Biodegradable Plastic From Crab Shells

Chitin is one of the components of crustacean shells, among other things.

With the increased popularity of single-use plastic products, one can only dream of the remaining waste disappearing into thin air or being magically converted into something useful. Why not? After all, all human inventions begin with a dream. One of these dreams — a truly biodegradable plastic — just may come true.

What if there were a natural, renewable, ecological source for biodegradable plastic — a plastic that not only is fully compostable, but also can be used as a fertilizer? What if this plastic were made from food waste instead of plant oils and food sources? What if you could drink from a cup, crumple it, throw it to the ground and have the plants say “thank you?”

Scientists have found a key to this dream in the substance chitin.

Looking to the Sea

The biodegradable plastic is made from chitin, derived from seafood shells.
Chitin.

Chitin is the second-most abundant organic compound after cellulose. Fungi, insects, and several types of sea creatures (mollusks, squids, octopuses, shrimps, lobsters and crabs) use it widely, in cell walls and shells, beaks, and tough exoskeletons. Chemically, chitin is a natural polymer of a N-acetylglucosamine, a relative of glucose and cellulose. The chains of chitin are very suitable for interchain hydrogen bonding, which adds strength. In nature chitin can be combined with a protein matrix to form sclerotin, or can form a nanocomposite with the calcium carbonate in mollusk shells.

Chitin is most commonly extracted from crab shells, but only a small portion of this resource is being used for chitin production. With annual world crab production exceeding 2 million tons (with China the top producer), there is a lot of unused potential.

Chitin is often used in a partially de-acetylated form called chitosan. Chitin and chitosan are used for water treatment, in cosmetic, biomedical and textile industries, and in biotechnology. Glucosamine, a monomer of chitosan, is a popular food supplement used for joint regeneration. Despite the abundance of available raw material for production, appropriate mechanical strength, and excellent biodegradability, chitosan has not been explored in terms of mainstream commercial production of everyday single-use products. At least, not until now.

Modified Mechanical Properties

Scientists from the Wyss Institute for Biologically Inspired Engineering in Boston studied and modified mechanical properties of chitosan polymer. Molecular characterization of chitosan films was performed by FTIR and X-ray diffraction. In films, prepared by solution evaporation, birefringence microscopy revealed the existence of millimeter-scale liquid crystal domains and molecular rearrangement upon stretching.

chitosan-plasticPliable chitosan liquid crystal material was further explored for making three-dimensional objects by casting and injection molding. Adding wood flour (a waste product of wood processing) as a filler resulted in solid drillable objects. The scientists also managed to confer water-resistance to chitosan objects by coating them with Parylene (a type of polymer that is vapor-deposited), and added natural colors, producing colorful transparent cups and egg containers. The objects created from chitosan can be either recycled (melted and recast), or composted and used to grow plants, as shown in the video below:

The scientists report their findings in Macromolecular Materials and Engineering:

Here we describe how analysis of differences in the molecular arrangement and mechanical properties of chitosan polymer that result from different processing methods led to development of a scalable manufacturing strategy for production of large three-dimensional (3D) objects of chitosan. This chitosan fabrication method offers a new pathway for large-scale production of fully compostable engineered components with complex forms, and establishes chitosan as a viable bioplastic that could potentially be used in place of existing non-degradable plastics for commercial manufacturing.

Image by Phu Thinh Co.
Image courtesy the Wyss Institute.
Source: “Manufacturing of Large-Scale Functional Objects Using Biodegradable Chitosan Bioplastic,” by J.G. Fernandez and D.E. Ingber, Macromolecular Materials and Engineering, (2014), doi: 10.1002/mame.201300426.
Source: “Biodegradable Plastic Option From Shrimp Shells,” by Stephen Luntz, iflscience.com, May 7, 2014.
Source: “World-Wide Chitin and Chitosan Production,” (pdf), ap360.net.
Source: “Global Chitin Market to Exceed 51.4 Thousand Metric Tons by 2012, According to New Report by Global Industry Analysts, Inc.,” prweb.com, April 15, 2008.
Source: “Global Market for Biopolymers Chitin & Chitosan to Exceed 118K Metric Tons by 2018, Predicts GII,” specialchem4polymers.com, December 24, 2012.
Video: “Chitosan Bioplastic,” by wyssinstitute, YouTube.com.