BIO325H5 Lecture Notes - Lecture 2: Biopolymer, Aragonite, Nacre
Document Summary
Variety of directions produces the desired properties. in plywood varying grain angles increases the work of fracture. One chitin nano fibre (see the 19 chains in vincent"s. 1 above) is 3 nm in diameter, 0. 3 micrometeres long. Nacre is composed of hexagonal platelets of aragonite (a form of calcium carbonate) 10 20 m wide and 0. 5 m thick arranged in a [sic] continuous parallel lamina. These layers are separated by sheets of organic matrix composed of elastic biopolymers This mixture of brittle platelets and the thin layers of elastic biopolymers makes the material strong and resilient, with a young"s modulus of 70gpa[gigapascal] (when dry). Strength and resilience are also likely to be due to adhesion by the "brickwork" arrangement of the platelets, which [dissipates work of fracture and so] inhibits transverse crack propagation. This mixture of brittle platelets and the thin layers of elastic biopolymers makes the material strong and resilient, with a young"s modulus of 70gpa[gigapascals] (when dry).
