Stronger, more flexible bioplastic packaging for food?

SOME 300 million tons of plastics are produced annually worldwide, with 99 percent made with fossil fuels and crude oil. As we know these plastics will take lifetimes to break up in nature, and discarding them by burning will only release carbon dioxide into the atmosphere and contribute to climate change.

When bioplastics came into the picture, they were hailed as the better alternative, being made from renewable plant-based materials like cornstarch and sweet potatoes that decompose much more easily in the ground. But this eco-friendly feature was somewhat lost among users in the packaging industry because bioplastics failed to meet their criteria for strength and flexibility. Hence petroleum-based plastic packaging still dominates. It is said that about one trillion plastic bags are distributed annually worldwide.

Addressing strength and flexibility in bioplastics is a continuing effort. The most recent solution was presented by Vijaya K. Rangari, Ph.D, graduate student Boniface Tiimob and colleagues at Tuskegee University during the 251^st National Meeting & Exposition of the American Chemical Society (ACS) from March 15-17.

The research involves fortifying bioplastics with tiny shards of eggshell to create biodegradable packaging material that can bend but will not easily break.

“We’re breaking eggshells down into their most minute components and then infusing them into a special blend of bioplastics that we have developed,” said Dr Rangari. “These nano-sized eggshell particles add strength to the material and make them far more flexible than other bioplastics on the market. We believe that these traits — along with its biodegradability in the soil — could make this eggshell bioplastic a very attractive alternative packaging material.”

Their experiments led to an ideal combination that would make the material degrade faster: 70 percent polybutyrate adipate terephthalate (PBAT), a petroleum polymer, and 30 percent polylactic acid (PLA), a polymer derived from cornstarch. PBAT, unlike other oil-based plastic polymers, is designed to begin degrading as soon as three months after it is put into the soil.

700% more flexible

For flexibility, eggshell was the material of choice – porous, lightweight, and mainly made of calcium carbonate that decays easily. To create the nanoparticle eggshells, the shells were washed, ground up in polypropylene glycol and then exposed to ultrasonic waves that broke the shell fragments down into nanoparticles more than 350,000 times smaller than the diameter of a human hair. Then, in a laboratory study, they infused a small fraction of these particles, each shaped like a deck of cards, into the 70/30 mixture of PBAT and PLA. Added to the mixture, it made the bioplastic 700 percent more flexible than other bioplastic blends. This characteristic makes the new material ideal for food containers, grocery bags and retail packaging.

Mr Rangari's team research receives funding from the National Science Foundation (CREST#1137681, RISE#1459007) and the Alabama Experimental Program to Stimulate Competitive Research (ESPCoR#1158862).

The American Chemical Society is a nonprofit organization chartered by the U.S. Congress, and also the world’s largest scientific society. Its meeting in March features more than 12,500 presentations on a wide range of science topics.