PVOH/EVOH copolyme

Clay nanocomposites are also being developed as barrier coatings for film and for containers. The nanocomposite is deposited on the film from a solution of PVOH/ EVOH copolymer in a mix of water and isopropyl alcohol which has been used in a supersonic dispersion system to nano-disperse 7 nm diameter silica and titanium dioxide particles. The ratio of polymer to silica depends on the barrier properties required. Typical microgravure equipment can be used to coat the solution onto a plastic substrate. The result reportedly is a transparent barrier coating which is superior to silica- and alumina-coated films, and is comparable to aluminum-coated materials. Oxygen permeability at a coating thickness of 2 pm is less than 1 cc/m d atm, and moisture permeation less than f g/m d. Costs are reported to be competitive with ceramic coatings [4]. 

Industrial water soluble polymers (IWSPs) represent just a small fraction of polymers used in packaging (mainly as polyvinyl alcohol (PVOH), ethylene-vinyl alcohol copolymer (EVOH), and ethylene-vinyl acetate copolymer (EVA)), but depending on additional research, two factors may lead to a growth of their relative importance the need to ensure (1) renewability and (2) biodegradability. 

EVOHs were first commercialised in Japan in the early 1970s to overcome the moisture sensitivity of the PVOH films. These copolymers are a family of random semicrystalline materials with excellent barrier properties to gases and hydrocarbons and with outstanding... 

Contrary to PE, PVOH has exceptional gas and odor barrier properties (the lowest permeability of any polymer available at dry conditions). PVOH is difficult to process, although it is water soluble. When the percent of VOH in EVOH ranges from 52 to 70 percent, the ethylene-vinyl alcohol copolymers obtained combine the processability and... 

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