The chitin market has been cornered by arthropods. Think of crabs shells and insect
exoskeletons and you get a clear picture of what chitin looks and feels like.
You probably know that certain biopolymers like DNA form a-
helices. Others form what are called b-sheets.
Chitin, of course, is one of these others, and it helps tremendously in biocomposite
applications. Here's the general shape of a b-
sheet. Note the "pleated" structure.
The chitin in a lady bugs shell is part of a composite. It's actually the fiber component.
Protein serves as the matrix component, and also forms b-
sheets. Since these two components have the same structure, their interaction is enhanced
and a strong composite is the result. Experiments have shown that the interface between the
chitin fiber and protein matrix is so strong that the fiber doesn't pull out. However, once fibers start to break, it's easier to break other fibers at that same
point, resulting in brittle failure. Think of this as scoring glass followed by a nice, clean
break.
Chitin is fibrous but it isn't always aligned in the same direction, especially around discontinuities
like holes. The layers of chitin are oriented in different directions so that stress is evenly
distributed. The structure is actually similar to that of plywood.
