆挤出机制备LDPE/PE-g-MA/Org-MMT纳米复合材料，并经吹塑成型制备薄膜。通过X射线衍射（X-ray diffraction）测定有机蒙脱土片层与纳米复合薄膜的粘土片层间距；借助透射电子显微镜（Transmission Electron Microscope, TEM）观测纳米复合薄膜中粘土的分散状态；采用氧气透过率分析仪（Oxygen Permeation Analyzer）测试纳米复合薄膜的氧气透过率（Oxygen Transmission Rate, OTR）。实验所得透气性数据通过修正的尼尔森模型进行拟合。实验结果表明，通过熔融共混可制备出以PE-g-MA为相容剂、添加Org-MMT的LDPE基纳米复合薄膜，其氧气透过性能优于纯LDPE薄膜。所制备的LDPE/PE-g-MA/Org-MMT纳米复合薄膜主要为插层型结构。当无机粘土负载量为3.14~5.09 wt%时，氧气透气性降低约50%。随着粘土含量增加，纳米复合薄膜的透明度略有下降。本研究确定9 wt%的PE-g-MA为最优负载量。修正的尼尔森模型可用于预测纳米复合薄膜的相对透气性，前提是能够准确获取无机粘土的长径比、取向角与体积分数。