Researchers in Alabama, US have cracked one of the problems of making biocompostable films. Eggshells are being explored as a sustainable filler/reinforcement in bioresins at Tuskegee University.
Vijaya Rangari is leading research at the university designed to incorporate nanoparticles from waste eggshells into plastic film made of bioplastic to create a material that is wholly sustainable.
“These nano-sized eggshell particles add strength to the material and make them far more flexible than other bioplastics on the market,” stated Rangari. “We believe that these traits — along with its biodegradability in the soil — could make this eggshell plastic a very attractive alternative packaging material.”
Rangari said in a phone interview that his group crushes chicken eggshells and then uses a combination of ultrasound and chemicals to make tiny particles about 10 nanometers or smaller in size. The resultant calcium carbonate nanoparticles have a very high surface area and are porous, boosting the mechanical and thermal properties of the composite. A small amount of residual protein present on the eggshell particles significantly improves bonding of the particles to the base resin, which can be polylactic acid or other naturally sourced polymers.
They produced a biocomposite that is 700% more flexible than other bioplastic blends. Film made of the new material could be used in retail packaging, grocery bags and food containers — including, of course, egg cartons. Calcium carbonate derived from mineral sources has long been used as a filler in plastics but the Tuskegee research shows a biological, sustainable waste stream could be tapped as a carbonate source.
Other applications for the eggshell nanoparticles are being explored for wound healing, drug delivery and bone regeneration.
Rangari said he and coworkers mix the eggshell-derived nanoparticles with bioresin in a small twin-screw extruder and then squeeze it through a thin-film die to get a packaging film. The unique film is biodegradable. The bioresin that showed best results was a mixture of 70% polybutyrate adipate terephthalate and 30% polylactic acid.
The researchers reported their latest results in a national meeting held by the American Chemical Society in San Diego, in mid-March. Rangari and other researchers have been working on the project for a few years but the recently announced results had not yet been published in relevant scientific journals. Earlier studies have been reported in ACS publications and the Journal of Applied Polymer Science.
Rangari said an undisclosed company in Texas has shown interest in the research but the researchers have not prepared large enough quantities of the biocomposite for general distribution and development. The work has been supported by the National Science Foundation and the Alabama Experimental Program to Stimulate Competitive Research.