Thursday, June 10, 2010

Nanocomposites and everyday things

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

How does this relate to the esoteric term, nanocomposites? The cause of most food spoilage is are either microbial or chemical- specifically oxidation. Microbes are relatively large (micron sized), so plastic films easily act as a barrier. A molecule of oxygen, however, is very small (more than 1000 times smaller than a microbe) and can be transported through plastics (also known as polymers) easily. This transport or permeability depends on the solubility of oxygen (or how well it dissolves) in the polymer and its ability to diffuse or move through the polymer.

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

Recently it has been found that when polymers are sequentially prepared into nanometer thick layer cakes, the barrier properties of the materials improve. Because polymers are glass-like structures, they tend to change or relax over time. This relaxation basically allows the polymer molecules to get closer together and this more compact structure blocks the transport of gas through the material. So controlling the nanostructure of polymer films could increase the shelf life of products and potentially eliminate the need for the expensive aluminum layer in packaging.

More specifically, a composite in a combination of materials. A polymer with nanosized additives would be called a nanocomposite. Adding nanosized particles to polymers can increase its strength, decrease its weight and improve its barrier properties (or how well it blocks oxygen). The nanosized material could be relatively inert clay materials or potentially antioxidant or antimicrobial particles.

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