Salehiyan Reza, Bandyopadhyay Jayita, Ray Suprakas Sinha
DST-CSIR National Centre for Nanostructured Materials, Council for Scientific and Industrial Research, Pretoria 0001, South Africa.
Department of Applied Chemistry, University of Johannesburg, Doornfontein, 2028 Johannesburg, South Africa.
ACS Omega. 2019 May 31;4(5):9569-9582. doi: 10.1021/acsomega.9b00940.
In this study, polyamide 6 (PA) is blended with ethylene vinyl alcohol (EVOH) to yield packaging materials with a balance of mechanical and gas barrier properties. However, the formation of gel-like structures in both polymers because of thermal degradation at high temperatures leads to a processing challenge, particularly during thin-gauge film extrusion. To address this challenge, nanoclays are introduced either directly or via a masterbatch of maleic-anhydride-grafted polypropylene to the PA/EVOH blend and time-resolved rheometry is used to study the effect of different modes of nanoclay incorporation on the kinetics of thermo-oxidative degradation of PA/EVOH blend and its nanocomposites. Time-resolved rheometry measurements allow the acquisition of accurate frequency-dependent linear viscoelastic behavior and offer insights into the rate of degradation or gel formation kinetics and cross-link density. The thermal degradation was studied by thermogravimetric analysis coupled with Fourier transform infrared spectroscopy and mass spectroscopy, allowing the prediction of the possible reactions that take place during the rheological property measurements. The results show that when nanoclays are incorporated directly, the oxidative reactions occur faster. In contrast, in the masterbatch method, oxidative degradation is hindered. The difference in the behaviors is shown to lie in the different nanoclay distributions in the blends; in the blends prepared by the masterbatch method, the nanoclays are dispersed at the interface. In conclusion, the masterbatch-containing blend nanocomposite would benefit processing and product development.
在本研究中，将聚酰胺6（PA）与乙烯-乙烯醇共聚物（EVOH）共混，以制备兼具机械性能和气体阻隔性能的包装材料。然而，由于高温下的热降解，两种聚合物中均会形成凝胶状结构，这给加工带来了挑战，尤其是在薄规格薄膜挤出过程中。为应对这一挑战，将纳米粘土直接或通过马来酸酐接枝聚丙烯母料引入到PA/EVOH共混物中，并采用时间分辨流变学方法研究不同纳米粘土引入方式对PA/EVOH共混物及其纳米复合材料热氧化降解动力学的影响。时间分辨流变学测量能够获取精确的频率依赖线性粘弹性行为，并深入了解降解速率或凝胶形成动力学以及交联密度。通过热重分析结合傅里叶变换红外光谱和质谱研究热降解过程，从而预测流变性能测量过程中可能发生的反应。结果表明，直接引入纳米粘土时，氧化反应发生得更快。相比之下，采用母料法时，氧化降解受到抑制。行为上的差异在于共混物中纳米粘土的分布不同；在通过母料法制备的共混物中，纳米粘土分散在界面处。总之，含母料的共混物纳米复合材料将有利于加工和产品开发。
