Yu Jingfang, Chen Chunping, Gilchrist James B, Buffet Jean-Charles, Wu Zhonghua, Mo Guang, Xie Fei, O'Hare Dermot
Chemistry Research Laboratory, Department of Chemistry, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, UK.
eBIC, Diamond Light Source, Oxfordshire, OX11 0DE, UK.
Mater Horiz. 2021 Oct 4;8(10):2823-2833. doi: 10.1039/d1mh00433f.
Whilst applying a coating layer to a polymer film is a routine approach to enhance the gas barrier properties of the film, it is counter-intuitive to consider that the gas barrier performance of the film would improve by ageing the coating dispersion for weeks before application. Herein, we report that the oxygen barrier performance of a 12 μm PET film coated with a dispersion of inorganic nanosheets in polyvinyl alcohol can be significantly enhanced by ageing this coating dispersion for up to 8 weeks before application. We found up to a 37-fold decrease in the oxygen transmission rate (OTR) of the PET coated film using aged dispersions of MgAl(OH) layered double hydroxide nanosheets (MgAl-LDH NS) in polyvinyl alcohol (PVA) compared to the film coated with an equivalent freshly prepared LDH/PVA dispersion. A limiting OTR value of 0.31 cc m day was achieved using the PET film coated with a 3 week aged LDH NS/PVA dispersion. X-ray diffraction experiments show that the degree of in plane alignment of LDH NS on the PET film surface increased significantly from 70.6 ± 0.6 to 86.7 ± 0.6 (%) (100% represents complete alignment of LDH NS platelets on the film surface) for the 4 week aged dispersion compared to the freshly prepared layer. We postulate that when the MgAl-LDH NS are aged in PVA the coiled PVA aggregates start to unwrap and attach onto the MgAl-LDH NS through hydrogen bonding and eventually form a hydrogen bonded ordered network that facilitates the alignment of nanosheet dispersions during the coating process. Our results suggest that the ageing of inorganic nanosheet dispersions in PVA or other potential hydrogen bonding adhesive systems could be a general approach to improve the alignment of the nanosheets on the polymer film surface once applied and thus improve their performance characteristics for barrier coating applications.
虽然在聚合物薄膜上涂覆涂层是提高薄膜气体阻隔性能的常规方法，但认为在涂覆前将涂层分散体老化数周会提高薄膜的气体阻隔性能，这与直觉相悖。在此，我们报告，在涂覆前将无机纳米片在聚乙烯醇中的分散体老化长达8周，可显著提高涂覆在12μm聚酯薄膜上的氧气阻隔性能。我们发现，与涂覆等量新鲜制备的层状双氢氧化物/聚乙烯醇（LDH/PVA）分散体的薄膜相比，使用老化的MgAl(OH)层状双氢氧化物纳米片（MgAl-LDH NS）在聚乙烯醇（PVA）中的分散体涂覆的聚酯薄膜，其氧气透过率（OTR）降低了37倍。使用涂覆了3周老化的LDH NS/PVA分散体的聚酯薄膜，实现了0.31 cc m day的极限OTR值。X射线衍射实验表明，与新鲜制备的层相比，4周老化分散体在聚酯薄膜表面的LDH NS面内排列程度从70.6±0.6显著增加到86.7±0.6（%）（100%表示LDH NS片晶在薄膜表面完全排列）。我们推测，当MgAl-LDH NS在PVA中老化时，卷曲的PVA聚集体开始展开，并通过氢键附着在MgAl-LDH NS上，最终形成氢键有序网络，在涂覆过程中促进纳米片分散体的排列。我们的结果表明，无机纳米片在PVA或其他潜在的氢键粘合剂体系中的老化，可能是一种通用方法，一旦应用，可改善纳米片在聚合物薄膜表面的排列，从而改善其作为阻隔涂层应用的性能特征。
