Large Scale Self-Assembly of Smectic Nanocomposite Films by Doctor Blading versus Spray Coating: Impact of Crystal Quality on Barrier Properties

Abstract

Flexible transparent barrier films are required in various fields of application ranging from flexible, transparent food packaging to display encapsulation. Environmentally friendly, waterborne polymer–clay nanocomposites would be preferred but fail to meet in particular requirements for ultra high water vapor barriers. Here we show that self-assembly of nanocomposite films into one-dimensional crystalline (smectic) polymer–clay domains is a so-far overlooked key-factor capable of suppressing water vapor diffusivity despite appreciable swelling at elevated temperatures and relative humidity (R.H.). Moreover, barrier performance was shown to improve with quality of the crystalline order. In this respect, spray coating is superior to doctor blading because it yields significantly better ordered structures. For spray-coated waterborne nanocomposite films (21.4 μm) ultra high barrier specifications are met at 23 °C and 50% R.H. with oxygen transmission rates (OTR) < 0.0005 cm3 m–2 day–1 bar–1 and water vapor transmissions rates (WVTR) of 0.0007 g m–2 day–1. Even in the most challenging environments (38 °C and 90% R.H.), values as low as 0.24 cm3 m–2 day–1 bar–1 and 0.003 g m–2 day–1 were found for OTR and WVTR, respectively.

Comparison of Crosslinking Efficiency in Dip and Roll-Deposited Coatings on Their Oxygen Barrier

“…20 This implies that a higher density of free hydroxyl groups may increase the permeability. On the other hand, the adsorption of water molecules results in the swelling of the coating, 15 allowing a higher diffusing area for oxygen. Such a swelling can be limited by the presence of well-intercalated MMT platelets in the coating with a strong interaction with the polymer.…”

Filter‐Through Method of Making Highly Efficient Polymer‐Clay Nanocomposite Membranes

“…Nanosheets of layered materials like clay (e.g., Na‐hectorite [Hec]), or graphene oxide (GO) are the most promising fillers for the fabrication of polymer nanocomposite barrier coatings . Barrier is of prime importance in applications spanning from automotive, furniture, construction, food, or optoelectronic packaging . According to Cussler, the barrier improvement factor is nonlinearly dependent on both aspect ratio and filler content.…”

Development of Clay‐Based Films

“…Synthetic smectites, including trioctahedral smectite, such as hectorite, and saponite,,,, are also used. In addition, mica,,,, vermiculite, layered double hydroxide, and layered titanate, have been assessed as clay fillers. While the aspect ratio of synthetic smectite is of the order of 10–100,, some natural smectite and synthetic mica have aspect ratios of hundreds to thousands, respectively.…”

“…prepared a thin, highly transparent, and flexible nanocomposite coating with exceptionally high oxygen and water vapor barrier properties using commercial polyurethane and organoclay modified by quaternized dimethylaminoethyl methacrylate with very large aspect ratios (∼25,000). Tsurko et al . proposed that spray coating is superior to doctor blading for producing highly crystalline structures, which are important for gas barrier applications.…”

“…The nylon‐6‐organosmectite composite material produced by Toyota Central Research Laboratory in 1985 is a well‐known successful example of a polymer‐clay composite material. Since then, polymer‐clay composites have been widely developed, and many reviews of such materials have been published . Most of these materials are polymer‐based composites, in which clays are added as a minor component (<10 wt%).…”