Nanocomposites and everyday things

just put some Saran wrap on leftovers. Was it Saran or some cheaperknock off? Does it matter? Probably not, since my family will eat ittomorrow regardless (they are not picky). However, if you were packing aproduct to be shipped around the world, like an expensivepharmaceutical product or even an inexpensive snack, you would care.Time is money - esp. when it is sitting on a store shelf.

Howdoes this relate to the esoteric term, nanocomposites? The cause of mostfood spoilage is are either microbial or chemical- specificallyoxidation. Microbes are relatively large (micron sized), so plasticfilms easily act as a barrier. A molecule of oxygen, however, is verysmall (more than 1000 times smaller than a microbe) and can betransported through plastics (also known as polymers) easily. Thistransport or permeability depends on the solubility of oxygen (or howwell it dissolves) in the polymer and its ability to diffuse or movethrough the polymer.

Different polymers have vastly differentgas transport properties and cheap polyethylene (Glad wrap) is much morepermeable to gases than polyvinylidene chloride (Saran wrap). However,if you look at the packaging after you finish those chips from thevending machine, you will see that they have an additional layer ofaluminum foil that really prevents gas transport.

Recently ithas been found that when polymers are sequentially prepared intonanometer thick layer cakes, the barrier properties of the materialsimprove. Because polymers are glass-like structures, they tend tochange or relax over time. This relaxation basically allows the polymermolecules to get closer together and this more compact structure blocksthe transport of gas through the material. So controlling thenanostructure of polymer films could increase the shelf life of productsand potentially eliminate the need for the expensive aluminum layer inpackaging.

More specifically, a composite in a combination ofmaterials. A polymer with nanosized additives would be called ananocomposite. Adding nanosized particles to polymers can increase itsstrength, decrease its weight and improve its barrier properties (or howwell it blocks oxygen). The nanosized material could be relativelyinert clay materials or potentially antioxidant or antimicrobialparticles.

While many people think of packaging as eithersomething for marketing or something that is waste issue, and indeedboth are true, good packaging prevents food spoilage and protects theactivity of pharmaceutical products. Every day we pack a lunch, saveleftovers, open a container from the store. Whether we like it or not,packaging is a part of our everyday lives.
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